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Volunteers help DFO track the spread of invasive crabs off B.C. coast threatening native species

Phillip Milligan displays 10 crabs on a folding table in his South Surrey garage, an alarming haul trapped a short drive down the road at Blackie Spit on Boundary Bay.

Distinguished by five-pointed spines next to each eye, the invasive European green crab out-competes native species and destroys eelgrass meadows, an important environment for juvenile salmon and Pacific herring.

“We have found more than enough green crabs to say that there is a concern here,” said Milligan, team leader of a volunteer crab trapping program funded by the Department of Fisheries and Oceans.

Milligan’s setup at Blackie Spit is one of three volunteer trapping operations in the immediate area organized by environmental non-profit Friends of Semiahmoo Bay.

Scientists say the results of “early detection” programs like this one indicate the invasive crab is riding a warming ocean north, posing a serious threat to native species in more remote and out-of-reach corners of the province. 

A group of crabs laid out on a paper towel on a table, being measured.
Phillip Milligan shows an array of European green crabs trapped by volunteers this summer off Blackie Spit on Boundary Bay. (Ben Nelms/CBC)

Invasive crabs set for population explosion

The crabs, which are often green but can also be red or yellow, originated in Europe and North Africa but spread around the world, clinging to the hulls of ships and drifting on ocean currents.

The species has been well established on the western coast of Vancouver Island for decades but was unable to defeat the stiff currents of the Strait of Georgia to reach the Lower Mainland.

That changed recently, said Christopher Harley, a zoology professor at the Institute of Fisheries and Oceans at the University of British Columbia. The first crabs to manage the crossing did so around 2018 and began appearing in Boundary Bay and Ladysmith shortly after that.

“We’re just at the point of the invasion where the pioneers have established,” he said. “Now we’re going to have a population explosion as they have all of their kids and grandkids.”

A person holds a large green crab close up to the camera. It is an olive colour, with a slight orange-speckle-like pattern.
Phillip Milligan shows the five distinctive spines on either side of a European Green Crab’s eyes. (Ben Nelms/CBC)

Volunteer trappers and scientists say their numbers are already up in Boundary Bay this summer.

Of the 10 crabs Milligan has stored in his freezer, eight are male, and two are female. Milligan worries that balance will allow them to reproduce in large numbers — if they haven’t already.

“The population of these crabs can really multiply,” he said.

The average European green crab lives up to seven years, and females can release up to 185,000 eggs multiple times a year.

Intervention still possible

Dense populations of European green crabs have long plagued coasts in eastern Canada and California, but climate change is bringing them farther north, said Thomas Terriault, a research scientist with the Department of Fisheries and Oceans at the Pacific Biological Station in Nanaimo.

Elsewhere, scientists have proposed a range of solutions, including turning the crabs into a biodegradable plastic alternative or even an appetizer.

A man holds a netted trap while crouching on a dock.
A volunteer kneels to check a trap for European green crabs at an Elgin Heritage Park dock on Wednesday. (Ben Nelms/CBC)

Although numbers seem to be rising in Boundary Bay and nearby locations, Terriault said it may not be too late to intervene and stop the spread in environmentally or culturally significant regions.

But that intervention requires an “all-hands-on-deck” approach, he said.

The DFO has partnered with volunteer groups, such as the Friends of Semiahmoo Bay and First Nations across the province, to help with early detection.

“It’s quite an interesting thing that we’ve found,” Milligan said, clutching a crab in his South Surrey Garage. “We want to do something about it.”

A person holds up a flyer that reads 'INVASIVE SPECIES ALERT!' with the European Green Crab on it. The flyer has been issued by the Department of Fisheries and Oceans.
A volunteer holds a pamphlet warning about the invasive European green crab. (Ben Nelms/CBC)

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