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Marine Ecology Progress Series

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MEPS 295:201-213 (2005)  -  doi:10.3354/meps295201

Effects of marine reserve protection on the mud crab Scylla serrata in a sex-biased fishery in subtropical Australia

S. Pillans1,3,6,*, R. D. Pillans2, R. W. Johnstone1,3, P. G. Kraft4, M. D. E. Haywood2, H. P. Possingham5

1CRC for Coastal Zone, Estuary and Waterway Management, Indooroopilly Sciences Centre, 80 Meiers Road, Brisbane 4068, Queensland, Australia
2CSIRO Marine Research, PO Box 120, Cleveland, Brisbane 4163, Queensland, Australia
3Centre for Marine Studies, 4Department of Zoology and Entomology, and 5The Ecology Centre, University of Queensland, St. Lucia, Brisbane 4072, Queensland, Australia
6Present address: Centre for Marine Studies, University of Queensland, St. Lucia, Brisbane 4072, Queensland, Australia

ABSTRACT: The impact of sex-biased fishing and marine reserve protection on the mud crab Scylla serrata was examined by comparing the catch rates (catch-per-unit-effort, CPUE), mean size, sex ratios and movement of crabs in 2 coastal marine reserves (1.9 and 5.7 km2) and 4 fished non-reserve sites in subtropical Australia. Five years after closure, both marine reserves supported higher catch rates and a larger mean size of S. serrata than non-reserve sites. Males dominated catches of S. serrata in both marine reserves, where CPUE was at least twice as high within the reserves compared to non-reserve sites. Male crabs were also 10% larger in the reserves compared to adjacent fished areas, and of the total male catch, over 70% were equal to or greater than legal size compared to less than 50% outside the reserves. The sex ratio of S. serrata was skewed towards females in all non-reserve sites, which was most likely a result of the ban on taking female S. serrata in Moreton Bay. As only male crabs of ≥15 cm CW made up the S. serrata fishery in Moreton Bay, sex ratios of mature male and female crabs were examined, revealing a strong skew (2:1) towards mature males in both marine reserves. Of the 472 S. serrata captured in this study, 338 were tagged in the reserves in order to document movement of the crabs between the reserve and non-reserve sites. Of the 37 recaptured crabs, 73% were recorded inside the reserves, with some spillover (i.e. cross-boundary movement) of crabs recorded in fished areas. This study demonstrates the effectiveness of small (<6 km2) marine reserves for sex-biased exploited fisheries species.

KEY WORDS: Marine reserves · Scylla serrata · Sex-biased fishery · CPUE · Sex ratio · Reserve size · Subtropical · Australia

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