Effect of Radio-Tagging on Escape Reactions of Adult Blueback Herring to Ultrasound

Abstract

Telemetry is a potential approach for assessing how effectively ultrasound steers blueback herring Alosa aestivalis away from undesirable locations. The objectives of this study were to determine (1) whether gastric implantation of radio tags prevented adult blueback herring from reacting to ultrasound and (2) if not, whether radio tag implantation diminished the fish's escape reactions. Eight groups, each consisting of four blueback herring in good condition, were exposed in a circular tank to a single pulse of broadband ultrasound eight times; each time was considered a trial. Radio tags were gastrically implanted in blueback herring from four of the groups. The four untagged groups were used to confirm that blueback herring would react to ultrasound in the tank, while the four tagged groups were used to determine whether tagging prevented a reaction. These reactions were confirmed by measuring the swimming speed immediately before and after a pulse of sound. Blueback herring in both the tagged and untagged groups swam significantly faster after a pulse of sound compared with before the sound pulse. Three of the tagged groups were compared to three of the untagged groups (tested at similar sound pressure levels) to determine whether tagging diminished escape reactions. The escape reaction metrics were the percentage of fish that moved away from the sound source, the percentage that exhibited a C-start (a sudden, high-energy swimming burst used by fish to avoid attacks by predators), and the standardized difference in swimming speeds measured immediately before and after a pulse of sound. There was no significant difference in the escape reactions of tagged and untagged blueback herring. These results suggest that telemetry can be used to assess how effectively ultrasound steers blueback herring away from undesirable locations.