Bluefin: Fast and Hungry
The word “tuna” comes from the Greek meaning “to rush.” Bluefin are able to reach speeds of up to 90 kilometers per hour. During high-speed acceleration, tuna are able retract their fins into slots. They undergo long migrations, constantly swimming to breathe and continually generating heat to elevate and maintain muscle, eye, brain and internal temperatures above ambient water temperatures.
As a result of bluefin tuna’s warm-blooded nature, they are voracious predators, requiring large quantities of nutritious prey to survive. Bluefin’s primary prey sources in the western Atlantic Ocean have also faced intense commercial fishing efforts. With record low populations of bluefin, we are now also facing low populations of their primary food sources.
Off North Carolina’s coast, Atlantic menhaden are the most common prey item, accounting for nearly 96 percent of their diet. Farther north, bluefin feed almost entirely on sand lance, with squid and other fish species making up an smaller portion of their diet. Atlantic mackerel and herring are important prey species in certain regions of the Gulf of Maine.
There are only two known spawning grounds for Atlantic bluefin. The Gulf of Mexico is the primary spawning ground for the western Atlantic stock. Though directed fisheries for bluefin have been banned in the Gulf since 1982, ongoing incidental catches continue to deplete the stock. As a result, the spawning stock of Atlantic bluefin tuna in the western Atlantic has declined by more than 82 percent.
Atlantic Bluefin Tuna in the US
Western Atlantic bluefin tuna are targets of tuna and swordfish fisheries all along the east coast of the U.S. and in the Gulf of Mexico.
The east coast directed fishery yields relatively small harvests of schooling and medium-sized bluefin, with recreational fishing forming the bulk of the catch. Commercial fisheries are currently allowed to catch and sell three large bluefin per trip, while recreational fishermen can keep one bluefin per day.
In the Gulf of Mexico, the directed harvest of bluefin is prohibited. However, fishermen in longline and trawl fisheries are allowed to keep one bluefin per trip as an “incidental” catch. Bluefin migrations bring spawning age tuna – at least nine years old -- into the Gulf from January to June.
As a result of high temperatures and depleted oxygen levels, bluefin caught in the Gulf experience extreme physiological stress and are more likely to die when caught and discarded in the longline fishery.
Prior harvests of bluefin tuna around the world have shown that this species is highly susceptible to population collapses resulting from commercial harvests, with some populations never recovering to commercially viable levels.
In particular, bluefin tuna populations off the coast of Brazil and northern Europe remain absent many years after supporting some of the largest bluefin landings in the world.
Unless we act fast to stop overfishing of bluefin tuna and preserve their prey, it is unlikely that bluefin will ever recover.