Fish recruitment varies widely interannually and is often difficult to predict. This variation may reflect responses to key environmental factors, including annual climatic conditions. Such factors are often correlated across broad spatial scales, leading to recruitment synchrony among spatially separated populations (i.e., the Moran effect), especially in large lakes and marine systems. We examined interannual variation in the relative year-class strength (RYCS) of vendace (Coregonus albula) and smelt (Osmerus eperlanus) in three large Swedish lakes-Va & uml;ttern, Va & uml;nern, and Ma & uml;laren-to assess whether there was evidence of intraspecific and/or interspecific recruitment synchrony. We used catch-curve residuals to index RYCS and compared populations using Z scores to test for synchrony. Additionally, we examined relationships between RYCS and climatic variables (monthly precipitation, wind speed, and temperature) to identify potential drivers of synchrony. Our results revealed no evidence of synchrony among smelt populations, but demonstrated strong, positive intraspecific recruitment synchrony for vendace. Several significant climate associations emerged for vendace RYCS, including a positive association with May mean temperature and negative associations with May and September precipitation, suggesting that vendace recruitment success is influenced by climate. Additionally, we found interspecific recruitment synchrony between smelt and vendace in lakes Va & uml;ttern and Va & uml;nern, which are deeper and more oligotrophic than Lake Ma & uml;laren. These findings suggest that recruitment synchrony in these large freshwater systems may occur at broader spatial scales than indexed by some previous studies, and that climate plays a significant role in vendace recruitment success across all three lakes.

Bioaccumulation of environmental toxicants in aquatic ecosystems presents a significant ecological challenge including potential implications for fish reproduction and population dynamics. Through this meta-analysis, we investigated how elevated mercury (Hg) and polychlorinated biphenyls (PCBs)-two prevalent and problematic contaminants-in large, and presumably old fish, affect toxicant concentrations in their eggs and subsequent offspring success. We synthesized published data to analyse: (1) the association between maternal size and egg toxicant loads, (2) the relationship between maternal muscle toxicant concentrations and egg toxicant loads and (3) the impact of egg toxicant loads on offspring hatching success, mortality and growth. Our results revealed that maternal size was strongly, positively associated with egg toxicant concentrations, with Hg showing an effect size nearly double that of PCBs. Similarly, toxicant concentrations in maternal muscle tissues were strongly, positively associated with egg concentrations for both contaminants. Additionally, elevated egg toxicant loads were associated with decreased hatching success and increased offspring mortality, whereas impacts on growth rates varied by toxicant, highlighting negative impacts on early life stages. These findings have important implications for fisheries management, particularly regarding the protection of 'big old fat fecund female fish' (BOFFFFs). Although BOFFFFs typically produce numerous eggs, our study shows these benefits may be offset by increased toxicant transfer to offspring in contaminated systems. Management strategies should consider the reproductive benefits of BOFFFFs and the potential disadvantages of maternal toxicant transfer when establishing conservation priorities, especially in historically or currently contaminated systems or populations more susceptible to bioaccumulation.

Habitat diversity is important to fisheries for promoting resiliency to interannual environmental variation. Historical land use change resulting in increased sedimentation has impaired fish rock reef habitats in Saginaw Bay, Lake Huron. Pursuant to the recovery of Saginaw Bay's walleye population, and to benefit other species, came the decision to restore the offshore habitat Coreyon Reef, a 0.8 ha rock reef complex. Following a pre-restoration assessment in 2014-2016 and construction in 2019, we conducted a comprehensive assessment from fall 2020 to spring 2022 to document the restored habitat's viability for fish spawning. This assessment featured two objectives: (1) to evaluate reproductive usage by lake whitefish and walleye, and (2) to evaluate their corresponding egg incubation environment. We sampled directly on Coreyon Reef and at nearby unrestored control sites for comparison, with gears standardized to the pre-restoration assessment. We confirmed spawning of lake whitefish and walleye on the restored reef less than 2 years post-construction. Relative to the pre-restoration assessment, peak egg deposition increased substantially for walleye and marginally for lake whitefish. However, concurrent reproductive utilization at nearby unrestored sites was consistent or even greater than directly on the restored site. Dissolved oxygen concentration was sufficient for embryo development, but invasive round goby were abundant and consumed eggs. The fish assemblage at our sampling sites was consistent before and after restoration. We predict eggs deposited on the restored site have improved survival relative to unrestored sites, as the new reef structure may protect incubating embryos from predation and sedimentation.

