Sustainable harvest of lobster pueruli : a way forward for rock lobster aquaculture

A major impediment to the development of spiny lobster aquaculture has been the inability to rear lobsters from eggs, through the delicate larval stages, to the settling puerulus stage. An alternative is to harvest pueruli from the wild for commercial on-growing. However, wild harvest of pueruli can potentially have a deleterious effect on the adult lobster fishery. Research presented here investigates both the feasibility and sustainability of an industry based on the harvest of southern rock lobster (Jasus edwardsii) pueruli. Pueruli were found to settle on a diverse range of substrata. Cheap, lightweight puerulus collectors constructed from readily available materials, such as trawl netting and shade cloth, proved to be significantly more cost-effective for large-scale harvest than collectors currently in use for scientific monitoring of puerulus settlement. A system of 'reseeding' wild habitat with hatchery-reared juveniles was evaluated as a method of ensuring sustainability of wild populations. Reseeding involves the release of a portion of ongrown ( na'ive) juveniles after one year to compensate for those that would have survived in the wild, and its success is predicated on high survival among released juveniles. Naive juvenile lobsters tracked acoustically behaved in a similar manner to wild animals, sheltering in appropriate hides during the day, often co-habiting with wild conspecifics, and then moving at night. The highest levels of activity occurred in the 12 h following release, while the distances moved by individual lobsters declined rapidly after this initial period. Stomach contents of tracked lobsters recaptured after 11 days revealed that na'ive lobsters adapted well to wild food sources, although their diet differed from that of wild lobsters. Mortality rates of tethered juvenile lobsters varied substantially between sites in southeastern Tasmania. However, these differences were not significant once results were corrected for experimental artefacts associated with differences in the predator assemblages among sites. Video footage of tethering trials showed that large wrasse and small octopus were the major predators of juvenile lobsters. Crabs and large lobsters also captured tethered juveniles, however experiments in a mesocosm showed that these captures were artefacts of tethering. Survival of naive lobsters estimated from mark-recapture trials was generally equivalent to that of tagged wild lobsters. An exception was where lobsters were released onto a small area of isolated patch-reef. Here, naive lobsters tended to ignore reef boundaries, moving away from shelter and onto sand. These results suggest that by following simple criteria in the selection of release sites, mortality among released naive lobsters is minimal, and equivalent to that of wild juveniles at the same stage. The overall conclusion is that reseeding is an effective method of compensating for puerulus harvest.