DIFFERENCES IN OTOLITH MICROSTRUCTURE BETWEEN HATCHERY-REARED AND WILD CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA)

Otolith microstructure exhibited some characteristic differences betwe en hatchery-reared and wild chinook salmon (Oncorhynchus tshawytscha) from the Cowichan River. Daily growth increments that formed in the ot oliths of the hatchery-reared chinook salmon after exogenous feeding w ere more regular in width and contrast than those in the otoliths of w ild chinook salmon. In a addition, otoliths from hatchery-reared indiv iduals frequently produced a check when the fish were released from th e hatchery. Eighty-nine percent of a sample of 67 chinook smelts that had been coded-wire tagged in hatcheries and later captured in the Str ait of Georgia were correctly identified as originating from hatcherie s based on otolith microstructure. These tagged fish originated from a t least 17 different hatcheries, indicating that the method could be u sed to identify chinook salmon originating from other hatcheries.