Nursery areas of juvenile northern rock sole (Lepidopsetta polyxystra) in the eastern Bering Sea in relation to hydrography and thermal regimes

Age-0 and age-1 northern rock sole were collected over large-scale areas of the eastern Bering Sea in the summers of 2003, 2008 and 2010. Age-0 presence was poorly predicted by a published resource selection model developed for the Gulf of Alaska, and the failure of that model may have been caused by oceanographic features in the eastern Bering Sea. Where a front (inner front) separated the well-mixed coastal domain from the stratified middle domain, age-0 fish were less abundant and occurred at fewer stations in the nearshore, thermally mixed coastal domain than expected by the Gulf of Alaska model. In contrast, where the inner front was not established, age-0 fish were present in the highest densities in nearshore and thermally mixed waters. North of Unimak Island, the same hydrographic pattern that inhibits the formation of the inner front also likely transports larvae near shore. Age-1 densities were highest in the coastal domain, and age-0 length decreased with distance from shore, suggesting northern rock sole move shoreward after settlement. Juvenile northern rock sole were abundant in a nursery area between Nunivak Island and Cape Newenham in a warm period (2003), but were almost completely absent in cold periods (2008 and 2010), leading to the hypothesis that climate variability limits the utility of this nursery area during cold periods.

Schooling pattern of eastern Bering Sea walleye pollock and its effect on fishing behaviour

Shen, H., Dorn, M. W., Wespestad, V., and Quinn, T. J. 2009. Schooling pattern of eastern Bering Sea walleye pollock and its effect on fishing behaviour. – ICES Journal of Marine Science, 66: 1284–1288 Walleye pollock (Theragra chalcogramma) form persistent midwater and near-bottom schools in the daytime during the winter spawning season in the eastern Bering Sea (EBS). Two spawning areas in the EBS, north of Unimak Island and near the Pribilof Islands, are the main fishing grounds. To study the schooling pattern of pollock and its effect on fishing behaviour on these two fishing grounds, a principal component analysis with instrumental variables was carried out using acoustic and observer data from 2003 and 2005. Significant differences between the school descriptors distinguished the schooling patterns among areas and years. The harvester, that is to say, the fishing vessel and its crew taken together, searched for fish aggregations, which were caught in a different manner when the schooling pattern changed. School density had a greater effect than school size on fishing behaviour. Aggregations were less dense in 2003 than in 2005, and the harvester tended to fish with longer tows, at higher speeds, when it encountered less dense aggregations.