Let them go free: Spatial behaviour following the experimental release of hatchery-reared juveniles Sciaena umbra and Dentex dentex

Abstract

As marine stocks and biodiversity are rapidly declining, the release of hatchery-reared individuals into the wild is a species conservation measure aiming at replenishing stocks of freshwater, anadromous and marine fish species. The aim of this study is to assess for the first time the post-release exploration behaviours, survival and dispersal in the wild of released hatchery-reared juveniles of D. dentex and S. umbra. For this purpose, twenty fish from each species were tagged with acoustic transmitters and released in a marine no-take zone located in Corsica (France). Most individuals were considered alive until their last detection (95% of S. umbra and 74% of D. dentex detected individuals). Fish were detected within the receiver array on average up to 11.3 (± 20.7) and 10.3 (± 10.3) days after being released for juveniles of D. dentex and S.umbra, respectively. Dentex dentex juveniles dispersed mostly southward along the shore whereas S. umbra juveniles tended to disperse along the shore both northward and southward from the acoustic receiver array. Before their rapid dispersion (i.e. within a few days) outside the studied zone, juveniles of both species displayed increasing cumulative MCP areas and increased their vertical niche revealing their gradual coverage and exploration of deeper habitats in the area. The results from our study highlighted that hatchery-reared juveniles of both species did not settle inside the studied area but seemed to start to acclimate to the natural environment. This work is a first step towards the assessment of the viability of restocking for both species.