LFC47 Program

Kenneth Frank, Research Scientist (Emeritus), Fisheries and Oceans Canada, and Adjunct Professor, Queen’s University

Our research on the early life history of capelin (Mallotus villosus) was initiated during the late 1970s and was focused on a research theme popular at the time, i.e., the “Recruitment Problem”. Capelin, a commercially exploited forage fish species centered off the east coast of Newfoundland, was an obvious choice for recruitment research: it was data-rich, estimates of year-class strength and spawning stock biomass were available, and our focused research could have important stock management implications with ramifications for the stability of the ecosystem. During late spring/early summer, capelin undertake extensive migrations from offshore waters to spawn intertidally near-synchronously across beaches facilitating a kind of “Field of Dreams” scenario which permitted directed sampling and experimentation at the initiation of spawning through to early development, hatching, larval drift and beyond – all from a single, land-based operation. One primary outcome of this research was the development of a mechanistic recruitment model that, until recently, has withstood re-evaluation, unlike virtually all non-mechanistic, correlative approaches to recruitment prediction. In the light of Cushing’s 1969 publication “The regularity of the spawning season of some fishes” we explore the potential drivers of spawning time variation from a century long time series of capelin beach spawning.

Susana Garrido, Senior Researcher, Portuguese Sea and Atmosphere Institute

Small pelagic fish species such as sardines and anchovies prosper in the productive waters of upwelling ecosystems and have long supported large fisheries around the world. Management of these fisheries is confounded by large variability in population size which is mainly attributed to recruitment variability. Variations in the recruitment strength of small pelagics is thought to be primarily driven by biological and/or physical factors impacting the early life history stages (eggs through to post-larvae). Vital rates of European anchovy and sardine (Engraulis encrasicolus and Sardina pilchardus) larvae have been estimated in laboratory conditions in relation to differences in several key physical and biological factors considered most important for regulating their growth and survival, such as temperature and food availability. Data such as tolerance limits throughout ontogeny, growth, survival, feeding rates and feeding behaviour, nutritional condition, swimming behaviour have been determined for both species. These data are being used to parameterize Individual based models coupled with hydrodynamic model developed for Iberian waters (northern limit of the Canary Current upwelling system). The simulations have allowed to examine links between climate and recruitment, stock connectivity and migration patterns with implications to management.

Edward Rutherford, Research Fishery Biologist, NOAA Great Lakes Environmental Research Laboratory

Long-term (>20 years) ichthyoplankton surveys (LTIS) are a key part of many fisheries oceanography programs, and have been conducted on a variety of species and early life history stages in marine, estuarine, and freshwater ecosystems that encompass a range of spatial scales. The following conclusions are drawn from several reviews of LTIS that illustrate their utility and identify potential limitations. LTIS data have provided support for and against hypothesized recruitment mechanisms that were previously derived from short-term field studies and experiments. Analysis of LTIS data has revealed the influence of ocean-atmosphere climate and teleconnection patterns (e.g., PDO, El Nino, AMO) on physical drivers of recruitment variability, and the distributions, abundances and vital rates of fish early life stages. LTIS indicate that while recruitment variability may be generated in the egg or early larval stages, recruitment often is not fixed until the late larval or juvenile stage when density dependent processes may occur. On a coarse level, LTIS data show that larvae assemblages may reflect those of adults, and larval densities and vital rates are sensitive to, and reflect effects of, ecosystem stressors and physical habitat degradation or restoration. Although LTIS are expensive to support and hard to maintain, their value tends to increase with time as climate and ecosystem conditions invariably change. LTIS often attract complementary efforts to monitor and model dynamics of larval prey or predators. In particular, biophysical models, mesocosm and laboratory experiments, and AUVs are used with LTIS data to determine the distribution and potential survival of fish early life stages in response to environmental factors.

Connections between reproductive and early life history characters in Lake Superior burbot (Lota lota)

Jill B.K. Leonard*, Michael J. Woodworth, Andrew J. Shapiro

Department of Biology, Northern Michigan University, Marquette, MI

Lake Superior burbot (Lota lota) are a native, cold water fish emerging as an important recreational fishery, but that is currently unmanaged and poorly understood. We studied burbot reproductive biology and early life history to understand its ecology and resilience to stressors. During the winters of 2021-23, we collected wild, adult burbot from Lake Superior embayments and its tributaries in the central Upper Peninsula (MI) to characterize female reproductive maturation and spawning. In addition, we collected gametes from several rivers and artificially spawned burbot to create families which we raised in the lab to evaluate fertilization rates, developmental timing, and asynchronous hatching at near-natural temperatures. We found that adult female maturation begins as early as November. River migrant fish spawned in January-February with a distinct migratory peak, while some fish in embayments were still maturing until at least April. Adult females demonstrated ovarian synchronous development, likely culminating in a single spawning event. Upon reaching ovulation the fertile window appears very short, likely <24 hours. Eggs develop slowly at cold temperatures (3^oC) with hatching occurring at ~30 days post fertilization.  Embryo families showed substantial hatching asynchrony ranging from 20 to 39 days in our study. This asynchrony led to early-hatching larvae with large yolk sac and small size demonstrating rapid growth relative to late-hatching larvae within and between families. Larval deformities and hatching issues varied depending on hatch time within the clutch. Overall, our findings suggested that substantial life history variation in burbot is manifested both in spawning site and timing, but pairs with a short fertility window which suggests vulnerability to perturbation. Larvae similarly demonstrated substantial early life history variability, likely as a defense against natural environmental variability during their ichthyoplanktonic phase.

Embryonic and larval development of dispersal mechanisms in burbot (Lota lota)

Alexis K. Pupo^1,* and Jill B.K. Leonard¹

¹Northern Michigan University, Department of Biology, Aquatics Laboratory

Burbot (Lota lota) is the only species of Gadiformes found in freshwater. The characteristics and spawning strategies of the burbot, such as very high fecundity, preference for cold temperatures, and pelagic larvae can be linked to its marine ancestry. Larval behavior plays an important role in dispersal and survival of temperate pelagic species, where planktonic larvae use phototaxis, temperature selection, and rheotaxis to orient themselves in a vertical column. Dispersal behaviors are also dependent on sensory development, including the lateral line. To gain a better understanding of how these behaviors develop in embryonic and larval burbot, we have devised multiple apparatuses that subject larvae to stimuli to record their behavioral capacity. Behavioral data were analyzed using Noldus Ethovision XT video tracking software. We also used 4-Di-2-ASP mitochondrial staining to illuminate the development of lateral line neuromasts in larval burbot.  Buoyancy of embryonic burbot slowly increased as they approached hatching, but they remained negatively buoyant. Recently hatched larval burbot did not display a preference for light or dark conditions, but chose light conditions over dark conditions more frequently as they approached 100 dpf. Responses to startle stimuli increased as the larvae approached 100 dpf. Once larvae inflated their swim bladders (~40 dpf) they chose colder water over warmer water. These preliminary results show substantial development of larval capability as they progress through the yolk sac stage while still in the planktonic phase.

Towards an understanding of the spawning ecology of Atlantic Cod (Gadus morhua) in the Northern Atlantic

Claire Pollet^1,2,*, Dominique Robert¹, Grégory Beaugrand²

¹Institut des Sciences de la Mer, Université du Québec à Rimouski, Rimouski, QC, Canada.
²CNRS, UMR 8187 Laboratoire d’Océanologie et de Géosciences, Université du Littoral Côte d’Opale, Université de Lille, Wimereux, HDF, France.

Study of the processes leading to variability in the recruitment of commercial fish stocks has been the focus of fisheries oceanography research since the early 20th century. Atlantic cod (Gadus morhua) has been more intensively studied than any other marine fish. Indeed, this species has supported some of the most important fisheries in both Northwest and Northeast Atlantic. To study variations in the recruitment of cod stocks, it is important to understand spatial variability in spawning habitat. In this context, the objectives of the present study are (i) to determine the environmental conditions associated with spawning, (ii) to model the distribution of eggs in time and space and (iii) to investigate the potential presence of a shift in the spawning period over time. Preliminary results suggest differences in environmental characteristics (in terms of temperature and light intensity) associated to spawning between the Northwest and Northeast Atlantic. The timing of spawning also occurs later in the Northwest Atlantic, which is likely due to the seasonal ice cover, delaying peak prey production relative to the Northeast Atlantic.

Fate of coastal fish larvae transported to offshore waters: lost at sea or potential recruits?

Sharon Z. Herzka^1*, Jesús C. Compaire², Paula Pérez-Brunius³, Omar Valencia-Méndez⁴

¹Marine Science Institute, University of Texas at Austin
²Centro de Investigaciones del Mar y la Atmósfera (CIMA/CONICET-UBA) and b) Instituto Franco-Argentino para el Estudio del Clima y sus Impactos (IRL 3351 IFAECI / CNRS-IRD-CONICET-UBA), Buenos Aires, Argentina.
³Paula Pérez-Brunius, Department of Physical Oceanography, Center for Scientific Research and Higher Education of Ensenada (CICESE)
⁴Omar Valencia-Méndez, Department of Marine Ecology, CICESE

The presence of fish larvae of adults that occupy coastal-neritic habitats has been repeatedly observed in the Gulf of Mexico’s (GM) deep-water region (depths > 1000 m). Their offshore transport may represent a loss of potential recruits. Alternatively, regional circulation could deliver them to suitable juvenile recruitment habitats on the inner shelf. We examine the distribution of coastal and neritic fish larvae throughout the deep-water region of the central and southern GM during three oceanographic cruises (XIXIMI-04, 05 and 06) held during the summers of 2015, 2016, and 2017. Zooplankton biomass and larval densities of coastal and neritic species were higher in the Bay of Campeche’s (BofC) oceanic waters than in the central, oligotrophic Gulf. This is consistent with the documented seasonal offshore transport of shelf waters. Gobiid larvae, whose adults occupy estuarine, coastal, or shallow reef habitats, were selected for a more detailed study; their relatively high larval density at some stations indicates offshore transport during the three cruises. The probable origin of gobiid larvae was inferred through numerical modeling experiments using the Hybrid Coordinate Circulation Model (HyCOM) and surface chlorophyll maps. The five stations with the highest densities of gobies for each cruise were selected and seeded with 20,000 particles at seven depths (0-200 m) and tracked backward in time for 15 and 35 days to infer larval origin. Five coastal provinces of probable origin were defined, spanning the shelves of Tamaulipas, Veracruz, Tabasco, Campeche, and Yucatan, Mexico. The percent of particles originating from each neritic province varied between cruises (range 0-27%) as a function of station location and the prevailing circulation patterns. Offshore dispersal was associated with cross-shelf transport due to the convergence of currents over the shelves, the interaction with the BofC cyclonic eddy with the upper slope and outer shelf in the western BofC, and westward transport off the Yucatan Shelf. Particle transport experiments will also examine whether transport delivers the larvae from the collection sites back to the shelves.  Determining whether the larvae of coastal and neritic fish species can recruit to suitable nursery habitats following their transport to offshore waters will contribute to understanding their recruitment and population dynamics.

Otolith chemistry reveals habitat use by early life stage Atlantic halibut in the Gulf of St. Lawrence

Charlotte Gauthier*¹, Jonathan Fisher², Dominique Robert³ and Pascal Sirois¹

¹Department of Fundamental Science, University of Quebec at Chicoutimi, Chicoutimi, Canada
²Centre for Fisheries Ecosystems Research, Fisheries and Marine Institute, Memorial University of Newfoundland, St. John’s, Canada
³Rimouski Institute of Marine Sciences, University of Quebec at Rimouski, Rimouski, Canada.

Atlantic halibut (Hippoglossus hippoglossus) is currently the groundfish with the highest commercial value per unit weight in the Gulf of St. Lawrence (GSL), Canada. Following a collapse in the 1950s and subsequent decades of low abundance, landings of Atlantic halibut have steadily increased since the early 2000s, with 2021 recording the highest catch in the last 60 years at over 1500 tons. Currently, the biggest knowledge gaps concerning halibut in the GSL involve larvae and young juveniles, with halibut appearing in scientific surveys only after reaching around 25 cm. Eggs have never been collected in the GSL, larvae have only been detected once, and the location of early juvenile nursery habitats remains unknown. Improving our knowledge of the habitat use of early life stage of Atlantic halibut in the GSL is crucial to ensure the long-term sustainability of the stock. Larvae and young juveniles have been hypothesized to occupy more coastal areas, not covered by scientific surveys. We tested this hypothesis using otolith chemistry to gain information on halibut early-life history and reconstruct habitat use during those critical stages. Transects of 200 otoliths of juveniles and adults were analyzed by LA-ICP-MS (⁸⁸Sr, ¹³⁸Ba and ²⁴Mg). The end of each transect, representing the capture site, was used to distinguish elemental fingerprints from shallow (<100 m) and deep (>100 m) waters, and split moving window analyses were used to infer movements between shallow and deep areas. Our results suggest that during the first years of life, Atlantic halibut in the GSL have a mixed utilization of both shallow and deep habitats. These new findings hint at an alternative hypothesis stating that young halibut could distribute in coastal shallow habitats in the summer and early autumn, when bottom trawl surveys are carried out, but move towards deeper and warmer habitats from late autumn to early spring to avoid suboptimal freezing temperatures.

