Zachary S. Feiner

Trophic Niche of Invasive White Perch and Potential Interactions with Representative Reservoir Species

Abstract The trophic dynamics of invasive species can yield insights into the mechanisms of invasion success and aid in the prediction of potential impacts on established species. Additionally, the predicted effects of an invader may differ depending on how it integrates into the resident food web and whether its resource use changes throughout the invasion process. We investigated the trophic dynamics of populations of invasive White Perch Morone americana in three large North Carolina reservoirs and evaluated the potential for impacts on members of the resident fish community. Specifically, we used stable isotope and diet analyses to evaluate their trophic niche relative to three representative species in each reservoir chosen for their widespread range, potential overlaps with White Perch, recreational value, and representation of ecological guilds based on habitat and prey sources. The species were a native littoral generalist invertivore (Bluegill Lepomis macrochirus), native littoral piscivore (Larg...

Rapidly shifting maturation schedules following reduced commercial harvest in a freshwater fish

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.

Environmental Biology of Percid Fishes

The large percids, including Perca and Sander species, are economically and ecologically important species that inhabit large temperature regions of the Northern Hemisphere. In this chapter, we provide an overview of the environmental biology of the Perca (including yellow perch P. flavescens and Eurasian perch P. fluviatilis) and Sander (including walleye S. vitreus, pikeperch S. lucioperca, and sauger S. canadensis) genera, on which the majority of fisheries and aquaculture practices are focused. Through a comprehensive literature review, we discuss how individual- and population-level vital rates, including growth, foraging, reproduction, recruitment, and mortality, are mediated by biotic (e.g., density dependence, resource availability) and abiotic (e.g., temperature, light) environmental variables. As fisheries exploitation is a major source of size-selective mortality in many percid populations, we also examine the potential impacts of fishing mortality on both population metrics and individual vital rates, and identify several research areas that require further investigation. Through this review we aim to identify the major environmental drivers of variation in percid vital rates and thereby inform management practices for both wild and cultured percid populations.

Does overwinter temperature affect maternal body composition and egg traits in yellow perch Perca flavescens

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.

A meta-analysis of the effects of exposure to microplastics on fish and aquatic invertebrates

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.

Species identity matters when interpreting trophic markers in aquatic food webs

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.

Environmental influences on fish assemblage variation among ecologically similar glacial lakes

The composition and structure of fish communities are affected by a variety of factors, both within the aquatic ecosystem and from the surrounding watershed. Many studies have examined what structures fish assemblages over broad spatial and environmental gradients. However, the influence of local environmental attributes on the observed variation in fish assemblages is less understood across finer spatial scales, where broad-scale climatic and anthropogenic factors are relatively similar. We used multiple linear regression to examine the relationships between environmental variables and various aspects of fish assemblages (including trophic function, community indices, and species composition) in 90 glacial lakes from northern Indiana, USA, from 1990 to 2010. Trophic structure and species composition were primarily related to water quality, whereas trophic level increased and omnivores declined as Secchi depth increased and phosphorus concentrations decreased. Species richness and diversity, in contrast, were positively linked to lake size and depth. We also found unique relationships among fish assemblages and environmental variables between samples collected using gill nets and night electrofishing, which may result from these gears sampling different assemblage components – therefore, relationships that were apparent in both sampling techniques (e.g., Secchi depth effects on trophic structure) may be the most robust and useful for improving aquatic ecosystem management on local scales.