Evaluation of coded wire tag retention in brown trout (Salmo trutta) fingerlings tagged at three anatomical locations

Abstract

The North Carolina Wildlife Resources Commission has used coded wire tags to mark fish. We evaluated coded wire tags placed at three different anatomical locations (left cheek, right cheek and snout) in brown trout (Salmo trutta) fingerlings (range of mean annual total lengths = 81.31 – 101.89 mm) prior to stockings (10,000 fish per tagging location). We determined the probability of tag retention at zero, 87 and 176 days posttagging across mean fish lengths. Anatomical tagging location influenced the probability of a fish being tagged. At all evaluation periods and for all mean sizes, brown trout fingerlings tagged in the left cheek had higher probabilities of being tagged than other positions of tags, with snout tags performing the worst. Intra-location comparisons revealed a decline in tag retention across temporal scales. Days posttagging had a negative effect on probability of tag retention, while length had a positive effect on the probability of tag retention. Our results indicated that the likelihood of a tag being present at 176 days was influenced by position of tag and initial tagging success more so than length or days posttagging. Although tag retention was generally high across all tag positions, differences in retention revealed the need to refine the tagging procedure. In addition, the underperformance of coded wire tags placed in the snout suggested that alternative marking locations should be explored.