In the years after the 2010 BP oil spill, the number of fish in the deeper parts of the Gulf of Mexico dramatically declined. According to a major multi-year study published Monday, fish populations dropped by about 60%, while krill that whales and others eat plummeted 72%. Researchers said there’s no other cause they could find for the drop except the BP oil spill. Dispersants used after the spill caused many problems, and new studies show that in future accidents, it would be better to avoid those chemicals and instead add agents that increase oil-munching microbes.