Preliminary Studies on the Visible Migrations of Adult Salmon

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Abstract
Techniques have been developed for observing and recording the behaviour of migrating adult salmon. Daytime movement through slow water (less than 5 ft/sec (1.5 m/sec)) is by steady swimming in schools. Such steady swimming is interrupted with resting periods at velocities between 3 and 5 ft/sec (1.0–1.5 m/sec) but can be sustained over long periods at velocities less than 3 ft/sec (1 m/sec). Movement through slow water in the Somass River system normally occurs along the line of the deepest channel, wherever this is well defined. Movement through rapids (velocities more than 5 ft/sec or 1.5 m/sec) is by darting interspersed with holding, salmon moving individually rather than in schools. Migration through pools, and through other obstructions such as fishways shows diurnal rhythms, modifications of which are associated with numbers of salmon moving, the time within the migratory season, and the species concerned. Nocturnal migration occurs.Entry of salmon into rivers during the migratory season occurs at intervals, the initiating stimulus for which is frequently related to the passage of atmospheric warm fronts over the river estuary.Techniques for field behaviour studies of salmon migration have a potential for management in that it is possible to undertake such studies in areas scheduled for industrial development and to utilize the revealed spatial and temporal migration patterns in the design of fish diversion facilities.

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