Southeast Bering Sea Carrying Capacity Regional Ecosystem Study

ISSUE

Approximately forty percent of the total U.S. commercial fishery 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 by 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 top 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, and 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.

NOAA's Coastal Ocean Program (COP) is responding to this need by supporting the Southeast Bering Sea Carrying Capacity (SEBSCC) Regional Ecosystem Study. SEBSCC researchers are increasing the understanding of the southeastern Bering Sea ecosystem, documenting the role of juvenile walleye pollock and factors that affect their survival, and developing and testing annual indices of pre-recruit (age-1) pollock abundance. The SEBSCC study is administered by the Pacific Marine Environmental Laboratory, the University of Alaska, and the Alaska Fisheries Science Center.

 

Spawning Grounds of Bering Sea Walleye Pollock

 

APPROACH

COP research has 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.

ACCOMPLISHMENTS

Over the past several years, COP researchers 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 (unicellular organisms with white calcareous coatings) developed, making the waters appear turquoise to milky white, and leading to decreased visibility through the water column. This was coincident with 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 and 1999 found that the coccolithophore bloom recurred, although physical conditions were quite different. Data is being analyzed to determine if causes can be identified, leading to predictive capabilities for such large ecosystem changes.

SEBSCC researchers have recently developed a new hypothesis for the control of energy flow in the Southeastern Bering Sea, termed the Oscillating Control Hypothesis, based on relationships between the timing of ice retreat and the occurrence of ice-edge vs. open-water phytoplankton blooms. When sea-ice remains relatively late in the year (late March), an ice-edge bloom develops, and the primary production is not translated into high zooplankton production. This leads to fewer juvenile pollock being supported, and is evidence of bottom-up control on production in the Bering Sea. During years when the ice-edge retreats relatively early (prior to mid-March), an open water phytoplankton bloom develops, which can fuel zooplankton production and support high juvenile pollock numbers. This leads to a top-down control on pollock production, as adult pollock are cannibalistic on juveniles. The Oscillating Control Hypothesis, if proven, has profound implications for year-class strength of pollock, and the management of the pollock fishery in the Southeast Bering Sea.

Related Websites

For more information contact:

Elizabeth Turner
CSCOR/Coastal Ocean Program
phone: 301-713-3338
e-mail: coastalocean@noaa.gov

Last Updated: October 31, 2002