Variable migratory patterns of different adult rainbow trout life history types in a southwest Alaska watershed

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adult, rainbow trout, trout, life history, history, telemetry, watershed, thermal, food, salmon, salmon eggs, eggs

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Transactions of the American Fisheries Society


Radiotelemetry was used to document population structure in adult rainbow trout(Oncorhynchus mykiss) from the Alagnak River, southwest Alaska. Rainbow trout (N 5 134)longer than 440 mm were implanted with radio transmitters and tracked for varying periods fromJuly 1997 to April 1999. Fifty-eight radio-tagged fish were tracked for sufficient duration (at least11 months) to allow description of seasonal migratory patterns. Unique seasonal movements offish suggested discrete, within-basin population structure. Telemetry data documented theexistence of multiple migratory and nonmigratory groups of rainbow trout, indicating unique lifehistory patterns. The observed groups consisted of what we defined as a lake-resident ecotype, alake-river ecotype, and a riverine ecotype; the riverine ecotype demonstrated both highlymigratory and nonmigratory movement behaviour. Considerable variation in movement patternswas found within both the lake–river group and the river migratory group. Radio-tagged trout didnot migrate between the two Alagnak watershed lakes in either year of the study, suggesting lakefidelity in the population structure. Alagnak River rainbow trout may have evolved the observedseasonal movement patterns to optimize winter thermal refugia and summer food availability ofsalmon eggs and carcasses.





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