Observations on the Migration of Young Sockeye Salmon (Oncorhynchus nerka) through a Large, Complex Lake System

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Abstract
The seaward migration of sockeye salmon smolts through the Babine Lake system to its outlet is examined by extensive tagging, direct observations and experimental orientation tests. The migration appears to be a well-oriented, non-random movement; it apparently commences from all lake regions at about the same time, suggesting a common triggering stimulus. When migrating, the smolts swim at a speed of 0.65 to 1.0 feet per second. The migration appears to take place primarily at near-surface depths; diurnally, most of the migration activity appears centered around the evening dusk period. There is a consistent increase in rate of travel as the season progresses; in large part this appears a result of increasing migration drive. Orientation tests with a view of only the sky show the smolts capable of time-compensated orientation in relation to celestial phenomena, and such tests at various points along the migration route show the preferred direction of smolts to correspond with the direction of most direct route to the outlet. Most smolts of the system show a constant preference for the northwesterly direction which would lead them rather directly to the outlet. However, one group which in the course of its migration to the outlet must make a 180° turn clockwise from southeast to northwest is found to have a corresponding shift in directional preference with time. Simple one-direction orientation, in one case shifting with time, is sufficient to account for ability to find the outlet. A positive relation is shown between rate of travel of tagged smolts and the hours of sunshine on days subsequent to their release.

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