Comparisons of the Coastal Distributions and Abundances of Juvenile Pacific Salmon from Central California to the Northern Gulf of Alaska
Joseph Fisher, Marc Trudel, Arnold Ammann, Joseph A. Orsi, Jack Piccolo, Cynthia Bucher, Edmundo Casillas, Jeffrey A. Harding, R. Bruce MacFarlane, Richard D. Brodeur, John F. T. Morris, and David W. Welch
Abstract.—In this chapter, we describe the distributions and abundances of juvenile Chinook salmon Oncorhynchus tshawytscha, coho salmon O. kisutch, chum salmon O. keta, pink salmon O. gorbuscha, and sockeye salmon O. nerka in six regions along the west coast of North America from central California to the northern Gulf of Alaska during the early summer (June and July) and late summer–fall (August– November) of 2000, 2002, and 2004. We also describe fish abundance in relation to bottom depth and to the average temperature and salinity of the upper water column. Salmon were collected in rope trawls from the upper 15–20 m over the open coastal shelf. Catch per unit effort was standardized across the different regions. Subyearling Chinook salmon were found only from central California to British Columbia. Yearling Chinook salmon were widespread, but were most abundant between Oregon and Vancouver Island. Juvenile coho salmon were widespread from northern California to the northern Gulf of Alaska, whereas chum, sockeye, and pink salmon were only abundant from Vancouver Island north into the Gulf of Alaska. Generally, the juveniles of the different salmon species were most abundant at, or north of, the latitudes at which the adults spawn. Abundances were particularly high near major exit corridors for fish migrating from freshwater or protected marine waters onto the open shelf. Seasonal latitudinal shifts in abundance of the juvenile salmon were generally consistent with the counterclockwise migration model of Hartt and Dell (1986). Subyearling Chinook salmon were associated with the high salinity environment found off California and Oregon, whereas chum, sockeye, and pink salmon were associated with the lower salinity environment in the Gulf of Alaska. However, within regions, evidence for strong temperature or salinity preferences among the different species was lacking. Subyearling Chinook salmon were most abundant in shallow, nearshore water.