D. Derek Aday

Factors Influencing Precision of Age Estimation from Scales and Otoliths of Bluegills in Illinois Reservoirs

Abstract We examined the effects of population-specific variation on age estimates from scales and otoliths of bluegills Lepomis macrochirus from Illinois reservoirs. We divided 12 reservoirs into four groups (north stunted, north quality, south stunted, and south quality) to examine the effects of latitude and fish size distribution on the precision of estimated ages. Ages of 40 bluegills from each reservoir (total N = 480) were independently estimated by two readers. Otoliths provided more precise age estimates than scales. Population size structure and sex had no effect on precision of ages estimated from either structure; however, latitude, age, and maturity stage all affected precision of ages estimated from scales. Age also affected precision of estimates from otoliths. Percent agreement, coefficient of variation, and age bias plots all provided useful interpretations of the data. Our results demonstrate the importance of examining population-specific sources of variation with multiple statistical m...

Direct and Indirect Effects of Gizzard Shad on Bluegill Growth and Population Size Structure

Abstract Competition with gizzard shad Dorosoma cepedianum has been shown to influence survival of larval bluegills Lepomis macrochirus as well as growth and size structure of largemouth bass Micropterus salmoides, which prey on these planktivorous species. However, little is known about how the presence of gizzard shad influences bluegills beyond the larval stage. We examined bluegill–gizzard shad interactions across 10 reservoirs with and 10 without gizzard shad to determine direct and indirect effects of gizzard shad on bluegill population size structure. In the presence of gizzard shad, bluegills exhibited smaller adult (>3 years old) size structure. Benthic invertebrate densities were higher in non-gizzard shad reservoirs, which may have contributed to increased bluegill growth in these systems. In contrast, zooplankton densities were similar in reservoirs with and without gizzard shad. Turbidity was higher in reservoirs with gizzard shad, which may have reduced foraging success and growth of bluegil...

ASSESSING POPULATION‐SPECIFIC AND ENVIRONMENTAL INFLUENCES ON BLUEGILL LIFE HISTORIES: A COMMON GARDEN APPROACH

Investigations into vertebrate life histories have demonstrated trade-offs between growth and reproduction that can result in individual and population-specific variation in life-history strategies. Mechanisms to explain variation among populations, however, often remain unidentified. We examined the relative strength of genetic (population source) and environmental (population social structure) factors on variation in growth and timing of maturation for juvenile male bluegill in a common garden experiment. We placed juvenile male bluegill collected from two different wild source populations, one with parental males that are large (>190 mm total length) and one with parental males that are stunted (<155 mm total length), in a common environment and varied the social structure by controlling the presence or absence of large, mature, male bluegill collected from a third population. Juvenile male bluegill from both populations allocated significantly more energy to reproduction in the absence of large males than in their presence. Within ponds, differences in growth and maturation rates between juvenile males from the two source populations were small but significant. These results indicate both genetic and environmental components to growth and maturation in bluegill but emphasize the importance of social interactions in shaping individual life-history strategies.

A Statewide Assessment of Mercury Dynamics in North Carolina Water Bodies and Fish

Abstract Mercury contamination of aquatic systems has received much attention recently because of potential health effects on humans and wildlife. Although the factors affecting mercury deposition, its conversion to biologically active methylmercury, and its bioaccumulation in aquatic systems have been identified, equivocal results for particular species and systems have hampered policy making. Our study addresses this problem through a comprehensive, statewide synthesis of the available data on fish mercury contamination in North Carolina and the environmental factors associated with methylmercury formation and transport through aquatic food webs. Using data collected by the North Carolina Department of Environment and Natural Resources, the U.S. Environmental Protection Agency, and others, we examined the relationships between a suite of biotic and abiotic factors and tissue mercury concentrations in fish from North Carolina water bodies. Multivariate tests were conducted to create predictive models rel...

Examining Interpopulation Variation in Bluegill Growth Rates and Size Structure: Effects of Harvest, Maturation, and Environmental Variables

Abstract Understanding how life history variation and the environment affect growth and population size structure is an important theme of fisheries ecology. However, the interactions among important biotic and abiotic factors and their relative importance in the context of population-specific variation are seldom considered. We used an information theoretic approach to investigate how environmental variables interact with important life history parameters to influence population size structure of bluegills Lepomis macrochirus. We sampled bluegill populations in 23 Illinois reservoirs to examine the effects of temperature, water transparency, and prey availability and bluegill density, harvest, and size at maturation on bluegill growth and population size structure. Good growth and large body size were associated with warm, clear lakes containing abundant prey resources. An exception to this pattern was early growth (length at age 2): Larger body size at age 2 was associated with relatively low Secchi dep...

