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Identifying future restocking options for Blue Swimmer Crabs (Portunus armatus)

Jenkins, G.I., Michael, R. and Tweedley, J.R.ORCID: 0000-0002-2749-1060 (2017) Identifying future restocking options for Blue Swimmer Crabs (Portunus armatus).



Non-technical summary of research findings

This project had two main aims, i.e. (i) attempt to culture and release Blue Swimmer Crabs (Portunus armatus) and (ii) produce an extensive literature review detailing existing knowledge on the biology/ecology of portunids, techniques for successfully rearing these species in aquaculture and review the successes and lessons learned from Portunid release programs around the world. Berried female P. armatus collected from the Peel-Harvey Estuary in October and November spawned in the hatchery each producing between 300,000 and 900,000 zoea. One of the two culture runs were successful, producing 175,000 megalopa from 340,000 zoea at a survival rate of 52%. Survival decreased dramatically following metamorphosis from megalopa to crablet (2.4%; i.e. 1.2% of the zoea). This was due to the morphological development of claws and the highly aggressive and cannibalistic nature of the crabs. Once the individuals were transferred to a tank with habitat to hide in, mortality decreased with 18% of the 500 crabs stocked surviving for 53 days before being euthanised. Of the 4,200 crablets produced, 3,700 were released, following clearance from the WA Department of Fisheries into the Peel-Harvey Estuary.

The literature review demonstrated that, in general, portunids are highly fecund, fast growing, short-lived species, with high natural mortalities and are opportunistic predators. These species are also subjected to high fishing pressure with an overall mean exploitation rate of 0.57% ± 0.15 (maximum Portunus trituberculatus at 0.82%), indicating that, on average, more crabs are captured by fisheries each year than die of natural causes. All release programs for portunids were initiated in response to declines in stocks caused by overfishing, disease, habitat degradation and climate change. In each case, successful hatchery techniques were developed to enable small-scale production, however, only in the case of P. trituberculatus was production increased to a commercial scale (~27-35 million juveniles per year). Hatchery-reared individuals are released at the crablet stage as stocking megalopae has not been effective. However, there is a trade-off between the economic cost of production and size-at-release and thus survival in the wild. This is poorly understood and likely requires detailed biological studies and bio-economic analysis to answer definitely.

Item Type: Report
Murdoch Affiliation(s): School of Veterinary and Life Sciences
Copyright: © 2017 Recreational Fishing Initiative Fund, South Metropolitan TAFE and Murdoch University
United Nations SDGs: Goal 14: Life Below Water
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