Spatial variation in the small-scale distribution of juvenile walleye pollock (Theragra chalcogramma) in the southeastern Bering Sea

Abstract

Juvenile walleye pollock (Theragra chalcogramma) is one of the primary prey items for bird and mammal predators in the Bering Sea and supports a large commercial fishery. An understanding of the abundance and distribution of juvenile pollock is needed to estimate the effects that change in these parameters may have on pollock predators and adult pollock abundance and distribution. During the summers of 2008 and 2009, surveys were conducted in three topographic zones (Middle Shelf, Outer Shelf, and Slope) near the Pribilof Islands in the southeastern Bering Sea. Multi-frequency (38, 70, 120, and 200) acoustic sampling occurred during the entire cruise duration with frequent environmental data sampling (e.g., temperature, salinity, dissolved oxygen, and chlorophyll a fluorescence) and targeted fish tows. These data showed that juvenile walleye pollock were primarily found in clusters of small, dense aggregations giving them a leopard spot appearance in the acoustical output. In both years, juvenile pollock distribution was highly variable on small spatial scales and was related to biological and physical features of the water column. These differences in juvenile walleye pollock distribution are likely to affect the use of habitat by predators and may have implications for future sampling.