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Title: Factors influencing retention of visible implant tags by westslope cutthroat trout inhabiting headwater streams of Montana

Author: Shepard, Bradley B.; Robison-Cox, Jim; Ireland, Susan C.; White, Robert G.;

Date: 1996

Source: North American Journal of Fisheries Management. 16(4): 913-920.

Publication Series: Scientific Journal (JRNL)

Description: Retention of visible implant (VI) tags by westslope cutthroat trout Oncorhynchus clarki lewisi inhabiting 20 reaches of 13 isolated headwater tributary drainages in Montana was evaluated during 1993 and 1994. In 1993, 2,071 VI tags were implanted in westslope cutthroat trout (100-324 mm fork length) and adipose tins were removed as a secondary mark to evaluate tag retention. Of 348 westslope cutthroat trout recaptured during the year they were tagged, 201 (58%) had retained their tags. Of 616 westslope cutthroat trout recaptured the year after tagging, 355 (58%) had retained their tags. Logistic regression analyses indicated that fish length was the most significant variable that positively influenced tag retention. Other significant variables were wetted width and channel gradient of the stream in which fish were tagged and quality of tag insertion (rated at time of tagging). Fish condition did not significantly improve deviance performance of logistic regression models that included fork length and tag insertion quality. Neither slopes nor intercepts of log10( length )-log10 (weight) regressions were significantly different (P > 0.10) between fish that retained tags and fish that lost them. Fish condition was not significantly different (P > 0.951; analysis of covariance) between previously tagged and untagged westslope cutthroat trout after differences between drainages and years were accounted for. We found no significant differences in slopes (P > 0.50) or intercepts (P > 0.05) of Iog10(length)-log10(weight) regressions between previously tagged and untagged fish. However, for 11 drainages where comparisons could be made, we found significant differences (P < 0.05) in length-weight regression slopes between previously tagged and untagged fish for one drainage and in regression intercepts for an additional three drainages. Ninety-five percent of all tags were readable at recapture. A logistic regression model predicted that tag retention would be 75% or higher for westslope cutthroat trout 155 mm FL or larger if tag insertion quality was good. In spite of relatively poor tag retention (<75%) by smaller (<155 mm) westslope cutthroat trout, VI tags were a valuable tool to assess movements of those fish retaining tags.

Keywords: westslope cutthroat trout, Oncorhynchus clarki, implant tages

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Shepard, Bradley B.; Robison-Cox, Jim; Ireland, Susan C.; White, Robert G. 1996. Factors influencing retention of visible implant tags by westslope cutthroat trout inhabiting headwater streams of Montana. North American Journal of Fisheries Management. 16(4): 913-920.

 


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