Atlantic blue fin tuna: physiology, reproduction, and characteristics

Atlantic Blue fin tuna is a part of the Scombridae family and its scientific name is Thunnus Thynnus. It is also known as Northern Blue fin tuna and is closely related to the Pacific blue fin tuna and the Southern blue fin tuna. They are a highly evolved fish species that have an average life span of 15 to 30 years.

Physical Description

The Atlantic blue fin tuna is one of the largest fishes alive today. It has a metallic blue color on top and a silvery white at the bottom to camouflage it in the deep oceans against predators such as whales and sharks. Their body is shaped like a torpedo and this gives them the speed to get away from predators as quickly as possible despite their big size and weight. An average Atlantic blue fin tuna can grow to about 6.5 feet in size and weigh a whopping 550 pounds. It is not uncommon to find blue fin tunas that are twice these measurements. The largest blue fin tuna ever found weighed 1,496 pounds and was caught off Nova Scotia in Canada (National Geographic, 2012). Despite its heaviness, its body is streamlined for speed and this makes it one of the fastest fishes in the marine world today. They are even capable of retracting their fins to zip through the water and they can dive into great depths. Most blue fin tuna have been observed to dive up to 1,000 meters or more.

These fishes are warm-blooded and have one of the most evolved circulatory system among fishes. They have the highest amounts of hemoglobin and this makes it possible for them to absorb oxygen quickly and efficiently.

Reproduction

They have a complex migratory cycle and the time of migration depends to a large extent on the age of the fishes. Research has shown the blue fin tuna that live in the eastern part of the Atlantic ocean mature faster than their counterparts on the western part, but the reason is still being debated.

The Atlantic blue fin tuna spawns in the warm Atlantic waters near the Balearic Islands and Gulf of Mexico. There is little research on why these fishes spawn in the warm waters, but they migrate thousands of miles from Canada and Norway to reach these places to produce their offspring. These eastern blue fin tuna spawn the most from June to August in the Mediterranean seas while the western tuna spawn from April to June in the waters of the Gulf of Mexico (Block, Dewar, Blackwell, Williams, Prince, Farwell, Boustany, Teo, Seitz, Walli & Fudge, 2001).

The female blue fin tuna spawns about 30 million eggs and this gives rise to substantial amounts of these fishes every year. However, commercial fishing, especially off the southern coast of Italy has reduced their numbers drastically.

Food

These fishes are carnivores and eat other smaller animals and fishes found in the Atlantic waters. Blue fin tunas have an enormous appetite and they are known to eat smaller fish, eels, squids, oysters and other crustaceans. Planktons and kelps are also other foods that fill their stomach when they find it hard to find other fish.

Why is it endangered?

Blue fin meat is considered to be a delicacy in Japan and sashmi eaters are willing to pay a hefty price for its meat. This has led to large scale commercial fishing of these fishes. The hunting period reached its peak during the 1970s when Japan's economy was booming and more people could afford to pay a high price for its meat. This huge commercial fishing brought it to the brink of extinction as large piles of fishes in their breeding age were caught for human consumption. In January 2012, a world record was set for the price of a blue fin tuna. A blue fin weighing about 269 kg was sold in a Japanese market for $736,000 (National Geographic, 2012). International awareness and conservation efforts have reduced their commercial fishing, but its is believed that illegal fishing continues to happen around the world.

Besides commercial consumption, these fishes were hunted extensively as a sport. Its quick dart and speed challenged numerous people and this became a popular sport among fishing enthusiasts in the United States, Canada, Spain and Italy. The dwindling numbers of Atlantic Blue Fin tuna finally put an end to this sport, though some environmental groups believe that this sport continues illegally.

In a study conducted by the Tuna Research and Conservation Center (TRCC), many of the blue fin tunas were electronically tagged to track their numbers. Based on these efforts, it was found that the eastern and western species mingle with each other and the larger western tunas are caught on the eastern side of the Atlantic when they are adults. Similarly, the eastern fishes are caught off the Western coast as adolescents and they end up being much smaller. Nevertheless, it is estimated that the western species have declined by more than 80% since the 1970s. This is why the International Commission for the Conservation of Atlantic Tunas (ICCAT) limits the fishes caught on the western coast to 3,000 tons per year as against the limit of 32,000 tons on the eastern part (Shwartz, 2005). Illegal fishing has further dwindled these numbers.

Conservation efforts

Numerous conservation initiatives have been taken by the ICCAT and environmental groups around the world to protect the blue fin tuna. However, they are not sufficient to protect these fishes because of illegal fishing. In fact, many scientists consider the 30,000 ton per year limit of the ICCAT to be high and believe it should be only about 15,000 tons a year. Also, an independent study conducted by Conservation Letters show that this species is collapsing so fast that it is categorized as critically endangered -- the highest category in conservation (The Economist, 2008). Other private environmental groups are lobbying for better control measures in different countries, especially in Spain, Italy and Japan because these are the three countries that are extensively involved in this trade. Many organizations such as Greenpeace International and Monterey Bay Aquarium have listed this fish on their seafood list and these act as a guide to avoid eating this fish because of its low numbers.

Despite all these efforts, overfishing is rampant all over the world because of the heavy price that blue fin tunas fetch in the market. These large fishes can be saved only with education and awareness besides stringent regulation.