Approximately forty percent of the total U.S. commercial fisheries landings by weight comes from the Bering Sea. Pollock abundance in the southeast Bering Sea has declined significantly since the mid- l980's with population levels fluctuating widely since the 1960's. This multi-billion dollar U.S. fishery is fully utilized and fluctuations in abundance are immediately felt in the industry.
Past studies have indicated that pollock larvae are a key component in the food web, and that the deep basin of the Bering Sea may not be able to maintain the abundance of larval fish needed to sustain the fishery and the feeding of predators, such as marine mammals and seabirds. Fisheries scientists and managers require better information to determine the integrated role of fishing pressure and changing environmental factors on Bering Sea resources, or to understand key ecosystem linkages. A management system tuned to the ecosystem “as a whole” is needed to manage resource levels, resolve utilization conflicts, and sustain this valuable ecosystem. CSCOR ’s research is responding to this need by increasing our understanding of the underlying physical and biological processes that regulate this ecosystem.
CSCOR research focused on pollock distribution and physical processes in the Bering Sea, and has evolved to support an integrated multi-disciplinary program of modeling, process studies, observations, and environmental valuation to improve the understanding and management of coastal and living resources, particularly in the context of integrated resource management. Current research efforts are focusing on understanding the linkages among environmental factors, recruitment, growth rates, predation and distribution of key fisheries, and other components of the Bering Sea ecosystem, with a special emphasis on the southeastern Bering Sea shelf.
CSCOR researchers over the past several years have greatly advanced the stock structure definition of Bering Sea pollock through determination of basin circulation, analysis of recent and historical survey data, and development of genetic testing methods. The research findings have shown that there are significant differences in genetic structure between fish from the eastern and western portions of the Bering Sea, which has helped support improved stock allocations and international agreements.
Conditions in the Bering Sea in 1997 were remarkable in that an extensive summer bloom of coccolithophores developed, making the waters appear opaque and milky white, and leading to extensive die-offs of short-tailed shearwaters, and low salmon returns to Bristol Bay, Alaska. SEBSCC researchers were in the field to monitor conditions leading to the bloom, document the extent of the bloom, and compare bloom conditions to data from previous years. Subsequent field studies in 1998 found the coccolithophore bloom recurred. Year-to-year variability allowed SEBSCC researcher to develop hypotheses about how the Bering Sea ecosystem functions and responds to climate and oceanic variability.
SEBSCC research led to a new paradigm for understanding the timing and fate of the spring phytoplankton bloom, based on the timing of sea ice retreat. During cold regimes, the ecosystem is limited by the production of phytoplankton and zooplankton, and pollock populations experience “bottom-up” regulation. When sea ice retreats early, and phytoplankton bloom earlier, more zooplankton are supported, leading to increased pollock populations. At these times, the pollock experience competition and cannibalism of older stages on younger pollock, and the populations are “top-down” regulated. Results of SEBSCC research have been compiled in the CSCOR Decision Analysis Series no. 24, The Southeast Bering Sea Ecosystem: Implications for Marine Resource Management. Research results such as these are leading to predictive capabilities for such large ecosystem changes.
Results of these studies have indicated that pollock in the Central Bering Sea are not a self-sustaining population and that there exists distinct American and Asian populations. This information has assisted resource agencies such as the International Convention on Conservation and Management of Pollock Resources and the U.S. North Pacific Fishery Management Council in managing pollock resources in the Central Bering Sea.
CSCOR ’s Bering Sea research is emphasizing an ecosystem approach in providing a pollock recruitment index to be incorporated into NMFS stock assessments for more accurate recommendations on allowable biological catch estimates. SEBSCC research results are used to provide an annual “state of the ecosytem” report to the North Pacific Fishery Management Council (NPFMC). New indices of ecosystem condition to predict pollock abundance were developed to provide information to the Scientific and Statistical Committee of the NPFMC.
