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Population-level reproductive success (recruitment) of many fish populations is characterized by high inter-annual variation and related to annual variation in key environmental factors (e.g., climate). When such environmental factors are annually correlated across broad spatial scales, spatially separated populations may display recruitment synchrony (i.e., the Moran effect). We investigated inter-annual (1966–2008) variation in yellow perch (Perca flavescens, Percidae) recruitment using 16 datasets describing populations located in four of the five Laurentian Great Lakes (Erie, Huron, Michigan, and Ontario) and Lake St. Clair. We indexed relative year class strength using catch-curve residuals for each year-class across 2–4 years and compared relative year-class strength among sampling locations. Results indicate that perch recruitment is positively synchronized across the region. In addition, the spatial scale of this synchrony appears to be broader than previous estimates for both yellow perch and freshwater fish in general. To investigate potential factors influencing relative year-class strength, we related year-class strength to regional indices of annual climatic conditions (spring-summer air temperature, winter air temperature, and spring precipitation) using data from 14 weather stations across the Great Lakes region. We found that mean spring-summer temperature is significantly positively related to recruitment success among Great Lakes yellow perch populations.

Lake Erie supplies drinking water to more than 11 million consumers, processes millions of gallons of wastewater, provides important species habitat and supports a substantial industrial sector, with >$50 billion annual income to tourism, recreational boating, shipping, fisheries, and other industries. These and other key ecosystem services are currently threatened by an excess supply of nutrients, manifested in particular by increases in the magnitude and extent of harmful planktonic and benthic algal blooms (HABs) and hypoxia. Widespread concern for this important international waterbody has been manifested in a strong focus of scientific and public material on the subject, and commitments for Canada-US remedial actions in recent agreements among Federal, Provincial and State agencies. This review provides a retrospective synthesis of past and current nutrient inputs, impairments by planktonic and benthic HABs and hypoxia, modelling and Best Management Practices in the Lake Erie basin. The results demonstrate that phosphorus reduction is of primary importance, but the effects of climate, nitrogen and other factors should also be considered in the context of adaptive management. Actions to reduce nutrient levels by targeted Best Management Practices will likely need to be tailored for soil types, topography, and farming practices.

Female yellow perch Perca flavescens exposed to three overwinter temperature regimes (4, 8 and 13° C) for 150 days spawned in markedly different proportions upon spring warming (37% of females in 4° C v. 64 and 91% in 8 and 13° C treatments, respectively), but exhibited no differences in fecundity, egg size or egg lipid content. Females held at 4° C also exhibited less within-clutch egg size variation than females held at 13° C. Moreover, eggs differed among temperature treatments in the overall proportions of 18 fatty acids, with the colder treatments resulting in potentially higher quality eggs containing more of the unsaturated fatty acids C16:1, C22:6-n3 and C18:2 cis. Female somatic condition also varied with temperature. Maternal somatic growth and protein content increased while lipid content decreased in 13° C compared to the colder treatments. There were, however, no differences among treatments in the fatty acid composition of maternal muscle. These results suggest that the temperatures experienced during winter may be less influential to P. flavescens egg size or number, which may exhibit relatively little plasticity in this species, but can alter both the number of females that spawn and the overall composition of eggs and maternal somatic tissues, which may have implications for future reproductive success.

Remnant populations of Cisco Coregonus artedi persist at the southern extent of their range among northern Indiana's glacial lakes, where most of their populations have become extirpated during the past century. Land-use practices have likely accelerated lake eutrophication, while climate change threatens to further degrade the habitat necessary to sustain Ciscoes in Indiana. However, because the effects of these stressors have not been ubiquitous, an understanding of the factors that have contributed to either extirpation or persistence of Cisco populations will better inform future conservation practices. We analyzed lake morphometric and land-use data to identify lakes that (1) are most likely to sustain Ciscoes, (2) are most likely to lose Ciscoes, and (3) have lost Ciscoes but are similar to current Cisco lakes and hence may be targets for restoration. We found that large, deep lakes located further north were more suitable for Ciscoes in the past, but that smaller lakes with a high ratio of lake area to catchment area have retained Cisco populations. This pattern supports the hypothesis that non-point-source nutrient loading is a driver of Cisco extirpations. Our results provide information to better manage a species of special concern in Indiana and of conservation interest in many other areas. Received August 5, 2015; accepted November 20, 2015

Publication- and citation-based metrics are commonly used to summarize the productivity and impact of individuals, institutions, and journals. We examined factors hypothesized to explain variation in 5 author-based performance metrics among 437 fisheries and wildlife faculty from 33 research-extensive universities in the United States. Regression analyses revealed that the elapsed number of years since conferral of the Doctor of Philosophy (Ph.D.) degree (academic age) was a strong predictor of performance metrics, with non-linear age effects for Hirsch's h-index, Brown's hb-index, the annual rate of increase in h (i.e., m quotient), and number of publications. Greater performance was observed for faculty with greater research appointments. Performance did not vary between Wildlife and Fisheries disciplines but did vary across sub-disciplines; metrics indicated that genetics and disease-related sub-disciplines had the greatest positive effect sizes, social sciences and management-oriented sub-disciplines had the smallest effects, and ecology, conservation, quantitative methods, and aquatic science showed intermediate effect sizes. On average, male faculty published more articles than females, but no sex differences were evident for the other 4 performance metrics. Earlier publication relative to attainment of the Ph.D. degree (publication precocity) was associated with performance for all metrics. Regression models explained 28–54% of the deviance and may prove useful in placing reported values for performance in context of performance by peers. As an alternative point of reference, named (i.e., distinguished) faculty on average exhibited performance 31–96% greater than the performance predicted for otherwise comparable faculty. Our regression models allow for more meaningful comparison of publication and citation performance relative to peers, but they represent only one aspect of faculty performance and should not replace qualitative peer review of productivity and impact. © 2016 The Wildlife Society.

In rivers, lakes, and other aquatic systems throughout the world, intake pipes withdraw huge volumes of water for industrial purposes, including power plant cooling. During this process, large numbers of small-bodied, early life-stages of fish are pulled into pipes (i.e., entrained) and may be subjected to physical, thermal and chemical stress. As a result of such entrainment, these organisms can suffer direct or indirect mortality. However, given that the vast majority of larval fish are likely to die during early life due to natural processes, it is not obvious that entrainment-related mortality will have a strong influence on subsequent adult population sizes. The ability to evaluate if larval fish are dead on arrival, moribund, or in poor condition (i.e., likely to die through natural processes) at the time of entrainment could shed light on likely population-level impacts. To this end, we review the potential use of RNA:DNA ratios to index condition of entrained larval fish. Through a meta-analysis of published research studies, we demonstrate that RNA:DNA ratios of larval fish are responsive to starvation stress, with effect size increasing with duration of starvation. We relate these results to a surrogate measure of irreversible long-term negative impacts to fish populations, and demonstrate that the timescale over which RNA:DNA ratios respond to stress may not be long enough to reflect before-and-after entrainment stress. We also highlight the diverse factors contributing to variation of RNA:DNA ratios, including methodological, ontogenetic, and thermal influences. We believe that the need to account for these influences when comparing among RNA:DNA values limits the utility of broadly using RNA:DNA ratios to evaluate entrainment effects. However, the method shows promise as a quick and efficient means of determining fish condition and, used in proper context (e.g., specific to a given set of environmental conditions; in conjunction with other assessment techniques), may provide a powerful tool in assessing the effects of entrainment on fish populations. Assuming that researchers can account for sources of background variation, RNA:DNA analyses may be most useful for assessing the condition of fish larvae susceptible to entrainment (i.e., physically in the vicinity of the water intake) and/or evaluating whether fish larvae are likely to die from natural processes independent of entrainment.

