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Australia’s Bigeye Tuna stocks are sustainable in the Pacific Ocean and depleting in the Indian Ocean. The separate biological stocks are managed by international commissions as a resource shared by many countries, including Australia.

Bigeye 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 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, tagging and genetic studies have not provided evidence of more than a single biological stock [Chiang et al. 2008, IOTC 2019]. Genetic studies have also indicated a single biological stock across the Pacific Ocean [Grewe and Hampton 1998]. 

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

Indian Ocean

The Indian Ocean biological stock is fished by Australian fishers endorsed to fish in the Western Tuna and Billfish Fishery (Commonwealth), and members of the Indian Ocean Tuna Commission. The assessments undertaken by the Indian Ocean Tuna Commission take into account information from all jurisdictions that take Bigeye Tuna is this region.

In the Indian Ocean, the most recent assessment [IOTC 2019] estimates that spawning stock biomass in 2018 was 31 per cent of the unfished level (80 per cent confidence interval 21–34 per cent). The biological stock is not considered to be recruitment impaired [Williams et al. 2020]. This assessment also estimated that the current fishing mortality was above the level associated with maximum sustainable yield (MSY) (120 per cent of fishing mortality at MSY; 80 per cent confidence interval 70–205 per cent). This level of fishing mortality is likely to cause the biological stock to become recruitment impaired [Williams et al. 2020].

On the basis of the evidence provided above, the Indian Ocean biological stock is classified as a depleting stock.

Pacific Ocean

The Pacific Ocean biological stock is fished by Australian fishers endorsed to operatein 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 take into account information from all jurisdictions that take Bigeye Tuna in this region.

In the Pacific Ocean, the most recent assessment in 2017 [McKechnie et al. 2017] was re-evaluated in 2018 using a new growth curve [Vincent et al. 2018], but maintaining the other inputs of the 2017 assessment, and estimates that the recent median spawning biomass was 36 per cent of the unfished level (range 30–41 per cent). There was a zero probability that the recent spawning biomass breached the limit reference point [WCPFC 2019]. The biological stock is not considered to be recruitment impaired [WCPFC 2019, Larcombe et al. 2020]. This assessment also estimated that the median recent fishing mortality was 77 per cent of the level associated with MSY (range 67–93 per cent). This level of fishing mortality is unlikely to cause the biological stock to become recruitment impaired [Larcombe et al. 2020, WCPFC 2019].

On the basis of the evidence provided above, the Pacific Ocean biological stock is classified as a sustainable stock.

Commonwealth – Commercial (catch) Catches reported for the Indian Ocean Tuna Commission and Western and Central Pacific Fisheries Commission are for 2018, the most recent year available; data for the Eastern Tuna and Billfish Fishery and Western Tuna Billfish Fishery are for 2018/2019.

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 – Recreational and Indigenous Recreational and Indigenous fishing sectors in the Indian Ocean are Western Australia, South Australia and Victoria; recreational sectors in the Pacific Ocean are Queensland, New South Wales and Tasmania. Measures listed here exist in one of these jurisdictions.

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 Bigeye Tuna - note confidential catch not shown

1. Chiang, H-C, Hsu, C-C, Wu, GC-C, Chang, S-K and Yang, H-Y 2008, Population structure of Bigeye Tuna (Thunnus obesus) in the Indian Ocean inferred from mitochondrial DNA, Fisheries Research, 90: 305–312.
2. Davies, C, Marsac, F, Murua, H, Fraile, I, Fahmi, Z, Farley, J, Grewe, P, Proctor, C, Clear, N, Lansdell, M, Aulich, J, Feutry, P, Cooper, S, Foster, S, Rodríguez-Ezpeleta, N, Artetxe, I, Nikolic, N, Krug, I, Mendibil, I, Agostino, L, Labonne, M, Darnaude, A, Arnaud-Haond, S, Wudiano, Ruchimat, T, Satria, F, Lestari, P, Taufik, M, Priatna, A, & Zamroni, A 2019, ‘Study of population structure of IOTC species and sharks of interest in the Indian Ocean using genetics and microchemistry: an update on progress and preliminary results’, paper submitted to the Scientific Committee Meeting, IOTC-2019-SC22-INFO-05, Karachi, Pakistan, 2 to 6 December 2019.
3. Farley, J, Eveson, P, Krusic-Golub, K, Clear, N, Sanchez, C, Roupsard, F, Satoh, K, Smith, N and Hampton, J 2018, ‘Update on age and growth of bigeye tuna in the WCPO WCPFC Project 81, working paper WCPFC-SC14-2018/SA-WP-01, WCPFC Scientific Committee fourteenth regular session, Busan, Republic of Korea, 8–16 August 2018.
4. Farley, J, Eveson, P, Krusic-Golub, K, Sanchez, C, Roupsard, F, McKechnie, S, Nicol, S, Leroy, B, Smith, N and Chang, S-K 2017, ‘Project 35: Age, growth and maturity of bigeye tuna in the western and central Pacific Ocean’, working paper WCPFC-SC13-2017/SA-WP-01, WCPFC Scientific Committee thirteenth regular session, Rarotonga, Cook Islands, 9–7 August 2017.
5. Farley, JH, Clear, NP, Leroy, B, Davis, TLO and McPherson G 2006, Age, growth and preliminary estimates of maturity of Bigeye Tuna, Thunnus obesus, in the Australian region, Marine and Freshwater Research, 57: 713–724.
6. Froese, R and Pauly DE 2009, FishBase, version 02/2014, FishBase Consortium.
7. Grewe, PM and Hampton, J 1998, An assessment of bigeye (Thunnus obesus) population structure in the Pacific Ocean, based on mitochondrial DNA and DNA microsatellite analysis, SOEST 98-05, JIMAR Contribution 98–320, Joint Institute for Marine and Atmospheric Research, University of Hawaii, Honolulu. 
8. Indian Ocean Tuna Commission 2019, Report of the twentieth session of the Scientific Committee, Karachi, Pakistan, 2–6 December 2019.
9. Larcombe, J, Patterson, H and Mobsby, D 2020, Eastern Tuna and Billfish Fishery, in H Patterson, J Larcombe, J Woodhams and R Curtotti (eds), Fishery status reports 2020, Australian Bureau of Agricultural and Resource Economics and Sciences, Canberra, pp. 377-399.
10. McKechnie, S, Pilling, G and Hampton, J 2017, ‘Stock assessment of bigeye tuna in the western and central Pacific Ocean’, working paper WCPFC-SC13-2017/SA-WP-05, WCPFC Scientific Committee thirteenth regular session, Rarotonga, Cook Islands, 9–17 August 2017.
11. Vincent, MT, Pilling, G & Hampton, J 2018, ‘Incorporation of updated growth information within the 2017 WCPO bigeye stock assessment grid, and examination of the sensitivity of estimates to alternative model spatial structures’, working paper WCPFC-SC14-2018/SA-WP-03, WCPFC Scientific Committee 14th regular session, Busan, Republic of Korea, 8–16 August 2018.
12. Western and Central Pacific Fisheries Commission 2019, Summary report of the fifteenth regular session of the Scientific Committee for the Western and Central Pacific Fisheries Commission, Pohnpei, Federated States of Micronesia, 12–20 August 2019.
13. Williams, A, Patterson, H and Mobsby, D 2020, Western Tuna and Billfish Fishery, in H Patterson, J Larcombe, J Woodhams and R Curtotti (eds), Fishery status reports 2020, Australian Bureau of Agricultural and Resource Economics and Sciences, Canberra, pp. 421-438.