Eliza Lugten^1*, Edward Rutherford¹, Maddie Tomczak², Paul Glyshaw¹, Henry Vanderploeg¹, David Wells², Doran Mason¹, David M. Warner³, Richard Nash⁵, Audrey Geffen⁴

¹NOAA – Great Lakes Environmental Research Lab
²University of Michigan, Cooperative Institute for Great Lakes Research
³USGS Great Lakes Science Center
⁴University of Bergen
⁵Institute of Marine Fisheries – Norway

Bloater (Coregonus hoyi) are an important deepwater prey for piscivorous fish in the Great Lakes. However, Bloater recruitment and abundance in the Great Lakes has fluctuated greatly over the last one hundred years due to overfishing and habitat change. Previous research on Bloater recruitment focused on the effects of temperature, prey size, and prey availability on larval fish growth and suggested that recruitment rates were higher during years with warmer water temperatures. Bloater eggs are spawned offshore and are demersal, while larvae vertical distributions have varied over time. In Lake Michigan in the 1980s, Bloater larvae were most abundant at the surface during periods of high recruitment and adult density. From early 2010 to 2019, larvae were scarce at the surface and highest densities were lower in the water column. Recent sampling of Bloater larvae in Lakes Michigan and Huron in 2021-2022 revealed their densities again were highest at surface. We hypothesize that vertical distribution of Bloater larvae may be correlated with the variable vertical concentration of zooplankton prey which, in turn, may affect their growth, potential recruitment, and adult abundance. Zooplankton densities can be influenced by light, chlorophyll and predation densities. To determine whether the vertical distribution of zooplankton taxa influences distributions of Bloater larvae, we analyzed data on the vertical distributions and densities of zooplankton, Bloater larvae diets, and ambient water column temperature, across periods of high and low density of Bloater larvae. Results of our preliminary analysis will be presented.

Luis Avila^1,*, Maria Martinez-Silva¹, Pascal Sirois², and Gesche Winkler¹

¹Institut des Sciences de la Mer, Université du Québec à Rimouski, Canada. E-mail: luisavilaromero@aol.com
²Chaire de recherche sur les espèces aquatiques exploitées, Université du Québec à Chicoutimi, Canada.

In the critical nursery habitat of the St. Lawrence Maximum Turbidity Zone (MTZ), the cryptic copepod species complex of Eurytemora affinis is presumed to be pivotal in shaping the recruitment dynamics of fish larvae. Despite its significance as prey for several species, knowledge on the trophic contribution of the sympatric E. affinis North-Atlantic clade (NA) and E. carolleeae, remains scarce. This study aims to analyse their specific roles in trophodynamics of fish larvae of rainbow smelt and Atlantic tomcod, two dominant species exploiting the MTZ as an important nursery. We conducted surveys in the summer of 2021 along a 100 km stretch of the St. Lawrence estuary revealing spatial heterogeneity in the distribution of the cryptic prey species and larval fish. Based on stable isotope analysis (δ13C and δ15N) the cryptic prey species showed trophic plasticity shifting between herbivory and carnivory based on habitat and season. This may cascade through trophic transfer to the next trophic level. Eurytemora was the primary prey of larval rainbow smelt. Based on a novel SYBR green qPCR assay, E. affinis NA was recognized as the dominant prey over E. carolleeae, suggesting that rainbow smelt larvae heavily rely on this species for successful recruitment. Diet analyses of Atlantic tomcod will be completed, and ongoing analysis of isotopic mixing models will provide clarity on the contribution of the complex and other abundant prey to the diet of larval rainbow smelt and Atlantic tomcod. These trophodynamics enhance our comprehension of the functioning of this important nursery area.

Les D. Warren^1*, Edward Rutherford², Steve Pothoven², David Bunnell³, Paris Collingsworth^1,4, and Tomas O. Hӧӧk^1,4

¹ Department of Forestry and Natural Resources, Purdue University
² NOAA Great Lakes Environmental Research Laboratory
³ USGS Great Lakes Science Center
⁴ Illinois-Indiana Sea Grant

The Lake Michigan alewife (Alosa pseudoharengus) population is a key component of the lake’s food web and supports recreational fisheries targeting various salmonid species. These fisheries are now threatened as the alewife population has reached historically low levels. Alewife spawn in multiple habitats in Lake Michigan including drowned-river mouth lakes (DRMLs), tributaries, and nearshore environments. Due to its large volume compared to other habitats, the nearshore region of Lake Michigan has been considered the primary source of alewife recruits.  However, Lake Michigan has undergone substantial changes including lower productivity and increased water clarity in recent years. In the past, habitats like DRMLs provided warm, high turbid environments, with relatively high prey availability. Thereby, young alewife in these environments experience relatively early hatch dates, high growth rates and high survival. To assess if these alternative nursery habitats are now producing a greater share of alewife recruits, during 2021-2022 we replicated a previous study (2001-2002) consisting of weekly sampling of larval fish in Muskegon Lake (a DRML) and the nearshore waters of Lake Michigan adjacent to Muskegon Lake. Muskegon Lake had warmer surface temperatures, lower water clarity and greater zooplankton densities than nearshore Lake Michigan. Larvae collected in Muskegon Lake also hatched earlier and had higher growth rates. These results remain consistent with the study performed 20 years earlier. We continue to compare the results of the two studies to evaluate the relative importance of these alternative nursery habitats in sustaining the alewife population in Lake Michigan. 

Shota Tanaka^1,*, Shizuna Togoshi¹, Naotaka Yasue², Masahiro Nakamura³, Corinne M. Burns⁴, Dominique Robert⁴ and Akinori Takasuka¹,

¹Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
²Wakayama Prefectural Fisheries Experimental Station, Wakayama, Japan
³Fisheries Technology Institute, Miyazu Field Station, Japan Fisheries Research and Education Agency, Miyazu, Japan
⁴Institut des Sciences de la Mer, Université du Québec à Rimouski, Rimouski, QC, Canada

Growth history recorded in otolith microstructure is characterized by serial autocorrelation in fish larvae. Our recent study showed that growth autocorrelation during the larval stage of three clupeoid species, Japanese anchovy Engraulis japonicus, Japanese sardine Sardinops melanostictus, and Pacific round herring Etrumeus micropus was relatively high compared to other species studied to date. A possible mechanism driving growth correlation is a retroactive loop between growth performance and feeding success. Understanding the effect of larval growth on feeding success is a key to understanding which individuals have the enhanced survival potential. Here, we investigated the effects of somatic size, growth rate per se, and morphological development on feeding success in Japanese anchovy larvae collected by a commercial trawl in the Kii Channel, Japan, on 29 July (n = 331), 30 August (n = 262), and 9 September (n = 313) 2021. Growth rate and feeding success were derived from the analysis of daily otolith increments and gut contents of larvae. Somatic size at a given age had positive effects on feeding success in all samples. Thus, the high growth autocorrelation in anchovy larvae would be explained by the positive somatic growth–feeding relationship. On the other hand, a dome-shaped relationship between growth rate per se and prey size was found for one of the samples. Morphological development had positive effects on prey number. Growth rate and morphological development may also influence feeding success independently of somatic size. Future work is needed to elucidate the factors that cause variability in the growth–feeding relationship under different environmental conditions.

Gabrielle Perugini*¹, Hannah Murphy², Dominique Robert³, and Maxime Geoffroy¹

¹ Marine Institute of Memorial University of Newfoundland, School of Fisheries, Centre for Fisheries Ecosystems Research
² Fisheries and Oceans Canada, Northwest Atlantic Fisheries Center, Pelagic section
³ Universit ́e du Qu ́ebec ` a Rimouski, Institut des sciences de la mer

Capelin (Mallotus villosus) is a key forage species in the Newfoundland and Labrador (NL) ecosystem, transferring energy from lower-level plankton to higher-level vertebrate predators. In 1990-91, the Newfoundland capelin stock collapsed and has yet to recover. Since 1991, recruitment of age-2 capelin into the stock is positively correlated with survival during the first two weeks post-hatch. In NL, larval survival of capelin can be driven by both bottom-up forcing and top-down processes (i.e., predation). It has been suggested that selective predation by Atlantic herring (Clupea harengus) on capelin larvae found in high densities may be a mechanism for explaining recruitment failure of capelin in the Barents sea, however, this is unknown for NL capelin. The growth-mortality hypothesis claims that because predation decreases with increasing size, growth rate during the larval phase is related to survival. In this study, we used otolith-derived daily ages to compare growth rates of the 2021-2022 capelin larval cohorts to surviving 2021-22 cohorts at age-1, to test if fast-growing larvae evade predation and dominate the age-1 population. Future work will then assess the diet of juvenile Atlantic herring sampled in the vicinity of capelin spawning beaches in Trinity Bay, NL to test the hypothesis that slow-growing capelin larvae are predated upon more frequently. We expect that these findings will provide insight into the drivers of capelin larval survival and may contribute to Fisheries and Oceans Canada’s capelin forecast model in support of an ecosystem-based approach to fisheries management.

Tomas O. Höök^1,2* and Scott Koenigbauer¹

¹Department of Forestry and Natural Resources, Purdue University
²Illinois-Indiana Sea Grant College Program

The size of eggs produced by female fish reflects the combined influence of multi-generational selective pressures, within-lifetime environmental experiences, and maternal effects (e.g., the common observation that larger, older fish produce relatively large eggs). The Laurentian Great Lakes contain a multitude of distinct populations that vary in terms of long-term selective pressures, environmental conditions and demography, facilitating examination of intra-specific egg size variation and factors contributing to such variation. Previously, we have documented inter- and intra-population egg size variation of various Great Lakes fish species including cisco (Coregonus artedi), walleye (Sander vitreus) and yellow perch (Perca flavescens). We will describe patterns of egg size variation for yellow perch related to individual identity, maternal size, year, and population. Specifically, we demonstrate that egg size of yellow perch increase with female size, is related to annual thermal conditions and decreases with system size. We hypothesize that the latter pattern is reflective of the stability of environmental conditions experienced by young fish in small versus large systems.

Rachel Mailhot*¹, Dominique Robert¹, Pascal Sirois²

¹ Institut des Sciences de la Mer de Rimouski (ISMER), Université du Québec à Rimouski, Rimouski, QC, Canada
² Département des sciences fondamentales, Université du Québec à Chicoutimi (UQAC), Chicoutimi, QC, Canada

Atlantic redfish (Sebastes mentella) and Atlantic cod (Gadus morhua) are two groundfish species targeted by the winter recreational fishery in the Saguenay Fjord (Canada). The Fjord is separated from the St. Lawrence Estuary by a shallow 20-m sill, which limits exchanges between the two systems. Nevertheless, previous studies based on genetics, phenotypic traits and surveys of larvae indicated that the Saguenay groundfish stocks would be sink populations of the Estuary and Gulf of St. Lawrence. Understanding the mechanisms of stock renewal in the Saguenay Fjord is essential to ensure a sustainable winter recreative fishery. The overall objective of this study is to determine the movements of early life stages of redfish and cod in the Fjord using otolith chemistry as a natural marker of environmental conditions. More specifically, the study aims to evaluate when in their ontogeny Atlantic redfish and Atlantic cod would enter the Fjord system, and then to determine if the populations are resident in the Fjord or if they migrate between the Saguenay and the St. Lawrence. A comparison of two periods (2008 vs. 2023) was also carried out to assess the stability of migratory patterns over the last two decades. Preliminary results from the otolith chemistry suggest that the stock renewal in the Saguenay Fjord would be dependent on the migration of juveniles from the St. Lawrence and that the fish would mainly remain residents of the Fjord afterward.

Henrique A. Peres^{1, *}, Dominique Robert², Pascal Sirois¹

¹ Chaire de recherche sur les espèces aquatiques exploitées, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada
² Institut des sciences de la mer de Rimouski, Université du Québec à Rimouski, Rimouski, QC, Canada

Recent considerations of the growth-survival paradigm during the early life history of fishes have highlighted the need of ground-truth evidence before assuming that fast growth is always advantageous for a fish larva. Studies with the typical methodology of characterization of the survivors have consistently pointed to a significant number of larval cohorts where slow-growing larvae outlived their faster-growing counterparts. In the Saguenay Fjord, eastern Canada, an anadromous Rainbow Smelt (Osmerus mordax, Osmeridae) population spawn in a relatively long period in spring and early summer. With a frequent sampling targeting the same year-class of this population over its first year of life, we will study their growth-survival dynamics and recruitment endpoint. We have sampled the larvae and juveniles of the 2023 year-class from June to November, on 10 occasions, and plan to sample winter survivors in spring 2024. The examination of otolith microstructure will reveal how mean growth trajectories and hatch-date distributions progress from one sampling to the other. By utilising this population as a model, our objective is to test several hypotheses: (1) Is early-life mortality growth-selective, does it favour fast-growing individuals and, if so, at which stages? (2) Is the recruitment endpoint situated close to the metamorphosis or later in ontogeny? (3) Is there a hatching period favourable to growth and survival? (4) Does mortality during first winter influence juvenile size distribution and abundance? We expect our study to contribute to the theoretical framework of the growth-survival paradigm in fishes.

Richard D.M. Nash^1,* and Audrey J. Geffen²

¹ Centre for Environment, Fisheries and Aquaculture Science (Cefas), Fisheries Laboratory Lowestoft
² University of Bergen, Department of Biological Sciences, Fisheries and Marine Biology Group

Winter does not favour smaller individuals, and winter mortality could have a significant impact on recruitment. Many temperate fish species avoid over-wintering as larvae (pre-metamorphosis) with strong reproductive seasonality and/or maximising larval or summer growth. Evidence is growing that many temperate fish species overwinter as pelagic larvae. This includes smelt, autumn-spawned herring, plaice and lemon sole. In other cases, young-of-year fish persist on nursery grounds throughout the winter as small individuals, even as most of the cohort departs for deeper water. There is a good theoretical basis that links winter mortality to growth/survival, and data on a number of species tracking pre- and post-winter survivors. However, direct observations of larval and YOY cohorts or sub-cohorts are rare, mostly due to the lack of standard larval or juvenile surveys through winter months. Better data coverage is needed during these periods for recruitment indices, although studies targeting winter survivors is challenging. We consider a multi-species view, evaluating the available overwintering data and including a consideration of cases with offset spawning seasons. Even though it is difficult to quantify processes that occur in the late- and post-larval period, it may be that these are significantly more important for recruitment. In future climate scenarios, it may be that mismatch of temperature and productivity may reduce overwintering, or else lead to higher levels of interactions (including cannibalism).

