Mayfield, S., McGarvey, R., Carlson, I. J., and Dixon, C. 2008. Integrating commercial and research surveys to estimate the harvestable biomass, and establish a quota, for an “unexploited” abalone population. – ICES Journal of Marine Science, 65: 1122–1130. A key challenge facing many fisheries managers is the absence of information on the level of harvestable biomass. We describe an integrated, two-stage survey approach that was used to measure the spatial distribution and harvestable biomass of a largely unexploited metapopulation of greenlip abalone (Haliotis laevigata) over a large area of northwestern Spencer Gulf, South Australia. In stage 1, commercial fishers conducted systematic surveys to identify subareas with abalone at harvestable densities. Cpue measures from these surveys were used to map and stratify a bounded survey subregion, within which leaded-line, research-diver surveys measured absolute density and harvestable biomass (stage 2). Decision tables, showing minimum biomass at various probabilities vs. harvest fraction, were developed to provide a risk-assessment framework for quota setting. Within two years, our approach allowed, first, the mapping of the broad-scale, spatial distribution and abundance of greenlip abalone in an area of 1143 km2, second, the estimation of harvestable biomass in a smaller (16.9 km2) area, and finally, the allocation by State fishery managers of an additional quota inside a newly defined management subzone. The collaborative approach we describe for providing estimates of absolute biomass over large spatial scales affords multiple advantages for the assessment and management of invertebrate dive fisheries.
Current ecological models predict that reef fish assemblages will be strongly influenced by habitat type. Here we test hypotheses about habitat types and abundance patterns of temperate reef fishes from broad spatial scales (100 s of km) to small spatial scales of metres to tens of metres. Habitat preferences are also described over long periods of time (22 years) for two abundant taxa. Patterns of distribution and abundance varied over ∼ eight degrees of latitude (29.9-37.5°S) along the coast of New South Wales, Australia. Ophthalmolepis lineolatus (Labridae) preferred kelp and Barrens habitats and juveniles were most abundant in habitats rich in algae. This species also increased in abundance from North to South. In contrast, Hypoplectrodes maccullochi (Serranidae) were usually only found in the Barrens habitat and great variation was found among locations. Both taxa were most abundant on urchin grazed deep reefs (over 10 m deep). Habitat preferences of O. lineolatus and H. maccullochi appeared resistant to major environmental perturbations that included large El Niño events in 1991, 1998 and 2002. Home ranges of O. lineolatus varied from 52 m 2 to 1,660 m 2 and often overlapped; fish of all sizes were most abundant in algal dominated habitat. Limited movements and small home ranges (2.1-11.6 m 2 ) combined with a strong affiliation for shelter indicated that most H. maccullochi are strongly siteattached. Habitat type is important to these taxonomically different fishes, but to varying degrees where H. maccullochi was more of a habitat specialist than O. lineolatus and would be more vulnerable to perturbations that alter Barrens. Changes in reef habitats will have a great influence on fish assemblages and this should also be considered in coastal planning (e.g. for Marine Protected Areas, MPAs) and the assessments of resistance and resilience of fishes to climate change.
The South Australian greenlip abalone (Haliotis laevigata) fishery was established in 1964, and commercial catches have been stable at approximately 350 t.yr −1 for over 20 years. This contrasts the status of fisheries for abalone outside Australasia, where rapid over-exploitation and stock collapse, without recovery, have been widespread. This study of the sustainability of the South Australian greenlip abalone fishery is based on a range of fishery-dependent and fishery-independent data, and it contrasts with a previous assessment based on fewer data that suggested these stocks were overfished. This fishery's success demonstrates that prolonged harvests can be obtained from wild abalone stocks. Key elements of the management system critical in preventing over-exploitation include early limitations on access to the resource, establishment of appropriate minimum legal sizes, and effective controls on total catches. A biological research program that focused explicitly on stock assessment and underpinned timely adjustments to management arrangements based on changes in stock status has also been critical. Recommendations by fisheries management committees involving resource managers, scientists, industry members, and other stakeholders have been underpinned by formal management plans. Sustainability of benthic invertebrate fisheries vulnerable to overfishing could be enhanced by adopting elements of the management system underpinning the South Australian abalone fishery since 1968.
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