ANALYSIS OF PATTERNS IN LARVAL WALLEYE POLLOCK THERAGRA-CHALCOGRAMMA SURVIVAL AND WIND MIXING EVENTS IN SHELIKOF STRAIT, GULF OF ALASKA

This study examines the possibility that wind mixing in Shelikof Strai t, Gulf of Alaska, is a critical factor for larvae of walleye pollock Theragra chalcogramma. The abundances of walleye pollock larvae hatche d on a given day and surviving through the early feeding stage were de termined by in situ sampling and otolith analysis for 1983 and 1985 to 1991. Periods of anomalously low or high larval survival were determi ned by comparing observed first-feeding date distributions of survivor s sampled in late May surveys with expected first-feeding date distrib utions from a model utilizing information on spawning time and abundan ce, measured egg mortality, assumed larval mortality, and survey date. The cube of the wind speed represented daily estimates of mixing for the same years; wind speeds were determined from gridded sea-level pre ssure data using a geotriptic wind model. When the resulting daily dis tributions of larval abundance and mixing were compared, 2 patterns em erged: (1) strong wind mixing events during the first-feeding period w ere associated with periods of lower than expected larval survival, an d (2) periods of higher than expected larval survival were associated with calm with periods often bracketed by strong mixing. The results i ndicate that over the 8 yr of observation strong mixing events during the first-feeding period were detrimental to survival of pollock larva e.