Fisheries Research Articles

Decline of a blue swimmer crab (Portunus pelagicus) fishery in Western Australia - History, contributing factors and future management strategy

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Fisheries Research




Blue swimmer crabs, Portunidae, Fishery decline, Juvenile recruitment, Breeding stock, Catch prediction, Management, Decision rule framework


Aquaculture and Fisheries | Marine Biology


Commercial blue swimmer crab (Portunus pelagicus) catches in Cockburn Sound, Western Australia, have declined significantly since 2000, due to low stock abundance resulting in closure of the fishery in December 2006. The fishery has remained closed for 3 years with predicted catches, based on juvenile recruitment indices, indicating that recovery has been slow. Like many other blue swimmer crab fisheries, management relied on a minimum legal size set well above the size at sexual maturity to allow crabs to spawn at least once before entering the fishery to presumably provide adequate protection to the breeding stock. However, a combination of biological, environmental and fishery-dependent factors contributed to a collapse and include: (1) vulnerability to environmental fluctuations as this species is at the southern extreme of its temperature tolerance, (2) a life cycle contained within an embayment and is self-recruiting, (3) a change in fishing method from gill nets to traps which increased fishing pressure on pre-spawning females in winter and reduced egg production to one age class, (4) four consecutive years of cooler water temperatures resulting in poor recruitment and (5) continued high fishing pressure during years of low recruitment resulting in low breeding stock. The strength of recruitment (juvenile 0+) from the previous season's spawn (September to January), and the residual stock (1+) near the completion of the current fishing season, have been incorporated in an abundance index that indicates the size of the next season's breeding stock and predicts the commercial catch. This catch prediction has been used in the development of a draft decision-rule framework for the future management of this fishery to determine the appropriate amount of fishing effort. The application of this approach to research and management may assist the sustainability of other blue swimmer crab fisheries at the extreme of their natural distributions.



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