Seaward Movement of Juvenile Fishes, Including Lunar Periodicity in the Movement of Coho Salmon (Oncorhynchus kisutch) Fry

Abstract

Following emergence, more than 51,000 coho salmon (Oncorhynchus kisutch) fry moved seaward from Lymn Creek. Peaks in movement occurred coincident with the new moon and progressively declined through four lunar cycles although 75% of the outmovement took place between early April and the middle of June. Coho smolt migration occurred simultaneously, the run peaking in late May during a period of maximum low tides between sunrise and sunset when the moon was full. Sticklebacks (Gasterosteus) moved seaward sporadically throughout the trapping period from April to September but their numbers increased markedly in August due to the appearance of underyearlings. The seaward movement of coho fry and smolts and of sticklebacks showed no apparent relationship to either stream discharge or temperature.Lunar rhythmicity in movement of coho fry and probable fate of fry are discussed within a framework of behavioral and ecologic concepts pertinent to the species’ life history in the juvenile stage and relevant to concern for enhancing coho salmon production.