In Saginaw Bay, a large productive embayment of Lake Huron, yellow perch (Perca flavescens) experienced a multi-decadal decline in adult abundance despite increasing fall age-0 abundance, suggesting a shift in recruitment dynamics. To assess the relative influence of ecosystem changes in altering yellow perch stock-recruit relationships, we compared candidate models, assuming either stationary or nonstationary dynamics, to evaluate potential shifts in the age at which year-class strength is set and the importance of environmental and biotic factors in explaining yellow perch age-0 and age-1 relative abundance (1970-2022). Results indicate that the age when year-class strength is established may have shifted from age-0 to age-1 in the early-2000s. Models incorporating nonstationarity best explained annual variation in yellow perch age-0 (~83%) and age-1 (~65%) relative abundance. High age-0 production was attributed to reduced competition and predation following the 2003-2004 collapse of alewife (Alosa pseudoharengus). However, increasing walleye (Sander vitreus) abundance, coincident with alewife declines, may have increased predation on age-1 yellow perch, leading to declines in age-1 relative abundance.

Aquatic ecosystems are highly dynamic environments vulnerable to natural and anthropogenic disturbances. High-economic-value fisheries are one of many ecosystem services affected by these disturbances, and it is critical to accurately characterize the genetic diversity and effective population sizes of valuable fish stocks through time. We used genome-wide data to reconstruct the demographic histories of economically important yellow perch ( Perca flavescens ) populations. In two isolated and genetically divergent populations, we provide independent evidence for simultaneous increases in effective population sizes over both historic and contemporary time scales including negative genome-wide estimates of Tajima’s D, 3.1 times more single nucleotide polymorphisms than adjacent populations, and contemporary effective population sizes that have increased 10- and 47-fold from their minimum, respectively. The excess of segregating sites and negative Tajima’s D values probably arose from mutations accompanying historic population expansions with insufficient time for purifying selection, whereas linkage disequilibrium-based estimates of Ne also suggest contemporary increases that may have been driven by reduced fishing pressure or environmental remediation. We also identified parallel, genetic adaptation to reduced visual clarity in the same two habitats. These results suggest that the synchrony of key ecological and evolutionary processes can drive parallel demographic and evolutionary trajectories across independent populations.

Physical factors such as water temperature, water column mixing, and light are crucial for the phytoplankton abundance and primary production in Lake Michigan. The potential impacts of climate change on these factors could significantly affect the dynamics of Lake Michigan's phytoplankton. In this study, we employed an integrated modeling framework to project the impact of climate change. This framework included a two-way coupled 3D lake-ice–climate system (GLARM), a hydrodynamic model (FVCOM), and a nutrient-phytoplankton-zooplankton-detritus (NPZD) model, further enhanced by a compartment representing the invasive quagga mussel (Dreissena rostriformis bugensis). Our approach encompassed historical simulations for the period 2005–2014, as well as two sets of future projections for the mid-21st century (2041–2049) and the late 21st century (2091–2099), utilizing the Representative Concentration Pathway (RCP) 8.5 scenario. Our findings indicate that changes in water temperature and water column mixing significantly influence the seasonal patterns of phytoplankton abundance and primary production. These changes notably alter the timing and magnitude of the winter-spring phytoplankton bloom and the depth of the chlorophyll layer. Furthermore, the model predicts an increase in primary production under the projected climate scenarios, with significant variations in both spatial and seasonal patterns.

