Mud crab ('Scylla serrata') and Marine Park management in estuaries of the Solitary Islands Marine Park, New South Wales

Abstract

Marine Parks have been designed to protect marine biodiversity and sustain wild fisheries in coastal ecosystems. They typically use zoning schemes to preserve the environment and biota while allowing access to recreational and commercial activities. However, there is seldom adequate scientific research to confirm whether zoning schemes are successfully protecting fish stocks or causing favourable demographic changes to fisher-targeted species. The Solitary Islands Marine Park (SIMP) in New South Wales, Australia, was formed in 1998 to manage human activities and to ensure the sustainability of the marine environment. Mud crab (Scylla serrata) populations are exploited in the Wooli, Sandon and Corindi estuaries, which form part of the SIMP. When the park was declared, different zones were implemented, restricting fishing in some areas while allowing unrestricted activities in others. The 'no fishing' zones aimed to maintain the area in its natural state. In so doing, it was hoped that commercial and recreational use could continue while ensuring a sustainable future for mud crabs. To assess the effectiveness of this zoning for protecting mud crabs, replicate fished and unfished zones were sampled each month from December 1998 (Wooli) and July 2000 (Sandon and Corindi) until August 2003 using commercial wire traps. The sampling program coincided with changes to the zoning schemes implemented by the NSW Marine Park Authority in August 2002 as part of a zoning review, which had otherwise been unchanged since 1991. This enabled the collection of pre- and post-zoning data and the assessment of mud crab population responses to areas which were reopened (Wooli and Corindi) or closed (Sandon) to fishing. Methods of tagging success were validated for mud crabs. Anchor t-tags inserted into the posterior margin of the crab did not hinder crab movements or become detached during moulting. These tags were effective for long-term tagging studies to describe movement patterns, and were used throughout the study. Crab behaviour around traps was assessed in special tanks. Video analysis revealed that male crabs were initially dominant around baited traps and entered first. However, all crabs of each sex entered the trap in a short period of time and did not escape. The sampling program provided evidence that no-take zones were protecting mud crabs from exploitation in the SIMP, as these areas contained greater numbers of crabs in all size classes. ... The results presented in this thesis help illustrate the effectiveness of estuarine protected areas in the SIMP for sustaining recreationally and commercially targeted species such as mud crabs. It provides information that can be used to justify the effectiveness of these areas to managing authorities and the public. I have been able to show how a management plan that recognises the biology of the species being protected (the mud crab), the behaviour of the fishers targeting that species, and the tools available (e.g. zones, gear restrictions, and natural barriers) can be integrated to design effective zoning schemes in MPAs.