Abstract

Reference	Blankenship, H. L. 1990. Effects of time and fish size on coded wire tag loss from chinook and coho salmon. American Fisheries Society Symposium 7:237-243.
Abstract	Coded wire tag (CWT) loss by salmonids has been treated and reported inconsistently by fishery agencies on the Pacific coast of the USA and Canada. Inconsistent treatment of tag-loss estimation can affect final estimates of the CWT groups. This report provides information on CWT loss rates, factors influencing tag loss, length of time over which tag loss occurs, and frequency of naturally occurring adipose fin loss. Four groups of Chinook salmon Oncorhynchus tshawytscha and four of coho salmon O. kisutch were tagged and held for up to 293 d after tagging, to estimate the level of CWT loss. The average size of the fish ranged from 0.9 to 7.6 g. Final tag-loss rates ranged form 1.1 to 5.3%. No significant tag loss was observed in any of the groups later than 29 d after tagging. With tagging-crew experience level and average fish size (2.1g) held constant, the effects of half-length (0.5mm long) CWTs and standard-length (1.1mm long) CWTs on tag loss were compared, and no significant difference was found. However when experience of the tagging crew and tag length (1.1mm) were held constant, fish sizes (mean, 1.6 and 1.1g) had a significant effect on tag loss. The mean tag loss for the smaller fish (1.1g) was 1.8%; the larger fish (1.6g) had a mean tag loss of 1.1%. Returning adult coho salmon were monitored at four Puget Sound hatcheries for naturally missing adipose fins, the frequency of which was 0.5%. Observations on naturally reared coho salmon smolts, and returning adults from several Puget Sound streams, showed that 0.06% of fish were missing adipose fins.
Tag	Coded Wire Tag (CWT)
Objective	Evaluate tags