Spencer T. Gardner^1,*, Mark D. Rowe², Pengfei Xue³, Xing Zhou³, Peter J. Alsip⁴, David B. Bunnell⁵, Paris D. Collingsworth^1,6, Edward S. Rutherford², and Tomas O. Höök^1,6

¹ Purdue University, Department of Forestry and Natural Resources
² National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory
³ Michigan Technological University, Department of Civil, Environmental, and Geospatial Engineering
⁴ University of Michigan, Cooperative Institute for Great Lakes Research
⁵ U.S. Geological Survey, Great Lakes Science Center
⁶ Illinois-Indiana Sea Grant College Program, Purdue University

In large lake ecosystems, e.g., Lake Michigan, USA, larval fish environmental experiences and recruitment dynamics are directly influenced by climate-controlled physical transport processes (i.e., wind and temperature). Water currents advect essentially-passive larvae through heterogeneous habitats affecting access to favorable (a)biotic environments with direct consequences to growth and survival. While the importance of physical transport processes have been well documented in marine systems, few examples have been compiled for freshwater systems. Here, we integrate a climate, hydrodynamics, biogeochemical, particle dispersion, and individual-based bioenergetic model to evaluate historic and potential future patterns of climate-induced larval (alewife – Alosa pseudoharengus; yellow perch – Perca flavescens) transport and assess consequences for larval overlap with suitable physico-chemical conditions and prey densities. Analysis of climate-controlled physical transport processes revealed a strong seasonal effect on larval advection patterns, with greater retention of larvae in more favorable nearshore habitats prior to summer stratification. Mid-century (2040-2050) forecasting of larval growth and survival suggested small increases in growth and survival rates which varied by species, hatch date and hatch region of Lake Michigan. Small increases in larval growth occurred despite increasing metabolic demands and lower overall densities of zooplankton. These results reiterate the significance of physical transport processes to larval recruitment in large lake ecosystems.

Christopher S. Murray^1,*, Lucas Jones², Emma Siegfried², Max Zavell², Zosia Baumann², David Wiley³, Nina Therkildsen⁴, Neel Aluru¹, Hannes Baumann²

¹Woods Hole Oceanographic Institution, Biology Department
²University of Connecticut, Avery Point, Department of Marine Science
³NOAA, Stellwagen Bank National Marine Sanctuary
⁴Cornell University, Department of Natural Resources and the Environment

Northern sand lance (Ammodytes dubius) embryos are unusually sensitive to ocean acidification (OA). Previous research has shown a 25% decrease in hatching success under elevated pCO₂projected for the Gulf of Maine this century. OA appears to interfere directly with the hatching process, as exposed embryos exhibit an extended hatching duration, and many normally developed embryos fail to hatch. We hypothesize that elevated pCO₂ disrupts the expression of choriolytic hatch enzymes, which are vital for pre-digesting the egg membrane prior to mechanical hatching. To test this hypothesis, we again reared Northern sand lance embryos under two pCO₂ treatments (400 and 2,000 µatm) crossed with two dynamic temperature regimes (10°→7°C and 10°→5°C). As predicted, embryos reared under 2,000 µatm pCO₂ experienced delayed hatching and a 62% reduction in average cumulative hatching success. The effect was stronger under warm (-73%) compared to the cool temperature treatment (-43%). To investigate the impact of elevated pCO₂ on the timing and extent of hatch enzyme gene expression, we sampled living embryos over an eight-day period spanning before, during, and after peak hatching. We identified DNA sequences for two hatch enzymes, high choriolytic enzyme (hce1 and hce2) and low choriolytic enzyme (lce1), in our recently assembled Northern lance genome. Treatment effects on gene expression were measured via quantitative real-time PCR. These results provide mechanistic insights for CO₂-induced hatching failure in Northern sand lance, with important implications for the future reproductive success of this foundational forage fish.

Neele Schmidt^1, *, Maddi Garate-Olaizola², Marc Hauber³, Jan Dierking⁴,Anssi Laurila², David Berger²

¹Department of Ecology & Genetics, Evolutionary Biology Centre, Uppsala University, Cramérgatan 3, 621 57 Visby, Sweden
²Department of Ecology & Genetics, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, 752 36 Uppsala, Sweden
³Department of Biology and Environmental Science, Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, 392 31 Kalmar, Sweden
⁴GEOMAR Helmholtz Centre for Ocean Research, Kiel, 24105 Kiel, Germany

The Baltic cod (Gadus morhua) population is severely depleted due to overfishing, poor management, and habitat degradation. Further, the population has suffered an alarming decrease of size at first maturation and growth. However, whether, and if so how, the reduced size of cod affects recruitment in the Baltic Sea, is not yet fully understood. We therefore investigated different traits of the offspring from Baltic cod in relation to parental fish size. Broodstock from the eastern Baltic cod stock were caught between February 2021 and March 2023 and kept in controlled tanks with seawater and natural light at the research station Ar, Gotland, Sweden. The study spans April to August 2023, covering the natural spawning period. Daily egg collection and weekly assessments of egg quality, including deformities, developmental stage, size, and thiamin content, were conducted. Additionally, 100 eggs per tank were incubated for 14 days, with daily monitoring of egg/larvae mortality and hatching. We analyzed total survival, hatching success, and larval quality, including deformities and length. This study aims to illustrate the effect of parental size on eggs and larvae of Baltic cod throughout one spawning season. Further, we aim to determine whether even small-sized cod can produce high-quality offspring in a controlled environment with a sufficient nutrient-rich feed supply. These findings will also impact the selection of broodstock in aquaculture, particularly for restocking initiatives, among other applications.

Max Zavell^1*, Jenna O’del^2,3, Matthew Mouland¹, Jacqueline Webb², and Hannes Baumann¹

¹Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340
²Biological Sciences, University of Rhode Island,  120 Flagg Road, Kingston, RI 02881
³Division of Coastal Resources, Rhode Island Department of Environmental Management, 301 Great Island Road, Narragansett, RI 02882.

Schooling in fishes increases foraging success and decreases predation risk, and sensory input from the lateral line system (LL) plays an important role. Previous studies have examined the effects of ocean acidification (OA, elevated CO₂) on other larval fish behaviors, here we present the first results on the effects of OA on schooling and development of the LL in silversides from fertilization to 25 days post hatch (dph) under control (400 µatm, ~8.15 pH) and elevated (4200 µatm, ~7.20 pH) pCO₂ conditions. Onset of schooling was inferred from changes in the distance distribution between larvae (from 2 to 25 dph) obtained from thousands of calibrated digital images. We found evidence that CO₂ delays the onset of schooling by 10 dph (control at 8 vs. elevated at 18 dph), as marked by a change in distance distributions (from random to a ,clumped’, ‘schooling’ pattern). This might be due to differences in timing of neuromast differentiation and LL canal development, which we subsequently assessed with fluorescent staining (4-di-2-ASP) and SEM, respectively. Preliminary analyses show no differences in the timing of increase in neuromast numbers or in the timing of LL canal development between CO₂ treatments. Further work is needed to explain this result, as a delay in the onset of schooling is predicted to be detrimental to larval foraging and ultimately to survival.

Robin DeBruyne^1,*, Stacy Provo^1,⁑, Stephen Chong², Stacey Ireland¹, Savannah Blower^1,⁑, Edward Roseman¹

¹U.S. Geological Survey, Great Lakes Science Center
²Ontario Ministry of Natural Resources and Forestry
^⁑Work done under contract with U.S. Geological Survey

The St. Marys River connecting lakes Superior and Huron has many fish spawning and nursery areas serving as major sources of production for riverine and Great Lakes fisheries. Documented larval densities and habitat use along the river continuum in 1985 showed that coregonines, including lake whitefish and cisco, occupied nearshore areas while prey fishes were more abundant in the deeper channel habitats. Recent research conducted near the St. Marys River Rapids revealed large densities of larval prey fish species, as well as evidence of coregonine reproduction. To gain new insight about larval fish community dynamics and habitat use throughout the St. Marys River, we sampled a variety of habitat types along the entire length of the river in 2022. Our objective was to determine the phenology, magnitude of larval fish drift/production, and habitat use of larval fishes throughout the St Marys River. Over 40,000 larvae were collected from April to September. Areas of the river with the highest catches of coregonine larvae were along the U.S. shore during April and May. Rainbow smelt had the highest catches in the upper river. Burbot were found throughout the river during the spring and early summer. Yellow perch were abundant in Munuscong Lake, a large bay with abundant vegetation. Other species captured in the river include sculpins, Catostomids, troutperch, Morone, and Cyprinids. All species present in the 1985 study were present in 2022, with additional species found likely due to environmental improvements and expanded sampling coverage. The distribution of fishes throughout the river and to the furthest downstream areas suggests that the St. Marys River continues to serve as a transit corridor for larval fishes between lakes Superior and Huron and a production source of larval fishes of interest (e.g., coregonines, rainbow smelt) for Lake Huron.

Sierra N. Wachala^1,*, Kevin D. E. Stokesbury

¹University of Massachusetts Dartmouth – School of Marine Science and Technology (SMAST), Marine Fisheries Field Research Group

Construction on the first commercial offshore wind farm in the United States began in 2023 off the coast of New England. While climate change has significant negative impacts on commercially important species and their local fishing communities, the growing concern is that new offshore wind farms will compound these negative effects. Larval fish are especially vulnerable due to their reliance on currents and mixing for movement and feeding which may be disrupted by the turbines, as well as sensitivity to electromagnetic fields produced by the power cables. This study is the first in the United States to establish ichthyoplankton community baselines in proposed/operating wind farm areas off southern New England. Using a Before-After-Control-Impact (BACI) design in the Vineyard Wind 1 area, the upper half meter of the water column was sampled at 30 stations in both the control and impact areas using a 1320-micron neuston net. Samples were collected from May through October for 2.5 years pre-construction (2019-2021), 1 year during construction (2023), and will be collected for 3 years post-construction (2025-2027). In the pre-construction phase, 6,114 fish were collected, primarily in the impact area during 2020 (n=4,165). The dominant fish was Urophycis sp. composing 81.3% of the samples, followed by Peprilis triacanthis and flatfish species composing 13% and 2.3% respectively. In the construction phase, the most abundant taxa was also Urophycis sp., and a total of 26 taxa were observed during this sampling period. Given that more than 95% of the individuals collected in our samples are commercial species, this research is essential to determine the long-term effects of offshore wind operations and to mitigate negative impacts in future proposed areas that could cause major financial and economic disruptions in the United States’ fisheries.  

Alison L. Deary^1*, Steven M. Porter², Todd Miller³, Hamilton W. Fennie², Kelia E. Axler²

¹ US Fish and Wildlife Service, Abernathy Fish Technology Center, Longview, WA USA
² NOAA Alaska Fisheries Science Center, Seattle, WA USA
³ NOAA, Alaska Fisheries Science Center, Auke Bay Laboratory, Juneau, AK USA

Sablefish (Anoplopoma fimbria) have an extensive native range in the eastern Pacific Ocean, extending from northern Mexico to the Bering Sea with the greatest abundance in the Gulf of Alaska (GOA). Sablefish are an extremely valuable commercial species in the United States, and in Alaska, ranking as one of the most valued species per pound. Their population was in decline from the 1980s until 2014, when subsequent year classes have been at or exceeded average recruitment. Year class strength is likely set early in the first year when Sablefish are most susceptible to environmental variability. Given the recent increase in duration, magnitude, and frequency of marine heatwave events in the GOA, we evaluated the impact of sea surface temperature (SST) on the starvation resiliency of first feeding Sablefish. Gametes were received from the Manchester Seawater Laboratory (NOAA Northwest Fisheries Science Center) and larvae were reared at the USGS Western Fisheries Research Center at two temperatures: 6°C (average spring SST) and 9°C (warming scenario). Specimens were collected daily from feeding trials to determine condition via morphometrics and RNA/DNA ratios. At 9°C, the time to starvation was ~50% shorter at 12 days (vs. 23 days). In the 9°C, larvae initially similar in size and weight between treatment but the fasted individuals were significantly shorter in length and weighed less compared to the fed treatment with an inflection happening around day 6. These data suggest that in a warming GOA, first feeding Sablefish are less resilient to starvation and are significantly shorter in length, which inhibits their ability to effectively forage for prey even before reaching the lethal point of no return. The results of this study contribute to data gaps identified in the current iteration of the established Sablefish Individual Based Model and refine future applications of the model to ecosystem-based fisheries management.

Hannah Sciarappa^1,2*, Evan D’Alessandro¹, Joan Browder², and Joe Serafy²

¹Rosenstiel School of Marine, Atmospheric, and Earth Sciences, University of Miami
²National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Fisheries Science Center

Spotted seatrout (Cynoscion nebulosus) are useful biological indicators of changing estuarine environments due to their lifetime residency in a single estuary. One such estuary, Florida Bay, has been negatively affected by decades of water management practices in South Florida depriving the bay of the historic freshwater sheetflow that is currently being restored by the Comprehensive Everglades Restoration Plan (CERP). The purpose of this study was to investigate potential relationships between environmental factors, temperature and salinity, and juvenile spotted seatrout growth in Florida Bay. Daily growth increments from otolith analysis of 95 individuals were paired with the mean daily salinity and temperature conditions that each experienced. First, the UPGMA classical clustering algorithm was used to group individuals according to similarity of the temperature regimes experienced. Next, regressions were run for each cluster group with cumulative otolith radius as the dependent variable and daily age as the independent variable, and ANCOVAs were performed to detect any significant differences in growth rates of the different cluster groups. Seatrout that lived in higher temperature regimes (mean of ~30°C) grew significantly slower than others that experienced lower temperatures. Seatrout that lived during a hypersalinity spike (>40ppt) grew faster than the other groups that experienced lower salinities. Most of the spotted seatrout in the hypersalinity group were caught around the same time and same place, so these results should be interpreted with caution. Temperature typically enhances fish growth, but in this study the high-temperature regimes of Florida Bay negatively impacted growth. This study’s findings are important to evaluate the future implications of the CERP and anthropogenic climate change on juvenile fish growth.

Max Zavell^1*, Matthew Mouland¹, Devan Barnum¹, Catherine Matassa¹, Eric Schultz², and Hannes Baumann¹

¹Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton CT, 06340
²Ecology and Evolutionary Biology, University of Connecticut, 75 N. Eagleville Road, Storrs CT, 06269.

