A Collaborative Study of the Dynamics and Ecosystem Implications of Post-Bloom Production at the Inner Front of the Southeast Bering Sea

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AbstractHunt U of CA, Irvine 9819251Zeeman U of New England 9907097Whitledge U of AK, Fairbanks 9819273Each year millions of short-tailed shearwaters (Puffinus tenuirostris) migrate from Australia to the Bering Sea to forage over the inner shelf. The evolution of this annual trans-equatorial migration implies that extraordinary amounts of prey must be readily available to these birds in the Bering Sea. In 1997 and 1998, unusual weather patterns in the eastern Bering Sea resulted in significant changes in hydrography and water circulation. The resultant ecosystem anomalies included the first recorded coccolithophore bloom in the Bering Sea, the starvation of about 10% of the migrant shearwaters present, and the collapse in both 1997 and 1998 of the Bristol Bay sockeye salmon fishery. This research project will continue testing the hypothesis that elevated primary production at the inner front of the southeastern Bering Sea continues longer than in non-frontal waters, and that this production provides an energy source throughout the summer for a food web that supports shearwaters, salmon, and their zooplankton prey. Based on findings in 1997 and 1998, additional hypotheses concerning the roles of storms and advection of nutrients will be tested using seasonal and inerannual comparisons. This collaborative study will collect and interpret observations on physical and biological features in the vicinity of the inner front to determine: 1) the availability of nutrients in the euphotic zone, 2) the physical processes responsible for enhanced vertical flux of nutrients, 3) primary production, 4) the distribution, abundance and trophic ecology of near-surface swarms of euphausiids and other macro- and micro-zooplankton, and 5) the distribution, abundance, and foraging ecology of shearwaters, and 6) by stable isotope enrichment, trophic pathways from phytoplankton to shearwaters at and away from the front.The southeastern Bering Sea supports one of the world's richest fisheries; walleye pollock, salmon, halibut and crab generate over 2 billion dollars in revenue each year. Despite this, the coastal domain and inner front, where shearwaters, young salmon and some crab larvae congregate to forage, has not been well studied. The study is important because it will: 1) relate how variation in weather patterns forces physical processes that affect ecosystem function; 2) be the first examination of the physical processes of the inner front during summer and of the role of the front in post-bloom primary production; 3) focus on the ecological role of the extended production, and 4) relate the evolution of trans-equatorial migration patterns of seabirds to biophysical processes that create predictable sources of prey. These questions are addressed by focusing on species and regions with which the investigators are familiar; however, the results can be applied to numerous continental shelf tidal fronts and species. Thus, the results should have a general applicability to understanding and managing some of the world's most productive seas.