Rocky reefs provide important spawning and refuge habitats for lithophilic spawning fishes. However, many reefs have been lost or severely degraded through anthropogenic effects like dredging, channelization, or sedimentation. Constructed reefs have been used to mitigate these effects in some systems, but these reefs are also subject to degradation which may warrant custodial maintenance. Monitoring and maintenance of natural or constructed spawning reefs are not common practices; therefore, few methodologies have been created to test the effectiveness of such tools. We conducted a literature review to assess available information on maintenance of rocky spawning habitats used by lithophilic fishes. We identified 54 rocky spawning habitat maintenance projects, most of which aimed to improve fish spawning habitats through the addition of spawning substrate (n = 33) or cleaning of substrate (n = 23). In comparison to shallow riverine studies focused on salmonids, we found little information on deep-water reefs, marine reefs, or other fish species. We discuss the possible application of potential spawning habitat cleaning methods from other disciplines (e.g., treasure hunting; archeology) that may provide effective means of reef maintenance that can be used by restoration practitioners.

Indiana is home to many types of aquatic ecosystems, including lakes, rivers, streams, wetlands and temporary (ephemeral) pools, which provide habitats for a wide range of plants and animals. These ecosystems will experience changes in water quantity, water temperature, ice cover, water clarity and oxygen content as the state’s temperature and rainfall patterns shift. The plants and animals living in these aquatic ecosystems will undergo changes that will vary based on the species and the specific places they inhabit. It is challenging to know precisely how organisms will respond to changes in climate. Effects on one species create a difficult-to-predict chain reaction that potentially influences other species in the same ecosystem. Some organisms will adapt and evolve to survive, or even thrive, as the climate changes, but they will have to adjust to more than just the changes in climate. They will also respond to changes in a wide variety of other environmental factors that affect them, including invasive species, habitat destruction, contaminants, nutrient runoff, and land management decisions. While these complicated interactions make it challenging to predict the long-term fate of Indiana’s aquatic species, enough is known about climate-related stressors to help managers develop strategies to avoid the most critical outcomes, hopefully avoiding species loss. This report from the Indiana Climate Change Impacts Assessment (IN CCIA) uses climate projections for the state to explore the potential threats to Indiana’s aquatic ecosystems and describes potential management implications and opportunities.

In aquatic systems, food web linkages are often assessed using diet contents, stable isotope ratios, and, increasingly, fatty acid composition of organisms. Some correlations between different trophic metrics are assumed to be well-supported; for example, particular stable isotope ratios and fatty acids seem to reflect reliance on benthic or pelagic energy pathways. However, understanding whether the assumed correlations between different trophic metrics are coherent and consistent across species represents a key step toward their effective use in food web studies. To assess links among trophic markers, we compared relationships between major diet components, fatty acids, and stable isotope ratios in three fishes: yellow perch (Perca flavescens), round goby (Neogobius melanostomus), and spottail shiner (Notropis hudsonius) collected from nearshore Lake Michigan. Yellow perch and spottail shiner are native in this system, while round goby are a relatively recent invader. We found some evidence for agreement between different trophic metrics, especially between diet components, n-3:n-6 fatty acid ratios, and stable isotope ratios (δ13C and δ15N). However, we also observed significant variation in observed relationships among markers and species, potentially due to taxonomic variation in the specific diet items consumed (e.g., chydorid microcrustaceans and Dreissena mussels) and species-specific biochemical processes. In many of these latter cases, the invasive species differed from the native species. Understanding the effects of taxonomic variation on prey and predator signatures could significantly improve the usefulness of fatty acids in food web studies, whereas diet contents and stable isotopes appear to be reliable indicators of trophic niche in aquatic food webs.

Microplastics are present in aquatic ecosystems the world over and may influence the feeding, growth, reproduction, and survival of freshwater and marine biota; however, the extent and magnitude of potential effects of microplastics on aquatic organisms is poorly understood. In the current study, we conducted a meta-analysis of published literature to examine impacts of exposure to microplastics on consumption (and feeding), growth, reproduction, and survival of fish and aquatic invertebrates. While we did observe within-taxa negative effects for all four categories of responses, many of the effects summarized in our study were neutral, indicating that the effects of exposure to microplastics are highly variable across taxa. The most consistent effect was a reduction in consumption of natural prey when microplastics were present. For some taxa, negative effects on growth, reproduction and even survival were also evident. Organisms that serve as prey to larger predators, e.g., zooplankton, may be particularly susceptible to negative impacts of exposure to microplastic pollution, with potential for ramifications throughout the food web. Future work should focus on whether microplastics may be affecting aquatic organisms more subtly, e.g., by influencing exposure to contaminants and pathogens, or by acting at a molecular level.

A variety of gears and analytical methods can be used to characterise lentic fish assemblages; however, the combined influence of gear type and analysis can affect conclusions about assemblage patterns. Fish assemblages sampled with night electric fishing, gillnets and trapnets from 153 lakes were evaluated using summary indices of species composition, pairwise community similarity comparisons and multivariate ordination. For a given amount of effort, electric fishing had the highest species richness, while gillnets had higher diversity and evenness. Pairwise comparisons between gears revealed that (1) richness was positively correlated among all gears, (2) diversity and evenness were generally not correlated across gears and (3) electric fishing and trapnets captured more similar species than all other pairwise comparisons. Gear-specific multivariate correlation and ordination revealed that gillnet and electric fishing samples more similarly characterised variation in assemblages among lakes, while trapnets characterised assemblages along different gradients of species composition. These results indicate that either electric fishing or trapnetting can be used when assessing shallow-water assemblages for diversity or evenness, gillnets and either electric fishing or trapnets should be used for whole-lake assessments, and either gillnets or electric fishing should be used when evaluating regionwide variation in lake assemblages.

We use an individual-based eco-genetic model to explore the relative selective pressures of size-dependent predation, overwinter mortality, and density-dependent energy acquisition in structuring plastic and adaptive energy allocation during the first year of life of a temperate fish population. While several patterns emerging from a suite of eco-genetic model simulations were consistent with past theoretical models and empirical evaluations of energy allocation by young fishes, results also highlight the utility of eco-genetic models for simultaneous consideration of plastic and adaptive processes. Across simulations, variation in genetic control of energy allocation was limited during very early ontogeny when size-dependent predation pressure was particularly high. While this stabilizing selection on energy allocation diminished later in the growing season, predation, overwinter mortality, and density-dependent processes simultaneously structured energy partitioning later in ontogeny through the interactive influence of plastic and adaptive processes. Specifically, high risk of overwinter mortality and low predation selected for high prioritization of energy storage. We suggest that simulations demonstrate the utility of eco-genetic models for generating null predictions of how selective pressures may structure expression of life history traits, such as early life energy allocation.

