Evaluation of visible implant elastomer (VIE) tags for use in supplementation of an endangered estuarine fish

Objective: Delta Smelt Hypomesus transpacificus are thought to be close to extinction in the wild, which has spurred multiagency conservation efforts to supplement their population. In conjunction with these recent efforts, monitoring is needed to assess the effectiveness of supplementation. Such monitoring often uses large-scale tagging of released fish to distinguish between hatchery-origin and wild-origin fish that are captured during later surveys. Methods: In this study, we evaluated the use of visible implant elastomer tags in Delta Smelt to determine whether fish survival, fish growth, or tag retention were dependent on (1) tag color (blue, green, orange, red, yellow, and no-tag control) or (2) tagged body location (posterior-dorsal, anterior-dorsal, mid-lateral line, and no-tag control). Result: Over 165 days of the first experiment, there was no difference in growth rate (mean = 0.073 mm/d, range = 0.072-0.075 mm/d) or survival (mean = 68%, range = 63-77%) among tag colors. Across all color groups, mean tag retention was 96% (range = 87-100%). Over 120 days of the second experiment, tag location had no influence on fish growth rate (mean = 0.064 mm/d, range = 0.062-0.067 mm/d) or survival (mean = 50%, range = 43-58%). For the surviving fish in experiment 2, the tags that were placed at the mid-lateral line were retained less (84% on day 120) than those at posterior-dorsal and anterior-dorsal locations (99% and 98%, respectively). Conclusion: Our results suggest that visible implant elastomer tagging is a suitable method for marking adult Delta Smelt (>50 mm fork length) for up to 165 days and can be useful for conservation monitoring efforts.