Investigation of Fishing and Climate Effects on the Community Size Spectra of Eastern Bering Sea Fish

The eastern Bering Sea (EBS) is a highly productive subarctic marine ecosystem that is exposed to considerable climate variability and is noted for conservative management of its fishery resources. The community size spectrum (CSS; relationship between animal abundance and size) of fish captured in EBS shelf bottom trawl surveys was examined for evidence of change over time and fishing and climate effects. The slope (indicative of fish size) and height (indicative of ecosystem productivity, or essentially fish abundance) of the CSS can change due to changes in fishing intensity and climate variability. Linear trends were not observed in EBS groundfish size or abundance during 1982-2006. The abundance of large-sized fish increased in 2001-2006 relative to 1982-2000. Observed changes in CSS height partially corroborated evidence for decreased productivity of the main fishery target species since the late 1990s, which may have been due to changes in relative species composition. In addition, abundance and size composition of nontarget fish decreased during 1982-2006, possibly related to changes in water temperature. In contrast, however, the size and productivity of fish that were primarily bycatch species increased during 1982-2006. Unlike in other ecosystems, changes in CSS slopes and heights for the EBS were not related to exploitation rates. Changes in the abundance of fish in areas that were normally occupied by cold bottom water (northwest inner and middle shelf) may have been related to the effects of temperature on fish distribution.