Size-selective harvest of fish stocks can lead to maturation at smaller sizes and younger ages, which may depress stock productivity and recovery. Such changes in maturation may be very slow to reverse, even following complete fisheries closures. We evaluated temporal trends in maturation of five Great Lakes stocks of yellow perch (Perca flavescens Mitchill) using indices that attempt to disentangle plastic and evolutionary changes in maturation: age at 50% maturity and probabilistic maturation reaction norms (PMRNs). Four populations were fished commercially throughout the time series, while the Lake Michigan fishery was closed following a stock collapse. We documented rapid increases in PMRNs of the Lake Michigan stock coincident with the commercial fishery closure. Saginaw Bay and Lake Huron PMRNs also increased following reduced harvest, while Lake Erie populations were continuously fished and showed little change. The rapid response of maturation may have been enhanced by the short generation time of yellow perch and potential gene flow between northern and southern Lake Michigan, in addition to potential reverse adaptation following the fishing moratorium. These results suggest that some fish stocks may retain the ability to recover from fisheries-induced life history shifts following fishing moratoria.

Natural resource governance, and fisheries management in particular, includes multiple governmental jurisdictions and stakeholders. For many fisheries, however, an understanding of the numbers of organizations involved in management and the relationships among those organizations remains lacking. Using an email survey, we investigated the affiliation network of formal and informal relationships of Great Lakes Fishery Commission (GLFC) policy and decision makers (i.e., organizations involved in the management of Laurentian Great Lakes fisheries). The 63 respondents identified 1516 relationships with 149 organizations which provide numerous opportunities for groups to share resources and information. Important organizational roles that can be identified through network analysis include the coordinating role of the GLFC׳s staff and connections through stakeholder representatives. Informal relationships are an important aspect of the affiliation network with more than one-third of all relationships identified as informal relationships and 16 organizations identified only through informal relationships. Identification of affiliation networks could be a useful tool for understanding the connection between diverse stakeholder organizations and natural resource managers.

The diets and energy content of sympatric populations of invasive age-0 white perch Morone americana and native age-0 white bass Morone chrysops were evaluated in Saginaw Bay, Lake Huron following >20 years of coexistence. Fish were collected during July-November in 2009 and 2010 to assess seasonal and interannual patterns of diet composition, diet similarity, feeding strategy and energy density for the two species. The diet composition by weight of age-0 white bass was dominated by various zooplankton taxa, fish, or emergent insects, depending on the month and year. Although fish occasionally comprised a large fraction of the diet biomass, they were eaten by

Fluctuations in water temperature can have important physiological consequences for fishes. Effects of daily thermal cycles are well studied and can be beneficial, increasing prey consumption and growth rates when mean and maximum temperatures of the fluctuations are at or below the species' optimum temperature. While less studied, subdaily temperature fluctuations are also common in many aquatic habitats and can be caused by both natural and anthropogenic processes. We performed laboratory experiments to examine how two fish species (yellow perch, Perca flavescens, and walleye, Sander vitreus) with similar thermal preferences respond to chronic exposure to subdaily temperature variability. We selected temperature treatments that reflected observed thermal variation after examining water temperature data from multiple aquatic systems. We then separately exposed yellow perch and walleye to a stable 23 °C treatment and 12-h cycles of 23 � 2 ° Co r 23� 4 °C for 45 days. Adult yellow perch exposed to fluctuations of 23 � 4 °C over 12 h expressed higher consumption, growth and food conversion efficiency than fish experiencing stable 23 °C. Temperature fluctuations, though, resulted in mortalities and the development of skin ulcers in yellow perch that did not occur under stable temperatures. In contrast, the same 12-h temperature fluctuations did not result in mortalities or stress responses in juvenile walleye. Moreover, unlike yellow perch, growth rates of walleye were lower under 12-h temperature fluctuations compared with the stable 23 °C treatment. Our results indicate that species with similar thermal preferences can respond differently to the same subdaily temperature fluctuations.

Fish stock-recruitment dynamics may be difficult to elucidate because of nonstationary relationships resulting from shifting environmental conditions and fluctuations in important vital rates such as individual growth or maturation. The Great Lakes have experienced environmental stressors that may have changed population demographics and stock-recruitment relationships while causing the declines of several prey fish species, including rainbow smelt ( Osmerus mordax ). We investigated changes in the size and maturation of rainbow smelt in Lake Michigan and Lake Huron and recruitment dynamics of the Lake Michigan stock over the past four decades. Mean lengths and length-at-maturation of rainbow smelt generally declined over time in both lakes. To evaluate recruitment, we used both a Ricker model and a Kalman filter-random walk (KF-RW) model which incorporated nonstationarity in stock productivity by allowing the productivity term to vary over time. The KF-RW model explained nearly four times more variation in recruitment than the Ricker model, indicating the productivity of the Lake Michigan stock has increased. By accounting for this nonstationarity, we were able identify significant variations in stock productivity, evaluate its importance to rainbow smelt recruitment, and speculate on potential environmental causes for the shift. Our results suggest that investigating mechanisms driving nonstationary shifts in stock-recruit relationships can provide valuable insights into temporal variation in fish population dynamics.

Transition from endogenous to exogenous feeding is thought to be a critical period for many fish larvae, when prey availability (type, size, and density) and ambient physical conditions (e.g., temperature, water clarity) can strongly influence survival. In Lake Michigan, two important fish species, yellow perch (Perca flavescens) and alewife (Alosa pseudoharengus), hatch and, presumably, begin exogenously feeding in the nearshore zone, an area characterized by short-term variation in environmental conditions. During 2010-2011, we examined environmental conditions and spatial and temporal distributions of larval yellow perch, larval alewife, and their potential prey in a nearshore region of southeastern Lake Michigan. To consider implications of environmental conditions on larval fish habitat quality, we quantified diet contents of young larval yellow perch and alewife and modeled bioenergetic growth rate potential (an index of habitat quality) under observed and predicted prey consumption scenarios. As expected, in this dynamic nearshore zone temperatures, light levels, zooplankton prey availability, and resulting growth rate potential were highly variable. Many larval fish digestive tracts were empty, suggesting that starvation may affect cohort survival. Among early-feeding larval fish, relatively small diet items were common, with larval alewives consuming diatoms and larval yellow perch consuming veligers of invasive dreissenid mussels. Though the mechanisms underlying such prey consumption and the consequences of ingesting these prey items remain largely unexplored, our results suggest dreissenid mussel veligers present early-feeding larvae with a relatively abundant prey source that may partially offset the apparent low consumption of other prey sources within Lake Michigan’s nearshore region.

On-going ecosystem alterations within Lake Michigan have drastically transformed species interactions and food-web assembly. Description of trophic interactions across broad spatial regions is likely necessary to fully appreciate the structure of this emerging food web. Spottail shiners, Notropis hudsonius, are numerically abundant in the nearshore zone of Lake Michigan, but their trophic interactions are under-described. To that end, we described fatty acid profiles of spottail shiner through spring, summer, and fall across western and eastern shorelines of Lake Michigan's southern basin. Fatty acids, used as dietary tracers, suggested a shift from benthic-based diets in spring to more pelagic-associated diets in summer and a reversal in fall. When time lag of fatty acid accumulation is accounted for in interpretations, diets likely follow spring plankton and summer/fall benthic invertebrate maxima. Fatty acid profiles also indicated differences in diet composition based on geographic location, with benthic tracers more prevalent among spottail shiner inhabiting the western shoreline. These interpretations were generally supported by stomach content data, with high Chironomidae consumption in spottail shiners from western waters. The presence of Coleoptera, Hymenoptera, and Odonata in spottail shiner stomach contents throughout the lake highlights its reliance on nearshore and potentially inshore areas. This study offers one of the most spatially broad depiction of spottail shiner foraging habits in Lake Michigan.

