Knowledge to improve the assessment and management of Giant Mud Crabs (Scylla serrata) in Queensland: Final Report

Abstract

This project researched Giant Mud Crabs to meet information needs and research priorities of the harvest strategy for the mud crab component of the Queensland Crab Fishery. It was conducted in collaboration with commercial crabbers, and between scientists from the Queensland Department of Primary Industries, CQUniversity and New South Wales Department of Primary Industries and Regional Development. Research aims were to investigate spatial stock structure, indices of abundance to monitor populations and assist in setting or predicting the Total Allowable Catch and biological information on regional populations. Whilst ubiquitous and relatively simple to catch, the complex behaviour, size-sex spatial habitat use, and variable catchability posed challenges to researching these topics. Abundance indices of pre-recruits were developed but were insufficient to robustly predict exploitable biomass and/or harvest. We suggest that whilst theoretically attractive, forecasting exploitable biomass of Giant Mud Crabs based on a pre-recruit index is unobtainable in the real world at the scale of the East Coast (EC1) and Gulf of Carpentaria (GC1) management units. The research generated new knowledge about Giant Mud Crabs, including confirmation of their genetic connectivity along the eastern Australian continental shelf (i.e., Queensland and New South Wales), estimates of regional size-at-maturity for males and females in Queensland (east coast and Gulf of Carpentaria), evidence of high insemination rates of females not supporting speculation of sperm limitation as a consequence of Queensland’s single sex harvest policy, new insights into the spawning migration of females through the successful application of archival pop-up satellite tags, and a review of biological aspects of potential female harvest – given the new knowledge acquired in the current project. An intangible outcome of the project was the extensive interaction and knowledge exchange between project staff and industry stakeholders.