Stock assessment of Queensland east coast endeavour prawns (Metapenaeus endeavouri and Metapenaeus ensis), Australia, with data to December 2021

Abstract

Endeavour prawns (Metapenaeus endeavouri and Metapenaeus ensis) are endemic to the tropical and subtropical waters of Australia and are widely distributed along the coastline of northern Australia from Shark Bay in Western Australia to the eastern coast of northern New South Wales. The species live approximately two years and have a maximum observed size of 44 mm carapace length for female and 32 mm carapace length for male blue endeavour prawns and 41 mm carapace length for female and 33 mm carapace length for male red endeavour prawns. Sexual maturity is reached at approximately 6 months of age and around 24–26 mm carapace length.

This is the first stock assessment conducted on Queensland east coast endeavour 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, however this did not lead to outcomes that were considered plausible by the project team.

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 (1970–1988), 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.

Fourteen 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. Project team preferred scenario results indicated that the endeavour prawn stock experienced a decline from the period 1958 to 1997 to reach 34% of unfished biomass. The biomass has been steadily rising since this time, and in 2021 the stock level was estimated to be 69% of unfished biomass (54–87% range across the 95% credible interval).