Pacific Sleeper Shark Bycatch in Bering Sea Fisheries: Relationship Between Size, Depth, and Trophic Ecology

In the North Pacific, Pacific sleeper sharks (Somniosus pacificus) are regularly taken as by-catch in multiple fisheries. Extensive at-sea observer coverage exists in these fisheries, however very little data are collected for sleeper sharks. The effect of these removals on both the population and ecosystem is an issue of increasing concern due to the limited data available about the life history, trophic role, and catch records. Observer data from 2003-2010, obtained from the National Marine Fisheries Service, were used to estimate size composition and determine temporal and spatial patterns of the shark by-catch. Feeding ecology of sharks in the Bering Sea and inferences about the ecosystem impact of shark removals were also investigated using carbon and nitrogen stable isotopes (δ¹³C and δ¹⁵N) from muscle tissue. Initial results from the analysis of by-catch data show seasonal differences in size composition and depth of capture and the stable isotope analysis revealed a relationship between shark length and trophic level. Understanding the by-catch of Pacific sleeper sharks and their ecological role in the Bering Sea is fundamental for effective ecosystem based management.