FY 1997

The relationship between the distribution of one-year-old walleye pollock, Theragra chalcogramma, and sea-ice characteristics

Wyllie-Echeverria, T.

In Ecology of Juvenile Walleye Pollock, Theragra chalcogramma, NOAA Tech. Report NMFS 126, Papers from the workshop "The Importance of Prerecruit Walleye Pollock to the Bering Sea and North Pacific Ecosystems", Seattle, WA, 28–30 October 1993, 47–56 (1996)

Distributions of one-year-old walleye pollock, Theragra chalcogramma, were obtained from bottom trawl surveys conducted on the southeastern Bering Sea shelf between 1972 and 1992. Coincidentally, seasonal sea-ice characteristics during this period were available from satellite imagery. These two data sets provided a time series for exploring the relationship between sea ice and fish. Years characterized by heavy ice conditions occurred in 1972-78, coincident with the highest abundance of walleye pollock in the outer domain. Years of light ice conditions occurred in 1979-87, when walleye pollock were most numerous over the middle domain. Intermediate ice conditions occurred in 1988-92, when walleye pollock were most numerous over the middle and inner domains. The link between walleye pollock distribution and ice cover lies in the relationship of ice and bottom-water temperatures. One-year-old walleye pollock do not concentrate in waters colder than 2°C. Thus the condition of seasonal sea ice on the eastern Bering shelf during winter forecasts the distribution of one-year-old walleye pollock on the shelf the following summer. This shift can be predicted from the duration of ice cover over the middle domain, T. When ice remains over the middle domain (south of 59°N) less than 20 weeks, most of the one-year-old walleye pollock will be found in the middle domain. When T is longer than 24 weeks, a higher proportion of fish will be located in the outer domain.