Black Sea Bass (BSB, Centropristis striata), the northernmost serranid in the northwest Atlantic, is an example of climate change mediated range expansions. Southern New England has seen a steep increase in abundance over the past decade, aided perhaps by exceptional warming rates, yet present inshore winter temperatures preclude a year-round presence, requiring individuals to migrate offshore. We quantified winter growth and lipid accumulation in juveniles over three experiments simulating two overwintering strategies: migrating offshore and staying inshore. Experiments 1 and 2 quantified mortality and individual length (GR) and weight-specific growth (SGR), and lipid content under constant food-levels and three static temperatures (Exp1; 6,12,19°C) or an offshore temperature profile (20-13°C) and seasonally contrasting food-levels (Exp2). Experiment 3 quantified these metrics across three size-classes and an inshore temperature profile (17-5-12°C). Across all experiments mortality was low and independent of size, while growth/lipid accumulation continued at temperatures ≤ 6°C. While individuals survived below 6°C, optimal overwintering occurs at 12°C (offshore), where lipid accumulation was greatest and average winter growth was 29 and 20× higher in length and mass in Exp2 (0.2 mm d^-1; 0.6% d^-1) vs. Exp3 (0.007 mm d^-1; -0.03% d^-1). Juveniles exhibit various strategies overwinter including compensatory growth (Exp2), and small individuals ‘defending’ a critical energy threshold by consuming 1.25× more food than larger conspecifics. While juveniles appear more cold-tolerant than previously thought, overwintering in inshore habitats is currently energetically unfavorable for BSB. Continued warming will further reduce winter severity and perhaps soon allow BSB to maintain a year-round inshore presence.

Øystein Langangen^1,*, Tora Olsen¹, Geir Ottersen², Elena Eriksen², Joël M. Durant¹

¹Department of Biosciences, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway.
²Institute of Marine Research P.O. Box 1870 Nordnes, NO-5817 Bergen, Norway.

Fish tend to alter their distribution according to local climate velocities. The population dynamics consequences of such distributional shifts are potentially key to understanding climate effects on fish. In general, suitable adult spawning areas may be less suitable for the larvae and juvenile stages. We investigate how the spring spawning location of Atlantic cod (Gadus morhua) in the Barents Sea may affect the size of the offspring in the fall. The size of the juveniles at this time of the year is likely a very important factor for year class formation and population dynamics. We analyze a time series of commercial landing-ticket data to quantify spawning location in spring combined with survey data targeting juveniles in the fall to investigate the effect of a northern shift in spawning on juvenile size. Our analysis reveals a negative association between northward spawning and juvenile size, a positive effect of sea temperature on size, and a negative effect of high spawning stock biomass on size. The size reduction is likely to greatly affect population dynamics and may have played a significant role in the recently observed reduction in the population’s spawning biomass.

Jennifer R. Powell^1,* and Nicholas E. Mandrak²

¹University of Toronto Scarborough, Department of Physical and Environmental Sciences, Mandrak Lab
²University of Toronto Scarborough, Department of Biological Sciences, Mandrak Lab

Larval light traps, while a useful tool, can also be difficult to deploy effectively due to wide variations in the effectiveness of different gears and light lures, issues that have been well documented in the literature. Another potential issue is the effect of within-trap predation by juvenile fishes on larval abundance in light traps. To test whether exclusion of juvenile fishes from quatrefoil light traps would improve larval collections, mesh was applied to traps of two different styles utilizing two different light lures and tested against unmeshed controls. Both the number and size of juvenile fishes entering the traps was significantly reduced in meshed traps. Conversely, the number of collected larvae significantly increased in meshed traps overall, although the effect varied depending on the type of light lure used.  Within-trap predation has the potential to significantly impact larval catch results and should be taken into consideration during study design.

Ghizlane Banousse^1,*, Christina Semeniuk², Céline Audet¹

¹ Institut des sciences de la mer de Rimouski (ISMER), Université du Québec à Rimouski (UQAR)
² Great Lakes Institute for Environmental Research (GLIER), University of Windsor

The negative impacts of climate change on aquatic organisms and the increased risk of extinction for many species have led to the implementation of captive breeding programs to preserve these species. However, extended captivity can modify key phenotypic traits such as behavior that are necessary for adapting individuals to natural conditions upon release. In this study, we examined behavioral traits in first-feeding fry (6 months post-fertilization) from two strains of Brook charr (Salvelinus fontinalis): a wild strain from Lambert Lake, Forestville, Québec, and the Laval strain, which originated from a distinct stock from Laval River, Forestville, Québec, and has been captive for six generations. Eggs and larvae from each strain were incubated and reared, respectively, under the same environmental conditions in the hatchery system of La Pourvoirie des Bouleaux Blancs, Forestville Québec. Using open-field, mirror, and anti-predator tests, we observed significant behavioral differences between the strains. Fry from the Laval strain showed greater boldness and aggression (p-value < 0.001) than the wild strain, which, in turn, exhibited higher anxiety (p-value < 0.001). Additionally, fry mass affected predator response, with larger fry showing stronger anti-predator behavior regardless of strain (p-value = 0.02). These findings highlight the effects of domestication on behavior and can inform strategies to enhance breeding environments for improved survival after release.

Emma Siegfried^1,2*, Darren Johnson¹

¹California State University, Long Beach, Department of Biological Sciences
²University of Connecticut, Avery Point, Department of Marine Sciences

Population recruitment is a dynamic process that is influenced by both the quantity and quality of offspring. Mortality is typically strong during the early life stages of fishes and can be highly selective with respect to phenotype. As a result, innate differences in larval phenotypes may be an important indicator of offspring quality. In a study of morphology and development of larval California Grunion, we show that there is an optimal set of values for larval morphology, and that families vary widely in the degree to which they match the phenotypic optimum. Developmental Inaccuracy is a metric that reflects average distance from the phenotypic optimum and the resulting decline in relative fitness. To infer developmental accuracy and optimal phenotype for our study population, we sampled 59 families and compared how their distributions of size-standardized morphology changed over time. Families that exhibited little change in morphology during development indicated high accuracy. Alternatively, families undergoing large shifts in morphology indicated low accuracy. Because shifts in morphology could occur via selective mortality or compensatory development, distance from the phenotypic optimum serves as a measure of fitness load. In this study, larvae with larger stomachs and smaller eyes had lower fitness. Surprisingly, the corresponding drop in fitness was due to reduced growth rather than immediate, selective mortality. These results indicate that larvae with suboptimal phenotypes can undergo compensatory development, but this compensation is associated with a substantial reduction in somatic growth. Another important result of this study was that the degree of developmental inaccuracy was highly variable among families. To examine this variation further, we tested whether developmental inaccuracy was related to maternal fecundity and found that mothers producing more offspring tended to have offspring with a higher degree of developmental inaccuracy and fitness load. Our results thus reveal a little known, but highly important, tradeoff between offspring number and offspring fitness.

Jacob Jaskiel^1,*, Hannah Aichelman¹, James Fifer², Christina Hernandez³, Jan Witting⁴, Sean Mullen¹, and Randi Rotjan¹

¹Boston University Department of Biology – Ecology, Behavior, and Evolution
²University of California San Diego – Rose Lab
³Cornell University
⁴Sea Education Association

Until recently, it was assumed that tuna populations were panmictic and each species represented a single stock because of their high migratory potential. This assumption shapes contemporary fisheries management practices which regulate pelagic fishes as basin-wide or global stocks. However, advances in genome sequencing have increased the capacity to detect differences in allele frequencies within and between populations, revealing signatures of population structure even in highly migratory species. The potential for previously unrecognized populations of commercially significant fishes demands a rethinking of how these species are managed spatially to avoid localized depletions and losses of genetic diversity in the face of anthropogenic impacts. The Central Pacific is an important tuna fishing and spawning ground, and together with the Western Pacific accounts for around 60% of the global tuna harvest. As such, there exists a clear need to better understand the population dynamics of tunas in this region to improve management and harvest strategies. For the present study, larval and adult Skipjack, Yellowfin, and Bigeye tuna were collected in the equatorial Pacific from 2015-2022 and DNA was sequenced using 2bRAD-seq. Here we confirm the identities of several species of tunas and detect preliminary indicators of potential population structure through analysis of outlier loci that are likely under selection. This study confirms the utility of 2bRAD for identifying species and profiling genetic variation in fishes such as tunas using low cost, high throughput sequencing techniques and highlights the need to update fisheries management practices and harvest strategies to account for cryptic genetic variation within commercially important fish species.

Thornton A. Ritz^1*& John M. Farrell¹

¹State University of New York – College of Environmental Science and Forestry, Department of Environmental Biology, Thousand Island Biological Station 

Estimating critical period survival (CPS) of fishes is difficult due to high mortality and the challenge in capturing small and elusive individuals in complex habitats. Historically, St. Lawrence River surveys have captured young-of-year (YOY) Northern Pike (Esox lucius) emigrating from wetlands following critical period development. As an r-selected species, estimation of Northern Pike CPS can be difficult using traditional mark-recapture methods highly sensitive to small sample sizes. Iterative mark-recovery models incorporating Bayesian inference have been used to estimate probability of survival and recovery of marked individuals and could help overcome these challenges. To test this, we released 32,347 Northern Pike swim-up larvae marked with oxytetracycline (OTC) while simultaneously monitoring dissolved oxygen and water temperature through the critical period. Northern Pike YOY were then captured daily over an 18-day period, and their otoliths were extracted and viewed for an OTC mark. Using our capture history, we fit a mark-recovery model with a multinomial likelihood and estimated the probability of recovery to be 0.252 and the probability of survival to be 0.013 during our study period. Water temperature had a significant positive effect on survival as warmer temperatures likely promoted growth and development of stocked individuals. Bayesian inference was essential in accurately estimating CPS survival and recovery of Northern Pike and could be useful in other studies attempting to estimate early life stage survival.

John E. Majoris^{1,2,3 *}; Micaela Justo²; Michael L. Berumen²; Simon J. Brandl³

¹ Department of Life Sciences, Texas A&M University-Corpus Christi, 6300 Ocean Drive, Unit 5800, Corpus Christi, TX 78412, USA
² Red Sea Research Center, Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, Makkah Province 23955-6900, Saudi Arabia
³Department of Marine Science, The University of Texas at Austin, Marine Science Institute, 750 Channel View Drive, Port Aransas, TX 78373, USA

Heterochrony, variation in the rate or timing of developmental processes, is an evolutionary mechanism that generates variation in morphological and behavioral traits among closely related species. The early life history of most marine organisms includes a pelagic larval phase, during which developing larvae experience substantial morphological changes that are accompanied by an increase in swimming performance among other behavioral changes. While previous studies have compared developmental processes across marine taxa, few have explored how heterochrony contributes to variation in larval morphology and performance traits among species within the same genera, and how such changes in early development relate to adult life history strategies. In this study, we compared early life history strategies among three congeneric Dottybacks (Pseudochromidae) and found subtle differences in growth rate, developmental transition timing, and swimming performance. Ultimately, heterochrony among species resulted in larvae with different morphologies at settlement. These differences correlate with variation in post-settlement habitat use and reproductive success, highlighting the intricacies of early life history variation among closely related species and their implications for understanding evolutionary processes in marine organisms.

Tony Miskiewicz ^1,2* and Kevin Conway ^1,3

¹ Ichthyology Department, Australian Museum Research Institute, Australian Museum, Sydney, NSW,2010
² School of Biological, Earth & Environmental Sciences, University of New South Wales, Sydney, NSW, 2052, Australia
³ Department of Ecology and Conservation Biology, Texas A&M University, College Station, TX 77843, USA

Clingfishes (F. Gobiesocidae) are a moderately sized family distributed worldwide in tropical and temperate regions in intertidal and subtidal marine waters.  In southern Australia waters, 10 genera occur.  Adults of different genera are small (2.5-10 cm SL) and vary considerably in their morphology, but all are characterised by well-developed ventral adhesive disc. Clingfish larvae are previously undescribed from Australian waters.  In this paper, larval development of species from five genera: Aspasmogaster, Barryichthys, Cocleoceps, Creocele and Parvicrepis are described.  Larvae of the different genera varied in their body morphology and the size of notochord flexion, disc formation, fin development and pigmentation patterns during larval development.  Based on the observed differences in larval characters, the larvae of the five genera will be compared with the phylogenetic classification into sub-families based on adult morphology.

Madeline Tomczak^1*, Edward Rutherford², Doran Mason², Mark Rowe², Peter Alsip², Paul Glyshaw², Eliza Lugten², Heather Truong¹, Tait Algayer¹, Rao Chaganti¹, Lucas Vanderbilt¹, Steve Ruberg², Kristen Rosier², Russ Miller¹

¹University of Michigan, Cooperative Institute for Great Lakes Research
²NOAA Great Lakes Environmental Research Laboratory

Factors that may affect distribution, survival and potential recruitment of larval Alewife, an important prey fish in Lake Michigan, are not well known. Past studies examining alewife larvae in southeast Lake Michigan indicate their survival may be negatively influenced by wind-generated upwellings. The larvae are advected away from warm and productive nearshore nursery habitats to colder, less productive environments offshore, potentially decreasing larval survival and growth. However, the entirety of the impact of Alewife larval dispersion including survival after upwellings is unknown. We hypothesized that early hatching Alewife may experience lower growth and higher mortality compared to larvae hatching in July, when temperatures and zooplankton biomass are favorable and upwellings are less common. We used hydrodynamic models, subsurface drifters, AUVs with acoustics, and plankton nets to forecast, track, and repeatedly sample distributions of alewife larvae, zooplankton prey, and environmental conditions before and after an upwelling event in June and July of 2023. All fish were identified and measured, and their ages, hatch dates, and growth rates were estimated from otolith analysis. Preliminary results indicate there was no overlap between cohorts of larval Alewife present before and after the upwelling in June. Individual growth rates, densities, and apparent survival were higher for larvae collected in July compared to those collected in June. We plan to repeat the study this summer (2024), and use a larval advection model to backcast possible hatch locations of the two cohorts of larval Alewife.

