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

The patterns of fish schools, mainly of Pacific hake (Merluccius productus), were studied in the Pacific Eastern Boundary Current during summer 1992. DiVerences between schooling patterns and depth preferenda offish schools in the north and south were elucidated through regression analysis of depth, size, and biomass information aboutfish 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 aVect the biomass and number of schools in these clusters as the product of their eVect on individual schools and on school density. The eVect of these environmental factors on school cluster biomass and numbers diVers from their eVect 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. ? 1997 International Council for the Exploration of the Sea