Map of survey area, sampling strata, sampling grid, and standardized survey bottom trawl stations.
(Click on image to enlarge)
The Eastern Bering Sea Group of the RACE Division Groundfish Assessment Program and RACE Shellfish Program are tasked with conducting an annual bottom trawl survey designed to describe the composition, distribution and abundance of demersal fish, shellfish and principle epibenthic invertebrate resources of the eastern Bering Sea. The continental shelf area of the eastern Bering Sea has proven to be one of the most productive fishing areas in the world in terms of both species abundance and commercial value.
Bottom trawl surveys covering the continental shelf area of the eastern Bering Sea have been conducted since 1975, and annually since 1979. Results of the survey are necessary for up-to-date estimates of biomass, abundance and population structure of groundfish populations in support of stock assessment and ecosystem forecast models that form the basis for groundfish and crab harvest advice. Additional data collected on the survey are used to improve understanding of life history of the fish and invertebrate species and the ecological and physical factors affecting their distribution and abundance.
The primary biological data include relative abundance (catch per unit effort) and size and age compositions of major species including walleye pollock, Pacific cod, yellowfin sole, northern rock sole, red king crab, and snow and tanner crabs. In addition, physical data such as surface and bottom temperatures are collected. With over 25 years of annual continental shelf surveys, valuable trends in both biological and physical measures can be examined.
Map of bottom temperatures (1982-2009) (Click on image to enlarge)
The Eastern Bering Sea Group is also responsible for surveys conducted over the eastern Bering Sea continental slope area. These surveys have occurred in 1979, 1981, 1982, 1985, 1988, 1991, 2000, 2002, and 2004. Dominant species examined here include Greenland turbot, short-spine thornyheads, dover sole, grenadiers, and 10 different species of skates. Learn more about eastern Bering Sea continental slope surveys in the 2004 slope cruise data report.
The Eastern Bering Sea Group has conducted research in such areas as trawl gear function, fish systematics, and life history and ecology:
Gear research has included examinations of physical and environmental effects on both trawl performance and fish availability to research trawls. Maintaining a time series as a representative measure of relative abundance for groundfish requires consistency in terms of both survey trawl performance and fish availability to the survey trawl gear. Trawl performance studies have included examinations of door and net spread, net height, and bottom contact and their influence on catch efficiency. Research on fish availability has included an examination of the effects of light on the vertical distribution of walleye pollock, and an examination of the vertical distribution of Pacific cod in relation to the survey trawl gear. References >>
The standard sampling gear used in the eastern Bering Sea trawl survey is the 83-112 eastern otter trawl, which has a 25.3-m headrope and 34.1 m footrope. Mesh sizes are 10.2 cm in the wings and 8.9 cm in the intermediate and codend. The codend has a liner of 3.2 cm. (Click on image to enlarge)
Map of the eastern Bering Sea upper continental slope bottom trawl survey area. (Click on image to enlarge)
Fish systematic research has enabled more accurate identification of species in the eastern Bering Sea and Aleutian Islands region. One of the products, "Field Guide to Sharks, Skates, and Ratfish of Alaska", will dramatically improve the species-level identifications of elasmobranchs in Alaska. Other research has included the identification of new species of skates and eelpouts. References >>
A wide variety of research relating to fish life history and ecology of eastern Bering Sea and Aleutian fishes has been conducted within the Eastern Bering Sea Group. Such research has included yellowfin sole distribution and reproduction, changes in walleye pollock distribution with temperature, Alaska skate and Aleutian skate ecology, Atka mackerel reproductive ecology, and larval fish vision and ecology. Archival tagging studies have shed light on the vertical migration patterns of Atka mackerel, Pacific cod, and northern rock sole. More generalized research has examined of the biodiversity of eastern Bering Sea fishes. Recent research includes the use of passive acoustics for studying spawning fishes, and an examination of the biology of marbled eelpout. References >>