Southern Bluefin Tuna
Learn about tuna
Tuna are beautiful torpedo-shaped fish and are one of the top predators in the ocean environment.
Just like other predators high up in the food chain, tuna regulate the populations of the species it feeds on.
Because of this, it is essential in helping to maintain the ecological balance in the marine ecosystem. Their diet includes a wide variety of smaller pelagic fish species such as anchovies or mackerel, as well as cephalopods, salps, and crustaceans. When grown to their full size, tuna themselves are mainly consumed by even larger open-ocean predators such as toothed whales, and sharks. Unfortunately, all known bluefin tuna species – the Southern bluefin tuna (critically endangered), the Atlantic bluefin tuna (endangered), and the Pacific bluefin tuna (vulnerable) are today listed on the IUCN red list (International Union for the Conservation of Nature), with concern of their wild populations collapsing in the near future. A small geographical area in the Indian ocean, south-east of Java, provides the only spawning ground for Southern bluefin tuna. Such dependence combined with their long juvenile period adds to their vulnerability and chances of population declines. We have grossly overfished tuna population stocks, especially that of the Southern bluefin and being the world’s most endangered tuna,
there is now a real chance that wild populations will not recover and may go extinct.
In the 1950s we began harvesting fish much more efficiently using commercial fishing methods such as long line fishing, bottom trawling, and purse seine fishing. These methods are still popular today and all risk chance of bycatch including whales, sharks, turtles and dolphins. Once caught, these animals are very likely to die of their injuries even in the case of later release. Younger, smaller individuals of target species are often caught as bycatch reducing ability for fish stocks to recover and grow. Population levels of the bluefin tuna are now 5% of what they were in the 1960s, before we exploited the seas to such a degree. To help their fish stock recover, fishing limitations have been put in place. Both adult and juvenile southern bluefin tuna travel vast distances within the oceans of the southern hemisphere and because of this, cooperative management between the biggest consumer countries were established. Included in this are Japan, Australia, New Zealand, Indonesia, Taiwan, Korea, South Africa, and the European Union. However,
the fewer fish there are of a certain species the more valuable each individual fish becomes. Unfortunately, this motivates a lot of illegal fishing activity.
Bluefin tuna is especially in demand on the Japanese sashimi market, where individual fish are being auctioned off for fortunes. The most expensive individual was sold for over $3.1 million in 2018. In the 1960s, experiments with aquaculture began in order to relieve some of the pressure on wild bluefin tuna. Today, the main regions in which bluefin tuna are farmed in captivity include the Mediterranean, Mexico, Australia, and Japan. Though there are advantages of farming fish, in that ideally fishing of wild populations would decrease, it does come with negative implications. The question remains as to whether aquaculture can satisfy demand while benefiting wild populations as there are still many flaws in its application. Most aquaculture still relies on wild juveniles being caught in order to be raised and fattened in aquaculture as scientists struggle to raise bluefin tuna from spawn in captivity. This unfortunately further decreases wild fish stock before juveniles can reach sexual maturity and a chance to repopulate. Furthermore, captive tuna are fed a wide variety of small pelagic fishes, further depleting wild fish stocks of these species. Natural conditions are rarely replicated in farming environments with fish kept at higher densities than would be found in the wild. Proximity of fish to one another increases the likelihood of disease and parasites spreading and often discharge of accumulated feces as well as antibiotics and chemicals used to treat fish may leak into the surroundings. However, factors such as environmental impact, animal welfare, and sustainability vary greatly between farms. Today, so much as half of the fish consumed worldwide by humans is derived from aquaculture. With the right information, it is becoming easier to avoid consuming fish species that are on the brink of extinction instead opting to support those fishing responsibly. The more we overfish our seas, the less likely it is for overexploited fish populations to recover and provide stable food sources for us and other marine life in the future.
Approximately 70% of the world’s overall fish stocks are used, overused or in crisis.
This alarming figure puts in perspective the rate at which we are harvesting our food resources and in highlighting this, could allow us to reflect and take steps toward changing how we view the ocean and its contents.
Species Fun Fact
Bluefin tuna are one of the few warm-blooded fish, enabling them to inhabit both warm and cold waters adjusting their body temperatures accordingly. This is possible due to a specialized blood vessel network helping them to store the energy they produce while swimming.
For reference, or to find out more please explore the following:
Berkshire Encyclopedia of Sustainability: Natural resources and sustainability. Daniel E. Vasey, Sarah E. Fredericks, Lei Shen, Shirley Thompson
All information was collected and up to date in 2020.