Seasonal abundance and distribution of pelagic and demersal fishes in southeastern Alaska

Abstract

We quantified seasonal and interannual variability of pelagic and demersal fishes available to marine predators in southeastern Alaska focusing on prey of the Steller sea lion ( Eumetopias jubatus). Estimates of abundance were determined from echo integration mid-water trawl and demersal longline surveys. The dominant species were walleye pollock ( Theragra chalcogramma) (average biomass 9057 t), Pacific hake ( Merluccius productus) (1715 t), Pacific herring ( Clupea pallasii) (1176 t), Pacific halibut ( Hippoglossus stenolepis) (average catch rate 524 kg per 1000 hooks), Pacific cod ( Gadus macrocephalus) (177 kg per 1000 hooks), sablefish ( Anoplopoma fimbria) (120 kg per 1000 hooks), and sandpaper skate ( Bathyraja interrupta) (26 kg per 1000 hooks). Of these species, seasonal differences in species abundance were detected for walleye pollock ( p = 0.03), Pacific cod ( p = 0.001) and sablefish ( p < 0.001) with walleye pollock the most abundant and widespread species year-round. Herring, hake, and juvenile (120–350 mm) and adult (>350 mm) pollock are pelagic species. Adult and juvenile pollock and hake were found in open water, while herring, young-of-the-year (<120 mm) and the smallest juvenile pollock were found in bays. Herring of all ages concentrate in dense schools. Pollock and hake form scattered layers throughout open water with juvenile pollock shallower than adult pollock and adult pollock shallower than hake. Halibut, sablefish, skates, Pacific cod and arrowtooth flounder are demersal species; sablefish were deeper than the other demersal species. These seasonal and annual changes in prey availability affected prey selection of sea lions which shifted their diet in response.