Lates calcarifer (barramundi) is a diadromous species consisting of seven genetic stocks in Queensland. All stock regions were assessed, except for the lesser fished regions of Princess Charlotte Bay and the South-East Coast, which had insufficient information. The Queensland stocks are genetically different to the stocks of the Northern Territory.
Barramundi are relatively long lived with some specimens reaching 20 to 35 years. They mature (mostly) as males first before changing into females, and move between salt and freshwater. Barramundi populations are environmentally driven, with river-flow affecting their growth, survival, and catchability.
Recent commercial catch in 2017 was around 839 tonnes in all of Queensland. With respect to the five genetic stocks considered in this assessment, the commercial catch in 2017 was 614 tonnes in the Southern Gulf of Carpentaria, 32 tonnes in the Northern Gulf of Carpentaria, 81 tonnes in the North East Coast, 55 tonnes in the Mackay, and 47 tonnes in the Central East Coast.
To assess the status of each barramundi stock, an age-structured population model with an annual time step was applied. The model data inputs included annual barramundi harvests, catch rates, age frequencies and life history characteristics.
The current stock assessment updates previous assessments by considering an age-structured model rather than a simple surplus model (as per Campbell 2007) for the five main genetic barramundi stocks. It also incorporates changes in legal size limits as well as a scenario analysis considering the effects of recreational harvest.
The model uses commercial catch data from 1988 to 2017 on the East Coast of Queensland and from 1989 to 2017 in the Gulf of Carpentaria. For scenario analyses, recreational survey data were used. For all but the Northern Gulf stock, length-and-age frequency data, collected by Fishery Monitoring (Fisheries Queensland) from commercial samples from 2000 to 2017 were incorporated in the model.
The assessment provides estimates of exploitable biomass in 2017 relative to 1988-89 levels and recommends Total Allowable Commercial Catches for five of the seven stocks
