Geography in the News: Bluefin Tuna Decline

Written by:
Hans Kruit, 20 November 2013

The Convention on International Trade in Endangered Species (CITES), an international agreement between governments, dealt a serious blow to the Atlantic bluefin tuna in March 2010. The convention voted to deny a proposed international ban on fishing and trading the bluefin. Many conservationists fear the overfished migratory tuna will completely disappear without the ban.

The Atlantic bluefin tuna (Thunnus thynnus) is commonly known as the Northern bluefin tuna. Highly migratory and sought after by many countries, bluefin tuna are found in the subtropical and temperate waters of the North Atlantic Ocean and the Mediterranean Sea.

Scientists know that small numbers of bluefin cross the Atlantic in as few as 60 days and are therefore widely distributed throughout the ocean. They are found from in the western Atlantic from Newfoundland, Canada, to the Gulf of Mexico. In the eastern Atlantic, they range from as far north as Norway south to northern West Africa. Once also found in the Black Sea, the bluefin is now believed to be extinct there.

Bluefin tuna can weigh up to 1,500 pounds (680 kg) and grow to lengths up to 9 feet (2.7 m), although they are more commonly found from 1.5-6.5 feet (0.5-2 m) in length.

If not for fishing, bluefins would live up to 30 years. Interestingly, bluefin tuna are warm-blooded and can thermoregulate. This means they can keep their body temperature higher than the surrounding water temperature, enabling them to live in cold waters. They can swim up to 70 miles per hour (113 km/hr). Bluefin tuna mostly live close to the water’s surface, hunting smaller species such as herring, mackerel, sardines, squid and crustaceans. They often reside in schools with other bluefins the same size.

Bluefin can migrate incredible distances, in some cases thousands of miles. Scientists have tagged bluefin in the Bahamas and re-captured those same fish in Norway and off the coast of Brazil. The International Commission for the Conservation of Atlantic Tunas (ICCAT) administers the Atlantic bluefin international fishery, although the fish’s migratory nature makes it very difficult to manage.

Historically, bluefin tuna were mostly fished for sport. However, when the Japanese specialty food market grew in the 1970s, tuna steaks, sushi and sashimi became more popular. A dramatic increase in fishing for tuna ensued.

Today, Japan consumes about 80 percent of the world’s bluefin catch. According to Business Week (May 17), bluefin is so prized in Japan that a two-inch (5 cm) piece of the fattiest part of the fish can cost more than 2,000 yen ($22) in a Tokyo restaurant.

Now, bluefin tuna populations are in decline. According to ICCAT studies, between 1957 and 2007 in the eastern and western Atlantic, bluefin populations dropped 74 percent and 82 percent respectively. Overfishing in the Mediterranean, where most eastern Atlantic bluefin are caught, combined with a low reproduction rate, contributes to the decline.

ICCAT data also show that from 1999 to 2007, fishermen caught as much as 66,000 tons (60,000 metric tons) a year of bluefin tuna. That number is almost twice the ICCAT-imposed quotas of between 32,500 and 35,250 tons (29,500 and 32,000 metric tons). In response, the ICCAT set the 2010 quotas to 14,800 tons (13,500 metric tons).

Japan lobbied hard against the ban on bluefin voted upon by CITES in March. The country hosted a sushi dinner for delegates and argued that the ban would be unfair to other countries that import the fish. Japan would prefer ICCAT manage the bluefin, though management is difficult as the fish migrate across international boundaries.