by Erin Loury

Science Communication Intern/M.S. Candidate at Moss Landing Marine Labs

The Gulf of Mexico oil spill may spell big trouble for the Atlantic bluefin tuna, one of the most commercially valuable species that is already beleaguered by overfishing.   The area of the Deepwater Horizon spill coincides with critical bluefin spawning grounds, which the fish return to with amazing fidelity, a new study finds.

Dr. Steven Teo of the University of California at Davis and Dr. Barbara Block of Stanford University recently published a paper in the journal PLoS ONE, which reveals pronounced differences in habitat use between bluefin and yellowfin tuna in the Gulf of Mexico.  Using electronic tagging and fisheries catch data, Teo and Block discovered that bluefin are highly specific in their habitat use.  These giant fish select cool, productive water masses in the slope waters of the northern Gulf of Mexico, with a site fidelity reminiscent of salmon returning to their natal streams.  In contrast to yellowfin tuna, which are more widely distributed throughout the warm Gulf waters, "The bluefins' habitat requirements are relatively exact, so we can predict with reasonable accuracy where bluefin tuna are likely to be spawning at any given time based on oceanographic data,” Dr. Teo said. 

Unfortunately, this predictive power leads to a troubling prognosis in the wake of the Deepwater Horizon oil spill.  A model created by Teo and Bock revealed two major hotspot regions within the Gulf where bluefin tuna are found – one in the eastern Gulf of Mexico to the north of the Loop Current, and the other in the western Gulf of Mexico. Much of the eastern site lies in the path of the oil slick.  The spill also could not have happened at a worse time – during the peak of bluefin spawning season (April-May).

As Dr. Barbara Block writes on the Tag-A-Giant Blog, this fish just can’t seem to catch a break: “At a time when our Gulf of Mexico bluefin stock is vitally important to protect, where every last fish that makes it out of the Gulf is vital to the future of this fishery, when it is imperative they spawn without disturbance, an oil spill happens.”  Read more at ScienceDaily.com.  Tag-A-Giant has released a fact sheet on how the oil and chemical dispersants may affect bluefin tuna larvae and adults.