Successful seeding of hatchery-produced juvenile greenlip abalone to restore wild stocks

Seeding of hatchery-produced abalone has the potential to enhance or maintain wild populations and ensure the viability of fishing grounds, but survival of outplanted juveniles has been poor in many previous seeding experiments. In our study hatchery produced Haliotis laevigata, age 18 months with a mean size of 28 ± 3 mm, were released at eight sites in South Australia. Because a pilot study showed significant increases in survival 2 months after release in reefs with two layers of boulders compared to a single layer, six reefs were established at each site, each with two boulder layers and approximately 6 m 2 in area. Juveniles were anaesthetised prior to individual tagging and then given 5 days to recover on settlement plates within cages. The cages were transported in cool boxes, opened and placed between boulder layers by divers within 6 h of leaving the hatchery. Six months after seeding almost all juveniles were in cryptic positions between boulders, but 9 months after seeding 17% of abalone were emergent at 56 ± 7 mm. Estimated minimum survival after 9 months was poor at two sites (0 and 23%) but at six sites survival ranged from 47 to 57%. Empty shell collections accounted for 10% of seeded juveniles during this period. A second seeding a year later at one site resulted in similar survival after 3 months. These results compare very favourably with previous seeding experiments, particularly considering the range of sites seeded and the number of reefs within each site. This was probably due to careful site selection, careful handling of seeded juveniles and the provision of a suitable, cryptic environment to reduce mortality. Poor survival at two sites appeared to be due to the presence of large numbers of predators soon after seeding.