Bluefin tuna are a very advanced oceanic fish which are warm blooded and capable of regulating their internal body temperature. Bluefin tuna are the largest species from the Scombrid family and weights of 500 pounds are not at all unusual. The largest tuna ever recorded was a Bluefin tuna caught off Nova Scotia which weighed 1,496 pounds or 679 kilograms. Bluefin tuna can rocket through the water at speeds of 43 mph or 70 kilometers per hour. Often they retract their dorsal and pectoral fins into slots to reduce drag. Bluefin tuna feed upon mackerel, herring, whiting, capelin, flying fish, anchovy, sardine, sand lance, bluefish, silver hake, white hake, lanternfishes, barracudinas, eels, mullet, squid and also crustaceans. Bluefin tunas constantly gorge themselves on whatever fish they encounter in order to grow to such an enormous size. Bluefin tuna have a sleek, torpedo-shaped body and are built for speed and endurance. Their streamlined bodies and crescent-shaped tails reduce drag and turbulence.
Bluefin tunas spawn only in the tropical waters of the Gulf of Mexico ( between mid-April and mid-June ) and in the Adriatic and Mediterranean Seas ( from June to August ). When female Bluefin tuna mature at around age eight they release nearly thirty million eggs in their spawning grounds in the Gulf of Mexico. Bluefin tuna are oviparous ( producing eggs that hatch after they are expelled from the body ) and iteroparous ( producing offspring several times during a lifetime ) and are also multiple batch spawners. The large Atlantic Bluefin tuna observed in Canadian waters gain rapidly at ten percent of their body weight per month. In January of 2012 a prime Bluefin tuna was sold on a Japanese fish market for $736,000. Since the 1970s demand and prices for large Bluefin tuna have soared worldwide and Bluefin stocks have plummeted as a result.
Bluefin tuna stocks have been driven to critically low levels throughout their range due to overfishing. Bluefin tuna have a very high level of vulnerability to being driven to extinction by overfishing rated at a level of 86 out of 100 with 100 representing certain extinction. The abundance of spawning Bluefin tuna has declined by 69 percent over the past forty years. While the cause of the decline, overfishing, is understood it has not ceased and it is not clearly reversible. Despite efforts to rebuild the stocks of Bluefin tuna over the last three decades there is little sign of population increase. Hence the general conclusion that excessive fishing has prevented the stocks of western Atlantic Bluefin tuna from increasing over the last four decades.
photo courtesy of DFO