Ongoing anthropogenic eutrophication and warming temperatures are expected to increase the extent and severity of hypoxia globally. Monitoring hypoxia has traditionally relied on costly surveys or sensor networks. While benthic macroinvertebrates are valuable indicators of hypoxia, community analysis is limited by small spatial scales of traditional grab sampling and labor-intensive processing. To address this, we combined benthic grab samples with underwater video to detect hypoxic habitats in two productive embayments of the Laurentian Great Lakes: Saginaw Bay, Lake Huron with periodic short-term hypoxia, and Hamilton Harbour, Lake Ontario with prolonged hypoxia. Using supervised classification, we identified significant grouping of in situ video data with cluster analysis, and then aligned video groups with environmental and biological datasets. These video groups were supported by cluster analysis of measured environmental variables, with clusters differing in duration of low near-bottom dissolved oxygen concentration and by depth. Independent cluster analysis confirmed significant separation of benthic communities among the selected video groups, with hypoxic habitats showing reduced species diversity and a higher proportion of tubificids. The gradient of conditions sampled in our study revealed assemblages of benthic invertebrates sensitive to and tolerant of hypoxia. The agreement among video, biological, and environmental data confirmed that video analysis can provide a novel, quick and reliable method to detect benthic habitats affected by hypoxia and determine their spatial extent once a baseline is established.

The landscape theory of food web architecture (LTFWA) describes relationships among body size, trophic position, mobility, and energy channels that serve to couple heterogenous habitats, which in turn promotes long-term system stability. However, empirical tests of the LTFWA are rare and support differs among terrestrial, freshwater, and marine systems. Further, it is unclear whether the theory applies in highly altered ecosystems dominated by introduced species such as the Laurentian Great Lakes. Here, we provide an empirical test of the LTFWA by relating body size, trophic position, and the coupling of different energy channels using stable isotope data from species throughout the Lake Michigan food web. We found that body size was positively related to trophic position, but for a given trophic position, organisms predominately supported by pelagic energy had smaller body sizes than organisms predominately supported by nearshore benthic energy. We also found a hump-shaped trophic relationship in the food web where there is a gradual increase in the coupling of pelagic and nearshore energy channels with larger body sizes as well as higher trophic positions. This highlights the important role of body size and connectivity among habitats in structuring food webs. However, important deviations from expectations are suggestive of how species introductions and other anthropogenic impacts can affect food web structure in large lakes. First, native top predators appear to be flexible couplers that may provide food web resilience, whereas introduced top predators may confer less stability when they specialize on a single energy pathway. Second, some smaller bodied prey fish and invertebrates, in addition to mobile predators, coupled energy from pelagic and nearshore energy channels, which suggests that some prey species may also be important integrators of energy pathways in the system. We conclude that patterns predicted by the LTFWA are present in the face of species introductions and other anthropogenic stressors to a degree, but time-series evaluations are needed to fully understand the mechanisms that promote stability.

Insight into fish annual reproductive dynamics (including spawn timing) can elucidate key determinants of recruitment. However, few methods, if any, are available to directly index individual spawn timing, hindering study of such processes. To this end, we developed two reproductive tags (RTs; internal and external) and evaluated their performance assessing spawn timing of female yellow perch (Perca flavescens). Internal RTs performed well, especially in comparison to external RTs, displaying consistent long-term tag retention and clear tag release synchronized with egg mass release during spawning. These results demonstrate the utility of internal RTs to investigate previously unexplored mechanisms of reproductive timing.

Scientific research is often supported by public funds for the public good, and there is a trend toward using public funds to support actionable science that can be integrated into policy or practice. Funding agencies can set research priorities through the focus and timing of their research calls and funding decisions. There is a need to study funding models to better understand the relationship between agency priorities and scientific discourse. We present a case study of the National Sea Grant College Program’s research funding. Sea Grant is a federally funded network of 34 state- or territory-​based programs that fund research and perform education and outreach work on coastal environmental and natural resource issues. Individual Sea Grant programs set research priorities based on local needs, often focusing on actionable science. To assess the contributions of Sea Grant-funded research, we analyzed available citations and abstracts from Web of Science and examined patterns in article authors, journals, citations, keywords, and abstracts. The study shows that Sea Grant has significantly contributed to the scientific literature while being effective on cost-per-​publication and cost-per-citation bases. The results illustrated how targeted funding can address important local issues while substantially contributing to the broader scientific literature.