Hannes Baumann^1*, Alvaro Gallardo², Cristian Gallardo², Mauricio Urbina³

¹University of Connecticut, Department of Marine Sciences
²Universidad de Concepción, Centro Interdisciplinario para la Investigación Acuícola (INCAR)
³Universidad de Concepción, Departamento de Zoología

Sabbatical freedom and an NSF grant allowed spending the past 8 months in Chile to find new collaborators and then design, construct, and execute a large common garden experiment on Chilean silverside (Odontesthes regia, Atherinopsidae) early life stages. The choice of an Atherinopsid was strategic, because it will ultimately facilitate comparisons to the well-studied Northern hemisphere silverside system (e.g., Menidia menidia, Atherinops affinis). Furthermore, O. regia’s large geographic distribution along the South-American Pacific coast (9°N – 43°S) enables such comparisons across another independent, large climate gradient that is suitable to study evolutionary patterns such as counter- and cogradient variation. It could lead to the discovery of a relationship between gradient and adaptation strength across space and – by inference – time. Overall, this first experimental year was a success, despite the capricious local impacts of a strong El Niño. Now, the first tantalizing patterns are beginning to emerge, indeed suggesting the existence of countergradient growth variation in a southern hemisphere fish.

^1* John B. Hume, ² MargaretF. Docker, ² SaraGood, ³ RalphLampman, ⁴ JacquesRinchard, ⁵ TrishaSearcy, ⁶ Michael P.Wilkie and ⁵ Nicholas S.Johnson

¹ Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI 48824;
² Department of Biological Sciences, University of Manitoba, Winnipeg, MB R3T 2N2;
³ Pacific Lamprey Project, Fisheries Resource Management Program, Department of Natural Resources, Yakama Nation, PO Box 151, Toppenish, WA 98948;
⁴ Department of Environmental Science and Ecology, State University of New York Brockport, Brockport, NY 14420;
⁵ US Geological Survey, Great Lakes Science Center, Hammond Bay Biological Station, Millersburg, MI 49759;
⁶ Department of Biology and Laurier Institute for Water Science, Wilfrid Laurier University, Waterloo, ON N2L 3C5.

Sea lamprey are a species of great management concern, both in the Great Lakes where they are non-native and in the Atlantic basin where they are native. One major impediment to sea lamprey management is access to and knowledge of certain life stages, such as young-of-the-year (YOY) and parasitic juveniles. Recently, a sea lamprey aquaculture initiative was established to fill these knowledge gaps by generating sea lamprey in the lab and attempting to complete the life cycle in captivity. Sea lamprey were spawned in 2022 and 2023 and reared under a range of conditions to establish survival and growth rates for the first 12 months of life. We found that static (58%) and flow-through (74%) set ups were suitable for high survival to hatching, more so than static water with water exchanges (44%). Density was the major factor influencing growth and survival of YOY sea lamprey. Growth rate was negatively correlated with density, and 2-3x greater rates of growth were observed in YOY reared at density of 0.15 – 5 larvae per m^2 compared to 15 m^2. Larvae grew to an average of 55 mm in just 6 months, and 71 mm after 12 months, values several times greater than is observed in the wild. Survival was greatest at densities < 5 larvae per m^2 (72 – 100%) whereas survival at 15 larvae per m^2 was just 3%. These data indicate early life stage survival can be high under certain conditions and growth can be rapid. Both factors could influence how sea lamprey managers make decisions.

Benjamin C. Young^{1, 2*}, Ali AL Shaikhi¹

¹National Livestock and Fisheries Development Program, Ministry of Environment, Water & Agriculture
²Taiwan International Cooperation and Development Fund

This study aims to assess the present state of larviculture among the leading aquaculture companies in Saudi Arabia, focusing on informing future sustainability strategies. Evaluations were performed on seven marine fish hatchery facilities. The factors estimated were production capacity, existing infrastructure, main culture fish species, source of broodstock and seed stock, and a range of water temperature and salinity. Six of seven coastline marine fish hatcheries lacked broodstock capacity. The live food production section was absent in five hatcheries. Most of the culture species in hatcheries were Asian sea bass (Lates calcarifer), Gilt-head bream (Sparus aurata), Sabaki tilapia (Oreochromis spilurus), and Sobaity seabream (Sparidentex hasta). Only two hatcheries produced fry, with an average monthly fry production of 500,000–1,000,000 individuals. The source of seedstock on five hatcheries depended on imports or other hatcheries. The sustainability strategies can be focused on increasing broodstock capacity, live food production, and new culture species.

Benjamin C. Young^{1, 2*}, Ali AL Shaikhi¹

¹National Livestock and Fisheries Development Program, Ministry of Environment, Water & Agriculture
²Taiwan International Cooperation and Development Fund

This study aimed to estimate the survival rate and growth performance of Snubnose pompano (Trachinotus blochii) larvae at various salinity levels: 25‰, 33‰, 39‰, and 42‰. The experiments were conducted in triplicate, each with 1000 larvae per tank. The control group was maintained at a salinity level of 42‰ and a temperature range of 28.3°C–31.0°C. Eighteen hours post-hatching, larvae were transferred directly to different salinities (25‰, 33‰, 39‰, and 42‰), and their survival rate and growth performance were monitored. The results indicated that the optimal salinity for larval survival ranged from 33‰ to 39‰, with 100% mortality observed within 4 days post-hatching (dph) at a salinity level of 42‰. While growth performance did not significantly differ among the experimental groups, there was a notable difference in the control group. After 21 days, stronger cannibalism was observed in the 25‰ groups compared to the other groups. In conclusion, this study suggests that pompano larviculture is feasible within salinity ranges of 33‰–39‰.

R. Christopher Chambers¹*, Beth A. Phelan¹, Ehren A. Habeck¹, Delan J. Boyce¹, Christopher R. Spino¹, Michael B. Dobiesz¹, and Daniel Ward²

¹NOAA, Northeast Fisheries Science Center, Howard Marine Sciences Laboratory
²Ward Aquafarms, LLC

High survival and robust condition of early life stages (ELS) of individuals from candidate aquaculture species are desired endpoints but these are often bottlenecks in the successful production of marine finfish.  Our research team of NOAA staff and colleagues from the fish-farming industry is examining these bottlenecks in the ELS of Tautog, Tautoga onitis, a spring-spawning, cold-water wrasse (Labridae) of the NW Atlantic.  Three factors are being evaluated.  First, how does egg quality vary within and among females across the spawning season?  Second, how does production of hatchlings and juveniles vary with thermal regimes?  Third, how does the production of juveniles vary with the stocking density of larvae and the quantity of live feed?  Response variables used to address these questions include 1) eggs size, 2)survival, period duration, size and condition at hatching, 3) morphometric-based size and shape of larvae across a 35-dph ontogenetic series, and 4) size and metabolic rates of early juveniles at the terminus of the rearing experiments.  The juveniles produced in these experiments and concurrent mass-rearing efforts are being used for grow-out studies on tautog juveniles by our collaborators at Ward Aquafarms.

Alison L Deary^1*, Cody Pinger², Christine Parker-Graham¹, Ronald Twibell¹, Freya Rowland³, Don Tillitt³, Jacques Rinchard⁴, Rachel Johnson⁵, Nate Mantua⁵, Dale Honeyfield⁶,

¹US Fish and Wildlife Service, Longview, WA, USA. E-mail: alison_deary@fws.gov
²NOAA/Alaska Fisheries Science Center, Juneau, AK, USA
³ United States Geological Survey, Columbia Environmental Research Center, Columbia, MO, USA
⁴SUNY Brockport, Brockport, NY, USA
⁵NOAA/Southwest Fisheries Science Center, Santa Cruz, CA, USA
⁶United States Geological Survey, Retired, Peralta, NM, USA

An exciting component of an emergent issue is that it represents a nexus of research facilitating a mobilization of expertise, facilities, and resources to address various facets of the issue. A challenge with a large-scale, rapid mobilization of resources and expertise is ensuring that data collection and analysis protocols are standardized to promote robust data sets that are comparable and reproducible. In 2022 and 2023, preliminary testing of salmonid eggs in the Pacific Northwest revealed that approximately 40% of tested individuals from some populations were deficient in thiamine, suggesting a possible mechanism for poor survival in hatchery reared fish. Thiamine deficiency has been detected since 2019 in California and for many decades in East Coast salmonids, providing a large body of information to inform testing, monitoring, and treatment decisions. The goal of this talk is to present on (1) the US Fish and Wildlife Service’s approach in the Pacific Northwest (Region 1) to promote data standardization via open communication and common collection protocols, (2) how this approach complements other efforts along the West Coast led by NOAA, and (3) the key contacts and sources of thiamine information. We hope to foster conversations to further data standardization considerations when mobilizing for emergent issues in the future.

Lee Fuiman^1,*, and Cynthia Faulk¹

¹University of Texas Marine Science Institute

Southern Flounder (Paralichthys lethostigma) populations have been declining throughout the species’ range since the mid-1980s. Several states have implemented stock-enhancement programs to augment flounder populations, but a high proportion of hatchery-produced fish are malpigmented (lacking most skin pigmentation), which makes them exceptionally vulnerable to predators. We investigated the physiological and developmental pathways responsible for malpigmentation to identify strategies to mitigate the problem or to develop early screening methods. At three developmental stages, we measured the expression of six focal genes involved in melanocyte differentiation and melanin synthesis. At 55 dph, the final pigmentation phenotype could be observed and the expression of four focal genes (sox10, gch2, asip1, and LOC109629521) differed significantly by pigmentation phenotype (P < 0.008). For larvae at mid-metamorphosis (34 dph), four of the focal genes (cyp26b1, aldh1a2, asip1, and LOC109629521) increased with spawn-wise malpigmentation rate and one gene (gch2) decreased. The upward trends for asip1 and LOC109629521 and the downward trend for gch2 were consistent with the differences observed at 55 dph. There were no apparent trends in expression of any of the focal genes relative to spawn-wise malpigmentation rate for early metamorphic larvae (27 dph). Taken together, these results suggest that five genes may serve as useful indicators of malpigmentation in Southern Flounder, and those indicators can be applied as early as 34 dph. However, results are not conclusive because malpigmentation rates for almost all spawns were unusually low. Gene expression is being measured for spawns from California Halibut (P. californicus) that had a wider range of malpigmentation rates to clarify the results for Southern Flounder.

Cindy J.G. van Damme^1,*, Kelly Chin¹, Ewout Blom¹, Norbert Rohlf², Matthias Kloppmann², Bastian Huwer³ & Richard D.M. Nash⁴

¹ Wageningen Marine Research, IJmuiden, The Netherlands
² Thünen Institute of Sea Fisheries, Bremerhaven, Germany
³ DTU Aqua, Copenhagen, Denmark
⁴ Cefas, Lowestoft, UK

Recruitment is one of the major drivers of fish stock dynamics. Monitoring early life stages, which indicate the strength and annual variability of incoming year classes well before they enter the fishery, can provide robust recruitment indices, essential for fisheries management. However, obtaining reliable estimates of future recruitment can still be elusive, even if there are dedicated surveys for larvae or juveniles. In the case of the North Sea herring stock (Clupea harengus), which consists of several stock components, there are two long-term larval time series: one on all the major spawning grounds (International Herring Larvae Survey, IHLS) providing an index of the recently hatched larvae, and the North Sea Midwater Ring Net Survey (MIK) targeting larger, foraging larvae. While the first provides Spawning Stock Biomass indices for the different North Sea herring stock components, the latter is used as a recruitment index for the entire stock. The MIK survey has been conducted since the 1970’s, and started as an add-on to an already existing survey, and provides a larval abundance index (0-ringer index) that became an important forecaster of herring recruitment in the stock assessment. However, while the index was once considered a very good predictor of herring recruitment, its ability to forecast year-class strength has degraded over the recent two decades. From its conception, it was clear that the MIK 0-ringer index never represented the entire North Sea herring stock, since the survey takes place in January/February and only targets larger larvae of the autumn spawning stock components. Offspring from the winter spawning Downs component, which are still very small at the time of the MIK survey, were always excluded from the index. As the autumn spawning components used to contribute most to the North Sea herring stock, the MIK 0-ringer index was a good recruitment predictor until the late 1990’s. However, shortly after the turn of the century, the IHLS showed that the winter spawning component significantly increased its contribution to the total stock. With the exclusion of the Downs offspring, the MIK 0-ringer index ceased to adequately represent the entire North Sea stock. In order to remedy this mismatch, a new survey timeseries has been initiated in 2018, the so-called Downs Recruitment Survey (DRS), which samples the offspring of the winter spawning component later in the year (April, when larvae have reached a similar size as the autumn spawned larvae caught in the MIK survey). With this new survey time series available, a new recruitment index has been developed, integrating data from the standard MIK and the DRS. This new combined index now aims to provide a more reliable recruitment forecast for the entire North Sea herring stock.

Katrin Marancik^1,*, David Richardson¹, Harvey Walsh¹

¹NOAA Fisheries Northeast Fisheries Science Center, Narragansett Laboratory

Long-term datasets allow us to assess stocks and address evolving questions about changes in phenology and distribution.  This is especially true when there is also an archive of physical samples to return to.  This is well illustrated though the Atlantic Mackerel (Scomber scombrus) egg data time series.  Atlantic mackerel are a commercially valuable migratory species that ranges in the western Atlantic from Newfoundland and Labrador to Cape Hatteras, North Carolina.  Egg identification was routine at the Northeast Fisheries Science Center from 1977-1987, but was discontinued with the end of the Marine Resources Monitoring, Assessment and Prediction program in the northeast U.S.  In 2015, the Northeast Fisheries Science Center re-established S. scombrus egg identification from archived eggs going back to 2000.  This was a response to international demands to link the northern and southern contingent assessments with a common index.  The northern contingent spawns in the Gulf of St Lawrence, Canada, and the southern contingent spawns in southern new England and Gulf of Maine waters.  An index based on egg abundance is now the only stock-wide index available.  The southern contingent is approximately 10% of the western North Atlantic population, which, as a whole, has dropped >90% since the 1980s.  In addition to this drop in abundance, Atlantic mackerel have experienced a northeastward shift in the distribution of eggs.  The level of egg production at historically important spawning locations in southern new England has significantly reduced.  The Gulf of Maine has now been the dominant spawning location for over a decade.  Management council and industry members began to question if changes to spatial and temporal distribution of spawning have emerged.  Once again, examining eggs from the NEFSC Plankton Archive collected in months surrounding peak spawning allowed us to answer some of these questions.  Long-term sampling programs and archived samples allow researchers to establish (or re-establish) analyses to address new and emerging questions.

