Dietary variability in two common Alaskan skates (Bathyraja interrupta and Raja rhina)

Abstract

Determining trophic relationships within and among species can provide insight into the structure and function of an ecosystem, and can inform the development of multi-species monitoring and management plans. The goal of this study was to address the need for dietary and trophic information of two common and abundant skates in Prince William Sound (PWS), the Bering skate, Bathyraja interrupta, and longnose skate, Raja rhina. Based on identification and analysis of stomach content data, both species were found to be generalist predators with diets dominated by crustaceans and supplemented with teleosts. The primary source of dietary variability for each species was total length, with spatial variables (i.e., latitude, longitude, and depth) also explaining a large portion of total dietary variability in the Bering skate. However, only a small proportion of the total intraspecific dietary variation was accounted for among the analyzed variables, suggesting substantial individual-based differences in the feeding habits of each species. Trophic level estimates indicated that the Bering skate and longnose skates <100 cm total length (TL) were secondary consumers, whereas longnose skates ≥100 cm TL were more piscivorous, tertiary consumers. Significant interspecific dietary differences were also evident, suggesting trophic separation, likely as a function of skate size. Given their abundance and generalistic feeding behavior, PWS skates can provide a means of monitoring demersal community health; information about their foraging ecology will be valuable in gaining a better understanding of trophodynamics within the PWS food web.