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The seasonal and dirunal movements of some pacific salmon fry with particular reference to the sockeye, onchorynchus nerka McDonald, John George

Abstract

The seasonal and diurnal movements of sockeye, pink and coho salmon fry are described. For sockeye, at least, the time of the seasonal migration froa the spawning area is related to the temperature "budget" during their period of development in the gravel. Their seasonal migration occurs earlier following an incubatory period in which above average temperature prevailed and later following relatively low temperatures. Emergence from the gravel appears to occur normally only after a certain stage of development is reached. The diurnal movements of all three species are precisely regulated by their response to light. The strong negative phototaxis exhibited by the fry at this time restricts their movement solely to the hours of darkness. The downstream movement of sockeye and coho and also apparently of pink fry is initiated within a three hour period following darkness. The presence of artificial light almost completely prevents this movement either throughout the night or until such time as the light is removed. The data indicate that a period of night blindness occurs which is common to the three species and that their downstream movement is initially a result of a displacement by the current. Once entered into the stream the migration continues until evacuation of the stream is complete or until daylight approaches. The response of sockeye fry to current during this continued movement appears predominantly positive in fast currents and negative in relatively slew currents. The migration is considered to result from both a displacement by the current and a movement directed on the part of the fry.

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