Status: Critically Endangered, depends on species.
Species: Albacore Tuna, Atlantic Bluefin Tuna, Bigeye Tuna, Pacific Bluefin Tuna, Southern Bluefin Tuna.
Estimated numbers left in the wild: Unknown but likely ranging in the hundreds of thousands.
Description: Bluefin tuna are large predatory fish, stocky and sharp-finned, whose size can range up to 4.5 meters and whose weight can be as high as 450 kilograms. Their coloration tends to be striking, with metallic blue upper surfaces and metallic white underparts. This colour gives these five species of tuna their general name of “bluefins”, and it serves a vital function in the species’ lives. The blue upper surfaces provide camouflage from above while the silvery underparts help conceal the prowling tuna from below, allowing them to close more effectively with their prey.
Bluefin tunas are all hunters. They prey mostly on smaller fish that form schools, or small squid that exhibit schooling or swarming behaviour. However, they will also eat pelagic red crabs, krill, and certain sessile animals also, such as sea anemones. Tuna are active predators who can put on spurts of up to 80 kilometres per hour to catch other fish. To achieve this performance, they are warm blooded, with the bluefin species having the most control over their internal temperature. Very high blood haemoglobin levels oxygenate the tunas’ muscles for strength and power.
Tuna are a migratory species and gather together in large numbers at chosen spawning grounds to produce their eggs. A single female tuna can produce anywhere from 5 million to 30 million eggs, though of course only a tiny fraction of the fry will ever grow to adulthood. If not caught by fishermen, a bluefin tuna can potentially live for anywhere from fifteen to thirty years.
Location: The various species of bluefin tuna are found in the Atlantic Ocean near Newfoundland and Iceland; the Gulf of Mexico; the Mediterranean; other areas of the Atlantic; and the Pacific Ocean. Tunas are deep water fish which need a thriving biome to survive, since they are predatory and feed on schools of smaller fish.
Threats: Overfishing is the chief threat to all varieties of bluefin tuna. The migratory habits of these large fish make it difficult for conservation efforts by any one government to make a significant difference in their overall fate, increasing the difficulty of tuna conservation. Sushi and sashimi are among the most common uses of this fish, meaning that demand and prices are very high in Japan, providing an ongoing market for fish caught in spite of various agreements, with 80% of the world catch going to Japan. Some secondary threat could also exist if the acidification of the oceans, caused by global warming, starts to affect the bluefin tunas’ food supplies.
Conservation efforts: A number of good faith conventions have been made to try to limit fishing of these important members of the pelagic ecosystem, but how well they are observed depends largely on local decisions by fishermen and governments. Both Australia and Japan are attempting farming as an alternative to catching wild tuna, but the fish are difficult to raise due to the length of time it takes them to mature.
Bluefin Tuna Videos
Monterey Bay Aquarium conducts research projects and tagging to study migration, habitats, diets, populations and protect different marine species like the Bluefin tuna.
Oceana is the largest international organization focused only on ocean conservation, protecting marine ecosystems and endangered species such as the Bluefin Tuna.