A team of scientists at the University of Miami published a study concluding that mahi mahi, a pelagic fish, exposed to Deep Water Horizon crude oil even for short periods of time struggle to swim.
According to a report by the Miami Herald , mahi which depend on speed in order to survive, have significantly slowed in it's ability to swim quickly then fish not exposed to the BP oily mixture.
The inch-long mahi-mahi, being used as part of a study to assess damage caused by the Deepwater Horizon oil spill that spread crude across the Gulf of Mexico for 87 days in 2010, were exposed when they were embryos to oil collected during the cleanup. Now, at 25 days old, the oil is doing exactly what scientists suspected it would do: hamper the swimming of one of the ocean’s fastest fish.
And significantly so. Young mahi usually swim at a rate of five body lengths per second. For perspective, imagine a six-foot man swimming 30 feet in a second. The fish, struggling against a current in a little tube attached to a propeller called a swim tunnel, can only muster three body lengths.
“Any life form is optimized compromise,” Martin Grosell, one of the study’s authors, said as a way of explaining physiology perfectly evolved to maximize speed. And if you mess with that treaty of parts, he said, “you’re going to increase its vulnerability.”
The treadmill study marks the second in recent months by the University of Miami Rosenstiel School of Marine and Atmospheric Science that has found that oil from the largest spill in U.S. history damages young pelagic fish, the large predators found in the open ocean. In March, UM researchers working with National Oceanic and Atmospheric Administration scientists determined that the BP oil also damaged the hearts of tuna embryos, a condition that likely killed them in the wild.
Both studies — refuted 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.
BP , of course, refutes the study, stating that the study only looked at juvenile fish and not adults.
“The tests only looked at impacts to fish under one year of age,” he said. “Even if there had been an effect on a single-year class of such fish, the study does not provide any evidence to show that an effect on that group of fish would have had a population-level impact.”
Mahi are carnivores and foragers, so they swim fast. But when he turned on the treadmill, Mager was surprised to see that the outwardly healthy fish swam much slower. The ones exposed as embryos swam 37 percent slower. Those exposed as juveniles dropped 22 percent.
Because they are so sensitive to change, pelagic fish — and particularly fragile embryos and juveniles — can act as a kind of canary in a coal mine. So the information that Mager and the team have collected for the study, one of several ongoing at the school, will be fed to modelers to determine a more expansive view of the ecosystem after the spill and help figure out the limits for how much oil it can tolerate before damage happens.