Manipulations of adult density and juvenile habitat quality in Northern Abalone stock restoration

Wild abalone populations throughout the world have declined dramatically over the past 40 years due primarily to market demands for the mollusc's edible foot. Northern abalone (Haliotis kamtschatkana), the only abalone species occurring in British Columbia (B.C.), is widely thought to be threatened by potential population collapse as a result of low adult densities that impair reproductive potential. This study examined the hypothesis that the abundance of wild northern abalone populations are below a critical density required for successful reproduction and assessed two techniques that may aid the 'recovery' of northern abalone in B.C. In the first study, I created dense aggregations of mature abalone during the reproductive period to test whether abalone preferred high density spawning aggregations that theoretically enhance reproductive potential. Twelve weeks following the manipulations, transplanted abalone had dispersed from enhanced densities at different rates and one year later, abalone densities had returned to pre-treatment levels. Slower rates of transplanted abalone dispersal at specific locations indicated that artificially aggregated abalone may have an enhanced theoretical reproductive potential. However, transplanted abalone dispersing to pre-treatment densities indicated that wild populations do not necessarily suffer from impaired reproductive potential. In the second study, I installed artificial habitats that provided standardized surrogate habitat for juvenile abalone and surveyed surrounding natural habitats to determine an index of juvenile abalone abundance. Juvenile abalone used artificial structures at greater mean densities than nearby natural habitat and juvenile abalone abundance was significantly different between sites but not within sites, suggesting artificial structures showed promise in their ability to detect area specific differences in recruitment and to easily measure juvenile abalone abundance. Benefits of these studies in relation to abalone stock restoration are discussed.