Approximately forty percent of total U.S. commercial fishery landings by weight come from the Bering Sea. In response to declining Walleye pollock abundance in the southeast Bering Sea, NCCOS supported the Southeast Bering Sea Carrying Capacity Regional Ecosystem Study from 1996 to 2002. SEBSCC researchers documented the role of juvenile pollock and factors that affect their survival and developed and tested annual indices of pre-recruit pollock abundance.
Why We Care
Walleye pollock, Theragra chalcogramma (Gadidae), abundance in the southeast Bering Sea declined significantly since the mid-l980s, with population levels fluctuating widely since the 1960s. This multi- billion dollar U.S. fishery is fully used, 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 use conflicts, and sustain this valuable ecosystem.
What We Did
NCCOS responded to this information need by sponsoring the Southeast Bering Sea Carrying Capacity (SEBSCC) Regional Ecosystem Study. SEBSCC researchers increased 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 was led by the NOAA Pacific Marine Environmental Laboratory, the University of Alaska, and the NOAA Alaska Fisheries Science Center.
When SEBSCC was launched, a prior NCCOS (then the NOAA Coastal Ocean Program) initiative, the Bering Sea Fisheries-Oceanography Coordinated Investigations (BSFOCI) program (1991–1997), was in its sixth year of studying stock structure and recruitment dynamics of walleye pollock in the Bering Sea. BSFOCI research focused on pollock distribution and physical processes in the Bering Sea, paving the way for SEBSCC to support an integrated multi-disciplinary program of modeling, process studies, observations, and environmental valuation. SEBSCC improved the understanding of linkages among environmental factors, recruitment, growth rates, predation and distribution of key fisheries, and other components of the Bering Sea ecosystem, particularly in the context of integrated resource management.
SEBSCC began operations in the final quarter of Fiscal Year 1996 with an abbreviated field season to allow continued monitoring of the southeastern Bering Sea while commencing modeling and retrospection efforts. Process-oriented studies were started in FY 1997. The first phase of research was from 1996–1998. The second phase (1999–2000) was followed by a third and final synthesis phase (2001–2002). About 30 research projects were funded.
Benefits of Our Work
SEBSCC researchers 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 showed 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 were analyzed to determine if causes could be identified, leading to predictive capabilities.
Elements of SEBSCC advances were used to develop indices for prediction of walleye pollock year-class strength (abundance). SEBSCC researchers 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 has profound implications for year-class strength of pollock, and the management of the pollock fishery in the Southeast Bering Sea. Building on the foundation of SEBSCC, further research efforts in the Bering Sea have expanded on the knowledge gained from this program.