As in freshwater and terrestrial systems, stocks of many marine species have been severely depleted due to over-harvesting, disease, or habitat depletion or degradation. Most marine organisms produce millions of offspring per parent, which increases the risks of both domestication and genetic depletion when restocking from aquaculture farms. Even if large numbers of parents are spawned to produce an offspring cohort, high initial mortality may result in very rapid selection to survive in farm conditions, producing different genotypes than would survive in the wild. Or, individuals may learn behaviour that is maladaptive in the wild.
Abalone are no exception. Even if natural foods are used, as in the France Haliotis farm, an absence of predators and natural habitats alters the selective regime, so that extensive experiments have been required to investigate the importance of wild broodstock, the interplay between predators of various sizes, various types of shelter and abalone size; and to determine the optimal habitat types and juvenile sizes to achieve minimal mortality and successful restocking programs. The results show the complex issues that should be considered in designing restocking programs or ecosystem restoration. The diversity and frequency of shelters in the seeding habitat is of particular importance.