Dynamic Trophic Linkages in a Large Estuarine System – Support for Supply-Driven Dietary Changes Using Delta Gamm

Trophic dynamics are a predominant regulator and modifier of fisheries production and are an integral component to ecosystem-based fisheries management.  We used a diet composition database of Chesapeake Bay fishes (10-years, multiple seasons) to demonstrate the application of a novel statistical approach to gain insight into trophic interactions while accounting for statistical issues commonly encountered with stomach content data.  We used two-part, delta generalized additive mixed models (GAMM) to 1) evaluate the effects of biological and environmental covariates on trophic interactions of 12 common fishes, and 2) infer dynamics of key prey groups (bay anchovy, mysids, bivalves).  Statistical models accounted for significant effects of predator length on prey occurrences that tended to be linear or parabolic in form.  Latitude, temperature, and depth effects were largely similar across predators for a given prey.  Annual consumption patterns of prey showed dramatic peaks shared by a majority of predators, despite varied feeding preferences and distributional characteristics.  Coherence in covariate effects and consumption patterns was consistent with supply-driven dynamics at regional and annual scales.  Delta GAMM results highlighted the utility of using multiple predators to infer prey dynamics and the synchrony in interannual consumption exhibited by a diverse suite of estuarine fishes.