Contrasting years of prey levels, feeding conditions and mortality of larval walleye pollock Theragra chalcogramma in the western Gulf of Alaska

Walleye pollock in Shelikof Strait, Gulf of Alaska, spawn in an area with strong interannual differences in the oceanic environment. Feeding conditions and mortality of walleye pollock larvae in Shelikof Strait were compared in 2 consecutive years of markedly contrasting oceanographic conditions. In 1990, winds were relatively calm, and a large eddy was formed in the lower portion of the strait; walleye pollock larvae were found concentrated in this eddy feature. In 1991, winds were very strong and sea surface temperatures were anomalously cold. Flow through the Shelikof region was strong in that year, and larvae were sparse. In 1990, copepod naupliar abundance was high throughout the study area. There were no geographic differences in feeding intensity of larvae, RNA content or larval growth. In 1991 the major differences occurred between inshore and offshore stations. Comparing conditions in 1990 and 1991, naupliar abundance, larval feeding intensity, RNA content and length-atage were all low in the stormy conditions of 1991. In 1991 estimated mortality was significantly higher than that measured in 1990, although part of the loss could have been due to strong advection out of the area. Survival of expatriated larvae is discussed in light of very low juvenile abundances in 1991. This study shows the dramatic effect of environmental conditions on early larval survival rates.