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Australia’s catch of Yellowfin Tuna taken out of the Western and Central Pacific Ocean stock is sustainable. In contrast, the Indian Ocean stock is depleting. The separate biological stocks are managed by international commissions as a resource shared by many countries that includes Australia.

Yellowfin Tuna in the Indian Ocean, and Western and Central Pacific Ocean are considered to be two distinct biological stocks and are managed by separate regional fisheries management organisations. The Indian Ocean stock falls under the jurisdiction of the Indian Ocean Tuna Commission (IOTC) while the Western and Central Pacific Ocean stock falls under the jurisdiction of the Western and Central Pacific Fisheries Commission (WCPFC). These two commissions are international organisations established to manage a number of highly migratory fish species within their defined geographic ranges.

In the Indian Ocean, analysis from a recent genetics and otolith microchemistry study found evidence for two distinct groupings of Yellowfin Tuna [Davies et al. 2020]. However, as the spatial delineation of these groups remains unclear [Davies et al. 2020], the IOTC stock assessment for Yellowfin Tuna [Nishida and Kitakado 2021] has continued on the assumption of a single biological stock. More detailed studies of Yellowfin Tuna stock structure in the Indian Ocean are underway and will inform future stock assessments. 

Similarly, although there is some evidence of genetically distinct populations of Yellowfin Tuna in the Pacific Ocean [Grewe et al. 2015; Evans et al. 2021], the findings are not sufficient to define biological stock boundaries, and thus stock assessments assume a single biological stock within the Western and Central Pacific Ocean (defined as west of 150 ºW) [Vincent et al. 2020]. 

Here, status is presented at the biological stock level—Indian Ocean and Western and Central Pacific Ocean.

Indian Ocean

The Indian Ocean biological stock of Yellowfin Tuna is fished by Australian fishers endorsed to operate in the Western Tuna and Billfish Fishery (Commonwealth), and members of the Indian Ocean Tuna Commission. The regional stock assessments undertaken by the Indian Ocean Tuna Commission account for information from all jurisdictions.

In the Indian Ocean, the most recent assessment [IOTC 2021] estimates that the biomass in 2020 of the biological stock was 31% of the 1950 (assumed unfished) levels (80% confidence interval 24–38% across the grid of models used). The biological stock is not considered to be recruitment impaired.

The assessment estimated that fishing mortality was above the level associated with maximum sustainable yield (MSY) (132% of fishing mortality at MSY; 80% confidence interval 68–195%). This level of fishing mortality increases the likelihood of the stock becoming recruitment impaired.

Due to ongoing technical challenges and issues associated with the assessment, the IOTC Scientific Committee has recommended that the most recent assessment be subject to an independent peer review [IOTC 2021].

Based on the evidence provided above, the Indian Ocean biological stock is classified as a depleting stock.

Western and Central Pacific Ocean

The Western and Central Pacific Ocean biological stock of Yellowfin Tuna is fished by Australian fishers endorsed to operate in the Eastern Tuna and Billfish Fishery (Commonwealth), and members of the Western and Central Pacific Fisheries Commission. The assessments undertaken for the Western and Central Pacific Fisheries Commission account for information from all jurisdictions that take Yellowfin Tuna in this region.

In the Western and Central Pacific Ocean, the most recent assessment [Vincent et al. 2020] estimates that the median recent spawning stock biomass was 58% of the levels predicted to occur in the absence of fishing (80% confidence interval 51–64% across the grid of models used). The probability that the recent spawning stock biomass had breached the limit reference point (LRP) of 20% of unfished levels was zero [WCPFC 2021]. The biological stock is not considered to be recruitment impaired. This assessment estimated that median recent fishing mortality was below the level associated with MSY (36% of mortality at MSY; 80% confidence interval 27–47%). The probability that the recent fishing mortality was above the level associated with MSY was zero. This level of fishing mortality is unlikely to cause the stock to become recruitment impaired.

Significant concerns and problems were found with the 2020 Yellowfin Tuna assessment and modelling approach and a cautionary approach was applied when interpreting the assessment outcomes to guide management decisions. Though the assessment was accepted, an independent review was recommended [WCPFC 2020]. An updated assessment addressing the concerns raised is currently being finalised.

Based on the evidence provided above, the Western and Central Pacific Ocean biological stock is classified as a sustainable stock.

Yellowfin Tuna biology [Itano 2000; Froese and Pauly 2009; Farley et al. 2020]

Distribution of reported Australian commercial catch of Yellowfin Tuna in 2021

Commercial (catch). Catches reported for the Indian Ocean Tuna Commission and Western and Central Pacific Fisheries Commission are for 2021, the most recent year available. 

Commonwealth – Recreational. The Australian Government does not manage recreational fishing in Commonwealth waters. Recreational fishing in Commonwealth waters is managed by the state or territory immediately adjacent to those waters, under its management regulations.  

Commonwealth – Indigenous. The Australian Government does not manage non-commercial Indigenous fishing in Commonwealth waters, with the exception of the Torres Strait. In general, non-commercial Indigenous fishing in Commonwealth waters is managed by the state or territory immediately adjacent to those waters. 

Commercial catch of Yellowfin Tuna - note confidential catch not shown

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