Bluefin tuna
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Bluefin tuna ( Thunnus thynnus ) |
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The bluefin tuna ( Thunnus thynnus ), even Big tuna , North Atlantic tuna or bluefin tuna called, is one of tuna and an important food fish. With a maximum length of 4.5 meters and a maximum weight of over 650 kilograms, it is one of the largest bony fish .
distribution
The bluefin tuna lives in the Atlantic , north of the equator , in the Mediterranean , in the Caribbean , the Baltic Sea and in the Gulf of Mexico . There is also a population on the coast of South Africa.
features
Bluefin tuna are usually three meters long and can weigh 300 kilograms by the age of 15. The largest fish caught was 4.58 meters tall and the heaviest fish weighed 684 kilograms. The bluefin tuna has a spindle-shaped body that reaches its greatest height in the middle of the first dorsal fin. Both dorsal fins are close together, the second is higher than the first. Behind the second dorsal fin and the anal fin are eight to nine small flippers. The applied pectoral fins reach behind the middle of the first dorsal fin. The pelvic fins are very small and always shorter than 80% of the length of the head. The tail fin stalk is reinforced by two lateral wedges.
Fin formula : dorsal XII – XIV / 13–15, anal 13–16.
The bluefin tuna is dark blue on top, silvery white on the sides and belly and without stripes or spots. The first dorsal fin is bluish or yellow, the second red-brown. The anal fin and the floss are bordered gray-yellow and black, the wedge in the middle of the caudal fin in adult animals is black.
Way of life
Bluefin tuna live pelagically in the open ocean from the surface of the water to a depth of 100 meters. Young fish tend to prefer warmer waters, while adult tuna can also penetrate into cold waters. The bluefin tuna is a warm-blooded animal with a relatively constant body temperature of usually 27 ° C and can increase or adapt its body temperature by a few degrees compared to the surrounding water temperature for a few hours. Therefore, its temperature tolerance is relatively large. Their diet consists of schooling fish from the high seas, including mackerel , hake , garfish , flying fish , anchovies and herrings , as well as squids . Smaller prey is filtered out of the water with the gill trap, larger animals are captured in sudden attacks, in which the tuna can reach speeds of up to 80 km / h.
Bluefin tuna undertake long migrations, during which they sometimes come close to the coast, and often move around in schools of fish of the same size, mixed with albacore , yellowfin tuna , bigeye tuna and thonine . Bluefin tuna also cross the Atlantic, so that there is an exchange between the west and east Atlantic populations.
Reproduction
The East Atlantic bluefin tuna spawns off the Strait of Gibraltar and in the western Mediterranean from June to August . A female can give up up to ten million eggs that are only one millimeter in diameter. Eggs and larvae are pelagic and drift near the surface of the water. The larvae hatch after two to three days and grow quickly. After three years they are about one meter long and weigh about 16 kilograms. With a length of 1.2 to 1.4 meters, a weight of 30 to 40 kilograms and an age of four to five years, they become sexually mature. They live to be a maximum of 15 years old.
After spawning, the parent animals of the East Atlantic population move north in search of food to the coasts of Scotland and Norway, the North Sea, the Kattegat and, rarely, to the western Baltic Sea.
Economical meaning
The bluefin tuna is an important food fish . It has deep, dark red meat that stays dark when heated. At first in Japan tuna were also caught live and fattened in cages off the coast so that they become fatter (and more valuable). This method is now widespread and known under the name "Tuna Farm". It should be noted here that the tuna (including females and young animals) do not reproduce in these cages, but only grow. Tuna are difficult to reproduce in captivity. The German-Australian entrepreneur Hagen Stehr succeeded in bringing captive tuna to spawn.
85 percent of the tuna caught in the Mediterranean is exported to Japan, where it is often made into sushi .
overfishing
The bluefin tuna is massively overfished and is on the IUCN (World Nature Conservation Organization) red list of endangered species . According to recent scientific studies, there are only around six percent of the original stocks left in the Mediterranean and the Eastern Atlantic. On June 11, 2007, the EU issued Regulation (EC) No. 41/2007 for the conservation of tuna stocks in the Atlantic. This is to prevent the extinction of this tuna species and enable the regeneration of the remaining stocks. Among other things, the regulation imposes closed seasons in the Eastern Atlantic and the Mediterranean.
Environmental protection organizations like WWF consider these measures to be inadequate. The director of the fisheries division of the United States Meteorological and Oceanography Administration , NOAA (National Oceanic and Atmospheric Administration) announced in October 2007 that the United States would be calling for a five-year total ban on bluefin tuna in the Mediterranean.