Prey Community Responses to Bluegill and Gizzard Shad Foraging: Implications for Growth of Juvenile Largemouth Bass

Abstract Bluegill Lepomis macrochirus, gizzard shad Dorosoma cepedianum, and largemouth bass Micropterus salmoides are common lentic species that may compete for invertebrate prey resources, and interactions among these species can have important consequences for aquatic community structure. Differential foraging behavior of bluegills and gizzard shad as juveniles, for example, may structure zooplankton and benthos communities and influence the growth of juvenile largemouth bass. We conducted a mesocosm experiment (1.6-m-diameter circular tanks) in which we allowed high and low densities of juvenile bluegills (70–100 mm total length [TL]) and gizzard shad (135–155 mm TL) to forage on established zooplankton and benthos communities for 6 weeks. After this period, we added juvenile largemouth bass (50–80 mm TL) to each tank for 4 weeks to examine growth and diets. Although foraging by bluegill and gizzard shad had limited effects on the total population densities of invertebrates, important taxon-specific e...

The Influence of Fish Length on Tissue Mercury Dynamics: Implications for Natural Resource Management and Human Health Risk

Consumption of fish has well-known human health benefits, though some fish may contain elevated levels of mercury (Hg) that are especially harmful to developing children. Fish length is most often the basis for establishing fishery harvest regulations that determine which fish will ultimately be consumed by humans. It is, therefore, essential to quantify the relationship between fish length and Hg accumulation in regard to harvest regulations for effective fishery and public health policy. We examined this relationship for three sportfish from six lakes across North Carolina, USA. Bluegill (Lepomis macrochirus) had the lowest Hg levels and only the very largest fish in the most contaminated site exceeded the US Environmental Protection Agency (USEPA) Hg screening level. Black crappie (Pomoxis nigromaculatus) had an intermediate level of Hg and larger individuals exceeded the USEPA screening level; however, they tended not to exceed this level before reaching the harvest length limit. Largemouth bass (Micropterus salmoides) exceeded the USEPA screening level at sizes below the fishery length limit in two lakes, leaving only higher risk fish for anglers to harvest and consume. Removing the effects of fish age and trophic position, we found strong positive correlations between Hg and fish length for largemouth bass and black crappie. We suggest public health officials and wildlife managers collaborate to structure fishery regulations and length-based fish consumption advisories that protect consumers from Hg exposure and communicate the relative risk of fish consumption.

Sex-specific life history patterns in bluegill (Lepomis macrochirus): Interacting mechanisms influence individual body size

The ultimate body size that an individual fish achieves can be a function both of direct effects of growth or indirect effects associated with the timing of sexual maturation (and associated energetic tradeoffs). These alternatives are often invoked to explain variation in body size within and among fish populations, but have rarely been considered simultaneously. We assessed how resource availability and timing of maturation interact to influence individual body size of bluegill (Lepomis macrochirus). Resource availability (high and low food) and the social structure of the population (presence or absence of large, mature males) were varied in experimental ponds. Food ration affected growth (larger fish in the high food treatments) and the social structure of the population affected timing of maturation (early maturation of males in the absence of large males). Treatment effects, however, were sex-specific; males responded to the social structure of the population and females were more responsive to resource availability. We also found individuals that became sexually mature were smaller than those that remained immature, although results were sex-specific and resource dependent. For males, individuals that matured were smaller when resources were limited; mature and immature females showed no difference in body size regardless of food ration. We show that both resource availability and the processes that control timing of maturation interact in sex-specific ways to influence body size of bluegill. These results suggest that a more robust explanation for variable body size requires consideration of sex-specific interactions between ecological (food and growth) and evolutionary (timing of maturation) mechanisms.

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...

Do national advisories serve local consumers: an assessment of mercury in economically important North Carolina fish

Consumption of marine fish provides both benefits (lean protein, omega-3 fatty acids and essential nutrients) and risks (main source of mercury (Hg) exposure for humans). Mercury is a potent neurotoxin and the source of more fish advisories nationwide than any other toxicant. Despite the widespread nature of Hg, it is unknown whether local Hg contamination reflects national and regional levels often used as bases to inform consumers of potential fish consumption risk. Thus, the objectives of our study were to examine Hg levels of six commonly consumed marine species harvested locally off the North Carolina coast and to compare our results to published regional (Monterey Bay Aquariums Seafood Watch List) and national (Environmental Protection Agency, EPA, and Food and Drug Administration, FDA) Hg averages, action levels, and guidelines. We found significant differences in Hg concentrations among collected species, and we identified correlations between Hg concentration and fish length and trophic levels. Collected mahi mahi and triggerfish were below the EPA fish tissue action level (0.3ppm). Wahoo and grouper exceeded the EPA action level but were below the FDA action level (1.0ppm). King mackerel had the highest Hg concentration among targeted species, exceeding both EPA and FDA action levels. Further, our local results were not always consistent with calculated averages from EPA and FDA databases for the same species, and although many of our findings were consistent with Monterey Bay Aquariums Seafood Watch List (southeast region), recommendations based on Hg levels would conflict with recommendations they provide based on sustainability. We find regional and national averages are not always reflective of local Hg contamination and suggest local data may be needed to accurately assess consumer risk.