Recent oligotrophication in Lake Michigan has contributed to reduced biomass of spring zooplankton and a shift in the zooplankton assemblage toward more calanoid copepods. These changes have likely altered prey availability for first feeding native fish species that hatch in early spring. While spring zooplankton densities and assemblage compositions are routinely monitored in offshore areas of Lake Michigan, zooplankton in nearshore areas such as shallow beach environments are less studied; and associated descriptions of diet characteristics among larval coregonine species are limited. In this study, we a) describe the nearshore (<1 m depth) zooplankton assemblage at four sites in northeastern Lake Michigan during early spring 2015–2019 and b) compare diets and diet selectivity of larval lake whitefish (Coregonus clupeaformis) and Cisco (C. artedi). Zooplankton composition varied among years, but calanoid copepods and copepod nauplii consistently dominated the zooplankton assemblage. Cisco and lake whitefish larvae were captured regularly, with Elk Rapids containing the highest proportion of ciscoes each year. For both species, calanoid and cyclopoid copepods were common in diets and were positively selected as prey. Although previous research has indicated high consumption of cyclopoid copepods by larval coregonines, our results provide new evidence that larval lake whitefish and Cisco in northeastern Lake Michigan will also consume and select for calanoid copepods when they are abundant. As such, should calanoid zooplankton continue to dominate the copepod community in Lake Michigan, larval coregonines appear capable of exploiting this abundant prey resource to improve their likelihood of survival to later life stages.

Freshwater river mouths may facilitate cross-habitat resource use and bidirectional subsidization through (a) active cross-habitat movement by consumers like fish and (b) water and material movement both downstream, from tributary to nearshore lake, and in the opposite direction due to backflow processes. Despite potential importance of freshwater river mouths, relative contributions of lentic and tributary energy sources to fishes along these ecotones remain understudied, in part because measuring cross-habitat subsidization is not straightforward. We assessed cross-habitat subsidization of three fish consumers round goby (Neogobius malanostomus), yellow perch (Perca flavescens), and alewife (Alosa psuedoharengus) in three river mouths of Lake Michigan, USA. Specifically, we (a) measured stable isotope ratios (delta 13C, delta 15N, delta 2H, delta 18O) in ambient water, bivalve shells, potential invertebrate prey, and fish soft tissue, and we assessed fish nutritional status based on essential fatty acid composition, and (b) estimated Bayesian ellipses and mixing models including either two (delta 13C-delta 15N) or three (delta 13C-delta 15N-delta 2H) isotope ratios. Results revealed evidence of bidirectional habitat subsidies for all fishes, but energy subsidies varied by species and across river mouths; likely related to differences in species-specific behavior and hydrologic differences among river mouths. Relative to nearshore oligotrophic Lake Michigan, fish in productive tributary environments contained relatively low essential fatty acid content, suggesting a possible trade-off between prey quantity and quality across habitats. This study advances our understanding of resource connectivity in lake ecosystems and the combined use of multiple stable isotopes (including mixing models) and fatty acids to document cross-habitat subsidies along freshwater ecotones.

Aquatic food webs are spatially complex, potentially contributing to intraspecific variability in production pathway reliance of intermediate trophic level consumers. Variation in trophic reliance may be described by well-established trophic indicators, like stable isotope ratios (δ13C, δ15N), along with emerging trophic indicators, such as fatty acid composition. We evaluated stable isotope ratios and fatty acid profiles of European smelt (Osmerus eperlanus) among and within distinct regions of three large Swedish lakes (Hjälmaren, Mälaren, Vättern) which differed in trophic status. We expected that smelts in more oligotrophic lakes and regions would be characterized by distinct stable isotope signatures and fatty acid profiles, with particularly high polyunsaturated fatty acid (PUFA) relative levels. However, we acknowledge that frequent movement of smelts among regions may serve to spatially integrate their diet and lead to limited within-lake variation in stable isotope ratios and fatty acid composition. As expected, in comparison with more productive lakes (i.e., Hjälmaren and Mälaren), smelts from ultra-oligotrophic Vättern were characterized by low δ15N, high δ13C and high percent of a dominant PUFA, docosahexaenoic acid (DHA). Smelts from different regions of the morphometrically complex Mälaren displayed differential stable isotope ratios and fatty acid relative concentrations, which were consistent with within-lake differences in productivity and water residence times, suggesting that smelts in this lake forage locally within distinct regions. Finally, at the individual smelt level there were particularly strong and consistent associations between a well-established trophic indicator (δ13C) and percent DHA, suggesting that the relative concentration of this fatty acid may be a useful additional trophic indicator for smelt.

