MIAMI — In a lab on Virginia Key, a group of baby fish are being put through their paces on a tiny fish treadmill.
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 6-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.
For a fish that needs speed to survive, this could mean bad news. Mahi, one of the most popular fish on menus, is already heavily fished. So losing a generation to an oil spill could take a toll. It also suggests that other fish suffered from the spill.
“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.