Atlantic Bluefin Tuna
Atlantic Bluefin Tuna
The Atlantic bluefin tuna is a species of tuna in the family Scombridae. It is variously known as the northern bluefin tuna, giant bluefin tuna and formerly as the tunny.
Scientific name: Thunnus thynnus
Conservation status: Endangered (Population decreasing) Encyclopedia of Life
Mass: 830 lbs (Adult) Encyclopedia of Life
Higher classification: Thunnus
Atlantic bluefin tuna is a large, slow growing and long lived species, making it vulnerable to overfishing. The stock has been significantly overfished since the 1970s, and illegal, unreported and unregulated (IUU) fishing has been a serious problem as individual fish can regularly be sold in excess of tens of thousands of pounds. Recent improvements in stock management, monitoring and enforcement under a recovery plan have had a positive effect on the stock. The 2014 assessment indicates that fishing mortality is now below the Maximum Sustainable Yield (Fmsy) and that the biomass is increasing. There remain large uncertainties in the assessment however, and it is not clear if the stock is still overfished. The East Atlantic component of the stock is likely important to the West Atlantic bluefin stock and the species remains listed as Endangered by the IUCN Globally and in the Mediterranean, and Near Threatened in Europe.
Adults are typically 3m in length, but can reach 4m, making the Atlantic tuna one of the largest bony fishes and the largest of all tuna species. Adults average 130-680kg, although the upper weight range is rarer now.
Bluefin tuna are built like torpedoes. Not only do they have a hydrodynamic shape, their pectoral (side) fins can be retracted and, unlike other fish, their eyes are set flush to their body. This means their bodies create little drag as they swim through water.
Atlantic bluefin tuna spawn in two widely separated areas. One spawning ground exists in the western Mediterranean, particularly in the area of the Balearic Islands. The other important spawning ground of the Atlantic bluefin is the Gulf of Mexico. Pop-up satellite tracking results appear to confirm in large measure the belief held by many scientists and fishermen that although bluefin that were spawned in each area may forage widely across the Atlantic, they return to the same area to spawn.
Atlantic bluefin group together in large concentrations to spawn, with males and females producing eggs and sperm synchronously nd resulting in many individuals mating at the same time. The tuna are highly vulnerable to commercial fishing at such times. This is particularly so in the Mediterranean where the groups of spawning bluefin can be spotted from the air by light aircraft and purse seines directed to set around the schools.
Female bluefin produce up to 10 million eggs during each spawning period. No parental care is provided. The bluefin tuna become sexually mature between 4 and 8 years old. The western and eastern populations of Atlantic bluefin tuna are thought to mature at different ages. It is thought that bluefin born in the east reach maturity a year or two earlier than those spawned in the west.Atlantic bluefin tuna can live for 30 years, but due to heavy fishing mortality and predation, few known specimens grow to a mature age.
Young and adult bluefin tuna specimens are large predators and opportunistic animals toward their food. Their diet can include several species of teleostei, invertebrates such as jellyfish and salps as well as dimersals and sessile organisms such as octopi, crabs and sponges, although big differences have been observed in the areas studied.
In general, young specimens feed on crustaceans, fish and cephalopods, whereas adults feed on fish such as herring (Clupea arengus), anchovies (Engraulis encrasicolus), sandeels (Ammodytes spp.), sardines (Sardina pilchardus), sprats (Sprattus sprattus), bluefish (Pomatomus saltatrix) and horse mackerel (Scomber scombrus). Three predominant species were found among the bluefin tuna stomach contents analyzed: the Atlantic herring and the sprat in the West Atlantic or the anchovy in the East Atlantic and the Mediterranean.
World Range & Habitat
Atlantic bluefins live in subtropical and temperate waters of the North Atlantic Ocean, the Mediterranean, and Black Seas. Bluefins are highly migratory and limited numbers of individuals may cross the Atlantic in as little as 60 days and are widely distributed throughout the Atlantic and can be found from Newfoundland all the way to the coast of Brazil. They range in the eastern Atlantic as far north as Norway and down to northern West Africa. Bluefins tagged in the Bahamas have been captured in Norway as well as off the coast of Brazil. Bluefins in the South Atlantic belong to a distinct southern population, with known spawning areas south of Java, Indonesia. The bluefin is a pelagic external link, schooling fish. They tend to group together according to size.