Elucidating physical transport phenologies in large lakes can aid understanding of larval recruitment dynamics. Here, we integrate a series of climate, hydrodynamic, biogeochemical, and Lagrangian particle dispersion models to: (1) simulate hatch and transport of fish larvae throughout an illustrative large lake, (2) evaluate patterns of historic and potential future climate-induced larval transport, and (3) consider consequences for overlap with suitable temperatures and prey. Simulations demonstrate that relative offshore transport increases seasonally, with shifts toward offshore transport occurring earlier during relatively warm historic and future simulations. Intra- and inter-annual trends in transport were robust to assumed pelagic larval duration and precise location and timing of hatching. Larvae retained nearshore generally encountered more favorable temperatures and zooplankton densities compared to larvae transported offshore. Larval exploitation of nearshore resources under climate change may depend on a concomitant shift to earlier spawning and hatch times in advance of earlier offshore transport.

ABSTRACTOptimal egg size theory implies that female organisms balance between fecundity and individual offspring investment according to their environment. Past interspecific studies suggest that fishes in large marine systems generally produce smaller eggs than those in small freshwater systems. We tested whether intraspecific egg size variation reflected a similar pattern by comparing egg size among yellow perch (Perca flavescens) populations inhabiting a range of system sizes. In 2018, 2019, and 2023, we collected yellow perch egg samples from 12 locations in systems ranging in surface area from 37 to 5,390,492 ha. First, we found that egg diameter significantly increased with maternal total length in five of eight individually tested populations. After accounting for these maternal effects, we found a significant interaction, where females inhabiting larger lakes, such as the main basins of Lakes Erie and Michigan, produced smaller eggs than those in smaller inland lakes, and the greatest differences were demonstrated among females of greater total length. This egg size variation in the largest females is consistent with interspecific egg size comparisons between marine and freshwater fishes. However, by examining a single species across vastly different environments, we were able to support theoretical expectations that maternal investment in offspring should vary with environmental conditions controlling early‐life resource acquisition and competition.

Sucker species (Catostomidae) are a common benthic invertivore in North American waterbodies yet are understudied in the Laurentian Great Lakes. Despite large biomass and potential competition with more economically valuable fish species, the diets of Great Lakes suckers are poorly described. We explored the gut contents of adult white suckers (Catostomus commersonii) in Lake Michigan and Saginaw Bay, Lake Huron, and longnose suckers (Catostomus catostomus) in Lake Michigan. Chironomidae was a primary prey for white suckers in both lakes, along with Amphipoda in Saginaw Bay. For longnose suckers in Lake Michigan, gut contents were dominated by Amphipoda and Isopoda. Relative to other benthic invertebrate taxa, white suckers positively selected Chironomidae as preferred prey (indexed via Chesson’s alpha). Moreover, the average length of consumed Chironomidae and Amphipoda increased with white sucker length, suggesting preferential size selection of prey as suckers grow. Although dreissenid mussels are overwhelmingly abundant in the benthos of Lake Michigan and Lake Huron, relatively few dreissenid mussels were consumed by either sucker species. Thus, suckers are unlikely to contribute to the control of these invasive invertebrates.

Juvenile stages of fishes are frequently bottlenecks to recruitment. Habitat use of early life stages and the extent to which fish rely on local resources may affect how they respond to habitat loss and alterations, with important implications for habitat management. To investigate the potential for prolonged reliance on local resources, we quantified stable isotope ratios (delta(13) carbon, delta(15) nitrogen, delta(18) oxygen and delta(2) hydrogen) of young-of-year (YOY) largemouth bass Micropterus salmoides and isotope ratios of locally collected water and potential prey across three study components, a controlled pond experiment, a multi-lake survey and a detailed single-lake survey. Across study components, we observed habitat and site fidelity of YOY largemouth bass in mid-summer, demonstrated by distinct spatial differences in young bass stable isotope ratios. Additionally, we observed significant, positive correlations between delta C-13 of YOY largemouth bass and delta C-13 of locally collected invertebrates and small bluegill Lepomis macrochirus in the single lake survey, suggesting localised foraging. Later in summer, spatial differences in largemouth bass stable isotope ratios were not apparent, indicating a transition to more spatially integrated foraging. Prior to switch to piscivory, YOY largemouth bass rely on local resources indicating that they may be more susceptible, both positively and negatively, to hyper-local changes in forage availability or disturbances. This study demonstrates that stable isotope ratios allow for differentiating environmental experiences among young fish in relatively close proximity in small freshwater systems. Moreover, high spatial variation of consumer stable isotope ratios demonstrates the importance of considering spatial heterogeneity in stable isotope studies.

