The northern Australian red snapper fisheries between the Kimberleys and Cape York comprise of five key species from the family Lutjanidae (Lutjanus erythropterus, L. malabaricus, L. argentimaculatus, L. johnii and L. sebae). Status reports indicate about 1500-1800 tonnes per year of red snappers are caught across northern Australia, with a landings value of $6-8 million. The stock range of the crimson and saddletail snappers extends well into Indonesian waters, with significant landings and overfishing by trawling outside of Australia’s Fishing Zone (AFZ). Illegal foreign fishing also occurs in the AFZ.
Limited data, the species longevity (30-40 years) and unquantifiable external catch compromises analytical assessments. Improved fishery monitoring and management in the AFZ is needed to ensure the sustainability and commercial profitability of red snappers.
In September 2007 the Northern Australian Fisheries Committee (NAFC) resolved to develop a Harvest Strategy Framework (based on the Commonwealth HSF) to guide the management of red snappers across northern Australia. NAFC’s Northern Management and Science Working Group (NMSWG) held workshops late 2007 to develop the HSF and identify means of improving our knowledge on the uncertain status of red snappers. It was clear that critical indicators developed from relative abundance indices and age composition data are needed to service management decision rules in a harvest strategy framework.
The next important requirement to finalise the HSF is to design databased reference points and a complementary monitoring program. Analyses on the historical data held by fishery agencies (WA, NT, QLD and Commonwealth) will lead to monitoring by industry vessels to provide independent data for the HSF. This high priority tactical work will enhance agency collaborations and deliver the needs for sustainable and profitable stocks. The HSF will provide greater certainty for managers and industry through an open and transparent process for ongoing adjustment to management arrangements.
Australia’s tropical snapper fisheries harvest six main Lutjanid species. They are the Crimson, Saddletail, and Goldband snappers, Red Emperor, Golden snapper and Mangrove Jack. These fish live up to 40 years of age, weigh up to five to ten kilograms and are highly valued for commercial marketing. The fisheries operate in tropical offshore waters across northern Australia from the Kimberley coast to the Gulf of Carpentaria. The fisheries are primarily commercial using demersal trawl, trap and line fishing gear. The fisheries have a long and varied history of foreign and domestic exploitation. Indicative foreign harvests were two to five kilotonnes per year up to 1990. After 1990, foreign vessel permits were removed and domestic fishing expanded landing in the order of two to three kilotonnes of tropical snappers annually.
In 2007, NAFC listed tropical snapper research as a priority. Past assessments and management settings required revision. New monitoring data on snapper abundance and age composition were needed for assessment of stock status and contemporary management procedures. In response, northern fisheries jurisdictions and the FRDC commissioned tactical research to develop a survey / observer structured fishery monitoring program and critically evaluate the potential use of data. A total of 39 data sets and a range of analyses were used in this process.
Statistical analyses of commercial fishery catch rates quantified variances to establish abundance indicators from structured monitoring. The variances were used to calculate the number of survey / observer days required to monitor tropical snapper catch rates (e.g., standardised number of fish caught per unit area swept by trawling). This result was required to ensure accurate monitoring of catch rates and fish ages so the data were directly aligned for estimation of fishing mortality or, possibly, biomass.
Keywords: Age frequencies, Catch curves, Catch rate standardisation, Fishery management, Lutjanidae, Monitoring, Population modelling, Simulation, Tropical snapper.