The Race for Space: Using Acoustic Telemetry to Understand Density-Dependent Emigration and Habitat Selection in a Released Predatory Fish

The dynamics of fish behavior, migration, and habitat use following stock enhancement will influence the outcome of recovery programs and indicate the ecological limits of the system. This study tested the effect of release density on emigration, activity patterns, and space utilization by releasing juvenile mulloway (Sciaenidae: Argyrosomus japonicus) at low and high densities and monitoring movement intensively for 336h post release. Mulloway released at high densities had faster emigration and greater overall emigration rates than low density releases. Also, mulloway released at high densities used sub-optimal habitats at a greater frequency. Released fish dispersed into habitat patches at densities proportional to the quality of the habitat patch, consistent with density-dependent habitat selection. Targeting releases of small numbers of fish to the carrying capacity of individual patches of habitat will contribute to the success and economic viability of release programs in open systems. Releases of high densities of individuals or repeated releases at the same site may lead to increased emigration and losses from the stocked system. The capacity of a target habitat to support released fish can be rapidly assessed using pilot releases and intensive monitoring of acoustically tagged fish, prior to the implementation of large-scale release programs.