What is a Southern Bluefin Tuna?

Southern bluefin tuna (Thunnus maccoyii) is a critically endangered species of tuna that is overfished because its flesh is considered a delicacy, particularly in Japan. The tuna, which generally resides in the Southern Atlantic, Pacific, and Indian Oceans, is a relative of the marlin and swordfish. Dark blue on its top and silver on its bottom, the southern bluefin tuna possesses a yellow band on its side. Fast swimmers, the tuna can reach speeds of more than 55 miles per hour (90 kilometers per hour) and can grow to lengths approximately six feet (two meters) in length and tip the scales at more than 300 pounds (135 kilograms).

Part of the Scombridae family of tuna, the muscular southern bluefin tuna has a curved tail, two dorsal fins, and retractable fins that lower resistance as the fish travel in the ocean. Migratory in nature, the southern bluefin tuna possess a unique circulatory and respiratory system that help it travel great distances. The tuna is able to keep a constant body temperature that is warmer than the water the tuna is traveling in. The creature also possesses a heart larger than most fish, allowing the tuna to expand a great deal of energy oxygen on its long journeys.

Around the age of nine, the southern bluefin is sexually mature. The tuna breeds between September and April and generally heads to the Indian Ocean to spawn in the temperate waters near Java, Indonesia. Typically, the tuna spawns in water with temperatures of 68° to 86° Fahrenheit (20° to 30° Celsius).

During spawning, a female southern bluefin tuna may release millions of eggs. The eggs take only a few days to hatch, releasing tuna of less than an inch (2.5 millimeters) each. The juvenile tuna spends about the first five years of life near the coast of Australia before departing for deeper waters that provide more feeding options.

The bluefin tuna can live up to 40 years and uses its heightened vision and hearing to catch prey such as krill, squid, octopus, and crustaceans. Predators of the bluefin tuna include sharks, birds, killer whales, and even other tuna. The tuna is heavily fished as the tuna is coveted for its fatty flesh, which is often served as gourmet food including fillets or sushi. Countries such as Japan, Australia, and New Zealand have limited the amount of southern bluefin tuna allowed to be caught.

The Southern Bluefin Tuna (Thunnus maccoyii) is a large, migratory species of tuna found in the open waters of the southern hemisphere. It is known for its speed, strength, and value in the commercial fishing industry. This species can grow up to 2.5 meters in length and weigh over 200 kilograms, making it one of the largest tunas.

Southern Bluefin Tuna are found throughout the southern hemisphere's oceans, particularly in the Atlantic, Indian, and Pacific Oceans. They prefer cooler waters and undertake extensive migrations for feeding and breeding. According to the Australian Government's Department of Agriculture, Water and the Environment, they are known to travel thousands of kilometers from their spawning grounds in the Indian Ocean.

The Southern Bluefin Tuna is a key species in marine ecosystems and a highly sought-after fish in the global market, especially for sushi and sashimi. Its economic value drives significant fishing activity, but this has led to overfishing. The species plays a crucial role in balancing marine food webs and supporting commercial fisheries.

The Southern Bluefin Tuna is listed as Critically Endangered by the International Union for Conservation of Nature (IUCN). Overfishing has severely depleted its populations. International efforts, such as the Commission for the Conservation of Southern Bluefin Tuna, are in place to manage fishing quotas and aid in the species' recovery.

Southern Bluefin Tuna have a relatively long lifespan, with individuals living up to 40 years. However, due to intense fishing pressure, many are caught before reaching full maturity. Their longevity is important for their reproductive success, as older, larger females produce more eggs.

Managing Southern Bluefin Tuna populations is challenging due to their migratory nature, high market demand, and illegal, unreported, and unregulated (IUU) fishing. International cooperation is crucial for effective management, as the fish cross multiple jurisdictions. Accurate stock assessments and enforcement of conservation measures are essential to ensure the species' sustainability.