Contaminants such as mercury are typically quantified as measures of central tendency, i.e. averaged across all sampled fish of the same species within the same body of water. More recent studies suggest that individual fish within a population do not all exhibit the same feeding and habitat residence patterns, and therefore have varying risks to contaminant exposure and accumulation. If popular sport fish such as yellow perch, Perca flavescens, or black crappie, Pomoxis nigromaculatus, exhibit diet plasticity and specialize for habitats such as pelagic or benthic habitats, then some groups of fish may pose a greater risk to consumers. Specifically, we hypothesized that diet plasticity and specialization in fish populations could lead to a bi-modal distribution of contaminant loads. Given that different contaminant exposure is likely to manifest through differential foraging strategies and habitat use, we collected fish of each species within 4 lakes in Northern Indiana to evaluate the potential for relationships between mercury loads, measured as total mercury, of individual fish and their diet/habitat specialization. We measured stable isotopes (ẟC & ẟN) for each fish and compared it to baseline isotopic measures from common prey items in benthic and pelagic habitats. We also used landmark morphometrics to characterize morphological specialization of fish. Finally, we utilized multiple linear regression to examine the interrelations between mercury, fish size & sex, morphology and isotope values.
Results/Conclusions
Our results in yellow perch and black crappie demonstrated both broad and lake specific patterns in trophic relationships, morphology and total mercury content. In general, yellow perch demonstrated a wider range of trophic feeding compared to black crappie. This pattern was reflected within their morphological variation in body shape and the variance in total mercury. Multiple linear regression found that specific lakes varied in the best predictors for mercury content, but general patterns in both fish showed that length, sex, and carbon isotopes were important variables in predictive models. Carbon isotopes can vary between benthic and pelagic resources and therefore may represent an important metric of within-lake specialization. If the degree of specialization is high, it may merit increased sampling to accurately characterize contaminant distribution of fish residing in habitats with different exposure risks. Understanding the level of variation of contaminant loads within individual lakes and their relationship to other population metrics, such as stable isotopes and morphology, could help federal and state agencies make informed decisions on fish consumption advisories.