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Phenotypic Correlates of Life-History Variation in Juvenile Chinook Salmon, Oncorhynchus tshawytscha
Eric B. Taylor
Journal of Animal Ecology
Vol. 59, No. 2 (Jun., 1990), pp. 455-468
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/4874
Page Count: 14
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(1) Chinook salmon, Oncorhynchus tshawytscha (Walbaum), commonly follow two life-history patterns as juveniles. `Stream-type' juveniles reside in streams for a year or more before abandoning territoriality and migrating to marine habitats. By contrast, `ocean-type' juveniles migrate to sea sometime during their first year of life, often as newly emerged fry. (2) At age 1, stream-type chinook showed a distinct reduction in positive rheotaxis during both `diurnal' and `nocturnal' current response tests, consistent with their downstream migration to the sea at this age in nature. By contrast, ocean-type chinook showed no pronounced shifts in rheotaxis after age 2-3 months. (3) Ocean-type fish that migrate seaward after 2-3 months in freshwater were more aggressive than those that migrate as fry, but both groups were less aggressive than stream-type chinook. (4) Ocean-type chinook grew at a faster rate than did stream-type. (5) Since these differences in phenotype were expressed in fish raised in a common laboratory environment they are concluded to have a genetic basis. Furthermore, the differences in behaviour and growth rate were appropriate for different durations of freshwater residence and, hence, probably reflect adaptive divergence within O. tshawytscha.
Journal of Animal Ecology © 1990 British Ecological Society