Stock assessment of Queensland east coast red spot king prawns (Melicertus longistylus), Australia, with data to December 2021

Abstract

Red spot king prawns (Melicertus longistylus, formerly known as Penaeus longistylus) are found in tropical waters of Australia from Shark Bay in Western Australia to near Yeppoon in Queensland. Red spot king prawns generally occur along the eastern coastline of Queensland above 22◦ S. The species live around two years and have a maximum observed size of 51 mm carapace length for females and 42 mm carapace length for males. Sexual maturity for females is reached at approximately 8 months of age and 33 mm carapace length.

This is the first stock assessment conducted on Queensland east coast red spot king prawns by Fisheries Queensland. Assessment work carried out during a Master’s Thesis did not produce comparable outputs.

This stock assessment includes input data through to December 2021. All assessment inputs and outputs were referenced on a calendar year basis (that is, ‘2021’ means January 2021–December 2021).

The assessment used a one-sex monthly delay-difference population model, fitted to catch rates. An age-structured model was also trialled.

The model incorporated data spanning the period 1958 to 2021 including mandatory daily commercial logbook data collected by Fisheries Queensland (1988–2021), historic voluntary logbook data (1980–1988), Queensland Fish Board data (1958–1981), historic catch records (1958–2014), survey and logbook gear data collected by Fisheries Queensland (1988–2021), high resolution vessel tracking data collected by Fisheries Queensland (2000–2021) and lunar data (1958–2021). Length data collected by Fisheries Queensland (1998–2009) were also incorporated in a modelling scenario.

The stock assessment was guided by a project team consisting of scientists, managers, and industry representatives.

Twenty-four scenarios were run using a delay-difference model, covering a range of modelling assumptions and sensitivity tests. All scenarios were optimised using Markov chain Monte Carlo (MCMC) to better explore the robustness of the models. The models had varying success across the 24 scenarios, with nine models achieving convergence. These nine scenarios resulted in a wide range of final biomass estimates, and some non-converged scenarios had better model fit. On this basis the stock level is reported as undefined. Full results for all 24 scenarios are presented in this report.