Southern Bluefin Tuna Thunnus maccoyii

Global biological stock

The biological stock of Southern Bluefin Tuna is fished by Australian fishers endorsed to fish in the Southern Bluefin Tuna Fishery (Commonwealth), and numerous other international jurisdictions. As well, the species is caught by recreational fishers in the waters off southern Australia, and there are other sources of unaccounted mortalities, including catches by fleets that are not members of the Commission for the Conservation of Southern Bluefin Tuna (CCSBT^b)^2,3. The reported global catch peaked in the late 1950s before declining substantially; it has been relatively stable since the mid-2000s.

In 2011, the CCSBT adopted a management procedure (analogous to a harvest strategy) to guide the recovery of the biological stock to 20 per cent of unfished biomass by 2035 with 70 per cent probability. Performance of the management procedure is measured using the biomass of fish that are 10 years and older. Since 2012, the agreed management procedure has been used to set the global total allowable catch, which was set at 10 949 tonnes (t) in 2013. In line with this, Australia’s total allowable catch for the 2012-13 fishing season was 4 663 t, of which 4 529 t was landed. The current level of fishing mortality from all sources is uncertain, but there are indications that it may be substantial³. The most recent assessment (2014) undertaken by the CCSBT takes into account reported catch from all international jurisdictions³. It also examines the sensitivity of the results to unaccounted mortalities, based on scenarios given the uncertainty.

The most recent assessment estimated that the biomass of fish 10 years and older in the Southern Bluefin Tuna biological stock is at 6–9 per cent of unfished levels³. The most recent estimate of spawning stock biomass is 8–12 per cent of unfished levels³. Projections of the performance of the management procedure under scenarios of different levels of unaccounted mortalities showed that these mortalities reduce the probability of rebuilding to below 70 per cent, the specified interim management target³. Although there has been a slight improvement in the estimated biomass of fish 10 years and older since the last assessment in 2011⁴, the biological stock is recruitment overfished at a global scale, and well below the interim target level agreed by the CCSBT^2,3. The level of fishing pressure may prevent the stock from recovering from its recruitment overfished state in line with the management procedure, and a significant trend of improvements in biomass is yet to be detected.

On the basis of the evidence provided above, the biological stock is classified as an overfished stock.