The Red List: Bluefin Tuna


Experts agree that certain types of seafood should be avoided because they come from overfished stocks or are harvested in a way that damages the environment. Check out our Know Your Seafood infographic and our GO! Fish campaign for more information on the Red List and the delicious and eco-friendly alternatives.

 

Bluefin tuna is well-known, perhaps for its rich meat used in sushi and other dishes world wide. As a top predator that travels vast distances across oceans, it affects all other species below it in the food web. Unfortunately it is also being fished to death, but demand still shows no sign of lessening. 

Biology.
The bluefin tuna (genus Thannus) is an amazing animal. It has been called the King of the Sea, and the Tiger of the Sea. It is a massive and agile top predator that can swim up to 60 mph. This incredible fish spends most of its life in the open ocean and feeds mainly on smaller schooling fish. The largest bluefin can reach 1500 lbs (684 kg) and 15 feet long (4.58 m). They are slow to grow and reproduce as they reach maturity around 8-12 years old and can live to 33 years old.

Bluefin have a high tolerance for a wide range of temperatures. That’s because, unlike other fish, these tuna can thermoregulate; they are essentially warm-blooded animals. When bluefin swim and create body heat, they can keep that heat in using a special system of blood vessels. Since they can maintain their body temperature higher than the surrounding water, they can survive in colder water.

There are several different species and populations of bluefin. The Southern bluefin (Thannus maccoyii) is the only species that can be found in multiple ocean basins: the Pacific, Indian, and Atlantic oceans. The Pacific bluefin (Thannus orientalis) lives throughout the Indo-Pacific region and migrates long distances across it. The Atlantic bluefin (Thannus thynnus) is the biggest species, and it grows to be the oldest, but is also very slow to grow. There are at least three distinct populations of this species – the western Atlantic, the eastern Atlantic, and the Mediterranean.

Overfishing.
While in some areas local, traditional fishing for bluefin has a long history, sport fishing for bluefin tuna began in the early 1900s. It was only after about 1970 that their popularity and price soared. They are now highly prized and have a very high commercial value. As a favorite among sushi and sashimi lovers, bluefin can be identified under several names including hon maguro, kuro maguro, minami maguro, or toro (the fatty belly meat). Sometimes it’s also known as horse mackerel or atun de aleta azul.

The combination of being large and slow to grow and reproduce, and truly delicious, has been a death sentence for bluefin tuna. Due to a history of insufficient management efforts by the regulating bodies and an extremely high level of illegal fishing, most bluefin populations are extremely overfished.

Indeed, it is incredibly difficult to stop illegal fishing for bluefin when the catching them is so profitable. In January of this year, one 269kg (593 lb) bluefin sold for $736,000, meaning that it sold for approximately $1,240 per pound. This unbelievably high market value is a huge obstacle to protecting them.

Populations.
Pacific: Pacific bluefin are considered fully exploited, with no room to increase the fishery, and the US Southwest Fisheries Center declared in 2011 that they were being overfished. Yet, they are in much less trouble than the other bluefin species, and the IUCN lists them as a species of Least Concern. Still, they are in a precarious position, and, like bluefin everywhere, are often caught by longlining, a type of fishing that results in high levels of bycatch.

Southern: Worst off is the Southern bluefin, listed by the IUCN as Critically Endangered. Since 1973, their spawning (adult) biomass has dropped about 85% and it has shown no signs of increasing. It’s now considered seriously overfished or depleted, and it’s been estimated that 100 years from now there could be less than 500 adult Southern bluefin left.

Atlantic: The Atlantic bluefin species is currently listed by the IUCN as Endangered and the US government lists it as a Species of Concern. However, the Western Atlantic stock is listed as Critically Endangered.

The biggest problem for them is poor regulation and enforcement. In 2008, scientists recommended a fishing limit for the Mediterranean of 8,500 to 15,000 metric tonnes (9,370-16,535 tons) to let the species rebuild. Instead, the fishing nations set a catch limit at 22,000 mt (24,250 tons). However, the catch for the prior year was reported to be 61,000 mt (67,240 tons) – four to six times the levels scientists recommended as safe.

Fortunately, in recent years, the regulatory body, International Commission for the Conservation of Atlantic Tunas (ICCAT), has improved its regulations; in 2010, it set a catch limit of 13,525 mt (14,908 tons) but there are still big problems with enforcement. A 2010 study found that international trade statistics show that high numbers of illegal bluefin are still reaching the market.

Ranching.
This is a relatively recent issue. “Ranching” is the practice of capturing wild bluefin tuna and keeping them alive in pens, where they are fed and fattened for some time before being killed and brought to market. While ranchers claim the practice is sustainable, it still removes bluefin from the wild populations, often under breeding size, – and in this case, there is even less regulation: fishermen don’t always have to declare their catch the same way regular fishermen do. Additionally, it takes extremely large amounts of other wild fish to fatten tuna in this way, and the farms often cause pollution and damage surrounding habitats.

Aquculture methods are being developed to make it possible to breed captive bluefin. While this would theoretically lessen demand on wild bluefin, the issues caused by the location and management of the farms, and the large amount of wild fish it demands are still problematic.

Solutions.
You. While governments around the world must work together to set reasonable quotas, and enforce them, this avenue has had limited success in changing overfishing thus far. The most immediate thing each of us can do is reduce demand by choosing to eat other seafood that is more sustainable. This would reduce the motivation of fishers worldwide to hunt so aggressively for bluefin.

Avoid purchasing or ordering bluefin tuna. Encourage your local grocery stores and restaurants to take bluefin off the menu; if you see bluefin, don’t eat there. Not only is this species endangered, the meat of such large, top-of-the-foodweb species is loaded with high concentrations of mercury and PCBs.

Chef Barton Seaver describes the flavor of bluefin as “unique” but he points out that “we have eaten our way through this species' ranks and have forfeited our ability to consume this fish.”

The best substitute for most recipes, he says is pole-caught yellowfin tuna, but for grilling he also suggests albacore or wahoo.

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