4. The large pelagic fishes
Tunas - Porsches of the SeasNorthern Bluefin Tuna (Thunnus thynnus)Big, fast, and valuable, a large northern bluefin tuna measures three metres long, weighs more than 600kg, and can accelerate to speeds of up to 80 kph. The bluefin's red oily flesh is much prized in Japan for gourmet sushi and sashimi, commanding enormous prices in the Tokyo fish markets. A large bluefin which can fetch over US$30,000 on the dockside, will sell at a Tokyo auction for US$60,000, and cost the customer US$200 a plate at a sushi bar. Eighty-five percent of Japan's bluefin tuna imports come from the Pacific, Indian, and eastern Atlantic Oceans, but Atlantic bluefins reach a greater size than those in the Pacific and are the most sought-after. Of the 13 species of tunas, those belonging to the genus Thunnus are subjected to the most intensive commercial fishing. The bluefin tunas, T. thynnus (northern bluefin), and T. maccoyi (southern bluefin) have suffered dramatic declines in the past few decades. Northern bluefin are pelagic but often frequent shallow coastal waters. Highly mobile, they make seasonal migrations which appear to be tied to spawning behaviour, water temperature, and prey concentrations. Tagged northern bluefin have travelled 7,770km across the Atlantic in 119 days - an average distance of 65km per day. Bluefin are social animals, forming large `peer' schools in which individuals of similar size are found together. Current data suggests that although there are two populations of northern bluefin in the Atlantic, there is only a single population in the Pacific, spawning in the western part of the ocean around Japan, and between Japan and the Philippines. At different stages of life, parts of this population migrate to the eastern Pacific but the extent and significance of these movements is not known. In the eastern Pacific, bluefin migrate northward from Baja California to the Gulf of Alaska. In the western Pacific , around Japan, they migrate north in summer and south in winter, and are found as far south as the Philippines.
In the western Atlantic, giant northern bluefin arrive in the warm waters of the Gulf of Mexico to spawn in January. Here they remain until June, migrating north for another feeding season off New England and maritime Canada after spawning is completed.
Only one other spawning ground - in the Mediterranean - is known for Atlantic bluefin.
Atlantic tunas have been under the management jurisdiction of the International Commission for the conservation of Atlantic Tunas (ICCAT)since it was established in 1966. ICCAT's 21 member countries include the major fishing nations with their powerful vested interests, so perhaps it is not surprising that the commission's efforts to manage bluefin have been largely unsuccessful. Conservationists have accused ICCAT of procrastination at best, and malign neglect due to conflicts of interest at worst. Although ICCAT has recommended specific quotas for western Atlantic bluefin, it has never adopted a recovery target or schedule for bluefin tuna or any species. As far back as 1981, ICCAT's scientists were recommending drastically reduced catches of western Atlantic bluefin, but the commission chose instead to set quotas which have proved completely unsustainable. A catch of 2,660 metric tonnes imposed in 1983 remained in force until 1991, but bluefin populations continued their inexorable decline with no recovery in sight. A proposal by Sweden in 1991 to list the western Atlantic bluefin population on Appendix 1 of CITES, and thereby shut down international trade, was fiercely opposed at the 1992 CITES meeting by Japan, the USA, and Canada, together with lobbyists from the tuna industry. Similarly, intense pressure led to the bluefin issue being completely withdrawn form the agenda of the 1994 CITES meeting. Under growing international criticism, ICCAT has recently agreed to some modest conservation measures, including a Statistical Document Programme that requires the monitoring of international trade in bluefin. In 1995, ICCAT asked its scientific committee for a new stock assessment and recovery options that could be taken for bluefin. These will be considered at the ICCAT annual meeting in late 1996. Today, ICCAT views the western and eastern Atlantic populations of bluefin as entirely separate and distinct. But recent studies suggest that there may be some mixing of the two - perhaps a 3 per cent west to east exchange across the Atlantic. However, it is still unclear whether individuals always return to their original spawning area to breed. This uncertainty has profound implications for conservation of bluefin in the western Atlantic. If some of the adults found in the western Atlantic are from the eastern population which return to the Mediterranean to spawn, then the actual breeding stock in the western Atlantic may be even lower than feared. ICCAT scientists will address this issue as part of the scheduled stock assessment and recovery planning exercise in 1996. |
Copyright 1996, The World Wide Fund For Nature