Within-Individual Analysis of Round Goby Trophic Metrics: How Do Stomach Content, Fatty Acid, and δ13c / δ15Ν Stable Isotope Signatures Compare?

Various metrics exist for indexing organisms’ trophic connections, including stomach contents, fatty acids, and stable isotopes (δ13C, δ15N). Each of these indices provides a unique temporal perspective of diet; stomach contents shed light on short-term consumption patterns, while fatty acids and stable isotopes represent longer spans based on tissue contents. The concomitant measurement of all three indices at the individual organism level represents a potentially powerful approach for assessing relatedness (and possible redundancy) of these three metrics. Moreover, comparisons across these three indices may shed light on the consistency of diet specialization by individual fish. To this end, during 2010-2011 we collected round goby from 11 sites in nearshore Lake Michigan and quantified stomach contents, fatty acids, and stable isotopes (δ13C, δ15N) of individual fish. We found that each trophic index varied with individual size and also differed across locations and seasons. Preliminary results suggest that when grouping across space and time, trophic indices are strongly related. However, these associations are much weaker when examining individuals within a season or location, suggesting that indices provide complementary, and not duplicative, information.