Upstream and Downstream Dispersal Behavior of Hard‐ and Soft‐Released Juvenile Atlantic Salmon

Abstract

AbstractFailure of reintroduction efforts of extirpated populations is thought to be linked to maladaptive behaviors exhibited by captive‐bred individuals in the environment where they are released. Soft‐release conditioning tactics attempt to reduce maladaptive behaviors by providing reintroduced animals an acclimatization period prior to release. We used implanted passive integrated transponder tags and antennae to monitor the spatial and temporal dispersal behavior of captive‐bred Atlantic Salmon Salmo salar that were acclimatized for 6 d prior to release (soft‐release), with fish that were directly released (hard‐release) into East Duffins Creek in Ajax, Ontario, Canada. In total, 232 of the 610 tagged fish (38%) dispersed from the release site. Downstream spatial dispersal did not differ significantly between the hard‐release (32%, n = 98 of 310) and soft‐release fish (30%, n = 91 of 300), but the hard‐release fish were significantly more likely to move upstream (11%) than were the soft‐release fish (3%). Timing of dispersal also significantly differed between the two groups: soft‐release fish were detected dispersing, on average, approximately 15 d earlier than hard‐release fish. These results suggest that soft‐release tactics do affect dispersal behavior, and the findings will be of particular interest to fisheries management agencies that are charged with improving the success for stocking salmonids as part of reintroduction efforts.