Stock assessment of black teatfish (Holothuria whitmaei) in Queensland, Australia, with data to June 2025

Abstract

Black teatfish, Holothuria whitmaei, is a target species of the Queensland Sea Cucumber Fishery due to its high value in Asian export markets. Although genetic analyses suggest a single biological stock spanning the Great Barrier Reef (GBR), this assessment separates black teatfish into two stocks. The northern and southern zones of the GBR fishery are split at 19 degrees south just north of Townsville.
Black teatfish have an average length of 27.38 cm and average whole weight of 1.8 kg. Length-at-maturity is estimated to be 26 cm.
A previous assessment estimated the stock in 2021 to be at 40–42% of unfished levels in 1877. Several key aspects of this assessment differ from the previous assessment. Firstly, two stocks were modelled rather than a whole GBR stock. Secondly, the present assessment was performed using Stock Synthesis whereas the previous assessment was performed using an age-structured surplus production model. Thirdly, the previous assessment considered historical catches and modelled the population between 1877 and 2021. The present assessment did not include these historical catches and modelled the north stock between 1989 and 2026 and the south stock between 1996 and 2026. Finally, the previous stock assessment included surveyed estimates of 1996 biomass and 1999 biomass; the present assessment only considered the biomass estimate for 1999 from a different study which was based on the same survey information.
The assessment used an age-structured Stock Synthesis model with an annual time step, fitted to standardised catch rates, length composition data and biomass survey data. The model incorporated data spanning the period 1989–2025, collected from the commercial sector and fishery independent surveys.
The results of this assessment indicated that for the north stock, the biomass ratio at the start of 2026 was between 45% and 125% of an assumed unfished state in 1989.
The results of this assessment indicated that for the south stock, the biomass ratio at the start of 2026 was between 73% and 138% of an assumed unfished state in 1996.