Seasonal oceanographic influences on Pacific herring and walleye pollock distribution and abundance in nearshore embayments of Kodiak Island, Alaska

Abstract

The importance of Alaskan embayments as adult walleye pollock and Pacific herring habitat is unknown. Seasonal hydroacoustic and trawl surveys were conducted in three oceanographically distinct bays to correlate abiotic and biotic habitat factors with nearshore fish distributions around Kodiak Island. Relationships between fish densities and sea surface temperature and salinity, bottom depth, zooplankton density and diversity, bottom temperature and salinity, and water column stratification were analyzed through General Additive Models (GAMs). Bathymetry and temperature were consistently included as important habitat variables. Relationships between fish density and habitat variables differed by season and location, suggesting factors defining preferred habitat vary seasonally. Herring appear to prefer warmer, fresher surface waters associated with the Alaska Coastal Current. Mean pollock density increased between February and August, indicating the nearshore area is important summer habitat, while it is less important for herring after winter spawning. Pollock and herring utilize different horizontal and vertical areas of the bays, with pollock in deeper waters. Pollock separated vertically by size class, but no vertical separation was found for herring of different size classes. The range of size classes and high densities of both species suggest these previously unsurveyed areas are important pelagic fish habitat.