© 1994 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
Relating the distribution of pollock schools in the Bering Sea to environmental factors
Applied Physics Laboratory HN-10, University of Washington Seattle, Washington 98105, USA
Department of Statistics, University of Washington Seattle, Washington 98105, USA
Quantitative Ecology and Research Station, University of Washington Seattle, Washington 98105, USA
Patterns in pelagic fish spatial distribution have been linked to environmental factors, especially depth and temperature (ocean fronts). This paper explores the relationship between school size, depth, temperature, and location data extracted from a summer 1991 Bering Sea Scientific fisheries acoustic survey, using morphological and other image enhancement techniques. A variety of mapping techniques, scatterplots, and histograms were used to elucidate environment-school relationships. A general regression tool (generalized additive models) then substantiated and tested the significance of these relationships. We found that bottom depth and ocean fronts influence the distribution and dynamics of the (predominantly) pollocks schools. School density (number of schools per unit transect length) and total school area were highest in shallow water either above or below the thermocline, but not both in the same area. School mass was highest for schools below the thermocline and in locations where the thermocline depth is intermediate (37–42 m). Pollock appeared to avoid cold temperatures and remained below the thermocline when mid-water temperatures were below 0°C. Pollock above the thermocline were largely age-0 pollock, while adults predominated below the thermocline, especially in deeper water. We hypothesize that the thermocline serves as an effective barrier in the summer, separating age-0 pollock from potentially cannibalistic adults. We suggest that adult pollock feeding, which occurs mostly during the crepuscular period, depends on diel migration of euphausiids below the thermocline, while younger pollock primarily feed on copepods in the upper water column.
Keywords: generalized additive models, acoustic surveys, temperature
Received 20 January 1994; accepted 29 June 1994.
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