Describing food web structure through either direct or indirect diet analysis is often a fundamental step in elucidating ecosystem dynamics and developing resource management goals. The present study examines spatial trophic connections in an opportunistic forager, juvenile yellow perch ( Perca flavescens ), through the concomitant use of stomach content, fatty acid profiles, and stable isotope ratio methods. During September 2010, yellow perch were collected at nine coastal locations representative of Lake Michigan's habitat heterogeneity. The three diet assessment methods revealed differential levels of spatial diet heterogeneity. In general, yellow perch relied on pelagic prey more along the eastern shoreline, and over rocky substrates within each shoreline grouping. Conversely, high benthivory was noted in yellow perch from sandy substrates and western locations. Intra-population spatial diet dissimilarity may be common yet over looked among other species within large systems. We further advocate the concurrent examination of chemical ecological tracers (e.g., stable isotopes and fatty acid profiles) and stomach contents to investigate diet patterns of predators.

Although the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) has been used for over 60 years to control sea lamprey Petromyzon marinus in the Laurentian Great Lakes, its potential non-lethal impacts on non-target species have not been fully evaluated. We exposed juveniles of two species of fish (lake sturgeon Acipenser fulvescens and rainbow trout Oncorhynchus mykiss ) and one adult fish species (fathead minnows Pimephales promelas ) to various concentrations of TFM (0.25–7.5 mg/L) in three sets of experiments examining TFM effects on growth, avoidance of TFM treated water, and predation susceptibility. Lake sturgeon and rainbow trout were monitored for two weeks after a 12 hour exposure to TFM to observe differences in instantaneous growth among four treatment levels (0, 2.5, 5, and 7.5 mg/L TFM). Growth rates did not differ significantly among control and treated fish of either species. Next, potential avoidance of TFM by rainbow trout was evaluated in a test tank where half the water was contaminated with TFM (0, 0.25, or 2.5 mg/L). No avoidance behavior was observed as rainbow trout spent equal amounts of time in TFM and control water. Finally, fathead minnows were exposed at three different concentrations of TFM (0, 2.5, and 7.5 mg/L) and placed in mesocosms with a non-exposed largemouth bass Micropterus salmoides predator. Two separate trials were performed, both with no significant differences due to treatments. In summary, results indicate that for the conditions tested, TFM has no detectable sub-lethal effects on growth, avoidance behavior, or predation mortality on the fish species tested.

Many aquatic ecosystems experience concurrent anthropogenic stressors that can have complex impacts on fish communities. Limited data and temporal associations among environmental stressors may confound the ability to attribute community-level impacts to single or multiple stressors. Instead, quantitative description of temporal changes in fish communities may shed light on the cumulative and individual impacts of diverse stressors. Saginaw Bay, Lake Huron, has experienced diverse anthropogenic stressors that have been inconsistently quantified over time. We used resampling and multivariate approaches to analyze long-term trawl data to describe how fish community patterns changed in Saginaw Bay from 1970–2011. Total, native, and moderately tolerant fish species richness generally increased from 1970–2011. Dynamic factor analysis and nonmetric multidimensional scaling revealed that fish community structure changed from 1970–2011 and that relative abundances of many fish species increased. In general, increases in richness and CPUE were correlated with decreases in total phosphorus, chl a , and water levels. In addition, breakpoint analyses revealed shifts in species richness in the mid-1980s and 1999. Temporal patterns are consistent with the hypothesis that the Saginaw Bay fish community has changed from one dominated by species tolerant of eutrophy to one with more sensitive species, likely a response to decreased phosphorous loading and resulting changes in water quality. More recently (1999–2011), richness and relative abundance of many fish species in Saginaw Bay declined, a pattern potentially reflective of larger food-web transitions in both Saginaw Bay and open Lake Huron.

Maternal effects have been observed to interact with genotypic and environmental influences to structure offspring phenotypes across a wide variety of taxa. In fishes, maternal effects may be especially important due to their potential influence on development and survival during early ontogeny - a period with high potential for population regulation. While previous studies have confirmed that maternal effects on offspring phenotype are common in fishes, the consistency with which they positively affect offspring fitness throughout early ontogeny remains largely unknown. We examined maternal effects on offspring fitness by quantifying relationships between maternal (length, mass and age), egg (diameter, mass and density) and larval traits (length, yolk-sac volume and survival) in yellow perch (Perca flavescens). Consistent with several past studies, positive relationships among maternal and egg traits were evident. While egg mass was positively related to larval size at hatching, direct relationships between maternal and larval metrics were not apparent. Larval survival appeared to have two critical periods; in contrast with expectations, survival in the first 5 days posthatch was strongly negatively related to female size and age, while survival over the following 9 days was unrelated to maternal traits. Throughout the study, survival was positively related to yolk-sac volume. Our unexpected observation of a negative relationship between maternal size and age and initial larval survival indicates that maternal effects may not be consistent throughout larval ontogeny. In fact, maternal effects appear to be dynamic influences on offspring fitness, and may have complex effects on individual- and population-level reproductive success.

Water temperature strongly affects aquatic ectotherms, as even slight temperature changes can have dramatic effects on physiological rates. Water bodies receiving industrial thermal discharges can undergo dramatic spatial and temporal changes in water temperature. To quantify effects on aquatic ectotherms, thermal habitat quality (bioenergetic growth rate potential; GRP) for zebra mussel, Dreissena polymorpha (Pallas), rusty crayfish, Orconectes rusticus (Girard), walleye, Sander vitreus (Mitchill) and smallmouth bass, Micropterus dolomieu (Lacepede) was estimated near two power plant thermal discharges on the Ohio River, USA, from 2010 to 2012 using bioenergetics models. These results were then compared with GRP under increased base temperatures representing climate warming. Growth rate potential for all species was low near the discharges during summer and highest in winter, with increasing prey consumption minimising the negative effects of increased temperatures. In their immediate vicinity, thermal discharges had a more adverse effect on GRP than plausible climate warming but primarily affected GRP over a small spatial area, particularly within 400 m downstream from the power plants. Examining thermal habitat suitability will become increasingly important as rising energy demand and climate change collectively affect aquatic organisms and their habitats.

The early life environment experienced by most larval fish is largely dependent on a combination of hatch site and water currents. Until larvae are able to swim fast enough to overcome currents, they are largely passively transported and have limited control over ambient environmental conditions, including temperature and prey availability. These factors strongly influence growth and survival of larvae, with direct consequences for subsequent recruitment. Early life survival of Saginaw Bay walleye was formerly limited by alewife predation on larvae; but following the collapse of Lake Huron alewives, the walleye population has rebounded and recruitment success may now be influenced by other factors including spawning habitat. We sought to assess the implications of successful hatching at multiple locations in Saginaw Bay, using a hydrodynamics model, particle transport model, and an individual-based bioenergetics model in series. Model results were compared to locations of young larvae collected in Saginaw Bay during 2009–2010. Results suggest that larval growth is strongly influenced by hatch date, driven by seasonal variation in temperature between sites. Larvae hatched at any location could be transported extensively within inner Saginaw Bay before reaching a sufficient size to swim independently of currents, and retention within the productive inner bay varied among years and sites. Our results indicate multiple larval walleye origins in the field, augmenting the continued production from the Saginaw River system. Successful hatching at more locations would serve to buffer walleye recruitment variation through portfolio effects, supporting arguments for more emphasis on diverse spawning habitat management and restoration.

