Long-term effects of marine park zoning on giant mud crab Scylla serrata populations in three Australian estuaries

Multiple-use marine parks are a powerful management tool to help protect marine biodiversity and sustain wild fisheries while allowing some access to recreational and commercial activities using zoning arrangements. Research has focused on fish but far less is known about the effectiveness of zoning for other groups, such as exploited crustaceans, especially in estuaries. In this 8 yr study, we tested the hypotheses that unfished zones, which had been closed to fishing since 1991, would have higher abundances (catch per unit effort) of the giant mud crab Scylla serrata in 3 estuaries (Wooli, Corindi and Sandon) of the Solitary Islands Marine Park (SIMP) in New South Wales, Australia, and that recovery after fishing closure would be rapid. Replicate fished and unfished zones were sampled from December 1998 (Wooli) and July 2000 (Corindi and Sandon) until April 2007. In August 2002, re-zoning occurred with some estuarine sections reopened to trapping, some newly closed and others either remaining closed or open. This enabled Before-After-Control-Impact analyses to test our hypotheses. Crab numbers increased rapidly after zone closure and unfished zones protected giant mud crabs from exploitation with catches 2 to 3 times greater than in fished zones. Although there was substantial temporal variation in crab abundance within and among the 3 estuaries, responses to zoning were consistent and spatial protection in estuaries in the SIMP proved effective for sustaining giant mud crab populations. This type of management shows promise for protecting or replenishing stocks of other species of crabs worldwide.