BFT Biology & Ecology
BFT are a pelagic (ocean going) species present in waters from 6 degrees Celsius to 22 degrees Celsius. They are largely a schooling species that feed on a variety of smaller fish (FAO, ). Individuals can reach more than 2 meters in length, and reach maturity at approximately 4 years (110 cm to 120 cm in length) (ICCAT, 2009) and are thought to live up to 30 years. During their lifetime they undertake huge circumglobal migrations to reach feeding and spawning grounds. Within the Atlantic two distinct "stocks" have been identified: The eastern stock spawns in the Mediterranean and Adriatic sea, and the Western stock spawns in the Gulf of Mexico (FAO, ).
Figure 1: Migration routes, including spawning grounds of the eastern and western BFT stocks.
"The breed of Tunnies comes from the spacious Ocean, and they travel into the regions of our sea when they lust after the frenzy of mating in spring. First the Iberians who plume themselves upon their might capture them within the Iberian brine; next by the mouth of the Rhone the Celts and the ancient inhabitants of Phocaea (Massalia) hunt them; and thirdly those who are dwellers in the Trinacrian isle (Sicily) and by the waves of the Tyrrhenian sea. Thence in the unmeasured deeps they scatter this way or that and travel over all the sea. Abundant and wondrous is the spoil for fishermen when the host of Tunnies set forth in spring". (Oppian Hal. 3.620ff.) The ancients valued the tuna fish immensely and profited by harvesting it. The fish inspired litterature and artwork, as well as being served as a sacrificial offering to the Gods.
Off the Spanish coast of Andalucia, fishermen have been taking advantage of the BFT spawning migrations to the Mediterranean for centuries. The fishing methods of these artisenal boats has changed little during this time. The problem is, although these fishermen have had limited impact on the BFT stock as a whole, the overfishing of their commercial counterparts means that these small artisenal fishermen are potentially scooping up the essential breeding stock of an already decimated population. The fishery targets the breeding stock as they pass through the Gibralta Straits on course for the Meditteranean to spawn. Unfortunately to ensure the survival and conservation of the species for future generations, the present day fishermen will lose their livelihood. Watch the video here.
Decline of global stocks
The following information is largely taken from "The End of the Line: how overfishing is changing what we eat" written by Charles Clover.
Tuna Farming or tuna fattening?
The concept of tuna "farming" began in Australia and involved purse seining the shoals of smaller tuna and then transfering them into sea cages. It may be assumed that the tuna were smaller in size due to fishing pressures, and larger adults were already removed leaving a smaller sized juvenile stock. The fish once in the sea cages, are then fed low value wild caught fish until they are essentially "fattened up". NO ACTUAL BREEDING TAKES PLACE.
Within the last ten years tuna farming has increased substantially throughout the Mediterranean sea- Malta, Siciliy, Italy, Croatia, Cyprus, Greece, Libya, Turkey, and Tunisia. See the map. The industry has generated a vast ampunt of business, but has severely compromised any accurate monitoring of blue fin tuna catches. Farmed blue fin tuna catches are hard to monitor as the fish are eventually landed in a different area to where they were caught. In 2004 WWF estimated that the actual annual blue fin tuna catch was some 1.5 times higher than the annual quota (WWF). Scientists of the International Council for the Exploration of the Sea (ICES) based in Copenhagen estimate that the Mediterranean is catching double the amount that is considered a sustainable catch of blue fin tuna.
The Intenationa Convention for the Conservation of the Atlantic Tuna treaty was first established in 1966 (Rio de Janeiro, Brazil) and now contains several member states, including the USA, Japan and the EU. Despite such a convention which should regulate overfishing of the blue fin tuna, the global stock appears under the heading "data deficient" on the IUCN red list. Europe has access to the largest remaining population of Atlantic blue fin tuna and should be protecting the remains of a vulnerable stock. However the reality is very different. Although tuna farming has been heavily criticed by conservation groups such as WWF as being unsustainable (the farms take the juvenile fish before they have had chance to spawn and provide the next generation), under EU rules tuna farms qualify for aquaculture subsidies. The EU have spent millions on such subsidies, allowing the continued growth of the industry throughout the Meditteranean.
A new concern is that this unsustainable farming initiative is spreading globally. Costa Rica is one of the latest countries to be tempted to establish a tuna farm in Golfito and is currently waiting for approval from the Environmental Ministry. Conservation group Pretoma are leading a national campaign to raise public awareness and prevent the tuna farm project from being approved.
Publications & articles
Protecting the last great tuna stocks
UN backs proposal for blue fin tuna trade ban