The green crab is an aggressive, non-native species, measuring about 10 centimetres long that was first introduced from Europe to the northeastern seaboard in the early 19th century.
The P.E.I. Shellfish Association is now trying to catch and destroy as many of the crabs as possible. Shellfish harvesters are concerned the crustaceans are eating their clams, mussels and oysters, reducing their catch.
Frank Hansen has been trapping the creatures for about eight weeks. It's a bit of an uphill battle just to keep the green crab population in check, he said. In the short period of time Hansen has been fishing, he has caught more than 25,000 crabs.
"We just wanted to try and get ahead of the population," he said.
The P.E.I. Shellfish Association is working with Neil MacNair, provincial aquaculture director, to find a solution to the green crab problem.
"It's an aggressive predator. It's been known to be an aggressive predator in other areas of the world. It's been blamed for the demise of softshell clam populations in the States," MacNair said.
"So yeah, there's a good reason to be concerned. It has an impact on habitat and also on our shellfish species."
The numbers of green crabs are increasing and the pests are now spreading to the west side of the Island. Hansen said there may be little anyone can do about it and efforts may be futile.
"I think we're kind of feeling the waters here now just to see if we could trap these things, and I'm not sure what impact we'll have with 50 traps but with more traps, maybe," Hansen said.
Green crabs were first spotted in eastern P.E.I. in 1998. Now they're found all the way to West Point on the South Shore and Malpeque Bay on the North Shore.
"We were surprised at the numbers that were in there," MacNair said, "We thought the numbers would be lower than they are. So he's getting a lot of crabs in there — more than we expected."
MacNair said attempts have been made to make a commercial fishery for green crabs.
"We've tried the live market, we've tried to develop a product that was edible with no luck. We tried it as lobster bait but we didn't have very good success with it," he said.
Hansen will be fishing until the fall, then depending on if the numbers show the fishing is making a difference, he may continue the fishing next year.
Green crab makes list of top 100 worst alien invaders
According to the federal Department of Fisheries and Oceans, the green crab is ranked among the 100 worst alien invasive species worldwide, and one of the most successful ones, being an aggressive competitor and a prodigious reproducer that is tolerant of a wide variety of marine environments, with the ability to alter entire ecosystems at great economic cost.
A 2006 Harvard University study indicated that the crab's northern success could be thanks to new lineages, added to northern populations in Nova Scotia, that may have adaptations that allow the species to persist in a wider range of environmental conditions.
Scientists say that once green crabs arrive, very little can be done to eradicate them. The green crab has already altered coastal environments around Atlantic Canada, British Columbia and the east coast of the United States.