23. May, 2020

The Atlantic Bluefin Tuna is back, but for how long?

There are three species of bluefin tunas: the Atlantic (Thunnus Thynnus the largest and most endangered), Pacific (T. orientalis), and Southern (T. maccoyi).  More distant relatives in the genus Thunnus are the bigeye tuna (T. obesus) and the yellowfin tuna (T. albacares).

The Atlantic bluefin tuna Thunnus Thynnus is the largest tuna and the largest species in the mackerel family that can live for 40 years.  It is native to both the western and eastern Atlantic. One spawning ground exists in the western Mediterranean, particularly in the area of the Balearic islands. Their other important spawning ground is the Gulf of Mexico.

Bluefins are tremendous predators, already seeking out schools of fish like herring, mackerel, and even eels just after birth. With their superb vision they hunt by sight, while their torpedo-shaped body and retractable fins made for speed allow them to reach almost  80 km per hour. Their specialized blood vessel system (called a countercurrent exchanger) serves to maintain a body temperature that is higher than the surrounding. Which facilitates movements such as rapid and powerful turnings of the body. To keep the blood oxygenated they swim constantly with their mouth open.

Atlantic bluefin tuna has been hunted down massively since it became the most highly prized fish used in Japanese raw fish dishes like sushi and sashimi.  In the restaurants in southern Spain (e.g. in the tuna paradise Barbate) the Atún Rojo is also a local delicacy. A small tin of tuna costs around 20 Euro. Driven by such high prices, fishermen have developed more refined techniques like anchored nets to catch tuna, with the fish disappearing as a result. Although tuna do provide food and livelihoods for people, they are more than just seafood. Tuna is a top predator in the marine food chain, maintaining a balance in the ocean environment

About 80% of the caught Atlantic and Pacific bluefin tunas are consumed in Japan, where it is considered as an ultimate delicacy. Most catches of the Atlantic bluefin tuna are taken from the Mediterranean Sea which is the most important bluefin tuna fishery in the world. 15 years ago the future for tunas looked really bad, reaching a low point in 2012.   A report of the International Commission for the Conservation of Atlantic Tunas (ICCAT) concluded that only 10% remained of the population that existed 50 years ago. The catch quota was then brought back in 2008 from 26.750 tons to 12.900 tons worldwide for a  4 year period, restricting the catch to species larger than 30 kilos. 

However illegal catch continued in the waters of Southern Spain. And when the tuna populations started to grow again, the ICCAT decided, under pressure from member countries such as Japan, France, and Italy,  to increase the catch quota of bluefin tuna from 24,000 tons annually to 36,000 tons annually. Scientists and conservationists fear that increasing the catch limit will set back the bluefin recovery effort enacted in 2008 after stocks of the prized sushi fish have badly overexploited in the Mediterranean and Atlantic.