Michigan Department of Natural Resources
Fisheries Research Report No. 2025, 1996.

Selected Factors Affecting Rate of Loss of Fine-Fabric Floy Tags
when Applied to Yearling Brown and Rainbow Trout


Andrew J. Nuhfer

Michigan Department of Natural Resources
Hunt Creek Fisheries Research Station
1581 Halberg Road
Lewiston, Michigan 49756

Roger N. Lockwood

Michigan Department of Natural Resources
Institute for Fisheries Research
212 Museums Annex Building

James L. Dexter, Jr.

Michigan Department of Natural Resources
621 North 10th Street
P.O. Box 355
Plainwell, MI 49080


Abstract.-We tested the potential suitability of FD-68B fine-fabric Floy tags for determining relative survival or angler recovery of different strains of small yearling rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta. We determined tag loss in small inland lakes for up to 37 months after tagging. We determined effects of Floy tagging, fin clipping, and tag color on brown trout mortality and effect of tag color on tag loss rates for up to 7 months. Rainbow trout lost tags at a rate of approximately 1% per month over 37 months. Brown trout lost tags at a rate of 1.6% per month over 37 months. Relative survival of three rainbow trout strains through 30 months was accurately ranked based on tag recovery. However, due to tag loss, relative survival through 30 months of three brown trout strains was not accurately ranked based on tag recovery. Significant differences in survival among brown trout strains were detected based on fin clip recoveries but no differences could be detected when survival was estimated from tag recoveries. Inverse relationships between tag loss and trout total length (TL) at tagging appeared to be a major cause of variation in tag loss between different trout strains. Small brown trout (<16.5 cm mean total length) tagged and stocked into a shallow, weedy spring pond lost 54% of their tags within 101 d after stocking during 1990 and 57% within 210 d after stocking during 1991. High tag loss by these trout was attributed primarily to their small size at tagging and anatomical location of tag insertion. Our data suggested that insertion of tags beneath the posterior half of the dorsal fin, where pterygiophores are smaller than the anterior half, contributed to poor tag retention. Brown trout tagged with orange or brown tags, lost tags at the same rate over a 210 d period. Daily mortality rates of four groups of brown trout: fin clipped and tagged with orange tags, fin clipped with brown tags, fin clipped only, and unmarked fish, were not significantly different through 210 d of residence in the spring pond.
Our findings suggested that fine-fabric Floy tags were poorly suited for evaluations of relative survival or return to creel of different trout strains or species when tagged trout were 17-cm long at tagging. Tag loss varied by species and strain of trout, size of fish, and anatomical location of tag insertion. Because of this variability, differences in the numbers of tags returned from different strains or species could not be readily attributed to performance differences between groups. Fine-fabric Floy tags may be suitable for short-term evaluations of angler harvest of rainbow trout (>=17 cm TL) in lakes where most fish are caught within the first six months after stocking.