Atlantic bluefin tuna spawn just once a year and do not reach reproductive maturity until they are 8-12 years old. This makes bluefin tuna more vulnerable to overfishing than some of the smaller tuna species that can spawn several times in a year. Female Atlantic bluefin can produce up to 10 million eggs per year, but just a small fraction survives to adulthood.
The difference in the age at which the eastern and western populations reach maturity in the North Atlantic may support the hypothesis of differentiated populations.Like most fish, egg production seems to depend on age (or size). Therefore, a 5-year-old female can produce an average of five million eggs per year, whereas females aged 15-20 years can carry up to 45 million eggs. Hatching occurs without parental care after an incubation period of 2 days.
Bluefin tuna larvae (3-4 mm) are generally pelagic and can be found in superficial waters throughout the Mediterranean Sea with greater concentrations in areas where there are whirlpools and fronts, especially at the end of summer. Larvae grow 1 mm per day until they reach a weight of 40-80 kg, and they separate into schools according to size.
These bluefin tuna larvae are mainly found in superficial waters with a temperature from 24 to 25ºC in areas where the water masses of the Atlantic and the Mediterranean mix.
In 2011, the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assessed Atlantic Bluefin Tuna as endangered due to a decline of 69% in adult abundance over the past 2.7 generations. The largest threat to Atlantic Bluefin Tuna is considered to be fishing mortality, both targeted and incidental. In Canada, they are harvested commercially from the Scotian Shelf, southern Gulf of St. Lawrence, Bay of Fundy, and the Grand Banks. Pollution is also considered a threat. In particular, there was concern about the potential impact of the Deepwater Horizon oil spill, which occurred in a portion of the primary spawning ground in April 2010. However, there has not been an observed impact on the 2010 year-class as it progresses through the fishery.
The spawning stock biomass (SSB) for the western population of Atlantic Bluefin Tuna declined substantially from the 1970s to 1992. However, following the implementation of a 20-year rebuilding plan in 1998, the SSB has shown signs of improvement. The last two International Commission for the Conservation of Atlantic Tunas (ICCAT) assessments (2012 and 2014) also showed positive signs of the biomass increasing.
Facts About Tuna
- Bluefin is the largest species of tuna. The can get up to six and a half feet long and can weigh as much as 550 pounds! That’s a lot of tuna!
- Bluefin are prized fish for use in sushi. Unfortunately, the sudden explosion of sushi popularity worldwide has increased the hunting of these fish to the point that they are being fished faster than they can reproduce, meaning that sooner rather than later they will be completely wiped out. That is unless things change, and change soon.
- Bluefin Tuna can live upwards of forty years! Let’s face it, that’s impressive. Most of us can’t imagine a fish living that long, right? Kind of makes you rethink that sushi, huh?
- A single Bluefin Tuna can sell from $500,000 to $1.7 million dollars. And unfortunately, in countries such as Japan, in spite of their endangered status, it is not illegal to catch, kill, and sell these animals. Because prices for these fish are so high, fisherman have become especially adept at catching these fish and even more determined to do so. This just increases the likelihood of the extinction of these fish so vital to the oceanic ecosystem.
- Bluefin Tuna are at the top of their marine food chain, meaning that their extinction could lead to a complete disruption of the balance. Species that they feed on would reproduce at normal rates but their populations would not be regulated and thus the whole ecosystem would be thrown off.
- Atlantic Bluefin Tuna are actually warm-blooded! This is extremely rare in fish and should be something to be relished, not hunted to extinction.
- Bluefin Tuna are highly migratory and Atlantic Bluefin Tuna can migrate from the Newfoundland area of Canada all the way to the Mediterranean and the Gulf of Mexico!
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