Abalone stock enhancement by larval seeding : effect of larval density on settlement and survival

Abstract

Abalone larvae of Haliotis rubra and Haliotis laevigata were released experimentally at sites in South Australia to determine the effect of density of larval release on subsequent survival. In one experiment, densities of post-larvae of Haliotis rubra, 19 days after release, were highest at intermediate release densities (16,000 larvae m^-2) compared with low (1 ,600 m^-2) and high (80,000 m^-2) release densities. Highest post-larval densities were about 4.5 times background densities at control sites. In a second experiment, densities of post-larvae of Haliotis laevigata, 6 days after release, were three times higher (317 m^-2) at high release densities of 120,000 larvae m^-2 than at low release densities of 2,000 m^-2. After 49 days average survival of post-larvae across treatments was about 0.5% and mean density was 3.8 m^-2. After 11 months the density of seed was about 0.6 m^-2 In both experiments the most cost-efficient densities of larval release were the lowest in tenns of the proportions of released larvae settling and surviving. Given the likely density-dependent mortality of post-larvae after settlement, larval release at even lower densities than those tried over larger areas is likely to be the optimal seeding strategy.

Keywords:

• abalone
• Haliotis rubra
• Haliotis laevigata
• reseeding
• seeding
• larvae
• early juvenile
• density-dependent mortality
• survival
• stock enhancement