We evaluated seasonal energy content of age-0 yellow perch Perca flavescens and walleye Sander vitreus in Saginaw Bay, Lake Huron in 2009 and 2010. We also determined the energy content of age-1 fish from the 2009 and 2010 cohorts the following spring (i.e., for fish that had survived one winter) to evaluate overwinter energy losses. As expected, larger fish within each species had disproportionately higher energy content (i.e., slope relating length and energy > 3.0) than smaller conspecifics. By contrast to expectations, allometric slopes were > 3.0 in nearly all months, not just the fall, and were higher for age-0 yellow perch than for walleye, even though increased allocation to growth would have seemingly been beneficial to even the largest yellow perch during summer. Seasonal energy allocation patterns differed between years. In 2009, length specific energy content increased from late summer to fall for both species. However, for the 2010 cohorts of fish, length specific energy content decreased between late summer and fall for yellow perch and did not change for walleye. There were 13–17% overwinter declines in length specific energy content between the fall (October or November) and the spring (May) with no major differences between cohorts within a species or between species for a given year. Because young yellow perch and walleye are similar physiologically but differ in size (i.e., yellow perch are smaller), it is possible that overwinter energy losses are more important for yellow perch than for walleye.

Identifying mechanisms influencing early-life survival may elucidate recruitment variability of fish populations. Yellow perch ( Perca flavescens ), are economically and ecologically important in Saginaw Bay, Lake Huron, but have recently experienced low recruitment despite strong production of age-0 fish. Recent year classes have been characterized by slow first-year growth, as indexed by fall size of age-0 yellow perch; however, seasonal growth patterns and accompanying diet and survivorship patterns have not been documented for age-0 yellow perch in Saginaw Bay. To this end, we collected age-0 yellow perch weekly (larvae) and monthly (juveniles) throughout the first year of life during 2009 and 2010 to track changes in growth and diet composition. We also evaluated predation and over-winter energy-loss as potential mechanisms of size-selective mortality. Yellow perch growth, energy accumulation and size-specific condition decreased during late summer and fall. During larval and juvenile stages, predominant components of yellow perch diets transitioned from copepods to Daphnia and other zooplankton; however, we observed only weak ontogenetic shifts toward benthic prey. Smaller yellow perch a) were preferentially preyed upon by walleye (the bay's main piscivore) and b) displayed lower mass-specific energy content, potentially increasing overwinter starvation risk, suggesting that slow growth increases mortality risk. Our results are consistent with the hypothesis that recruitment dynamics are influenced by an interplay of size-selective mortality and diet-induced reductions in growth.

Age-0 lake whitefish Coregonus clupeaformis (11–160 mm total length) were collected from Saginaw Bay, Lake Huron during April–November 2009 and 2010 for diet analysis and for the evaluation of ontogenetic changes in feeding ecology. Lake whitefish ≤ 50 mm ate mainly zooplankton, after which their diets switched mainly to benthic macroinvertebrates. Cyclopoida were the dominant prey consumed by very small lake whitefish ( Daphnia were the most common cladoceran in the diets, but for fish 31–50 mm Bosminidae were also relatively important. Although the shift to Daphnia could represent an ontogenetic point when lake whitefish were large enough to effectively handle this prey, it also took place when the relative availability of Daphnia increased. Once lake whitefish were > 50 mm, Chironomidae larvae became a dominant prey item and this shift to benthivory coincided with a 55% increase in length-adjusted energy content between June and July. However, as fish grew (around 110–120 mm), Sphaeriidae and the benthic zooplankton Chydoridae became increasingly important in the diet. As these less energetically rich prey were incorporated into the diet, there were corresponding 21 and 15% decreases in length-adjusted energy content from July to August and September, respectively.

Predatory invertebrates can be a major factor in structuring zooplankton communities. We collected zooplankton and the predatory cladocerans Bythotrephes longimanus and Leptodora kindtii at 4 stations in inner Saginaw Bay, Lake Huron during May–October 2009 and April–November 2010. Production of zooplankton prey was estimated using temperature and biomass based empirical models. Population consumption rates of Bythotrephes and Leptodor a were estimated using a combination of conversion efficiency, bioenergetics and experimental based models. Bythotrephes biomass peaked in July of 2009 and 2010, and in 2010, the biomass rebounded in the fall after a late summer decline. Leptodora biomass was generally lower than that of Bythotrephes except in June 2009 and August 2010. Zooplankton biomass, production and composition showed strong seasonal patterns, with biomass more than tripling between May and June each year, largely due to an increase in biomass of Daphnia in June. By contrast, total zooplankton biomass declined by over 70% between June and July owing to declines in Daphnia biomass. Population consumption by predatory cladocerans was a large percentage or even exceeded prey production during July and August in Saginaw Bay regardless of which consumption models were used. This short term ( Bythotrephes rather than Leptodora . Bythotrephes likely play an important role in food web function and should be accounted for when evaluating the flow of energy within the Laurentian Great Lakes systems.

In Saginaw Bay, Lake Huron, yellow perch ( Perca flavescens ) constitute an ecologically important component of the ecosystem and support both recreational and commercial fisheries. Over the past 40 years, Saginaw Bay has experienced multiple ecosystem-level changes (e.g., non-indigenous species introductions, reduced nutrient loading and variable temperatures). In turn, abundances and growth rates of yellow perch and their predators and prey have fluctuated. Recent changes to Saginaw Bay and Lake Huron foodwebs have potential to influence prey composition and subsequently, growth and condition for yellow perch; but a complete description of yellow perch diet composition across seasons has not been undertaken in recent years. We calculated mean relative weight (W r ), an index of condition, of age-1 and older yellow perch in Saginaw Bay annually for 1970–2011. We found high interannual variation in condition and documented low mean W r during 1978–1991. We developed regression models to explain this variation using phosphorus load, temperature, forage fish density, and yellow perch density as potential explanatory factors. Patterns of W r were associated with changes in yellow perch densities, although interannual variation was not significantly associated with any of the available explanatory variables. Diet analysis of yellow perch collected in 2009 and 2010 demonstrated that age-1 and older yellow perch consumed a fundamentally different diet from a previous study (1986–1988), exhibiting a greater reliance on non-indigenous prey (e.g. Bythotrephes longimanus ).

Littoral zones of lentic systems are important nursery habitats for age-0 fish as they provide foraging habitat and refuge from predation. While local habitat characteristics in a lake's littoral zone can affect abundances, mean lengths, and trophic interactions of age-0 fish, lake-scale characteristics may also influence these factors. Given that local and lake-scale characteristics are probably related, it may be difficult to interpret perceived associations between habitat characteristics and fish population metrics, as well as elucidate consequences of anthropogenic alterations of habitat. We used classification and regression tree (CART) analysis to evaluate relationships between local and lake-scale habitat characteristics, abundances, and mean lengths of age-0 Largemouth Bass Micropterus salmoides and Bluegills Lepomis macrochirus collected from glacial lakes in northern Indiana during 2009 and 2010. We also evaluated habitat influences on stomach contents of age-0 Largemouth Bass. Our res...

