Fishermen on Canada's East Coast are worried that a tiny shellfish called the "cockroach of the sea" is jeopardizing their multimillion-dollar industries.

The green crab, which has no natural enemies, has been eating its way up the coast, feeding on clams, oysters, mussels and small fish.

The creatures originated in Europe. They settled in Maine, decimating the crab fishery. They've now invaded most of the shallow bays and estuaries of Nova Scotia and half of those of Prince Edward Island.

On the West Coast, the green crab has invaded waterways from San Francisco to Vancouver Island.

Permits to destroy the crabs

Last fall, the Department of Fisheries and Oceans agreed to issue permits allowing fishermen to legally catch and destroy the crabs.

Fishermen John Gotell, who works the Brudenell River in Prince Edward Island, says he's found the number of eels in his nets declining over the past few years, while the number of green crabs has increased significantly.

On a single day recently, he collected 40 eels and 300 green crabs.

"Seems like there's no end to them," he says. "You just get as many one day as you do the next.

Gotell and 15 other fishermen have permits to destroy the crabs they disentangle from their nets, an effort supported by those who make their living from oysters, clams and mussels.

The hungry predators are known to eat 40 clams a day.

Crystal McDonald, head of the the P.E.I. Aquaculture Alliance, says the crabs are extremely aggressive and hardy.

Turning a pest into food

But while fishermen consider them a pest, researchers are looking at the possibility of a green crab food fishery.

In a sterile test kitchen of the P.E.I. Food Technology Centre in Charlottetown, researchers have been cooking up green crab bisque, a kind of seafood soup.

Up until now, everyone thought the green crab was too small to bother with. At just 10 millimetres across, there's more shell than meat. But researchers here have found a way to separate bone from meat efficiently.

Richard Ablett, who works at the centre, says researchers are satisfied they can get enough meat out of the shell to make a fishery worthwhile. "We're getting something like a 30 per cent meat yield, which is quite high relatively," he says.

Ablett says the crab meat could be used by restaurants for chowder, or be packaged as frozen nuggets – or the crabs could be sold intact to markets in Europe.