BP Deepwater Horizon Oil Spill Wildlife Update: Bluefin Tuna

When the Deepwater Horizon oil rig blew, the timing couldn’t have been worse for the Atlantic bluefin tuna, a fish already living perilously close to the edge. The western population returns to breeding grounds in the Gulf of Mexico and the Florida straights in March, and the peak spawning period is April to May—coinciding with tens of millions of gallons of crude gushing into the Gulf.
 

Photo: NOAA

Wildlife experts were concerned that oil might foul adults’ gills, or that the dispersants used to break up the slick might cause the larvae to sink, threatening their survival. (Females lay up to 10 million eggs that float just beneath the water’s surface, most of which become dinner for other fish.)
 
While experts are still assessing the impact—and likely will be for years—it looks as though the breeding grounds, at least, weren’t as heavily hit as feared. “Although some historical bluefin tuna larval habitat was in the vicinity of the oil spill, it appears the majority of this historical bluefin tuna larvae habitat is outside the spill area,” NOAA said in an email.
 
NOAA scientists are employing a number of approaches to determine the effects of the oil spill on bluefin, which can reach 9.8 feet, weigh 1,400 pounds, and live for three decades.
 
Scientists aboard the NOAA ship Gordon Gunter are conducting an annual survey to gather more data on the distribution of larvae during the spawning period and further assess what proportion of the bluefin spawning area that may have been affected by the oil spill.
 
Researchers are also tagging the fish with satellite tags. Last May, they tagged four bluefin caught in the vicinity of the oil spill. “All fish completed their migration up to the Grand Banks and Gulf of St. Lawrence, where the tags separated from the fish on schedule after 90 days, floated to the surface, and reported data on the bluefins’ movements via satellites passing overhead,” NOAA said.
 
This year, researchers are deploying an additional 46 tags as part of a study that’s been expanded to assess the range of depths bluefins inhabit and the length of time they spend in the Gulf of Mexico each year. “The bluefin tagging studies will contribute to scientists’ understanding of this species’ potential exposure to hazardous chemical compounds following the BP spill,” NOAA said.
 
The voracious carnivores (check out the video above) feed on fish, squid, and crustaceans; in turn, they’re hunted by killer whales, pilot whales, and sharks. But humans pose the biggest threat to the species. Its flesh—the darkest and fattiest of any tuna species—is prized as sushi and sashimi, and overfishing has depleted its numbers. The highly migratory fish is managed domestically by NOAA, as well as internationally by a variety of organizations.
 
Bluefin fishing is prohibited in the Gulf because it’s such an important nursery; the western population is at about 18% of what it was in 1975, according to a 2008 NOAA assessment. Intensive overfishing has led the eastern population, which breeds in the Mediterranean, to be listed as endangered.
 
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Related articles:

Book Review: Four Fish: The Future of the Last Wild Food, by Paul Greenberg.

Toxic Brew: Carl Safina, a prominent ecologist and marine conservationist, explores the repercussions of the BP oil spill for sea life, and its uncertain future.

Atlantic bluefin tuna spotlight: A researcher investigates whether there are breeding grounds outside the Gulf, and a timeline documents the fish’s decline, and efforts to boost the population.