Current Status: Critically Endangered (Western stock)

“Close your eyes. Think fish. Do you envision half a ton of laminated muscle rocketing through the sea as fast as you drive your automobile? Do you envision a peaceful warrior capable of killing you unintentionally with a whack of its tail? These giant tuna strain the concept of fish.” – Carl Safina, Song for the Blue Ocean¹

The Atlantic bluefin tuna (Thunnus thynnus) is so depleted by overfishing that many have called for its listing as an endangered species like the great whales before it, yet current management measures under the International Commission for the Conservation of Atlantic Tunas (ICCAT) have failed to end unsustainable fishing. Both commercial and recreational fisheries pursue the North Atlantic bluefin tuna, the former for its highly prized meat for sushi and steaks and the latter primarily for the prestige of catching such a fierce fish. Ever since the early 1970’s, the spawning stock biomass (total population mature enough to spawn) has decreased rapidly as more young, immature Atlantic bluefins have been caught before they can spawn. Current biomass levels have fluctuated for the past few years at about 20% of the stock spawning biomass in 1975.²

Biology and Ecology

Bluefin tuna are recognized as two distinct Western and Eastern stocks in the North Atlantic. The Western Atlantic stock spawns in the Gulf of Mexico while the Eastern Atlantic stock spawns in the Mediterranean Sea. The bluefin has evolved over time to travel long distances in search of food, and is built for speed and efficiency; some individuals can cross the Atlantic in only 60 days.³ This means both stocks have a wide habitat range, from Newfoundland to the Caribbean in the West and from Greenland to the Canary Islands in the East. Tagging studies confirm that the ranges of both stocks overlap in the Atlantic while feeding. However, tagging studies have also confirmed that these two stocks are distinct breeding populations. Bluefin can live up to 20 years, possibly longer. Because they live so long they are slow to mature; the Eastern stock is assumed to first begin spawning at the age of four or five and the Western stock at age eight. They can grow to nearly 10 feet and can weigh more than 1,400 pounds.⁴

The bluefin tuna’s diet consists mainly of smaller schooling fish such as mackerel, herring, whiting, flying fish, and mullet, as well as squid and some crustaceans.⁵ These so-called forage fish are a main source of food for many top predators in the oceans. The availability of forage fish to bluefin tuna and other predatory fish, mammals and seabirds is increasingly threatened by large-scale commercial reduction fisheries that grind up vast quantities of forage fish and convert them into fishmeal to be used as feedstock for domestic livestock, the aquaculture industry, and pet foods (for more information see www.foragefish.org ).

In 1969, the International Commission for the Conservation of Atlantic Tunas (ICCAT) was established in order to protect a range of Atlantic tuna species, including the bluefin. By 1982, ICCAT set up regulations including catch quotas for Western Atlantic bluefin, then began regulating the Eastern Atlantic stocks in 1994. Despite this regulation, biennial stock assessments by ICCAT reveal that both Western and Eastern stocks are overfished and are still experiencing overfishing.⁶ Analysis by ICCAT revealed an estimated decrease of 82.4% in spawning stock biomass since 1970.⁷

Figure 1: the spawning stock biomass of Atlantic bluefin tuna in millions of tons.⁸

One reason the catch quotas are ineffective is that bluefin tuna are a transboundary species. Because they migrate through the territorial waters of many different countries, controlling fishing mortality on these fish is very difficult. The fact that there is no way to distinguish between the Eastern and Western stocks while fishing means that a high level of international cooperation is necessary to protect the species.

Earlier this year, Monaco petitioned the Convention on International Trade in Endangered Species (CITES) to ban all international commercial trade in bluefin tuna in hopes that this ban would effectively reduce the incentive to continue overfishing. The United States supported the proposed ban at the CITES meeting in March 2010, but the proposal was opposed by Japan, Canada and other fishing nations who claimed that ICCAT was sufficient to manage the stocks. The proposal was defeated by a vote of 20 votes for and 68 against.⁹

Bluefin Tuna and the Gulf Oil Gusher

The current oil spill in the Gulf of Mexico poses a serious threat to the Western Atlantic bluefin tuna stock because the Gulf of Mexico is where the population spawns. Spawning begins mid-April and lasts through June, and the oil spill is currently moving over the preferred spawning area of the bluefin. In a recent study it was discovered that bluefin tuna, unlike their close relative yellowfin tuna that also spawns in the area, have a high fidelity to two particular regions of the Gulf of Mexico for spawning: one in the east and one in the west along the slope where the continental shelf meets the deep sea. The bluefin will return to these regions in the spring for cyclonic eddies of slightly cooler more productive waters, and unfortunately the east spawning region is being encroached upon by the Deepwater Horizon oil spill.¹⁰

Figure 2: The movements of a tagged bluefin tuna in the Gulf of Mexico with an overlay of the Deepwater Horizon rig oil spill as of May 24, 2010.¹¹

It is considered likely that the larger, mature fish have already left the area and are moving back north, but the concern is for the eggs and larvae left behind. The larval stage of the Atlantic bluefin tuna is when the fish is most susceptible to the toxic effects of oil, and neither the eggs nor the larvae are able to move away from the likely lethal oil.^{12, 13}

The serious effects of the oil spill may not be immediately seen in the Western Atlantic bluefin tuna stocks, as with many other species impacted by the spill, but the long term effects may be seen years down the road when the population declines because very few fish survived this spawning season.¹⁴

Action Items

Want to do more? Many of our member groups are actively involved in bluefin tuna conservation and the oil spill response; here are some of their campaigns:

The Pew Charitable Trusts

The Gulf Restoration Network   

Greenpeace

Environment Florida

*FOOTNOTES LINK