Seeding small numbers of cultured black-lip abalone (Haliotis rubra Leach) to match natural densities of wild populations

Haliotis rubra Leach, the black-lip abalone, is a valuable, commercially harvested species, but populations have declined since the onset of commercial fishing. Seeding juvenile cultured abalone into natural habitats can enhance and/or re-establish populations. This is often done in numbers well above natural densities of both unfished and fished populations, but is usually unsuccessful (probably because of increased mortality from predation or other density-dependent factors) and is potentially problematic for the ecology of the habitat. A major aim was, therefore, to assess survival of H. rubra when seeded in small numbers. The current study is one of a few experimental investigations to improve understanding of the potential of re-seeding. We test: (1) the importance of the spatial and temporal configuration of seed; (2) the usefulness of the urchin, Centrostephanus rodgersii, to act as a potential shelter from predators; and (3) differences in survival when using the deployment devices versus urchins. After a few days, total recovery among treatments ranged between 3 and 31%. The configuration of abalone or their proximity to urchins did not affect long-term survival. Survival in devices may be greater than with urchins, but these results were spatially variable. Recovery dropped to 0.2-3% from 1-2 months, and 0.05-2% after 6 months. Nevertheless, these results show that seeding fewer abalone (rather than previous attempts at mass out-planting) can sustain populations close to average natural densities of adults previously observed in Australia (1-3 abalone perm(2)). It may be more productive and ecologically conservative to release fewer and therefore larger abalone, which are known to survive better in the wild.