Retention of Passive Integrated Transponder Tags in Stream-Dwelling Rainbow Trout

Abstract

Passive integrated transponder (PIT) tags have been widely used as a tool for various monitoring and research needs, but the retention of PIT tags has rarely been tested in resident salmonids. We quantified the short-term (≤1 week), annual (1 year), and long-term (≥1 year) retention rates of PIT tags placed in the peritoneal cavity of small resident rainbow trout Oncorhynchus mykiss in 11 study streams and assessed whether fish size and gender affected tag retention. Short-term retention rates were at least 92% and averaged 96% for all streams, but a paired t-test nevertheless indicated that experienced taggers had significantly higher short-term retention rates (mean, 98%) than did inexperienced taggers (mean, 95%). Annual retention rates for PIT tags averaged 81% among all study streams, ranging from a low of 67% to a high of 92%. Annual retention rates were lower for larger rainbow trout than for their smaller counterparts. Long-term tag loss for females was the same as for males for fish smaller than 15 cm but significantly higher for fish 15 cm or more, suggesting that egg expulsion was the primary cause of tag loss.

Received August 27, 2010; accepted January 3, 2011

ACKNOWLEDGMENTS

We thank John Cassinelli, Dan Schill, and four anonymous reviewers for providing helpful comments that improved the manuscript.