The benthic amphipod Diporeia is an ecologically and biogeochemically important constituent of deep freshwater lakes in North America. The proliferation of dreissenid mussels in the mid-1990s coincided with a sharp decrease in Diporeia populations in several Laurentian Great Lakes; however the ultimate cause and mechanisms of their decline are still unknown. Here we examined the composition of DNA viruses associated with Diporeia collected from populations of Lake Michigan that had declined and stable populations in Lake Superior and Owasco Lake (Finger Lake in central New York State). Viral metagenomic libraries from Owasco Lake and Lake Superior were comprised primarily of bacteriophages, which may infect bacteria within the amphipod microbiome. In contrast, the metagenomic library from Lake Michigan contained well-represented ssDNA circular viral genomes. The prevalence and viral load of one putative Type V ssDNA circular virus (LM29173) that recruited almost 30% of total viral sequence reads in the Lake Michigan library was analyzed by quantitative PCR. The prevalence of LM29173 was over two orders of magnitude greater in Lake Michigan compared to the other two lakes. Although further research is necessary to establish the pathology and epidemiological extent of viral- Diporeia interactions, our data suggest that viruses may be numerically significant constituents of the Diporeia microbiome, and if pathogenic some of these viruses may be a stressor of Great Lakes Diporeia populations. Our data further indicate that special attention should be given to the circovirus that was prevalent in the declining Michigan population but uncommon in the other two lakes.

Dietary niches of fishes have traditionally been evaluated at the population level, with diet pattern central tendencies compared spatio-temporally among habitats and populations. More recently, however, studies have emphasised the importance of within-population diet variation and niche partitioning. Several studies have examined diets of young yellow perch (Perca flavescens) at the population level and have described an ontogenetic transition from zooplankton to benthic prey during the first year of life. However, independent of ontogenetic diet shifts, intrapopulation variation of young yellow perch diets remains largely unexplored. We quantified patterns of diet composition in age-0 yellow perch collected from Saginaw Bay, Lake Huron, USA during July-October, 2009 and 2010. We observed substantial variation in diet composition among individuals across and within sites, but found relatively weak evidence indicating an ontogenetic diet shift. Zooplankton were the dominant prey for age-0 yellow perch on most occasions, and individual diets were composed primarily of either zooplankton (e.g. Daphnia spp., Calanoida) or benthic (i.e. Chironomidae larvae, Chydoridae) prey. These patterns were not simply attributable to differences in prey availability and ontogenetic diet shifts, because a) not only diet composition, but also prey selectivity (Chesson's a) varied among sites and b) individual and spatial diet differences were evident independent of ontogeny. Within-cohort differences in diet composition may be an important, but often overlooked, phenomenon with implications for cumulative trophic interactions and intracohort growth and survival among young fish.

Offspring size determines offspring survival rates; thus, understanding factors influencing offspring size variability could elucidate variation in population dynamics. Offspring size variation is influenced through multigenerational adaptation to local environments and within‐lifetime plastic responses to environmental variability and maternal effects among individuals. Moreover, offspring size variation may represent trade‐offs in energy allocation within individuals that influence lifetime reproductive success. However, the mechanisms whereby environmental conditions influence offspring size, e.g., via inducing adaptive and plastic variation in population‐scale maternal effects, remain poorly understood. We evaluated intra‐specific variation in maternal effects, egg size, and intra‐individual egg size variation in six populations of walleye (Sander vitreus) and related among‐ and within‐population patterns to thermal conditions. Egg size was conserved within populations and negatively related to long‐term thermal conditions among populations, while maternal effect strengths were positively related to thermal conditions, suggesting that populations inhabiting warmer environments adapted to produce smaller eggs but stronger maternal effects. Within a population, egg size was positively related to colder winters, suggesting cold winters may alter egg size through effects on maternal condition or as an adaptive maternal effect to improve offspring survival. Intra‐individual egg size variation varied little among populations or with female size, but declined with increasing summer and decreasing winter temperatures. Our result suggests that environmental conditions could impact not only short‐term offspring production but also spur adaptive changes in offspring phenotypes. Thus, it is necessary to account for adaptive responses to predict population dynamics under environmental changes.

Research productivity and impact are often considered in professional evaluations of academics, and performance metrics based on publications and citations increasingly are used in such evaluations. To promote evidence-based and informed use of these metrics, we collected publication and citation data for 437 tenure-track faculty members at 33 research-extensive universities in the United States belonging to the National Association of University Fisheries and Wildlife Programs. For each faculty member, we computed 8 commonly used performance metrics based on numbers of publications and citations, and recorded covariates including academic age (time since Ph.D.), sex, percentage of appointment devoted to research, and the sub-disciplinary research focus. Standardized deviance residuals from regression models were used to compare faculty after accounting for variation in performance due to these covariates. We also aggregated residuals to enable comparison across universities. Finally, we tested for temporal trends in citation practices to assess whether the "law of constant ratios", used to enable comparison of performance metrics between disciplines that differ in citation and publication practices, applied to fisheries and wildlife sub-disciplines when mapped to Web of Science Journal Citation Report categories. Our regression models reduced deviance by 1/4 to 1/2. Standardized residuals for each faculty member, when combined across metrics as a simple average or weighted via factor analysis, produced similar results in terms of performance based on percentile rankings. Significant variation was observed in scholarly performance across universities, after accounting for the influence of covariates. In contrast to findings for other disciplines, normalized citation ratios for fisheries and wildlife sub-disciplines increased across years. Increases were comparable for all sub-disciplines except ecology. We discuss the advantages and limitations of our methods, illustrate their use when applied to new data, and suggest future improvements. Our benchmarking approach may provide a useful tool to augment detailed, qualitative assessment of performance. © 2016 Swihart et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Diel vertical migration (DVM) of some zooplankters in eutrophic lakes is often com- pressed during peak hypoxia. To better understand the indirect consequences of seasonal hypolimnetic hypoxia, we integrated laboratory-based experimental and field-based observa- tional approaches to quantify how compressed DVM can affect growth of a cladoceran, Daphnia mendotae, in central Lake Erie, North America. To evaluate hypoxia tolerance of D. mendotae, we conducted a survivorship experiment with varying dissolved oxygen concentrations, which demonstrated high sensitivity of D. mendotae to hypoxia (≤2 mg O2 l �1 ), supporting the field obser- vations of their behavioral avoidance of the hypoxic hypolimnion. To investigate the effect of tem- porary changes in habitat conditions associated with the compressed DVM, we quantified the growth of D. mendotae, using a 3 (food quantity) × 2 (temperature) factorial design laboratory experiment. Neither food quantity nor temperature affected short-term growth in body length of D. mendotae. However, D. mendotae RNA content (an index of short-term condition) decreased under starvation, indicating an immediate response of short-term feeding on condition. We further evaluated the effect of hypoxia-induced upward shifts in vertical distribution by quantifying the RNA content of D. mendotae from central Lake Erie before and during peak hypoxia. Despite high temperature and food quantity in the upper water column, RNA content in field-collected D. men- dotae remained low during peak hypoxia. Furthermore, D. mendotae collected during peak hypoxia consisted of only small-bodied (

