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

Abstract

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.

Received April 26, 2011; accepted September 9, 2011

ACKNOWLEDGMENTS

We thank the following people for providing support, reviews, or data for this manuscript: C. Rooper, J. Olson, K. Aydin, O. Ormseth, and B. Lauth (NMFS); F. Mueter (University of Alaska Fairbanks); J. Rice (Fisheries and Oceans Canada); and two anonymous reviewers. We are grateful to all scientists and crew who have collected bottom trawl survey data over the years. We also thank our funding sources: Fisheries and the Environment; and the Joint Institute for the Study of the Atmosphere and Ocean (JISAO). This publication was partially funded by JISAO under National Oceanic and Atmospheric Administration Cooperative Agreement NA17RJ1232, Contribution Number 1885.