In mid-June 2008, EU Fisheries Commissioner Joe Borg decided to end the bluefin tuna fishery in the Mediterranean and Eastern Atlantic from June 16 for all tuna vessels using purse seine nets flying the Cypriot , French , Greek , Italian or Maltese flag of the year. For Spanish tuna seiners the ban will apply from June 23rd. The reasons given are serious violations of international fisheries directives and non-compliance with specified fishing quotas.
Environmental organizations question the effectiveness of this measure. Shortly after the fishing ban, Italian purse seiners were discovered on a fishing trip as well as search planes cooperating with the fishermen to track down schools of tuna, which are illegal to use.
At the World Conservation Congress in Barcelona in October 2008, the two nations of Spain and Japan agreed to support a temporary ban on catching the threatened bluefin tuna. In the spawning season from May to June, the catch should therefore be completely stopped and severely restricted in the rest of the year. Spain is the most important catching nation, Japan is the main market for tuna.
In April 2009 the environmental foundation WWF published an analysis of population stocks and the existing number of reproductive animals, which came to the conclusion that if the level of fishery remained the same, the bluefin tuna in the Mediterranean would be extinct in 2012. In November 2009, the International Commission for the Protection of Tuna in the Atlantic (ICCAT) failed to agree on an absolute fishing ban at a conference in Recife .
In March 2010, the delegates to the CITES conference in Doha voted against an international trade ban. Monaco had tabled a motion to this effect, but only 20 countries accepted it, while 68 countries rejected it - with 30 abstentions. The decision was particularly welcomed in Japan, where 80 percent of the Atlantic bluefin tuna is imported and made into sushi .
Filmmaker Mark S. Hall deals with overfishing of the bluefin tuna in the 2011 documentary Sushi - The Global Catch .
literature
- Bent J. Muus, Jørgen G. Nielsen: The marine fish of Europe in the North Sea, Baltic Sea and Atlantic. Kosmos, Stuttgart 1999, ISBN 3-440-07804-3 .
- Kurt Fiedler: Fish (= textbook of special zoology. Vol. 2: Vertebrates. Part. 2). Gustav Fischer, Jena 1991, ISBN 3-334-00338-8 , p. 389.
Web links
- Bluefin tuna on Fishbase.org (English)
- Thunnus thynnus in the endangered Red List species the IUCN 2006. Posted by: Safina, 1996. Retrieved on 12 May, 2006.
- International Commission for the Conservation of Atlantic Tuna
- FAZ article on overfishing of bluefin tuna. FAZ , August 25, 2006, archived from the original on March 5, 2016 .
- The last bite. In: Greenpeace magazine . 6.10.
- Arte documentation (click on the lock)
- SAFE and its impact on tuna stocks
Individual evidence
- ↑ 300-kilo tuna caught by Germans on the Baltic Sea. Retrieved September 11, 2018 .
- ↑ Takashi Kitagawa, Hideaki Nakata, Shingo Kimura, Sachiko Tsuji: Thermoconservation mechanisms inferred from peritoneal cavity temperature in free-swimming Pacific bluefin tuna Thunnus thynnus orientalis. In: Marine Ecology. Progress Series. Vol. 220, 2001, ISSN 0171-8630 , pp. 253-263, doi : 10.3354 / meps220253 .
- ↑ Regulation (EC) No. 41/2007
- ↑ SAFE and its impact on tuna stocks. on: delphinschutz.org
- ↑ EU decisions against illegal fishing and ground trawling are inadequate. on: wwf.de , October 17, 2007.
- ↑ Stop fishing for bluefin tuna and thus secure its future. on: europa.eu , June 17, 2008.
- ↑ Absolutely at the limit: Bluefin tuna in the Mediterranean before extinction. ( Memento from October 1, 2010 in the Internet Archive ) at: kleinezeitung.at , November 17, 2008.
- ↑ Tuna extinct in the Mediterranean by 2012? on: wwf.de , April 16, 2009.
- ↑ Ban on fishing for threatened bluefin tuna failed. In: The time . November 16, 2009.
- ↑ Trade in bluefin tuna is still allowed. In: The time . March 18, 2010.
- ↑ Japan avoids trade ban on sushi tuna. In: Handelsblatt . March 19, 2010.
- ↑ Fishing would be one solution. on: taz.de , June 7, 2012 (Review of the documentary Mark S. Hall: Sushi - The Global Catch. )