Hannah M. Murphy^1*, Samantha Trueman¹, Janine O’reilly¹, Dominique Robert²

¹Northwest Atlantic Fisheries Centre, Fisheries and Oceans Canada, 80 East White Hills Rd, St. John’s, Newfoundland and Labrador, Canada A1C 5X1
²Institut des sciences de la mer de Rimouski, Université du Quebec a Rimouski, Quebec, Canada G5L 3A1

Capelin (Mallotus villosus), a forage fish with a sub-arctic circumpolar distribution, collapsed in the Northwest Atlantic (NAFO Divisions 2J3KL; Newfoundland and Labrador shelves) in the early 1990s and has had minimal recovery. The capelin stock was in the critical zone from 1991-2006 and is currently above its limit reference point (cautious/healthy zone). The drivers of capelin larval survival have not been identified but interannual differences in annual larval daily growth rates was found among three capelin year-classes which may be related to prey availability. This study uses six years of larval diet data (2002, 2006, 2014, 2020-22) to determine if there were differences in diet between periods when the stock was in the critical zone and above its limit reference point. We dissected 1063 larval stomachs and identified prey to the lowest taxonomic level possible. Capelin larvae had a high proportion of empty stomachs (median: 0.85). We found that diet differed between these two periods with Pseudocalanus nauplii and Temora nauplii more common in the critical period and Calanoid nauplii, Oithona copepodites, and Pseudocalanus copepodites in the cautious/healthy period. The findings from this research will provide a mechanistic understanding of what is driving capelin productivity in the Newfoundland ecosystem. 

Corbin D. Hilling^1,*, Ryan E. Brown², Holly S. Embke³, Nicole Gostiaux⁴, Amy E. George^5,6, P. Ryan Jackson⁷, Patrick M. Kočovský⁶, Christine M. Mayer², Jeremy J. Pritt⁸, Song S. Qian², Catherine A. Richter⁵, James J. Roberts¹

¹U.S. Geological Survey Great Lakes Science Center Lake Erie Biological Station, 380 Huron Street, Huron, OH 44839, U.S.A.
²University of Toledo, Lake Erie Center, 6200 Bayshore Road, Oregon, OH 34618, U.S.A.
³U. S. Geological Survey Midwest Climate Adaptation Science Center, St. Paul, MN, U.S.A.
⁴Michigan Department of Environment, Great Lakes, and Energy, Bay City District Office, 401 Ketchum Street, Suite B, Bay City, MI 48708, U. S. A.
⁵U.S. Geological Survey, Columbia Environmental Research Center, 4200 New Haven Road, Columbia, MO 65201, U.S.A.
⁶U.S. Geological Survey Ecosystems Mission Area, 12201 Sunrise Valley Drive, Reston, VA 20192, U.S.A.
⁷U. S. Geological Survey, Central Midwest Water Science Center, 405 N. Goodwin Avenue, Urbana, IL 61801, U.S.A.
⁸Ohio Department of Natural Resources Division of Wildlife, 10517 Canal Road, Hebron, OH 43025 U.S.A.

Invasive species are a major contributor to global change and threaten biodiversity worldwide. Grass Carp Ctenopharyngodon idella is an invasive herbivore that has been observed in the Laurentian Great Lakes since the 1980s with records from all lakes except Lake Superior. Identification of juvenile Grass Carp from the Sandusky River, a Lake Erie tributary, prompted targeted efforts to evaluate the status of Grass Carp reproduction in the Lake Erie basin. In 2014, researchers from the U. S. Geological Survey and University of Toledo began surveys to assess Grass Carp spawning in the Great Lakes, with the discovery of fertilized eggs in 2015 in the Sandusky River. Initial work identified specific flow and temperature conditions that triggered spawning. Hydrodynamic modeling was used to estimate locations within the river where spawning occurred. Together this information helped field crews target times and locations that were best for removing spawning fish in the Sandusky and later Maumee Rivers. Removal efforts during spawning conditions have considerably higher catch rates than during non-spawning periods. At a larger spatial scale, eight tributaries have been surveyed for evidence of spawning, with three identified, although only two regularly produce eggs or larvae. Further, this research program could inform management of other invasive carps with similar life histories should they enter the Great Lakes. The research program has provided the most valuable tool available to target spawning aggregations of invasive Grass Carp and demonstrates the value of ichthyoplankton research to target the control of emerging invasive species.

Casondra A. Adams^1*, Corbin D. Hilling¹, Robert D. Hunter¹, Steven E. Butler², Duane C. Chapman³, Eden L. Effert-Fanta⁴, James T. Lamer², Brent A. Murry⁵, Mark W. Rogers⁶, P. Ryan Jackson⁷, Joseph J. Parkos III², Quinton E. Phelps⁸, James J. Roberts¹, Daniel R. Roth⁴, Michael J. Weber⁹

¹U.S. Geological Survey Great Lakes Science Center
² Illinois Natural History Survey, Prairie Research Institute, University of Illinois
³U.S. Geological Survey Columbia Environmental Research Center (Retired)
⁴Eastern Illinois University
⁵West Virginia University
⁶U.S. Geological Survey Tennessee Cooperative Fishery Research Unit
⁷U.S. Geological Survey Central Midwest Water Science Center
⁸Missouri State University
⁹Iowa State University

Invasive species possess certain biological traits, such as broad environmental tolerances and high reproductive outputs, that allow them to establish and expand in novel habitats. Grass Carp (Ctenopharyngodon idella), Silver Carp (Hypophthalmichthys molitrix), Bighead Carp (Hypophthalmichthys nobilis), and Black Carp (Mylopharyngodon piceus) were introduced to North America and have spread extensively within the Mississippi Basin. Invasive carp require riverine spawning habitats with sufficient velocities or turbulence to maintain eggs in suspension until hatching. This study characterizes broad invasive carp spawning patterns based on ichthyoplankton collection locations, refining our understanding of macroscale spawning habitat requirements. We used a random forest algorithm to model invasive carp egg and larvae collection probability in relation to habitat factors in the National Hydrography Dataset Plus (NHDplus). Model results helped create a map of the Great Lakes and the Mississippi River Basin waterways, depicting invasive carp spawning probabilities based on characteristics of stream reaches. The resulting algorithm modeled and visualized the probability of detecting invasive carp ichthyoplankton in rivers where spawning was previously undetected (i.e., unsampled rivers or those without invasive carp egg/larval collections) to inform monitoring efforts This study fills a knowledge gap in the scientific literature on invasive carp spawning by synthesizing range-wide invasive carp spawning patterns in the U.S. and provides a collective dataset on invasive carp spawning locations and spawning probability estimates for rivers beyond the known spawning range. This work could inform monitoring and management actions by aiding the prioritization of rivers likely to support invasive carp spawning and development.

Martin Breton^1*, Pascal Sirois¹, Antoine Richard² and Olivier Morissette¹

¹University of Quebec at Chicoutimi, Department of Fundamental Sciences, Research Chair on Exploited Aquatic Species (CREAE), Fish Sclerochronology Laboratory
²Ministry of Environment, Fight Against Climate Change, Fauna and Parks (MELCCFP), Department of Wildlife Management of Gaspe Region and Magdalen Islands

Off the coasts of the Magdalen Islands in the Gulf of St. Lawrence, Canada, commercial and recreational rainbow smelt fisheries (Osmerus mordax) are carried out during winter, representing approximately 14 tons of smelts harvested annually. However, we do not know if those fishes come from local reproduction in the very few streams on the Magdalen Islands or from external reproduction areas (e.g. Gaspé peninsula, Prince Edward Island, Nova Scotia, Newfoundland) or both. The project aims to identify the origin of rainbow smelts captured off the coasts of the Magdalen Islands. To reach this objective, we will analyze and compare the elemental fingerprints measured by LA-ICP-MS in the core of the otoliths of adult specimens collected by commercial fisheries with the signature of larvae collected in local streams. An analysis of the quality of the spawning habitat will also be carried out to determine which streams are the most productive and suitable for spawning of rainbow smelts in this isolated environment for this species. Results will provide important information for the conservation of the species and restoration of habitats, since most of the streams of Magdalen Islands are strongly affected by human activities (e.g. livestock breeding, development, agriculture, etc.).

Mike Diefenbach^1,*, Jason Smith², Liz Mandeville¹, and Jill Leonard¹

¹Northern Michigan University
²Bay Mills Indian Community

Lake whitefish Coregonus clupeaformis plays a critical role in the culture of many communities and supports some of the largest commercial fisheries in the Great Lakes. Prior research has evaluated factors that affect post-hatch survival in lake whitefish. However, almost no work has evaluated factors affecting egg survival.  Our goal is to determine if fertility varies by spawning area and if the presence of diseases at these locations may be contributing to low recruitment.  We collected lake whitefish from spawning locations in Green Bay WI (Fox River, Lake Michigan), Whitefish Bay (Lake Superior), Cedarville MI (Lake Huron), and Little Traverse Bay (Lake Michigan) in late fall of 2023.  Adult lake whitefish were spawned and resultant families were kept separate throughout the duration of incubation at LTBB Odawa’s Fisheries Enhancement Facility.  Half the eggs from each family were treated with iodine and half were left untreated.  The adults and a subsample of eggs from each female were then tested for Flavobacterium psychrophilum, Renibacterium salmoninarum, and Carnobacterium maltaromaticum.  Preliminary results show that fertility was not affected by iodine treatments, but possibly by the relative timing of when each population was spawned.  There is an expected variability in spawning stage when doing an egg take from a wild population.  The estimated stage of each adult spawned was recorded at time of spawning (ripe, half spent, mostly spent, spent).  The location that had the highest fertility rates were Cedarville (treated 89.6%; untreated 89.2%) with the majority at the “ripe” stage. Whitefish Bay (treated 57.1%; untreated 61.8%) and Green Bay (untreated 57.3%; untreated 61.3%) had a mix of “ripe” and “half spent” fish.  Little Traverse Bay showed the lowest fertilization rates (treated 28.5%; untreated 22.6%) for the 2023 season with the majority “mostly spent” prior to artificial spawning.  The results of the disease testing could give more insight to what could be affecting low fertility at these locations. Our preliminary analysis demonstrated substantial variability in egg success between spawning locations and suggests techniques that may increase productivity from cultured lake whitefish.

Anna Z. B. Hill¹, Paris D. Collingsworth^1,2,David B. Bunnell³, Joel C. Hoffman⁴, Tomas O. Höök^1,2

¹ Department of Forestry and Natural Resources, Purdue University
² Illinois-Indiana Sea Grant, Purdue University
³ US Geological Survey Great Lakes Science Center, Ann Arbor, Michigan, US
⁴ United State Environmental Protection Agency, Office of Research and Development, Great Lakes Toxicology and Ecology Division, Duluth, MN, 55804, USA

Since their introduction to Lake Michigan in 1949, alewives (Alosa pseudoharengus) have become an important part of the Lake Michigan food web. To understand early life history of alewife in Lake Michigan, scientists participating in the Cooperative Science and Monitoring Initiative (CSMI) conducted three surveys (in 2010, 2015, and 2021) focused on studying the timing of emergence and early growth rates of larval fish. This presentation highlights the results from the latest survey in 2021, which was designed to understand where alewife are produced and how larval alewife grow across the entire Lake Michigan system. By sampling 15 different transects at varying distances from the shore throughout July, this survey provided valuable insights into the early life stages of alewives with the added benefit of a lake wide perspective. The present study will categorize the age, growth, of alewife larvae from the 2021 survey. Initial analysis of the catch data suggests changes in the abundance and growth rates of alewife larvae between 2015 and 2021. Specifically, results from the 2015 survey indicated lower alewife growth rates (0.5 mm/d) compared to 2005-2010 (0.8 mm/day) but by 2021 we see evidence of intermediate growth rates (0.7 mm/d), particular along near shore to offshore gradients. Densities also varied across the northern half and southern half, with northern sites such as Manistique (4.02/100m³) and Sturgeon Bay (6.85/100m³) having the highest mean density. By examining the timing and growth patterns of alewife larvae in Lake Michigan, we will provide important insights into how environmental factors influence prey fish populations and help inform better management of the Lake Michigan ecosystem.

Romaric Jac^1,2*, Lola Coussa³, Elisabeth Van Beveren³, Stéphane Plourde³, Olivier Le Pape², Pablo Brosset², Pascal Sirois⁴, and Dominique Robert¹

¹Institut des sciences de la mer de l’Université du Québec à Rimouski, Rimouski, Canada
²UMR DECOD, L’institut Agro, Ifremer, Inrae, Rennes, France
³Maurice Lamontagne Institute, Fisheries and Oceans Canada, Mont-Joli, Canada
⁴Université du Québec à Chicoutimi, Chicoutimi, Canada

Small pelagic fish species play fundamental roles in marine ecosystems, exerting considerable ecological and economic influence. Among these, capelin (Mallotus villosus) emerges as a keystone species, especially noteworthy in the Gulf of St. Lawrence (GSL, Canada), where it serves as a crucial forage species for marine fish like Greenland halibut and Atlantic cod, as well as for marine mammals and seabirds. However, their populations often undergo drastic fluctuations influenced by environmental changes and overexploitation. Understanding the dynamics of these species is crucial for sustainable resource management, particularly regarding the challenges posed by climate change. Despite their importance, the GSL capelin stock lacks comprehensive data on migration patterns, habitat utilisation, and environmental drivers. Embarking on a newly initiated Ph.D. project, this research aims to fill this knowledge gap by leveraging otolith microchemistry to investigate the spatial dynamics of capelin populations within the GSL, especially during its early life larval stages (larvae and juveniles). With a focus on confirming spatial distribution patterns, assessing interannual variability, and pinpointing environmental factors influencing growth disparities, the study employs a multi-faceted methodology. Over three years, capelin individuals from various GSL regions and life stages will be sampled, and their otolith microchemistry analysed to deduce origin and migration routes. Additionally, growth data will be integrated with environmental variables to elucidate spatial connectivity, interannual stability, and the environmental determinants of capelin population dynamics. Anticipated outcomes include insights into capelin spatial behaviour, resilience under climate change, and informed strategies for resource conservation and management. By investigating both the early life larval stages and potential nursery grounds, this research aims to provide a comprehensive understanding of capelin population dynamics, thereby facilitating informed decision-making and fostering sustainability in marine ecosystems.

