Spatio-Temporal Variation in Vertical Distributions of Pacific Salmon in the Ocean

Abstract

The vertical distribution of Pacific salmon ( Oncorhynchus spp.) is of interest to biologists and the fishing industry. An understanding of the normal vertical distribution and movement of salmon facilitates better manage- ment of both directed and non-salmon fisheries and better evaluation of research data. Salmon vertical distribu - tion can vary spatially in relation to distance from shore, depth of the water column, and by ocean region, and temporally by life-history stage, season, time of day, and ocean conditions. In coastal waters, juvenile salmon were usually less than 15 m from the surface. In offshore waters, salmon were usually within the top 40 to 60 m, above the thermocline, but occasionally were found from 80 to 120 m. They usually were near the surface at night, and moved vertically during the day. Sockeye salmon displayed the shallowest vertical distribution, followed by pink, coho, chum, and Chinook salmon. There are limited data for winter, but vertical distributions may not change substantially from summer in offshore waters, while it may shift in some species in coastal and shelf areas. There is a need for more long-term data, throughout the marine residency of individual fish.