Cooperative Fish and Wildlife Research Units Program: Tennessee
Education, Research and Technical Assistance for Managing Our Natural Resources

Abstract.— Hatchery-induced fin erosion can be used to identify recently stocked catchable-size brown trout Salmo trutta during annual surveys to qualitatively estimate contributions to a fishery. However, little is known about the longevity of this mark and its effectiveness as a short-term (≤ 1 year) mass-marking technique. We evaluated hatchery-induced pectoral fin erosion as a mass-marking technique for short-term stocking evaluations by stocking microtagged brown trout in a tailwater and repeatedly sampling those fish to observe and measure their pectoral fins. At Dale Hollow National Fish Hatchery, 99.1% (228 of 230) of microtagged brown trout in outdoor concrete raceways had eroded pectoral fins one day prior to stocking. Between 34 and 68 microtagged and 26 to 35 wild brown trout were collected during eight subsequent electrofishing samples. In a blind test, one observer correctly identified 91.7 to 100.0% (mean of 96.9%) of microtagged brown trout prior to checking for microtags based on visual examination of pectoral fins up to 322 d post-stocking. In the laboratory, pectoral fin length and width measurements were recorded to statistically compare the fin measurements of wild and microtagged brown trout. With only one exception, all pectoral fin measurements on each date were significantly larger on average for wild trout compared to those of microtagged brown trout. Based on the number of pectoral fin measurements falling below 95% prediction intervals, 93.7% (148 of 158) of microtagged brown trout were correctly identified as hatchery fish using regression models up to 160 d post-stocking. Only 72.2% (70 of 97) of microtagged brown trout were identified correctly after 160 d using pectoral fin measurements and the regression models. We concluded that visual examination of pectoral fin erosion was the most effective way to identify stocked brown trout up to 322 d post-stocking.