Fish Exposed to Oil From BP Gulf Spill Swim Half as Fast

This is the second study in several months suggesting that the BP Deepwater Horizon spill has had lasting harmful effects on fish

A female mahi-mahi
Stephen Frink/Corbis

It's not hard to imagine that the 2010 BP Deepwater Horizon oil spill, in which 4.9 million barrels of oil spewed into the Gulf of Mexico, hurt the wildlife there. But how much? Studies addressing this question have begun to come out, and they don't paint a rosy picture.

In March, research found that in several species of fish, including Bluefin tuna, young animals that were exposed to oil from the spill developed numerous heart defects that often proved fatal. Now, another study, by many of the same researchers, has found that young mahi-mahi exposed to oil from the BP spill swam nearly half the speed of unexposed fish. 

Mahi-mahi are among the fastest-swimming fish in the world (and a favorite on dinner plates, too). These slower mahi-mahi would be more likely to be caught and eaten in the wild, and to not make it to adulthood, the scientists said. "The worry is that if you have reduced swimming performance you’re going to be less effective at capturing prey, and less effective in avoiding (predators)," Martin Grosell, a study author and professor at the University of Miami, told Reuters.

That's not good news. As the Miami Herald noted:

Both studies — disputed by BP — are worrisome because tuna, whose numbers have dropped by as much as 75 percent in the last 40 years, and mahi began their spring spawning just as the spill occurred, sending fragile embryos across warm surface waters and into a patchwork of oil slicks that covered more than six square miles.

The scientists didn't directly measure fish in the wild, but created conditions in the lab similar to those that would have been found in the Gulf at the time of the spill, using oil collected from near the damaged wellhead and the water's surface in the summer of 2010. They exposed embryos and larvae of mahi-mahi to the oil for 48 hours and found that a few weeks later, these fish swam 37 percent slower than those that hadn't grown up in oily environs. 

Young mahi-mahi (Coryphaena hippurus), also known as dolphinfish, usually swim at a rate of five body lengths per second, the Herald reported. That's the equivalent of a six-foot human swimming 30 feet in a second. But young oil-exposed fish only swam three body-lengths per second.

Get the latest stories in your inbox every weekday.