Testing wild mahi mahi, the team found for the first time that even low amounts of oil can cut survival rates in half within a week of exposure. The fish also stopped spawning for at least a month.

“Those are massive numbers,” said Martin Grossell, lead principal investigator for one of 12 research groups funded by the BP’s Gulf of Mexico Research Initiative and a professor at the University of Miami Rosenstiel School.

The findings were first published in September in the journal Environmental Science and Technology.