Bluefin tuna is an endangered predator fish. Last week, we explained that other species like sardines and mackerel are also endangered due to overfishing. This week, we will focus on this species and we will explain its biology and distribution, in addition to the reasons why it is under threat.
BIOLOGY
Bluefin tuna (Thunnus thynnus) is the biggest species of the Scombridae family and one of the biggest bony fishes. Despite they can achieve a length of 3 meters, they usually range between 0.4 and 2 meters. Moreover, they weight between 140 and 680 kilos, but it is difficult to find an organism that exceed 450 kilos. It is a migratory animal with a high economical value for its red and dusky meat. The body is fusiform and can be distinguished from the rest of tunas by pectoral fins: they are rather short and reach the 11th or 12th dorsal spine.
Back and upper sides are dark blue to black, with a grey or green iridescence. Inferior sides are silvery with grey spots and bands. Anal in is dark and yellow.
Diet of bluefin tuna includes squids, eels and crustaceans, but also schooling fishes like herrings and mackerels.
DISTRIBUTION
Bluefin tuna lives in subtropical and temperate waters of North Pacific, Atlantic, Mediterranean and Black Sea. Despite bluefin tuna can be found along the year in the Mediterranean, they are present mainly in June and July.
CONSERVATION STATUS AND PROBLEMS
According to IUCN, bluefin tuna is endangered and its population is in decline. Due to overfishing, being the most important the illegal fishing, it is estimated that Western Atlantic population has decreased in an 87% since 1970. Anyway, other references indicates that this drop has been between 29 to 51%. In 1996, scientist alarmed that worldwide catch quotas must be reduced an 80% to recover populations in 20 years, but in fact they were increased. Nevertheless, it seems like the reduction of captures recently has produced an increase of populations.
Because they achieve maturity in an advanced age, they are specially vulnerable to overexplotation. Despite catch quotas have been established, the measure have not had always success for several reasons: disembark of small fishes (and big) has continued, the lack of regulations in some areas, fishermen ignore restrictions in some countries and the lack of fines when breaking the lows.
Between 2000 and 2004, it had been captured about 32,000 – 35,000 tonnes per year in the Eastern Atlantic and Mediterranean, achieving 50,000-60,000 tonnes in 2006, so the stock status is overexploited. Nowadays, the catch quota is restricted to 13,500 annual tonnes, but 3,000 tones are for Spain.
This tuna is captured with different types of fishing: purse-seine, longline and tramps. The reason of its fishing is to meet demand of Japanese market of sashimi (just one piece of tuna can be sold for 90,000€), what caused its overfishing. In addition, it is a goal species in recreational fishing of United States and Canada.
So, fisheries are being reduced and, at the moment, neither European Union nor other countries have acted to save it. In addition, governments have ignored experts.
¿WHAT WILL IT HAPPEN IF WE RUN OUT OF BLUEFIN TUNA?
Bluefin tuna is a predator of jellyfishes. Its reduction, together with the rise of sea temperature, is causing a rising of jellyfishes. Moreover, its disappearance would produce an imbalance of food webs.
If you are worried about the status of bluefin tuna and the oceans, when you go to a fish market, don’t buy it and also when you go to a Japanese restaurant, refuse to eat any dish with tuna. Only reducing the demand, we will be able to stop its fishing.
REFERENCES
- Schultz, K (2003). Field guide to Saltwater fish. Wiley (1 ed).
- IUCN: Thunnus thynnus.
- Slow Food: El atún rojo.
- WWF: Atún rojo
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