Bluefin Tuna

Bluefin tuna is one of the largest tuna species. The popularity of bluefin tuna is reflected in highly lucrative global tuna markets. Estimated to be worth more than $10 million annually, Canada’s bluefin tuna fishery is the target of more than 750 licensed harvesters.

The species is distributed throughout the Atlantic and Pacific oceans in subtropical and temperate waters, as well as in the Indian Ocean. The Atlantic bluefin tuna fishery is conducted in Canadian waters over the Scotian Shelf, in the Gulf of St. Lawrence, in the Bay of Fundy, and off the coast of Newfoundland. The fishing season is related to the highly migratory pattern of tuna and generally takes place between July and November when tuna migrate into Canadian waters.

Because bluefin migrate long distances, and fisheries for bluefin often occur on the high seas, international co-operation is necessary for management decisions:

• Atlantic bluefin tuna is managed by the 48-member International Commission for the Conservation of Atlantic Tunas (ICCAT)
• Bluefin tuna in the north Pacific is co-operatively managed by two regional fisheries management organizations: the 16-member Inter-American Tropical Tuna Commission (IATTC) and the 26-member Western and Central Pacific Fisherienes Commission (WCPFC).
• Southern bluefin tuna, which frequents both the Pacific and Indian Oceans, is managed by the five-member Commission for the Conservation of Southern Bluefin Tuna (CCSBT).

The popularity of bluefin tuna in highly lucrative markets has led to extensive exploitation in several areas. Canada has been a strong advocate for conservation and taking the precautionary approach to stock management. While ICCAT has been slow in implementing these approaches, particularly in the Eastern Atlantic and the Mediterranean, stronger measures adopted in 2009 are encouraging. Canada will continue to press the ICCAT Members to follow through on these commitments.

Information below on the status of bluefin stocks has been gleaned from the 2008 assessment of ICCAT’s Standing Committee on Research and Statistics and the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean. Refer to: www.iccat.int/Documents/SCRS/ExecSum/BFT_EN.pdf and http://isc.ac.affrc.go.jp/isc8/ISC8rep.html for more details.

Eastern Atlantic and Mediterranean Bluefin Tuna

The ICCAT assessment indicates that the spawning stock biomass of this stock continues to decline while fishing mortality is increasing rapidly, especially for big tuna that are then fattened in cages for the sashimi and sushi market.

The scientific advice for this fishery determined several years ago that a total allowable catch of 15,000 tonnes (t) would be sustainable and after years of overfishing and pressure from Canada and its allies, ICCAT members who fish this stock have now reduced their quota to a sustainable level.

Western Atlantic Bluefin Tuna

The total catch of Western Atlantic bluefin, including discards, has been relatively stable since 1982, due to the imposition of quotas. However, while Canadian catch levels have remained generally stable, U.S. catch levels have declined considerably, and these differences are reflected in the total catch level of the Western Atlantic bluefin stock. From 3,319t in 2002, total catch in this area has declined steadily to 1,624t in 2007. At the 2008 annual meeting of ICCAT, members adopted a lowered overall quota of 1,900t for 2009 and 1,800t in 2010 to achieve stock objectives outlined in the Western bluefin tuna recovery plan. Canada’s share of this total catch will be a little more than 500t in each year.

Satellite tagging conducted by Canadian and American scientists, as well as recent origin of birth studies, have revealed that the bluefin tuna fished by Canadian harvesters were born in the Gulf of Mexico, whereas the birth origin of bluefin harvested in U.S. waters included both the Gulf of Mexico and the Mediterranean Sea. While research in this area continues, the results of these studies provide evidence of the ‘mixing’ of Western and Eastern Atlantic stocks. This is important because the severe overfishing that has been taking place in the Eastern Atlantic and Mediterranean Sea might have seriously impeded the health of Western bluefin. Age-growth studies conducted by Canadian and American scientists may also improve future assessments of Western Atlantic bluefin because new growth data will be used to better reflect the characteristics of the Western bluefin stock within the bluefin tuna growth model.

Northern Pacific Bluefin Tuna (Eastern and Western Pacific)

It is assumed that there is one single stock of Pacific bluefin that spawn in waters between the Philippines and Japan before migrating more than 11,100 kilometres to the Eastern Pacific, only to return to their birth waters to spawn again. Most bluefin catches in the Eastern Pacific Ocean are taken by purse seiners from May through October. Bluefin caught in the Western Pacific are exploited by various gears at different times of the year: trolling from July to October of younger fish about 15-30 cm in length; trolling from November to April of younger fish about 35-60 cm in length; purse seining of older fish from May to September; and other gears (traps, gillnets, pole-and-line, longlining) throughout the year. The total catch of Pacific bluefin tuna has fluctuated widely from 1952 to 2004: from 9,000t to 40,000t.  Recent catch is near the average for this period (~22, 000 t). Canada does not have a directed Pacific bluefin tuna fishery nor is Pacific bluefin tuna caught incidentally by its albacore fishery.

The most recent stock assessment of Pacific bluefin tuna was conducted in 2008 by the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific. It noted that while the spawning biomass is currently at historically median levels at 20,000 t, the recruitment of young fish (age 0) is highly variable, catch weight is dominated by young fish and juveniles (ages 0 to 3), and current fishing mortality is greater than the reference points that are generally used by scientists as potential target for fishing mortality. The Committee also assessed the effects of environmental changes on these tuna. Based on their observations and uncertainties, the Committee advised that current levels of fishing could continue if environmental conditions remained the same, but they also noted that if fishing effect was reduced, it could, over time, lead to higher yields. Finally, the Committee cautioned that increases in current fishing levels or any unfavourable changes in environmental conditions might reduce recruitment and noted that this would be cause for concern.

Southern Pacific Bluefin Tuna

Southern bluefin tuna are found throughout the southern hemisphere mainly in waters between 30 and 50 degrees south. The only known breeding area is in the Indian Ocean, south-east of Java, which takes place from September to April. From December to April, bluefin tend to congregate near the surface of the coastal waters off the southern coast of Australia, and spend the winter months in deeper, temperate oceanic waters. After age five, Southern Pacific bluefin are seldom found in near shore surface waters. The main method for catching Southern Pacific bluefin is longline fishing, except in Australia, where the fishery is conducted using purse seiners.

According to the CCSBT’s Scientific Committee report in 2008, overall recruitment levels of southern bluefin tuna remain lower than the 1990s and considerably lower than the 1980s. Major quota holders in 2008 were Australia at 5,265t and Japan at 3,000t.