UC San Diego

Analyzing stable isotope values from the tissues of marine consumers is useful for reconstructing animal trophic ecology and movement patterns. However, interpretation of isotopic values from predators can be confounded by variability in the stable isotope values of their prey species, which differ spatially and temporally. Some factors affecting stable isotope values include environmental conditions, nitrogen cycling, primary production at the base of the food web, and trophic interactions. Understanding the potential for isotopic variation in common prey species for top predators is necessary for the best use of stable isotope analysis in marine systems and for tracing energy through food webs. In this study, I measured the stable carbon (δ13C) and nitrogen (δ15N) isotope values in muscle tissue from common mid-trophic level fish and squid species in the eastern Bering Sea over two years to compare values across years and size/age classes. I found interannual changes in the δ15N and δ13C values between 2014 and 2016 in atka mackerel, Pacific herring, sockeye salmon, squid, and walleye pollock, and variation in the δ13C and δ15N values across age/size classes in Pacific herring, sockeye salmon, and walleye pollock. I compared my data to those collected from the same size class fish in the Bering Sea in 1997 and found increases in the δ15N and decreases in the δ13C values consistent with expectations from higher ocean temperatures in 2016 and continued increased inputs of anthropogenic, isotopically light carbon.