Table 1: Stock status determination for Bigeye Tuna
Jurisdiction |
Commonwealthb |
Stock |
Indian Ocean
(IOTCd, WTBF) |
Pacific Ocean
(ETBF, WCPFCe) |
Stock status |
|
↓ |
Sustainable |
Transitional–depleting |
Indicators |
Spawning stock biomass, fishing mortality |
Spawning stock biomass, fishing mortality |
ETBF = Eastern Tuna and Billfish Fishery (Commonwealth); IOTC = Indian Ocean Tuna Commission; WCPFC = Western and Central Pacific Fisheries Commission; W TBF = Western Tuna and Billfish Fishery (Commonwealth)
The Indian Ocean and Pacific Ocean are considered to comprise two distinct biological stocks and are managed under separate regional fisheries management organisations. Genetic studies have indicated a single biological stock across the Pacific Ocean1. In the Indian Ocean, tagging studies have indicated large movements of Bigeye Tuna, supporting the assumption of a single biological stock2. The Indian Ocean biological stock is under the jurisdiction of the Indian Ocean Tuna Commissiond. The Pacific Ocean stock is under the jurisdiction of the Western and Central Pacific Fisheries Commissione. Since biological stock delineation is known, status is reported at the level of individual biological stocks.
The data used to determine stock status are from 2008 or 2009 because of lags in reporting catch data to the Indian Ocean Tuna Commission and the Western and Central Pacific Fisheries Commission.
Indian Ocean biological stock
In the Indian Ocean, the most recent assessment3 estimated that the biomass of the Bigeye Tuna biological stock in 2009 was 34 per cent of initial unfished biomass. The biological stock is therefore unlikely to be recruitment overfished. This assessment also estimated that fishing mortality in 2009 was below the level associated with maximum sustainable yield (MSY) (79 per cent of mortality at MSY). This level of fishing mortality is unlikely to cause the biological stock to become recruitment overfished. On the basis of the evidence provided above, the Indian Ocean biological stock is classified as a sustainable stock.
Pacific Ocean biological stock
In the Pacific Ocean, the most recent assessment4 estimated that biomass of the Bigeye Tuna biological stock in 2008 was 32 per cent of initial unfished biomass. The biological stock is therefore unlikely to be recruitment overfished. This assessment also estimated that fishing mortality was well above the level associated with MSY (128–197 per cent of mortality at MSY). The current fishing mortality is likely to cause the biological stock to become recruitment overfished. On the basis of the evidence provided above, the Pacific Ocean biological stock is classified as a transitional–depleting stock.
Table 2: Bigeye Tuna biology5
Longevity and maximum size |
~16 years; 200 cm FL |
Maturity (50%) |
~3 years; ~100 cm FL |
FL = fork length
Figure 1: Distribution of reported commercial catch of Bigeye Tuna in Australian fisheries, 2010
- Pelagic longline is used to fish for Bigeye Tuna, both in Australia and globally. Outside of Australian waters, juvenile Bigeye Tuna are also captured in other nation’s purse-seine fisheries targeting Skipjack Tuna, especially when fish-aggregating devices are deployed.
- In Australia, Bigeye Tuna is managed using a range of input and output controls:
- Input controls include limited entry to the fishery through longline and minor-line boat statutory fishing rights, as well as gear and area restrictions.
- Output controls include total allowable commercial catches. These were in place in the Western Tuna and Billfish Fishery (Commonwealth) in 2010 and have been implemented in the Eastern Tuna and Billfish Fishery (Commonwealth) since March 2011.
- In the Western Tuna and Billfish Fishery (Commonwealth), there were 3 active longline vessels and 1 active minor-line vessel that caught Bigeye Tuna in 2010; in the whole Indian Ocean Tuna Commission Area of Competence, an estimated 3947 industrial vessels and several thousand artisanal vessels were active in 2009.
- In the Eastern Tuna and Billfish Fishery (Commonwealth) there were 54 active longline vessels and 3 active minor-line vessels that caught Bigeye Tuna in 2010; in the whole Western and Central Pacific Fisheries Commission Convention Area, 5274 industrial vessels and several thousand artisanal vessels were active in 2009.
- Australian catch of Bigeye Tuna in the Western Tuna and Billfish Fishery (Commonwealth) for the 2010 calendar year was 65 tonnes (t). Total Bigeye Tuna catches in the Indian Ocean Tuna Commission area for 2009 were 101 960 t.
- Australian catch of Bigeye Tuna in the Eastern Tuna and Billfish Fishery (Commonwealth) for the 2009–10 fishing season was 518 t. Total Bigeye Tuna catches in the Western and Central Pacific Fisheries Commission area for 2009 were 118 023 t. Estimates of Australian recreational and Indigenous catch are not available.
Figure 2: Commercial catch of Bigeye Tuna in the Western and Central Pacific Fisheries Commission and Indian Ocean Tuna Commission areas,
1970–2009 (calendar year)
Catches of Bigeye Tuna in the Western and Central Pacific Fisheries Commission area have been relatively stable since the late 1990s. Overall catches in 2009 declined slightly because of relatively high catches of smaller individuals in the purse-seine fishery and a reduction in the catch taken by longline. In the Indian Ocean Tuna Commission area, catches in the western Indian Ocean have been slowly declining, as a result of piracy off the coast of Somalia, which has deterred fishing effort. Australian catch of Bigeye Tuna peaked at 1156 t in 2001 in the Eastern Tuna and Billfish Fishery (Commonwealth) and 436 t in 2000 in the Western Tuna and Billfish Fishery (Commonwealth).
- Following completion of Ecological Risk Assessments in the Western Tuna and Billfish Fishery (Commonwealth), no species were identified as high risk6. In the Eastern Tuna and Billfish Fishery (Commonwealth), a total of nine species were identified as being at high risk or precautionary high risk. This is the priority list of species for attention under the Eastern Tuna and Billfish Fishery ecological risk management strategy; it includes two species of sunfish, four species of shark, two species of cetacean and one species of marine turtle7–8.
- No target species, ecological communities or habitats were assessed to be at high risk from the effects of fishing in the Eastern Tuna and Billfish Fishery (Commonwealth) or Western Tuna and Billfish Fishery (Commonwealth).
- Australia implements regulations to minimise the environmental impact of fisheries for tuna and tuna-like species on pelagic ecosystems, specifically on seabirds, sea turtles and sharks. Both the Indian Ocean Tuna Commission and the Western and Central Pacific Fisheries Commission have passed conservation and management measures that are broadly consistent with each other and with Australia’s domestic requirements.
- Australia has prohibited the practice of shark finning in longline fisheries managed by the Commonwealth and the use of wire traces in these fisheries, to reduce fishery impacts on sharks.
- The distribution and abundance of tuna can be affected by environmental factors9–10. For example, seasonal changes in the abundance of Bigeye and Yellowfin Tuna on the east coast of Australia are linked to the expansion and contraction of the East Australian Current11.
a Australian Bureau of Agricultural and Resource Economics and Sciences
b Information related to management arrangements in Australian fisheries has been updated to be current for 2012.
c The Indian Ocean Tuna Commission and the Western and Central Pacific Fisheries Commission are intergovernmental organisations established to manage a number of highly migratory fish species.
d www.iotc.org
e www.wcpfc.int