Climate Impacts on Bering Sea Ecosystem and Fisheries

Long-term time series are a necessary element for understanding how variations in climate affect marine ecosystems.  The longest time series of fisheries and ecosystem observations in the eastern Bering Sea are on the order of 30 years and shorter than other regions (e.g. North Sea, NW Atlantic, California Current).  However, through a series of medium-term research programs (4 – 5 years each), NOAA and its partners have observed the processes through which the eastern Bering Sea ecosystem responds to shorter-term fluctuations in atmospheric forcing.  These observations contributed to the formulation of the Oscillating Control Hypothesis (OCH) which is used to predict the impacts of climate on regional fisheries.

The eastern Bering Sea is an ecotone between the boreal and arctic biogeographical provinces and sea ice is a major structuring element in this ecosystem.  Short-term process studies combined with the longer-term observations have given us much insight into how sea ice extent regulates bottom up processes that affect the early life history stages of the major commercial species in this region.  In many (but not all) cases these processes are thought to regulate recruitment success of commercial species.  Less well known in this system are the top-down processes that may also contribute to the recruitment strength of individual year classes.  Application of our increased understanding to resource management is evolving.  In an early example, during a period of regional and global warming, state variables and the OCH were invoked to support proposals for lowering the Total Allowable Catch of walleye pollock (Theragra chalcogramma) at a time when the formal stock assessment predicted population declines.  This precautionary approach reduced the stress to the population during a period of very low recruitment.  At present, scientists are working to directly incorporate climate-related ecosystem metrics and indices into the individual stock assessments.