Publication Date

11-2009

Series Number

196

Publisher

Department of Fisheries, Western Australia

City

Perth, Western Australia

ISBN

1 921258 73 X

ISSN

1035 - 4549

Abstract

Final FRDC Report – Project 2005/074

The Western Australian fishery is the only remaining significant fishery for pearl oysters in the world and comprises most of the exported pearl product of Australia, currently worth around $125 million annually. The majority of pearl shells used to culture pearls come from the pearling beds in the inshore waters near Broome. The fishery for pearl oysters preferentially targets smaller ‘culture’ shell (4-5 years age class, 120mm - 160mm shell length) that are more suitable for growing pearls, leaving larger MOP oysters (6+ age class, 175mm+) on the fishing grounds.

Silver-lipped pearl oysters (Pinctada maxima) harvested from wild stocks and transferred to farms are experiencing considerable levels of infestation of bioeroding sponges. Bioeroding sponges can damage the shell and sometimes the pearl and thus reduce the value of the pearls. Despite the potential loss to the industry, little was known about bioeroding sponges in pearl oyster wild stocks at the start of this project.

Data on bioeroding sponge species that excavate shells of the pearl oyster, Pinctada maxima, was collected from the main fishing grounds in North Western Australia. Estimates on infestation rates across size/age classes of shell are provided from the main fishing grounds and over three consecutive fishing seasons. Minimal infestation occurred in smaller shells therefore lowering the minimum size provides one approach to minimizing the impact of these sponges. Estimates of infestation rates in calcareous substrates of the fishing ground are also provided and compared on an area basis with shell infestation rates, including shell density and calcareous substrate density estimates of the fishing grounds. Techniques were developed to estimate the volume of bioeroding sponge erosions in pearl oyster shells and results are compared between different sponge species and fishing grounds. A field guide was developed to demonstrate the most common visual appearances of bioeroding sponge infestations. Industry and research personnel can use this field guide for bioeroding sponges in general and as a guideline to determine grades of infestation during field surveys.

Number of Pages

48

Keywords

Bioeroding sponges, Calcareous habitat, Erosion area, Biomass, Pearl oyster, Pinctada maxima, Pione velans, Cliona dissimilis, Western Australia

Disciplines

Aquaculture and Fisheries | Laboratory and Basic Science Research | Marine Biology | Natural Resource Economics | Natural Resources and Conservation | Natural Resources Management and Policy

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