Green crabs invade Shediac Bay

The population of the invasive green crab has exploded in Shediac Bay.

"We had seven last year in three samplings for the three months. This year we have over 400 in two samplings; [we’re] expecting about 600 in three samplings so it's a significant increase," said Jim Weldon, manager of the Shediac Bay Watershed Association.

More precisely, researchers have found 442 green crabs in their traps. Weldon said that the rapid expansion was a surprise, and that he'll spend the next three days in the field monitoring the Shediac Bay watershed.

The green crab is a 10-centimetre long invasive species from Europe. It was first spotted in New Brunswick in the Bay of Fundy in the 1950s.

The species was first introduced on the northeastern seaboard in the early 19^th century and migrated north from there. It has since worked its way around Nova Scotia towards the Northumberland Strait.

The green crab eats oysters, mussels and clams. They are also known to eat large quantities of the shellfish seeds used in the aquaculture industry.

Weldon said he expects that the crabs will continue their spread northward until they reach water that is too cold for them.

"They have a tendency to just travel along the shore; they've been doing it ever since they were introduced in New England and then into the Bay of Fundy and around Nova Scotia," he said.

"Now they've started up the Northumberland Strait and they'll continue; we expect the pattern will be to continue until the temperature becomes too restrictive farther north."

Weldon said that the green crab can be used as a resource, but that it’s not an easily marketable species.

"There are processing plants that produce fertilizer and fish food," he said. "If we could figure out a way to trap thousands and ship them to one of these processing plants."

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.