A relationship between adult recoveries of chinook salmon (Oncorhynchus tshawytscha) and lunar phase at time of their release from a hatchery on the Rakaia River, New Zealand

Abstract

Studies on chinook salmon (Oncorhynchus tshawytscha) juveniles held at the Glenariffe Salmon Research Station on the Rakaia River, New Zealand, have shown cyclical surges in plasma thyroxine, apparently associated with lunar phase. Since thyroid secretions are implicated in salmonid smoltification, data from batches of tagged chinook salmon released from Glenariffe were analysed to compare percent adult recovery with time on the lunar cycle when they were released as smolts. Results from a total of 136 batches were examined, covering 7 year classes released between 1979 and 1985. A relationship was found between survival to adulthood and lunar phase at the time of smolt release. A mathematical model, utilising both smolt weight at release and time of release within the lunar cycle, was developed to fit the data. According to this model, theoretical maximum recoveries would come from releases made 3-6 days before new moon. © 1992.