Stock assessment of Queensland east coast common coral trout (Plectropomus leopardus), Australia, with data to December 2021

Abstract

Queensland’s common coral trout (Plectropomus leopardus), a species of grouper, is a line-caught fish forming a single population (stock) across the Great Barrier Reef. The stock extends north from the Great Barrier Reef into the eastern Torres Strait where it is under Australian jurisdiction. There is evidence to suggest that common coral trout stay on the same individual reefs after settlement as larvae, and their larvae do not travel long distances after spawning, so the Torres Strait component of the harvest is not considered in the assessment. Common coral trout are protogynous hermaphrodites (born female, many later changing sex to male) and aggregate to spawn during spring and summer. They can grow to more than 5 kg and live for more than 18 years.

This assessment builds on previous assessments that estimated the stock was at 60%, 68% and 59% of unfished biomass in 2012, 2019 and 2020 respectively. This stock assessment includes updates to the input data but keeps the methodology in line with the 2020 assessment. This stock assessment was conducted on calendar years and included input data through to December 2021.

This assessment used a single-sex, age-structured population model, fit to age and length data, constructed within the Stock Synthesis modelling framework. The model was spatially structured with two subpopulations: a “blue region” subpopulation, associated with reefs in the Great Barrier Reef that remained open to fishing after the introduction of the Representative Areas Program in 2004; and a “green region” subpopulation, associated with reefs that have been closed to fishing since the introduction of the Representative Areas Program.

Five scenarios were run, covering a range of modelling assumptions. Base case (most plausible) results suggested that biomass declined between 1953 and 2011 to 46% unfished biomass. At the beginning of 2022, the stock level was estimated to be 60% (50–70% range across the 95% confidence interval) of unfished spawning biomass.