Abiotic and biotic factors affecting recruitment variability of walleye pollock (Theragra chalcogramma) off thePacific coast ofHokkaido,Japan

Abstract

AbstractAbiotic and biotic factors affecting the recruitment variability of the Japanese Pacific stock (JPS) of walleye pollock (Theragra chalcogramma) were examined using a bivariate regression and multivariate combined model. Of the abiotic variables aroundFunkaBay (spawning ground), February sea surface temperature (SST) and wind direction index showed significant bivariate relationships with recruitment. FebruarySSTwas positively related to recruitment, suggesting that warmer water temperature inFebruary favorsJPSrecruitment. On the other hand, the relationship betweenFebruary wind direction index and recruitment predicts highJPSrecruitment under predominant northwest winds in February. For the biotic variables in theDoto area (nursery ground), significant and negative bivariate relationships with recruitment were observed for catch per unit effort ofKamchatka flounder (Atheresthes evermanni),Pacific cod (Gadus macrocephalus), and walleye pollock, implying an important impact of predation by these groundfishes onJPSrecruitment. The overall model incorporating these abiotic and biotic factors successfully reproduced the variability inJPSrecruitment. Temperature and wind conditions around the spawning ground along with predator condition in the nursery ground appear to play a dominant role in the recruitment dynamics ofJPS. Based on these results and prior knowledge, we propose a new hypothesis to explain the processes controllingJPSrecruitment.