Effects of Floy and Soft VIalpha Tags on Growth and Survival of Juvenile Arctic Char

Abstract

The Floy FTF-69 fingerling tag and the new soft VIalpha (VI) tag can both be used on small fish (>100 mm and >150 mm, respectively) according to their manufacturers, but information on their use and effect on fish has not been available. In this study, these two tags were compared for one year on wild Arctic char Salvelinus alpinus, parr (lake dwelling), and smolts (100–229 mm) from two small lakes in northern Norway. Comparisons of growth rate, survival, and tag retention were analyzed. In general, VI-tagged smolts grew significantly better than Floy-tagged smolts in the sea. However, the difference was largest for the smallest fish (100–189 mm); for the larger fish (190–229 mm), there was less or no difference. Survival rates in the sea were also significantly higher (11–15%) for the smallest (<170 mm) VI-tagged smolts than for Floy-tagged smolts of the same size; larger VI-tagged smolts (≥170 mm) only survived at a slightly higher (1.5–4.0%) and nonsignificant rate than corresponding Floy-tagged smolts. Tag retention for Floy-tags was generally high for lake-dwelling char after 1 year and for postsmolts after their sea migration (>96% in total, all length groups). However, the lake-dwelling char in one lake retained only 82% of the Floy tags. Retention of soft VI tags was less than the Floy tags rates but generally better than reported retention of the original rigid VI tag on other salmonid species. However, retention of soft VI tags was strongly size-dependent and was better for lake-dwelling char (<150 mm = 67–73%, ≥150 mm = 96%) than for smolts tagged in the river (<150 mm = 46%, ≥150 mm = 85–92%). Most losses of this tag took place just after the tagging and seemed to be positively related to water temperature.