Analysis of the summer distribution of fish schools in the Pacific Eastern Boundary Current

Abstract

The patterns of fish schools, mainly of Pacific hake (Merluccius productus), were studied in the Pacific Eastern Boundary Current during summer 1992. Differences between schooling patterns and depth preferenda of fish schools in the north and south were elucidated through regression analysis of depth, size, and biomass information about fish schools, extracted from acoustic backscatter data. Hake schools appeared to be clustered, based on both visual and statistical evidence. School clusters were larger (more schools) and had more biomass in the north than in the south, but inter-cluster spacing was also larger in the north. Temperature, bottom depth and school depth all significantly affect the biomass and number of schools in these clusters as the product of their effect on individual schools and on school density. The effect of these environmental factors on school cluster biomass and numbers differs from their effect on both individual schools and numbers of schools per arbitrary transect length (e.g. 5 nmi segments). School clusters may be a widespread phenomenon for schooling fish.