Tunas and Marlins Officially Classified as Threatened

An underwater photo of Southern Bluefin Tuna swimming above a fish farm net.
The Southern Bluefin Tuna (Thunnus maccoyii) is listed as "critically endangered" on the IUCN's Red List of Threatened Species. If its population continues to decline, the species faces the possibility of extinction. It's not alone. Scientists classified the Atlantic Bluefin Tuna (T. thynnus) as "endangered" and Bigeye Tuna (T. obesus) as "vulnerable." (Ian Gordon / Auscape International)

Extinction is a real possibility for three species of tunas. That’s one of the messages from a new study released today online in the
journal Science

Researchers assessed the range and populations of all 61 species of scombrids (tunas, bonitos, mackerels and Spanish mackerels) and billfishes (swordfish and marlins).  They determined that five fish are officially “threatened," a category that describes species that are "critically endangered," "endangered," or "vulnerable." The five species are:

Five out of 61 may not seem significant, but the scientists warn otherwise. These species are among the ocean’s top predators. If their populations decline, the impacts will move like a ripple through the marine foodweb

The report, authored by Bruce Collette, a senior scientist with NOAA’s Fisheries Service, and 32 other scientists used the criteria set forth by the IUCN Red List to assess the global populations of these fish. The IUCN Red List is a scientific and peer-reviewed method of measuring the conservation status of the world’s plants and animals. 

Overfishing is one of the main factors behind the population decline of these fish. Consumers will pay top-dollar for tuna, bluefin in particular. The sale of a single bluefin made headlines earlier this year when it fetched nearly $400,000 in a Japanese auction. 

The tuna’s biology also complicates its outlook. It takes some bluefin as many as eight years to reach sexual maturity. This means that it will take time – not only effort – to increase stocks of these fish. And because bluefin tuna spawn for only short periods of time in specific places, like the Gulf of Mexico, the study says they’re more “susceptible to collapse under continued excessive fishing pressure.” 

Could we just shutdown some of the fisheries? That is an option, but the report warns that without rules and deterrents the fish would likely be illegally harvested. A major investigation by the International Consortium of Investigative Journalists, published in 2010, explores some of the illegal practices and trading that already occur with the Atlantic bluefin tuna fishery

The Science study acknowledges the political challenges of managing fish that migrate across maritime boundaries. Nations currently work through Regional Fishery Management Organizations (RFMOs) to monitor and manage tuna and other fish. The report comes just before the tuna RMFOs meet next week in La Jolla, California.

Editor's Note: Dr. Bruce Collette is a zoologist with the National Systematics Laboratory of NOAA's Fisheries Service, located in the Smithsonian's National Museum of Natural History. You can see photos and maps, listen to a podcast, and explore other resources related to the Atlantic Bluefin, here on the Ocean Portal.

July 2011