Major commercial fish stocks around the world could collapse within decades as global warming compounds damage from pollution and overfishing, according to the UN.

“You overlay all of this and you are potentially putting a death nail in the coffin of the world fisheries,” the head of the U.N. Environment Program, Achim Steiner, has said.

His agency has released a report detailing new research on how rising ocean surface temperature and other climate changes are affecting the fishing industry. It says more than 2.6 billion people get most of their protein from fish.

The research sheds new light on an undersea flushing mechanism that helps renew fish stocks in three-quarters of the world’s primary commercial fishing grounds. Report author Christian Nellemann said global warming is disrupting this circulation.

“If this mechanism stops, we may risk a collapse in major fishing grounds” in the coming few decades, he said.”We are seeing shifts in marine life that we have never observed before,” he said.