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Migration timing of female kokanee salmon Oncorhynchus nerka: diel patterns and effects of maturation state


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Diel patterns of migration and migration speed were compared between reproductive timing phenotypes in female kokanee salmon Oncorhynchus nerka. Females of varying degrees of reproductive maturation were captured on their migration route to the Meadow Creek Spawning Channel (British Columbia, Canada), were tagged with passive-integrated transponders (PIT tags) and were subsequently monitored with stationary receivers. Females showed crepuscular migration timing, with approximately equal detections at dawn and dusk. In particular, peaks of movement were associated with the appearance of the sun over the mountains in the east and the disappearance of the sun over the mountains in the west. Over 25 m, migration speed was 1·0 body lengths (measured as fork length; LF) s−1 and did not depend on maturation state. Over 3 km, migration speed was much slower (0·2–0·3 LF s−1) than over the short distance, with less mature females migrating more slowly than more mature females. Less mature females appeared to be in less of a hurry to reach breeding areas compared with more mature females.