Effects of rearing practice on post-release young-of-the-year behavior: Acipenser sturio early life in freshwater

Abstract

Stocking is becoming an increasingly important conservation tool as biodiversity trends continue to decline. The European sturgeon Acipenser sturio is a Critically Endangered species subject to a stocking program in which a better understanding of its life history and stocking achievement is crucial for its conservation. In this study, acoustic telemetry assessment of postrelease behavior of 3 mo old fish was carried out for the first time on a sturgeon species. We aimed to improve the knowledge of movement, distribution and survival of the species' freshwater early juveniles within the context of stocking practices. Fish belonging to 2 half-sib families were reared in enriched and traditional hatchery conditions, tagged and monitored for 21 d in the Dordogne River, France. Fish overall survival proxy was 69.3% (52.2 to 90.9%); the lowest survival was found for 1 family reared traditionally. After release, most movements (85.7%) occurred during the first 3 d after stocking and were oriented in a downstream direction. Over the course of the study, 82% of fish were detected within 13.5 km of the release site. No differences in total distance covered (7.5 ± 7.0 km) were found between treatments. Three enriched-reared fish reached the tidal area (26 to 32 km from the release site) but none reached the saline zone of the estuary. Fish were mainly active at night, but traditionally-reared fish were significantly more active during the day than enriched-reared fish during the first 3 d. The study provides the first insights into early life in freshwater for this species; this knowledge will help improve stocking practices.