Abstract
The silver-lipped pearl oyster, Pinctada maxima, is the primary species used for the culture of pearls in the Indo-Pacific region. The Western Australian fishery relies on wild-caught animals, and as such, knowledge of the status and distribution of P. maxima underpins sustainable management of the fishery. Eighty Mile Beach, in tropical Western Australia, is the key harvest area for P. maxima, with oysters collected by divers to depths of ∼35 m, although there are anecdotal accounts of oysters beyond diving depths. Image-based, and acoustic methods were used to elucidate distribution patterns of P. maxima off Eighty Mile Beach, including data from 862 km2 of multibeam survey and 119 towed video transects spanning an area from the 20 to 100 m contour lines. We quantified habitat characters including depth, substrate, and benthic community composition associated with pearl oyster distribution. Multibeam sonar data was also coupled with towed video data to produce predictive statistical models of P. maxima habitat. We found P. maxima to depths of 76 m, although more than 90% of individuals occurred shallower than 40 m and less than 2% were found deeper than 50 m. Oysters occupied flat, sandy habitats with neighbouring benthic communities of filter feeders (>98% of observations). These results show P. maxima predominantly occurs in depths <40 m, with no evidence that extensive populations extend into deep water in the region.
Highlights
Distribution patterns of organisms are regulated through a range of ecological processes, including dispersal and recruitment (Marshall et al, 2010)
91.8% of P. maxima observations occurred in depths shallower than 40 m and only 1.8% of P. maxima were observed in depths >50 m, despite sampling effort being greatest in the 40–70 m depth range (Figure 5A)
Despite extensive searching in waters between 40 and 100 m offshore of Eighty Mile Beach, we found no evidence of deep pearl oyster beds in the region
Summary
Distribution patterns of organisms are regulated through a range of ecological processes, including dispersal and recruitment (Marshall et al, 2010). Dispersal for sessile marine invertebrates hinges on the nature of a species larval phase. Sessile adults may produce broadcast spawned gametes that disperse while they fertilise and develop within the water column, or alternatively release developed larvae that have the potential to settle quickly (Thorson, 1950). The final phase of the larval cycle – larval settlement and recruitment behaviours – are important to interpretations of the spatial distribution of populations (Jenkins, 2005; Marshall et al, 2010). The Silver Lipped Oyster, Pinctada maxima, exhibits a complex life cycle; adults broadcast spawn gametes which develop to larvae within the plankton.
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