Sea lampreys are leaving their mark on the Great Lakes and if their population isn't controlled they could damage the fishing industry, according to experts.

Jessy Nowak said he fishes all over Southern Ontario and he notices scars on his catch.

"You’ll see lamprey marks on them. Sometimes you’ll even find fish with lamprey on them around Wheatly and Lake Erie," said Nowak, who has been fishing for more than 60 years.

He says two out of every ten fish he catches will have lamprey bites on them.

Lampreys have mouths like suction cups that are lined with small teeth.  They made their way into the great lakes from the Atlantic Ocean decades ago.

The U.S. and Canadian governments kept lampreys under control using barriers a chemical sterilization, or lampricides.

But experts say their numbers are spiking again, and they aren’t sure why.

"They will attach themselves onto them and destroy the flesh of the fish and destroy the tissue," said Barbara Zielinski, who is conducting research on lampreys at the University of Windsor.

According to Zielinski, lampreys are very strong swimmers and they've been around for more than 800-million years.

They've lived through several ice ages and can adapt to different environments, she said.

Paul Sullivan with the Department of Fisheries and Oceans said lamprey’s wiped out 98 per cent of the fish population in some of the Great Lakes in the ‘60s.

Though they’re not large, less than a metre in length, lampreys are still a big fish in a little pond, Zielinski said.

"The great lakes are a much smaller area compared to the Atlantic Ocean so you have a concentration of these animals that are strong swimmers, with strong senses for reproduction," she said.

If nothing is done Nowak is concerned sea lampreys won’t just feed on the fish, but on the livelihood of those in the fishing industry.