Integrating commercial and research surveys to estimate the harvestable biomass, and establish a quota, for an “unexploited” abalone population

Abstract

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.

Detecting change in density and biomass of a benthic marine invertebrate following commercial fishing

“…Consequently, the survey design described in this study to obtain FI survey estimates of density, biomass and population size structure could provide reliable and efficient measures of change in population size and structure for similarly distributed species among complex reef systems with limited accessibility. This is because it conveys many of the advantages associated with the LL survey method that has become more broadly accepted as the current standard of abalone population survey design (Hesp et al, 2008;Mayfield et al, 2008Mayfield et al, , 2011b. participated in this study.…”

“…Under this approach, 100 m LL transects are laid between predetermined GPS points from a vessel, following which a pair of divers count and measure (mm, shell length (SL)) all greenlip within 1 m of each side of the transect. In cases where fishery-dependent data have been either uninformative or unavailable, this method has been used to assess stocks, inform TACCs, manage fisheries and estimate lost production due to the implementation of marine protected areas (Hesp et al, 2008;Mayfield et al, 2008Mayfield et al, , 2011b.…”

Multispecies survey design for assessing reef-fish stocks, spatially explicit management performance, and ecosystem condition

“…These findings suggest that both the visual and catch-sampling surveys are more or less sampling the area occupied by the same reef-fish stocks, but also highlight the need to cross-validate data from multiple survey sources prior to conducting quantitative stock assessments (Mayfield et al, 2008).…”

Evaluation of Post-Release Behavior, Recapture, and Growth Rates of Hatchery-Reared AbaloneHaliotis asininaReleased in Sagay Marine Reserve, Philippines

“…Density of the unexploited abalone population in South Australia ranged from 0.5-5.8 ind 100 m −2 (Mayfield et al, 2008). In British Columbia, abalone density was consistently lower (<5 ind 100 m −2 ) in areas occupied by predators (sea otters) while higher in areas without predators, ranging from 1-53 ind 100 m −2 (Watson, 2000).…”