Outplanting the seeds of success; Abalone stock enhancement.

Cameron Dixon, Rob Day, Slyvain Huchette and Scorsby Shepherd

University of Melbourne, POINT LONSDALE, AUSTRALIA

THEME: ASFB

Successful seeding of hatchery reared abalone has the potential to enhance wild populations and ensure the viability of commercially important fishing grounds. However survival of outplanted juveniles has been poor in previous seeding experiments. Hatchery reared greenlip abalone, Haliotis laevigata, with an average size of 28mm, were released at eight sites near Backstairs Passage, South Australia. At each site six reefs were established, each consisting of two boulder layers approximately 6m2 in area. Results from a pilot experiment showed that survival was greater in reefs with two layers of boulders than a single layer. After juveniles were collected from hatchery pipes, they were individually tagged and placed onto settlement plates within cages. The cages were placed within boulder layers to allow natural movement onto the reef. Minimum survival of abalone at 7 sites was 57% after six months, with most mortality occurring in the first month. At one site survival was only 16%, 5% and 1% after 1, 3 and 6 months respectively. Mortalities were likely to be caused by the large numbers of 11arm starfish, Coscinasterias, observed in the survey area. The high survival rates at all other sites may be attributed to the methods of release, suitability of the seeding habitat, behavior of the species and size of the abalone seeded. Another important factor may have been the flow through pipe system in which juveniles were raised, providing dark conditions similar to cryptic habitats beneath boulders, where juveniles would be protected from predators.