The Effects of Adipose Fin Clipping and Coded Wire Tagging on the Survival and Growth of Spring Chinook Salmon

Abstract

Each year, millions of Pacific salmon are identified by the insertion of a coded wire tag and removal of the adipose fin. To evaluate the effects of adipose fin clipping and coded wire tagging on the survival, growth, and straying of spring Chinook salmon Oncorhynchus tshawytscha, we coded-wire-tagged juveniles over a 3-year period and excised their adipose fins at three hatcheries on the Columbia River. In addition, the study fish and control fish were marked with otolith marks so that returning adults without tags and the untagged controls could be distinguished from untagged strays. We collected otoliths, tags, and length data from adults returning to the three hatcheries. Because the proportions of fish with coded wire tags returning to the hatchery were similar to those released and there was no discernable pattern of increase or decrease, we concluded that coded wire tags and adipose fin marks did not affect juvenile-to-adult survival. Although there was an indication that coded-wire-tagged fish were more likely to to be smaller when they returned than fish without coded wire tags, the size discrepancy was less than one standard deviation of the natural biological variation in size. Tagged juveniles released at the rearing site did not tend to stray when they returned as adults. Based on these results, we concluded that coded wire tagging is a useful method for gathering information with minimal bias on the fates of groups of fish.