Information on the status of the Atlantic bluefin tuna (Thunnus thynnus) populations

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1 Information on the status of the Atlantic bluefin tuna (Thunnus thynnus) populations General points: The exploitation of the Atlantic bluefin tuna in the Mediterranean Sea dates back to the first millennium B.C. and already at that time the Romans took advantage of the bluefin tuna s migratory patterns for spawning purposes in order to capture it. Catches of bluefin tuna did not remain stable over the first thousand years of exploitation, showing significant fluctuations in the long term, which may have been due to environmental changes in the migratory routes of the bluefin tuna. The Atlantic bluefin tuna (Thunnus thynnus) is a fish that plays a key role in the ocean food chain. The bluefin tuna can live up to forty years, measure up to 4 metres long and weigh over 700 kilograms. As they have a warm-blooded metabolism, they are capable of stabilising their body temperature whenever they dive down to depths of over 900 metres into cold waters. The species is also known for its potential to attain the highest commercial prices on international markets with unit prices capable of reaching over 150,000 US$. The extremely high prices paid for the Atlantic bluefin tuna, boosted by the international sushi market, have led to increasing and uncontrolled overfishing, threatening the species with extinction. Biology of the bluefin tuna: Juvenile and adult bluefin tuna are opportunistic eaters (like most predators) and their diet may include jellyfish, salps, as well as octopus, crab and sponges. Juveniles feed mainly on crustaceans, fish and cephalopods, whilst adults chiefly eat fish, mostly herrings, anchovies, sand-eels, sardines, sprats, bluefish and mackerel. The fish hatched in June, measure approximately cm and weigh around 1 kg by October. One year later, they will have reached 4 kg and 60 cm. Whilst their weight increases, growth in length tends to be lower in adults than in juveniles. When it reaches 10 years old, a bluefin tuna measures close to 200 cm and weighs 150 kg, and approximately 300 cm and 400 kg at the age of 20. The bluefin tuna is long-lived with a lifespan of up to 40 years, as recent studies using radiocarbon dating have shown. Several observations suggest that a single female does not spawn every year but every two or three years in the month of June. Geographical distribution of bluefin tuna populations and reproductive biology The International Commission for the Conservation of Atlantic Tunas (ICCAT), the Regional Fishery Organisation in charge of assessing the status and managing the Bluefin Tuna, has divided the latter into two entities, separated by the 45 W meridian line: the Eastern stock and the Western stock, with their spawning grounds in the Eastern Mediterranean, and the

2 Gulf of Mexico in the west. These are identified spawning areas, but it is not impossible that the species may reproduce in an opportunistic manner in other areas should the conditions it finds be favourable. Even prior to the advent of industrial fishing, the Western stock was 10 times lower than the Eastern stock, for various ecological reasons. For example, the Mediterranean bluefin tuna (Eastern stock) becomes mature at the age of 4 (approximately 25 kg) whilst those in the Gulf of Mexico (Western stock) become mature at approximately 8 years old (approximately 140 kg). Collapse in bluefin tuna stocks and eligibility for listing on CITES appendix I ICCAT scientists predicted that if the current level of fishing mortality continued, the Eastern Atlantic spawning stock would fall to 18% of the 1970 level and only 6% of the historical level. This trend is corroborated by the dramatic decline in the mean size of fish caught. - The decline in the Western Atlantic stock was 80% between 1970 and The decline in the Eastern Atlantic stock was 74.3% between 1955 and Evolution in the biomass of the reproductive population of bluefin tuna (Eastern Atlantic and Mediterranean) (Source: SCRS, 2008) For the Eastern Atlantic stock (the largest), the current rate of decline of the population is 3.2% per year.

3 2. Information on the recent decline of the population (blue line) taken from SCRS ICCAT, bluefin tuna stock assessment, 2008; dashed red line on forecasted trajectory of the population estimated by WWF. The population has been cut by half in less than 5 years ( ). If nothing is done, spawners might become virtually extinct by As far as the Western Atlantic stock is concerned, only very few reproductive individuals remain in the Gulf of Mexico. Furthermore, fishing of the bluefin tuna is prohibited in the Gulf of Mexico. The entire panel of experts, with the exception of the Japanese, representing the members of the Food and Agriculture Organisation of the United Nations (FAO), established that the Eastern and Western populations of the Atlantic bluefin tuna both meet the biological criteria set by CITES to list the bluefin tuna on appendix I. What are the CITES criteria? For a commercially exploited aquatic species, such as the bluefin tuna, the population, evaluated in tons of biomass, must fall below the threshold fixed at 15% of the maximum historical level (also called virgin biomass ) These criteria are defined in CITES resolution Conf (Rev. CoP14)

4 What are the key figures for the bluefin tuna? The maximum historical level has been estimated at between 1 million and 10 million tons, which makes the 15% threshold approximately 150,000 tons. The information collected and available on the Atlantic bluefin tuna clearly shows that Western and Eastern stocks of the species are consistent with the criteria for appendix I ( Several other elements give us an idea of the current level of deterioration of the populations and the length of time necessary to enable bluefin tuna stocks to replenish: ICCAT scientists estimate that if fishing ceases in 2010, there is a 67% probability that by 2019 the biomass will be beneath the 15% threshold, in other words, there is only a 33% chance that stocks will recover to a level of above 15%. According to the data on the recent decline of the population (blue line) taken from SCRS ICCAT, bluefin tuna stock assessment, 2008, the population has been cut by half in less than 5 years ( ). According to a 2009 study by Oshida et al. presented to the SCRS last year (and approved by the ICCAT), if fishing continues by limiting catches to 8,000 tons, the probability of achieving a stock regeneration whereby the biomass level reaches the maximum sustainable yield (MSY) within 10 years (by 2019), is scarcely 50%. This biomass level, which would enable the MSY to be attained, is naturally very much inferior to that of the virgin biomass (or maximum historical level). Conclusion: The increase in the market value of bluefin tuna has led to the growth of sea-ranching in the Mediterranean: captured alive using a seine net, the tuna are towed in floating cages and then kept in cages anchored close to the shore. They are fed with small pelagic fish mainly caught off the African coast. They are fattened in captivity until the quality of their meat meets the requirements of Japanese importers. Since 2006, it has been a commonly acknowledged fact that in the Mediterranean the fishing capacity of the fleets of seining vessels (over 250 boats), longliners and artisanal fisheries largely exceeds the production capacity of the resource. The extremely lucrative sushi and sashimi market, which ignores quotas, encourages illegal fishing by scorning the recommendations and warnings of scientists. All estimations show that the Atlantic bluefin tuna population is on the verge of collapse. Time is running out and the time has come to add the Atlantic bluefin tuna to appendix I of CITES.

5 3. Average size of reproductive tuna caught by the Tunisian fleet with a purse seine. Source: Data for 2001 taken from ICCAT document SCRS/02-50 (Copemed Scientific Document) ; Data for 2008 based on official records available at ICCAT Bluefin Tuna Catch Document (BCD) database.