Émilie Leblond^1,*, Dominique Robert¹, and Céline Audet¹

¹Université du Québec à Rimouski, Institut des sciences de la mer de Rimouski (ISMER)

Recruitment of fish is primarily dependent on larval survival. Annual fluctuations in year-class size can be attributed to annual variations in the growth of early-life-stage individuals, which drives mortality. Estuaries are variable environments where a limited number of species are found at high abundance. They also provide ichthyoplankton with a nursery habitat where conditions are favorable for their development. In estuaries, larval assemblage can be subject to significant changes in abundance and composition. In this project, we aimed to describe the fish larval community in the Baie des Chaleurs, an embayment of the Gulf St. Lawrence for which limited contemporary data is available. From May to July 2022, we carried out 6 sequential surveys in the area, during which a total of 49 stations were sampled. Zooplankton samples were collected throughout the surface layer. At each sampling station, a vertical profile of temperature and salinity conditions was obtained. In the laboratory, sorting of the zooplankton samples was carried out, and fish larvae were isolated. For each larva, a detailed description of morphological characteristics was made, and photographs were taken for identification and classification according to their development stage. Visual identifications were confirmed using barcoding. Interestingly, larvae from species at risk (Atlantic cod, American plaice, winter flounder) were the most present in the assemblages and were present throughout the sampling season. The results suggest a high nursery potential of the Baie des Chaleurs for these fish species.

Brian P. O’Malley^1,*, Alex J. Gatch², Dimitry Gorsky³, Nick M. Sard⁴, Scott D. Stahl¹, Brian C. Weidel¹

¹U.S. Geological Survey, Great Lakes Science Center, Oswego, NY
²U.S. Geological Survey, Great Lakes Science Center, Cortland, NY
³U.S. Fish and Wildlife Service, Lower Great Lakes Fish and Wildlife Conservation Office, Basom, NY
⁴State University of New York, Oswego, NY

Evaluation of species restoration programs requires a life stage based approach to assess program success and improve understanding of recruitment bottlenecks. Prior to their extirpation, Lake Ontario bloater (Coregonus hoyi) were last detected in 1983. Since 2012, bloater of Lake Michigan origin have been stocked in Lake Ontario to reestablish a population. Capture locations from bottom trawls and acoustic telemetry data during 2015-2023 suggest that stocked bloater have dispersed throughout the main lake, although most recaptures have occurred in U.S. waters. We present a new Lake Ontario ichthyoplankton survey set to begin in 2024, designed to inform bloater restoration by evaluating natural reproduction with a larval survey. We applied information on bloater early life history and surveys from the upper Great Lakes to inform our study design. Our work complements existing long term annual bottom trawl surveys more effective at assessing older life stages. Study objectives include: (1) Determine the spatial extent and vertical distribution of Lake Ontario bloater larvae, and (2) Compare findings in Lake Ontario to recent surveys in lakes Michigan, Huron, and Superior, to guide future operations to evaluate restoration progress and assess populations. We anticipate our survey will not only inform Lake Ontario restoration, but also benefit cross-lake comparisons of coregonine early life history and our understanding of contemporary distributions.

Imanol Boussion^{1, *}, Olivier Morissette¹, Pascal Sirois¹

¹ Chaire de recherche sur les espèces aquatiques exploitées

Yellow Perch (Perca flavescens) has been heavily exploited in many north American lakes such as Lake Saint-Pierre, a fluvial lake located along the Saint-Lawrence River, Canada. Despite the Yellow Perch fisheries’ moratorium imposed in Lake St-Pierre since 2012, the abundance of spawning perch remains low. The abundance of young-of-the-year (YOY) Yellow Perch is, however, staying high. The one-year-old individuals has also significantly decreased during the last 25 years, suggesting a high winter mortality. Along with the abundance decline, the mean size of YOY also decreased during the same period. The main objective of this project is to test the hypothesis of size-selective mortality of young Yellow Perch during their first winter in Lake Saint-Pierre, determining whether the decrease in size of YOY led to the observed recruitment failure. To reach this objective, a comparison will be made between the pre-winter YOY size and size-at-age one of winter survivors from two year-classes (2020 and 2021). This comparison will establish a size threshold for winter survival. Additionally, this project will also aim to investigate whether the Double-crested Cormorant, a well-known fish predator, selectively prey on YOY Yellow Perch. The size-at-age of the fish will be determined using otolith microstructure. The results are expected to demonstrate that Yellow Perch in Lake Saint-Pierre undergo size-selective mortality, partially caused by the Doubled-crested Cormorant.

Guilhem Colomines¹^,*, Victoria Bogstad¹^,*, Sarah Brown-Vuillemin¹, Lucienne Chénard¹, Jacob Burbank², Dominique Robert¹

¹Institut des Sciences de la Mer de Rimouski (ISMER), Université du Québec à Rimouski (UQAR), Rimouski, QC G5L 3A1, Canada​
²Fisheries and Oceans Canada, 343 Université Avenue, Moncton, NB E1C 9B6, Canada​

The Atlantic herring (Clupea harengus) stock from the southern Gulf of St. Lawrence, Canada, is in the critical zone and a fishery closure has been implemented in 2023. One of the main factors explaining the collapse of this stock is the lack of strong recruitment events over the past 20 years. Like for many herring stocks, it is hypothesized that recruitment failure is associated to a change in habitat quality during early life stages, but the mechanisms that regulate survival remain unknown. One major change that has occurred in the region over the past two decades is a major shift in the taxonomic composition of the zooplankton assemblage associated to climate warming. In the present study, we investigate the trophodynamics of young-of-the-year (YOY) herring captured during the summers of 2021 and 2022. We aim to describe diet composition at the highest resolution possible to identify key prey taxa on which juvenile herring rely prior to their first overwintering. The number of preferred prey as well as overall feeding success will be related to a condition index. Results from the present project will allow to detect potential bottom-up control mechanisms during a key early life stage of herring.

Audrey J. Geffen¹  and Richard D.M. Nash²

¹University of Bergen, Department of Biological Sciences, Fisheries and Marine Biology Group
²Centre for Environment, Fisheries and Aquaculture Science (Cefas), Fisheries Laboratory Lowestoft

The iconic model of fish early life history puts emphasis on growth and development during the warm, productive spring and summer, leading to metamorphosis and building up of resources to survive the first winter of life. Autumn and winter observations of late-stage larvae, of different species and in different geographic locations, suggests that there are other strategies for survival. Rainbow smelt is one example in Lake Michigan. During regular ichthyoplankton sampling in the early 1980s, smelt larvae sized 40-70 mm were present throughout the year. At the same time, 0-group smelt sampled with bottom trawls in summer had a wide mixture of hatching dates (determined from length-frequencies and otolith increment counts). However, 0-group smelt captured in pre- and post-winter trawl samples showed static length-frequency distributions and otolith increment counts. Since length and increment counts in these small rainbow smelt did not increase as expected over the winter, it seems likely that the smallest individual of the smelt population experience virtual cessation of growth and ring deposition, and overwinter in a pre-metamorphosed condition. This overwintering pattern, which is also seen in autumn-spawning herring and several flatfish, suggests that growth slow-down/cessation may allow individuals to survive as pelagic feeders, and metamorphose as the largest members of the following spring cohort.

Sarra Nasraoui^1,*, Céline Audet¹, Richard Cloutier², and Dominique Robert¹

¹ Université du Québec à Rimouski, Institut des sciences de la mer de Rimouski
² Université du Québec à Rimouski, Department of Biology, Chemistry and Geography, Paleontology and Evolutionary Biology Laboratory

Fluctuations in the abundance of fish populations are largely regulated by survival during the larval stage. This relationship is associated with the extremely high mortality rate that characterizes the transition period from endogenous yolk-based feeding to exogenous planktonic prey consumption. High mortality rates occurring in both natural and aquaculture environments during this short critical period have greatly prompted fisheries oceanographers and scientists to further investigate potential factors controlling the feeding success, growth and survival of a critical stage of the fish life cycle. While several studies have been independently conducted on certain aspects influencing critical periods of larval fish feeding success, we are unaware of any studies looking at the interaction between intrinsic factors specific to the larval fish (e.g., jaw and digestive system development) and extrinsic factors in the environment (e.g., nature and abundance of prey). The proposed research project stands out for its significance in addressing a crucial topic, bringing together the two complementary disciplines of developmental biology and larval ecology to identify with unprecedented precision the timing and factors responsible for critical periods of high mortality during flatfish larval ontogeny. It involves a combination of studying the morphological (size and shape) and anatomical (chondrocranial development) development of reared and wild flatfish larvae, as well as the study of the ontogeny of wild larval diet composition. Winter flounder (Pseudopleuronectes americanus), with its dietary ontogenetic patterns that accompany morpho-anatomical adaptations, is used as a model in this study.

Etienne Germain^1*, Pierre Lavoie¹, Jacob Burbank², and Dominique Robert¹

¹ Institut des sciences de la mer, Université du Québec à Rimouski, Rimouski, QC, Canada
² Gulf Fisheries Centre, Fisheries and Oceans Canada, Moncton, NB, Canada

In 2023, the commercial fishery for spring-spawning Atlantic herring (Clupea harengus) was closed in the southern Gulf of St. Lawrence, Canada (sGSL). The main reason explaining the stock collapse is the continuous recruitment failure over the past two decades. Even though factors involved in sGSL herring recruitment regulation remain unknown, a positive link between fast growth during early life and recruitment has been reported for numerous small pelagic fish species, including herring. In the present study, we aim to test the relationship among growth achieved during larval life, and year-class strength. To do so, we are relying on possibly the longest herring otolith time series in Canada, which comprises annual otolith samples from young-of-the-year and one-year-old juvenile herring from 1979 onward. Individual larval growth trajectories (daily increment widths from core), as well as growth integrated over the first year of life (radius at first annuli) will be derived from otoliths of juveniles either belonging to cohorts characterized by strong or weak recruitment over the full time series. We will test the hypotheses that individuals associated to strong recruitment events are characterized by faster larval growth and an overall larger size at the age of one year compared to individuals from weakly-recruiting cohorts. A better understanding of the links between growth and survival potential will help further identify the determinants of herring dynamics in the sGSL, and more broadly across Atlantic Canada.

Anna Schwarzkopf¹, Stacey Ireland^1,*, Robin DeBruyne¹, Edward Roseman¹, Heather Hettinger², Daniel Zielinski³, Reid Swanson³

¹U.S. Geological Survey, Great Lakes Science Center
²Michigan Department of Natural Resources, Fisheries Division
³Great Lakes Fishery Commission

Adult and juvenile fish have been shown to sustain injury and experience mortality after entrainment through dam and hydropower infrastructure, but the impact on larval fish is largely unknown. Habitat restoration efforts on the Boardman (Ottaway) River system near Traverse City have resulted in the removal of three dams, with a fourth on Union Street to be replaced by a bi-directional selective fish pass system (FishPass). Characterization of the larval fish community and potential damage caused by the dam structure prior to dam removal is ongoing to facilitate current and future assessment. Larval fish were sampled passively using D-frame nets downstream and upstream of the Union Street Dam to identify if and what types of damage are incurred while entrained in the dam’s primary spillway, as well as document any infrastructure related mortality. To quantify corresponding strain rate and turbulence length scales of the dam flow field, field measurements and model estimates were utilized for future evaluation of the driving factors behind observed injury and mortality. A framework for categorizing and rating injury severity was established for entrainment injury characterization. In-field processing of live larvae produced a mortality rate of 50.3% (n=38 of 73 larvae collected).  Out of the 73 larvae preserved (Percidae, Catostomidae, 5-25 mm TL), 280 injuries were noted, the most prevalent being fin fold damage (68.9%), followed by other injuries (26.1%) including eyeball luxation and rupture, head indentation, and full eye detachment. Impacts of these injuries on long term larval fish development and survival were not assessed in this study but could be considered in future river infrastructure assessments. The future FishPass structure is designed to minimize strain rate, suggesting a reduced frequency in observed injury and mortality post dam replacement.  These findings support larval and juvenile fish conservation regarding dam entry mitigation and downstream habitat restoration.

Paula Joseph* and Stuart A. Ludsin¹

¹ Aquatic Ecology Laboratory, Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus, OH

Effective management of fish populations requires a thorough understanding of the factors influencing their dynamics. This need has only grown due to the effects of human-driven environmental change. Herein, we quantified the relative contributions of recruits to western Lake Erie’s age-0 (juvenile) Walleye (Sander vitreus) population from the Sandusky River, which has historically supported a large spawning population. We quantified relative contributions to the juvenile population between a moderately strong (2015) and weak recruitment (2016) year, expecting minimal contribution from the Sandusky River in both years due the Ballville Dam limiting access to much of this river’s spawning habitat. We analyzed the otolith core of juvenile Walleye obtained from agency bottom-trawl assessment surveys conducted in August 2015 and 2016 for strontium (Sr) using laser-ablation inductively coupled plasma-mass spectrometry because the Sandusky River has higher concentrations of strontium [Sr] compared to other Lake Erie spawning locations. We used a logistic regression classification function developed from larvae captured in their natal sites to predict the probability of each juvenile originating in the Sandusky River, based on its otolith core [Sr]. Of the 99 juveniles analyzed, only one typed back to the Sandusky River, with it being captured near the Sandusky River mouth, thus supporting our hypothesis. Our results suggest that the Ballville Dam has historically limited this spawning stock and that the recent (2018) removal of the Ballville dam might benefit Walleye recruitment. We encourage a follow-up study focused on contributions since 2018.

