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Fish stock assessment reports

Stock assessment of Australian east coast snapper (Chrysophrys auratus)

Author/s:
Wortmann, J., O’Neill, M. F., Campbell, M. J. and W. Sumpton from Agri-Science Queensland, Department of Agriculture and Fisheries. J. Stewart from the Department of Primary Industries, New South Wales.
Publication:
Department of Agriculture and Fisheries
Published:
February 2018

Summary

The fishery assessment report describes the Australian east coast snapper fishery operating between Mackay in northern Queensland and Eden in southern New South Wales. These east coast snapper form a single genetic population and fish can potentially live for up to 40 years and weigh in excess of 10 kg.

The scope of the investigation was conducted to estimate snapper fishery indicators for the whole east coast across jurisdictions and included commercial, charter, recreational and research data from both New South Wales and Queensland. The assessment grouped the dynamics of the fishery into four fishing sectors: namely, 1) New South Wales trap, 2) New South Wales commercial line and charter, 3) Queensland commercial line and charter and 4) New South Wales and Queensland recreational. Changes in management arrangements through time were incorporated.

The 2017 management arrangements for snapper in New South Wales differed from those in Queensland. New South Wales had a snapper minimum legal size of 30 cm (total length) and a recreational in possession bag limit of 10 snapper per person, whereas Queensland had a minimum size of 35 cm and a recreational in possession bag limit of four snapper per person (only one fish allowed over 75 cm). No harvest limits (other than these size limits) applied to commercial fishing. Fish trapping (which is not allowed in Queensland) was the main commercial fishing method for snapper in New South Wales. Line fishing was used in both States and by both recreational and commercial fishers.

An historical perspective was key to the analysis. The fishery for east coast snapper commenced in 1880. Annual harvests taken by commercial, charter and recreational anglers steadily built to peak at over 1400 t per year during the 1980s. Since then estimated snapper harvests have reduced and have been in the range of 700–800 t per year since 2014. Recorded and standardised catch rates of snapper from trap and line fishing declined to historic low levels in 2002, after which the trap sector showed a recovery while the line sectors generally did not.

The stock assessment analyses of snapper data, using an annual age-structure population model, indicated that estimated fish population sizes in 2016 were between 10 and 45 per cent of the earliest estimates made for population sizes when fishing pressure was very low in 1880. The estimates generally varied below the maximum sustainable harvest reference point of 40 per cent for population size. Results from using the trap catch rates as an index of snapper abundance were more optimistic at 20–45 per cent than from line fishing at 10–23 per cent. There was an accelerated nature of decline in population size between 1950 and 1990 when large annual harvests were taken.

Estimates for long term harvest strategies that achieve population levels that are 60 per cent of unfished biomass for snapper in all fishing sectors in east-coast waters ranged 600–940 t per year. Maximum sustainable harvest estimates for 40 per cent of unfished biomass were estimated to be between 800 and 1200 t per year. Estimated annual harvests since 2014 only just fell below the 800 t level. Lower harvests were suggested in the short term based on results for the snapper population size in 2016.

From the analyses we conclude that snapper is likely to be overfished past maximum sustainable levels. New management procedures could seek to build catch rates to a higher target level (i.e. move snapper populations to a rebuilding state). Changes to sectoral fishing allocations and allowable harvests are recommended. This is advised to meet the Queensland Government’s Sustainable Fishing Strategy objectives which seek to set sustainable harvest limits that achieve a 40-50 per cent fish population size by 2020 and a 60 per cent population size by 2027.

View a copy of the report

The full report is available in electronic format from the Research information service.