In large freshwater systems, the dominant production pathways supporting food webs are often spatiotemporally variable. We used stable isotope analysis and analysis of covariance (ANCOVA) models to investigate spatial and interannual variation in the dominant production pathways supporting fish consumers within the central basin of Lake Erie. We examined C and N stable isotope ratios of zooplankton, benthic invertebrates, and four species of fish common to nearshore areas of the central basin (yellow perch, Perca flavescens; white perch, Morone americana; rainbow smelt, Osmerus mordax; and round goby, Neogobius melanostomus) using tissue samples collected in 2017 and 2019. δ 13C values varied by location consistent with expected baseline differences in nutrient loading (13C was more enriched in the southern region) in two of six ANCOVA models. Furthermore, δ 15N values varied with individual fish size and by location in a manner consistent with spatial patterns of nutrient loading from surrounding agricultural landscapes (15N was more enriched in the northern region) and a longitudinal gradient of eutrophication, decreasing from west to east. These patterns were not exhibited by all species and did not necessarily persist across years, suggesting that additional factors (e.g., regional diet differences, river plume dynamics) also contributed to observed δ 13C and δ 15N variation. We suggest that spatiotemporal variation of stable isotope ratios should be accounted for in studies of trophic basis of production and food web structure in Lake Erie.

Ecological models can provide critical guidance to conservation programs both as problem-solving tools and by projecting future outcomes, specifically when time and resources limit directly testing alternative management approaches and scenarios. Due to the complexity of aquatic systems, environmental and climatic factors co-vary, multiple risk factors interact, and driving ecological and evolutionary processes are characterized by non-linear, higher-order interactions. Recent modeling advancements allow for better accounting of variation across time and space in ecological and genetic processes, but more progress is needed to inform conservation and address biodiversity decline. Modeling approaches that can explicitly incorporate the ongoing, rapid transformation of climate and landscapes and demogenetic and eco-evo consequences are useful for supporting and informing conservation planning strategies. In this narrative perspective, we present the history and role of individual-based models (IBMs) in aquatic systems to guide management. We present exemplary cases that cover (1) the conservation and management of native species in systems impacted by invasive species, (2) life history evolution impacts on the management of fisheries, (3) predictions of the interaction between changing environments and management decisions, and (4) testing factors that drive system dynamics in order to prioritize management decisions. We summarize potential platforms and software available to researchers and managers and discuss future opportunities and challenges. While this review focuses on the use of IBMs in aquatic systems, we assert that this foundational knowledge is applicable across systems and encourages researchers and managers to consider incorporating individual-based modeling perspectives to inform conservation as appropriate.

How to identify the drivers of population connectivity remains a fundamental question in ecology and evolution. Answering this question can be challenging in aquatic environments where dynamic lake and ocean currents coupled with high levels of dispersal and gene flow can decrease the utility of modern population genetic tools. To address this challenge, we used RAD-Seq to genotype 959 yellow perch (Perca flavescens), a species with an similar to 40-day pelagic larval duration (PLD), collected from 20 sites circumscribing Lake Michigan. We also developed a novel, integrative approach that couples detailed biophysical models with eco-genetic agent-based models to generate "predictive" values of genetic differentiation. By comparing predictive and empirical values of genetic differentiation, we estimated the relative contributions for known drivers of population connectivity (e.g., currents, behavior, PLD). For the main basin populations (i.e., the largest contiguous portion of the lake), we found that high gene flow led to low overall levels of genetic differentiation among populations (F-ST = 0.003). By far the best predictors of genetic differentiation were connectivity matrices that were derived from periods of time when there were strong and highly dispersive currents. Thus, these highly dispersive currents are driving the patterns of population connectivity in the main basin. We also found that populations from the northern and southern main basin are slightly divergent from one another, while those from Green Bay and the main basin are highly divergent (F-ST = 0.11). By integrating biophysical and eco-genetic models with genome-wide data, we illustrate that the drivers of population connectivity can be identified in high gene flow systems.