Max Zavell^1*, & Hannes Baumann¹

¹Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton CT, 06340

Ocean acidification is known to affect numerous traits in early life history stages of fishes, but the experimental results do not allow generalizations to be made. It has been suggested that species resilient to elevated CO₂ levels inhabit more CO₂-variable inshore environments, but that species that move between inshore and offshore bottom habitats (with more stable CO₂ levels) remain understudied. We determined the CO₂-sensitivity of the larvae of northern stock Black Sea Bass (Centropristis striata, BSB), an ecologically and economically important fish that migrates from offshore overwintering grounds to coastal spawning and nursery areas. We reared larvae from wild-caught fish at three pCO₂ levels (~400 [‘control’], ~2200 [‘elevated’], ~3000 [‘extreme’] µatm), from 0 to 10 days-post-hatch (Onset of flexion and end of the initial exogenous feeding stage). No statistical effects of pCO₂ were found on hatching success or survival to 10 days-post-hatch. Larval growth increased with increasing pCO₂ (‘control’: 0.11 mm d^-1; ‘elevated’: 0.15 mm d^-1; ‘extreme’: 0.17 mmd^-1), with ‘extreme’ individuals growing 55% faster (were 1.2× larger) than control conditions (~400 µatm) which was unexpected. Tolerance to high levels of CO₂ by early larvae is acquired either by high CO₂ exposure in inshore spawning grounds or conferred by adult exposure to high CO₂ in productive inshore environments or at offshore depths during overwintering.

Kaleigh Arnold^1*, John Majoris ², and Kory Evans¹

¹ Rice University, Department of Ecology and Evolutionary Biology
² Texas A&M University-Corpus Christi, Department of Life Sciences

This study explores the early ontogenetic allometry of neurocranial and jaw structures in Amphiprion bicinctus (Pomacentridae) from hatch through day 14 post-hatch, a period marked by critical life history events such as benthic hatching, pelagic/planktonic stages, and reef settlement. This developmental stage, characterized by significant environmental, morphological, and functional changes, presents an ideal window for investigating allometric processes. Utilizing micro-CT scans and 3D geometric morphometrics, this research measures and compares the allometric growth of these structures across key developmental stages (preflexion, flexion, metamorphosis, postflexion), driven by rapid environmental transitions. We predict that early larval stages will exhibit positive allometric growth in neurocranial and jaw structures to rapidly adapt to environmental changes, whereas later stages will show more consistent isometric growth as they stabilize functionally upon approaching reef settlement. This study sets the groundwork for comparative analyses within the genus and across different fish families, aiming to uncover potentially conserved or divergent allometric patterns linked to ecological and life history variables.

Anthony Donahue*, Erick Ortiz, Anne Slaughter, Wim Kimmerer, Michelle J. Jungbluth

San Francisco State University | Estuary & Ocean Science Center, Tiburon, CA, USA 

Fish populations in the San Francisco Estuary (SFE) have been declining for decades due to multiple interacting factors, including a reduction in tidal wetlands and a decline in zooplankton abundance throughout the estuary. Tidal wetlands in the SFE are being restored to enhance fish populations by providing beneficial habitat and food web resources, such as a richer zooplankton assemblage than in open waters. Longfin smelt (LFS; Spirinchus thaleichthys) is a declining native fish and a threatened species. Copepod abundance in wetlands directly affects LFS populations, since larval LFS rely on copepods as their primary food source. The purpose of this in progress study is to identify food web resources in close proximity to wetland restoration sites, compare them with ecological indicators in wetlands at different stages of restoration (early, intermediate, mature), and identify zooplankton indicator species associated with beneficial habitat for LFS. High-throughput sequencing (HTS) will be utilized to identify the diversity of prey available in the water column, including calanoid and cyclopoid copepods (Eurytemora carolleeae, Acanthocyclops americanus, Acanthocyclops robustus, Pseudodiaptomus forbesi), and indicator species in diets of larval fishes, specifically LFS, Pacific herring (Clupea pallasii), and Prickly sculpin (Cottus asper), which use wetlands as nursery grounds during the same time of year as LFS. HTS is advantageous for DNA diet analysis as it can identify diverse zooplankton in the diets of larval fishes, including species not previously described as a food source that microscopy was not able to identify. HTS will identify the DNA of prey consumed by the larval fishes, ambient zooplankton species available to the larval fishes, and indicator species at each wetland restoration site. This study will expand upon current limited databases for copepod identification, provide information for zooplankton monitoring near wetlands, provide information for wetland restoration managers; including prey availability of species of zooplankton for larval fishes in their nursery grounds, an understanding of how these prey differ across wetlands at different stages of restoration, and key characteristics of wetlands that support zooplankton abundance and larval fish populations, which will ultimately benefit declining fish populations in the SFE.

Matthew K. LeFauve^1,2, Cayla L. Carlson², Benjamin H. Stahlschmidt², Amy E. George^2,*

¹ United States Environmental Protection Agency, Chicago IL
² Columbia Environmental Research Center, United States Geological Survey, Columbia, MO

Grass Carp (Ctenopharyngodon idella) and Silver Carp (Hypopthalmichthys molitrix) are large-bodied riverine fishes that were introduced in freshwater systems across the United States. Their introduction has had consequences to native fish habitats, such as degrading the spawning grounds and increasing the risk of widespread eutrophication. An improved understanding of anatomy and physiology during early life stages is vital for the development of control methods. Here, we focus on development of the visual system through visuomotor behavior, retinal development, and midbrain development in larval grass and silver carps. As evidenced by the optomotor response behavioral assay, visuomotor reflex was weakly present by 3 days post hatch (DPH) in Grass Carp and 4 DPH in Silver Carp. This corresponds to the development of retinal ganglion cells and retinorecipient regions in the midbrain at similar age ranges. This assessment of visual system development provides key information to help understand larval carp invasion biology. The views expressed in this abstract are those of the authors and do not necessarily represent the views or policies of the US EPA.

Zachary P. Stamplis¹*, Franz J. Mueter¹, Esther D. Goldstein², Dion S. Oxman³

¹ College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Juneau, AK
² Alaska Fisheries Science Center, REFM/NOAA, Seattle, WA
³ Alaska Department of Fish and Game, Juneau, AK

Daily ages estimated from juvenile fish are invaluable to fisheries managers, improving forecasts of recruitment, mortality, growth, and hatch dates.  These immature age estimates can supplement traditional annual aging data, providing insight on the vulnerable early life history of fish that ultimately determine age-class success.  However, producing daily ages from otoliths is difficult, time consuming, highly subjective, and has changed little since the 1970’s.  A promising new method for predicting age from otoliths, Fourier-transform near infrared spectroscopy (FT-NIRS), has recently been demonstrated as an extremely rapid alternative to traditional aging methods.  FT-NIRS offers a novel, non-destructive means of estimating age from whole, unprocessed otoliths in under a minute.  Despite this, few studies have investigated the efficacy of FT-NIRS to predict daily ages, instead focusing on annual stock assessment applications.  This project seeks to demonstrate for the first time the suitability of using FT-NIRS to predict daily age in Gulf of Alaska (GOA) juvenile Pacific cod (Gadus macrocephalus).  A time-series of fish reared at NOAA’s Little Port Walter (LPW) research station will be used to build a FT-NIRS calibration model.  This model will be used to determine whether daily age can be predicted from whole juvenile cod otoliths.  The LPW FT-NIRS model will then be tested against otoliths from wild-caught cod throughout the GOA to determine how widely applicable the model may be.  If successful, FT-NIRS could offer researchers a method to estimate daily ages in near real-time and improve in-season management of fisheries.

Sara E. Ang^1*, Kevin Keeler¹, Chuck Madenjian¹, Vinnie Siegel¹ Lyle Grivicich¹, Paul Haver², Roger Gordon², Donald Tillitt³, Thomas Blowers⁴, and Jacques Rinchard⁵

¹U.S. Geological Survey—Great Lakes Science Center
²U.S. Fish and Wildlife Service – Jordan River National Fish Hatchery
³U.S. Geological Survey – Columbia Environmental Research Center
⁴U.S. Fish and Wildlife Service – Green Bay Fish And Wildlife Conservation Office
⁵ SUNY Brockport

The Northern Refuge within Lake Michigan was established in 1985 as part of an effort to restore a self-sustaining Lake Trout population to the lake. Despite the stocking of millions of Lake Trout into the refuge and survival of these stocked fish to reproductive adulthood, signs of recruitment by Lake Trout in the refuge have been limited. Thiamine deficiency complex (TDC) results from the inability to acquire or retain thiamine (an essential B vitamin for metabolism and nervous system function) and could be limiting recruitment of Lake Trout in the refuge. To determine the role of TDC in natural reproduction, eggs were collected from adults in the Northern Refuge during October 2019. Laboratory determinations of egg hatching and survival rates of fry were conducted in 2020. Thiamine concentrations of the fry raised in the laboratory were determined as well as that of eggs from ovulating females in 2019-2022. Egg hatching rate averaged 93%. Survival rate of Lake Trout fry up to five weeks after hatching averaged 97%. Mean (standard error) thiamine concentrations in eggs of Lake Trout caught in 2019, 2020, 2021, and 2022 were 19.1 (3.6), 5.9 (1.3), 6.2 (0.4), and 6.0 (0.6) nmol/g, respectively, which are above the lethality threshold concentration of 2.3 nmol/g, suggesting the likelihood of TDC-induced mortality in fry is low. Thiamine concentrations in Lake Trout fry at the end of the laboratory experiment averaged 11.2 nmol/g, and abnormal behavior in the fry was not observed. TDC-induced fry mortality does not appear to be a major impediment to Lake Trout rehabilitation within the Northern Refuge of Lake Michigan. Eggs were also collected in October 2023 with additional thiamine supplements to determine the role of TDC in fertilization, hatching success, and mortality. Results are anticipated from these laboratory experiments in 2024.

Alex Kruithof^1,* and Jill Leonard¹

¹Biology Department, Northern Michigan University, Marquette MI

Burbot (Lota lota) are the only freshwater member of Gadiformes and are a cold water species that could be utilized for intensive aquaculture. We sought to characterize rearing conditions for embryos in various temperatures and water types. Using wild-caught burbot from the Lake Superior watershed, we spawned families at a 1:1 ratio, and then transferred their embryos into 96-well microplates for observation. The microplates were filled with dechlorinated tap water, autoclaved river water, or replenished RO water and housed in incubators at 1^oC, 2^oC, 4^oC, and 6^oC. There was no survivorship at 6^oC, while 4^oC had 67% greater mortality than 2^oC. Variations to the asynchronous hatching window expanded as temperatures lowered, but the number of degree days at 50% hatch was not significantly different between temperatures. Preliminary analysis shows no significant differences in hatch rate or mortality between water types. There was a 15% increase in spinal deformities at 4^oC. Our results suggest northern Great Lakes burbot embryos should be held at 2^oC to minimize mortality and deformities. 

Harvey J. Walsh¹, Katey E. Marancik^1,*, and David E. Richardson¹

¹ NOAA Fisheries, Northeast Fisheries Science Center, Oceans and Climate Branch

Offshore wind development along the east coast of the US is moving rapidly. Goals for development are set for 30 Gigawatts (GWs) of offshore wind from platforms by 2030, and 15 GWs of floating offshore wind by 2035. Impacts of offshore wind development and production may affect the ecosystem and the NEFSC ability to monitor the ecosystem. The Center conducts many long-term programs to monitor the region including the Ecosystem Monitoring (EcoMon) Program that provides data on ichthyoplankton abundance for use in assessments. The use of ichthyoplankton data in ongoing impact assessments of wind development in the region highlight the importance of long-term data programs. EcoMon uses a randomly-stratified survey design with 47 strata from North Carolina to the Gulf of Maine. Nineteen of those strata have planned wind energy area (WEA) projects or may be open to potential development in the future. Abundance of larval fish collected in strata with WEAs and without WEAs was compared from collections during 1981 to 2021 to assess impacts. Almost 50 % of larval fish were collected from strata with WEAs. Abundance varied among seasons, regions, and species. Seasonal percentages ranged from 27 % in the spring to 70 % in the fall. Potential spawning in or near WEAs was indicated by the presence of yolk-sac and pre-flexion larvae for several species. Impacts are currently highest in the Mid-Atlantic Bight and Southern New England regions where more projects are moving forward. Impacts to more northerly species inhabiting the Georges Bank and Gulf of Maine regions will depend on future development of floating platforms. The continued use of plankton sampling using consistent survey methods among WEAs should allow for monitoring changes in spawning and larval fish distributions.

Daniel F. Ramirez^1,2* & Jeremy T. Claisse^1,2

¹California State Polytechnic University Pomona, Biological Sciences Department
²Occidental College, Vantuna Research Group

Variability in climate cycles and regional oceanographic conditions have the potential to alter early life history and phenological patterns in teleost fish. The timing in the appearance of the planktonic larval phase is indicative of both adult spawning patterns, and pelagic larval distribution and survival. Preference to specific thermal regimes is a driving mechanism that can trigger adult reproductive behaviors (e.g., nest building, migrations, courtship) and physiology (e.g., hormone production, oocyte development). Ocean temperature also influences larval growth, metabolism, and pelagic larval duration. As mean sea surface temperature in the Southern California Bight has risen in recent decades, offshore studies have shown patterns in peak larval abundance of fishes temporally shifting earlier or later in the year depending on the species. King Harbor in Redondo Beach, California has been the site of continuous nearshore ichthyofauna monitoring by Vantuna Research Group at Occidental College since 1974. Monthly ichthyoplankton tows have largely gone uninterrupted over a period of global climate change, multiple oceanographic decadal cycles, and more acute temperature events such as El Niño. This study is investigating patterns of phenological change in nearshore annual peak larval abundance of Garibaldi, Hypsypops rubicundus, and changes to annual larval abundance which has seen a sharp increase within the last decade. Garibaldi are an abundant nearshore species with a distinct spawning season. Detected temporal shifts will be correlated with interannual and decadal climate cycles such as El Niño Southern Oscillation and the Pacific Decadal Oscillation to measure climatic sensitivities for change in phenology. In addition, local oceanic variables such as zooplankton volume and upwelling intensity will be correlated with temporal shifts to determine if larval occurrence has trended with maximum plankton productivity. I will also examine whether temporal shifts and larval abundance is related to temporal patterns in adult Garibaldi abundance in King Harbor. Results of this study may provide insight into the potential mechanisms for population level effects of nearshore demersal fish due to long term climate change and more acute temperature events