Fish egg sizes vary intra-specifically among stocks and individuals, and such variation may reflect a combination of maternal and environmental influences. As egg size variation has important implications for individual and population recruitment success, it is useful to quantify egg-size variation and identify potential factors underlying such variation. We evaluated 1) within-stock maternal influences on egg size and 2) the relative elucidatory power of maternal effects versus stock in explaining inter-individual mean egg size based on eggs collected during 2007–2008 from five walleye Sander vitreus stocks in the North American Laurentian Great Lakes region. We used both linear regression models and classification and regression trees (CART) to describe egg-size variation. Egg size tended to increase with female length and for some stocks was greatest for intermediate maternal ages. However, maternal influences on egg size were relatively low and variable between years. In contrast, stock had a stronger effect; walleye egg-size variation was greater among stocks than within stocks. After controlling for the influence of maternal age and length, we found that egg size was relatively small for fish spawning in Maumee and Sandusky Rivers (western Lake Erie), intermediate in Oneida Lake and Tittabawassee River (Saginaw Bay, Lake Huron), and relatively large in Van Buren Bay (eastern Lake Erie) and Little Bay de Noc (northern Green Bay, Lake Michigan). Such inter-stock differences in maternal influence adjusted egg size appeared to be negatively associated with a system's productivity; suggesting a potential adaptive response of egg size to early life habitat conditions.

article i nfo Over the past two decades, Diporeia in all of the Laurentian Great Lakes, except Superior, have declined dra- matically. These declines have seemingly coincided with expansion of invasive Dreissena polymorpha and D. bugensis, however the exact mechanisms underlying decreasing Diporeia densities are obscure. We explored the use of RNA:DNA (R/D) ratios as a conditional index for Diporeia by experimentally demonstrating that Diporeia R/D responds to periods of starvation. Moreover, during 2008-2009 we collected Diporeia from throughout the Great Lakes and Cayuga Lake (New York, USA), and used R/D ratios to index condition of these in situ collected animals. We evaluated spatial and temporal variation of nucleic acid indices using clas- sification and regression tree (CART) analysis with a suite of environmental variables included as potential predictors. Diporeia R/D of in situ collected specimens exhibited pronounced spatial and temporal variation, but multiple CART models described only a small amount of this variation. While we observed some variation in Diporeia R/D among lakes, nucleic acid ratios appeared to respond weakly to Diporeia population charac- teristics and local environmental conditions. Specifically, CART analyses revealed that Diporeia R/D was par- ticularly low at extreme depths, and interestingly, Diporeia nucleic acids were not strongly associated with the presence of dreissenids. In summary, while a limited amount of variation in Diporeia R/D was attributable to environmental conditions, the majority of Diporeia R/D variation was unaccounted for. Hence, the causa- tive factors underlying spatio-temporal variation of Diporeia R/D and the mechanistic reasons for Diporeia declines in the Great Lakes remain largely unknown.

The benthic amphipod Diporeia spp. was once the predominant macroinvertebrate in deep, offshore regions of the Laurentian Great Lakes. However, since the early 1990s, Diporeia populations have steadily declined across the area. It has been hypothesized that this decline is due to starvation from increasing competition for food with invasive dreissenid mussels. In order to gain a better understanding of the changes in Diporeia physiology during starvation, we applied two-dimensional gas chromatography coupled with time of flight mass spectrometry (GCXGC/TOF-MS) for investigating the responses in Diporeia metabolome during starvation. We starved Diporeia for 60 days and collected five organisms every 12 days for metabolome analyses. Upon arrival to the laboratory, organisms were flash frozen and served as control (day 0). We observed an increase in lipid oxidation and protein catabolism with subsequent declines of essential amino acids (proline, glutamine, and phenylalanine), down-regulation of glycerophospholipid and sphingolipid metabolism, and decreased polyunsaturated fatty acid abundance in nutritionally stressed Diporeia. Abundance of 1-Iodo-2-methylundecane, a metabolite closely related to insect pheromones, also declined with starvation. This research has further substantiated the applicability of GCXGC/TOF-MS as a research tool in the field of environmental metabolomics. The next step is to apply this new knowledge for evaluating nutritional status of feral Diporeia to elucidate the underlying cause(s) responsible for their decline in the Great Lakes.

Summary 1. Previous studies in a variety of ecosystems have shown that ecologically and economically important benthic and bentho-pelagic fishes avoid hypoxic (

The holarctic amphipod Diporeia spp. was historically the most abundant benthic macroinvertebrate in the offshore region of the Laurentian Great Lakes basin. However, since the 1990’s, the numbers of Diporeia have declined precipitously throughout the region. Competition for food with introduced dreissenid mussels may be partly to blame for this decline. Thus, a better understanding of how Diporeia responds and adjust to starvation is needed. For this purpose, we used liquid chromatography (LC) coupled with time-of-flight mass spectrometry (TOFMS) to study the metabolite profiles of Diporeia during starvation. Diporeia were collected from Lake Michigan, brought to the laboratory and starved for up to 60 days. During the starvation period, metabolite levels were determined at 12-day intervals and compared to those of day 0. Principal component and cluster analyses revealed differential abundance of metabolite profiles across groups. Significantly down-regulated metabolites included polyunsaturated fatty acids, phospholipids, and amino acids and their derivatives. Overall, starved organisms relied predominantly on glycerophospolipid metabolism and protein based catabolism for energy production. This research demonstrates that LC-MS based metabolomics can be used to assess physiological status and has shown that unique metabolite profiles are distinguishable over several weeks of starvation in this freshwater amphipod. More importantly, these unique metabolites could be used to gain insights into the underlying cause(s) of Diporeia’s decline in the Laurentian Great Lakes.

As in various freshwater and coastal marine ecosystems worldwide, seasonal bottom water hypoxia is a recurring phenomenon in Lake Erie's central basin. While bottom hypoxia can strongly affect sessile benthic animals, its effects on mobile organisms such as fish are less understood. We evaluated the potential for bottom hypoxia to affect the growth rates of yellow perch Perca flavescens, a species of ecological and economic importance in the lake. To this end, we (1) conducted laboratory experiments to quantify the effects of reduced dissolved oxygen on consumption, somatic growth, and RNA : DNA ratios (an index of short-term growth) of young yellow perch and (2) explored the effects of bottom hypoxia on young yellow perch growth in Lake Erie's central basin by collecting individuals in hypoxicand normoxic regions of the lake and quantifying their RNA : DNA ratios. Yellow perch consumption and growth in our experiments declined under hypoxic conditions (≤2 mg O2/L). While yellow perch RNA : DNA r...

In temperate environments, seasonal selective sources of mortality (e.g., starvation and predation) may drive season-specific energy allocation patterns of young-of-year fish. However, when quantifying such phenomena, the effect of ration is rarely considered. We conducted two experiments to investigate the effect of ration on seasonal energy allocation patterns of age-0 largemouth bass (Micropterus salmoides) during summer and fall. In a laboratory experiment designed to evaluate short-term effects of ration on energy allocation, recent ration history strongly affected body dimensions and length-adjusted energy content. In outdoor raceways, young largemouth bass grew at different rates under different ration levels. In response, length-adjusted energy content, a size-independent index of condition, differed among raceway ration treatments during late summer. However, during fall, high- and low-growth treatment fish expressed similar length-adjusted energy content. Thus, while low-growth fish appeared to ...

Use of RNAlater (Ambion, Inc.) solution to preserve whole organisms for nucleic acid analysis is gaining popularity, in part because it effectively preserves both RNA and DNA without the need for freezing the organism. Similar preservatives have been shown to cause short-term changes in animal length, and such changes must be accounted for as analyses progress. We examined the rates and degrees of shrinkage for freshwater amphipods Diporeia spp. and larval yellow perch Perca flavescens after preservation in RNAlater solution in comparison with more common preservatives. We found that after 2 months of preservation, Diporeia shrank by 3% in RNAlater versus gaining length by 5% in diluted ethanol and by 1% in diluted formaldehyde. After 5.5 months of preservation, larval yellow perch lengths decreased by 23% in RNAlater, 10% in diluted ethanol, 12% in diluted formaldehyde, and 19% when frozen in water. Overall length reduction for Diporeia and larval yellow perch was significantly greater in RNAlat...

SUMMARY 1. Hypoxia occurs seasonally in many stratified coastal marine and freshwater ecosystems when bottom dissolved oxygen (DO) concentrations are depleted below 2–3 mg O2 L )1 . 2. We evaluated the effects of hypoxia on fish habitat quality in the central basin of Lake Erie from 1987 to 2005, using bioenergetic growth rate potential (GRP) as a proxy for habitat quality. We compared the effect of hypoxia on habitat quality of (i) rainbow smelt, Osmerus mordax mordax Mitchill (young-of-year, YOY, and adult), a cold-water planktivore, (ii) emerald shiner, Notropis atherinoides Rafinesque (adult), a warm-water planktivore, (iii) yellow perch, Perca flavescens Mitchill (YOY and adult), a cool-water benthopelagic omnivore and (iv) round goby Neogobius melanostomus Pallas (adult) a eurythermal benthivore. Annual thermal and DO profiles were generated from 1D thermal and DO hydrodynamics models developed for Lake Erie’s central basin. 3. Hypoxia occurred annually, typically from mid-July to mid-October, which spatially and temporally overlaps with otherwise high benthic habitat quality. Hypoxia reduced the habitat quality across fish species and life stages, but the magnitude of the reduction varied both among and within species because of the differences in tolerance to low DO levels and warm-water temperatures. 4. Across years, trends in habitat quality mirrored trends in phosphorus concentration and water column oxygen demand in central Lake Erie. The per cent reduction in habitat quality owing to hypoxia was greatest for adult rainbow smelt and round goby (mean: )35%), followed by adult emerald shiner (mean: )12%), YOY rainbow smelt (mean: )10%) and YOY and adult yellow perch (mean: )8.5%). 5. Our results highlight the importance of differential spatiotemporally interactive effects of DO and temperature on relative fish habitat quality and quantity. These effects have the potential to influence the performance of individual fish species as well as population dynamics, trophic interactions and fish community structure.

Bottom hypoxia has reemerged as a prominent feature of Lake Erie's central basin during late summer. Similar to coastal and marine systems, the influence of hypoxia on pelagic organisms remains largely enigmatic in Lake Erie. During 2005, we used a plankton survey system (a sensor package consisting of an optical plankton counter, fluorometer, dissolved oxygen sensor, light sensor, and conductivity–temperature–depth sensor), coupled with a fish hydroacoustics system, to explore how the distribution of phytoplankton (chlorophyll), mesozooplankton, and fish varied vertically and horizontally in relation to oxygen concentrations. To do so, we conducted surveys of the entire water column on a continuous basis during mild (August) and severe (September) hypoxia. Our surveys included two sampling designs: 1) basin-wide transects sampled during day and night to define broad-scale patterns of spatial overlap among pelagic organisms; and 2) shorter (5 km) transects sampled every 4 h over a 24-h period to explore how diel vertical migration and hypoxia interact to affect time-specific spatial overlap among fishes, mesozooplankton, and phytoplankton. Our findings indicated that fish avoided regions of the hypolimnion with dissolved oxygen concentrations

Bottom hypoxia has reemerged as a prominent feature of Lake Erie's central basin during late summer. Similar to coastal marine systems, the impacts of hypoxia on pelagic organisms in Lake Erie remain largely enigmatic. During summer 2005 and 2007, we used pump sampling for mesozooplankton and fish acoustics to test the hypothesis that mesozooplankton use hypoxia as a refuge from predation. We explored species-specific diel vertical migration (DVM) of mesozooplankton and spatial overlap with planktivorous fishes at several offshore stations in the central basin of Lake Erie with similar thermal structure, but varying hypolimnetic dissolved oxygen (DO) concentrations (range: 0.3 to 4.6 mg l−1). The tendency of a zooplankter to use the hypolimnion under normoxic conditions and its sensitivity to DO defined its DVM and overlap with fish, which were generally more sensitive to hypoxia than mesozooplankton. The diaptomids (calanoid copepods) and the predatory cladoceran Leptodora kindtii were largely unaffected by hypoxia, using the epilimnion during both day and night. Daphnia mendotae and the predatory cladoceran Bythotrephes longimanus, both of which migrated from the metalimnion and epilimnion to the hypolimnion during the day under normoxic conditions, avoided the hypolimnion at DO levels ≤ 2.0 mg l− 1. Dissolved oxygen levels between 1.0 and 1.2 mg l− 1 were critical avoidance thresholds for most other mesozooplankton species, with the copepod Mesocyclops edax, a migrator between the epilimnion and hypolimnion, avoiding DO ≤ 1.2 mg l− 1. By contrast the cool water, hypolimnetic copepod Diacyclops thomasi and Daphnia longiremis continued to use the hypolimnion during the day until DO became ≤ 1.0 mg l− 1. These species aggregated in the metalimnion (primarily) and epilimnion (secondarily) at night. Only Bosmina was found in abundance in the hypolimnion at DO levels equal to 0.3 mg l− 1. Hypoxia-intolerant species (e.g., D. mendotae, B. longimanus) that were compressed into the thin metalimnion during day likely faced high predation pressure from visual-feeding planktivorous fishes (e.g., rainbow smelt Osmerus mordax, emerald shiners Notropis atherinoides) as well as the predatory cladoceran, B. longimanus. By contrast, hypoxia-tolerant species (e.g., D. thomasi, D. longiremis, and B. longirostris) that remained in the hypolimnion may have found refuge in hypoxic areas with DO > 1.0 mg l− 1, although fish were occasionally observed making feeding excursions into hypoxic waters.

Maturation schedules, key determinants of fish stocks' harvest potential and population dynamics, are influenced by both plastic and adaptive processes. Various indices are used to describe maturation schedules, and these have differential advantages for discriminating between plastic and adaptive processes. However, potential sampling-related biases associated with different maturation indices have not been fully evaluated. We analyzed three maturation indices for walleyes Sander vitreus in Lake Erie; Saginaw Bay, Lake Huron; and Oneida Lake, New York: age and length at 50% maturity, midpoint of age-specific maturity ogives (age-specific length at which probability of maturity = 0.50), and midpoints of probabilistic maturation reaction norms (PMRNs; age-specific length at which probability of maturing in the following year = 0.50). We then compared estimated maturation indices to evaluate sensitivity of different maturation indices to sampling-induced biases and to assess the relative importance...

Eco-genetic individual-based models involve tracking the ecological dynamics of simulated individual organisms that are in part characterized by heritable parameters. We developed an eco-genetic individual-based model to explore ecological and evolutionary interactions of fish growth and maturation schedules. Our model is flexible and allows for exploration of the effects of heritable growth rates (based on von Bertalanffy and biphasic growth patterns), heritable maturation schedules (based on maturation reaction norm concepts), or both on individual- and population-level traits. In baseline simulations with rather simple ecological trade-offs and over a relatively short time period (

To better understand the feeding ecology of two important Laurentian Great Lakes prey species, rainbow smelt Osmerus mordax and emerald shiners Notropis atherinoides, we quantified the diet composition, selectivity, daily ration, and diet overlap of both species in offshore central Lake Erie during May through October 2005, which spanned a period of severe hypolimnetic hypoxia (