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

Phillip Milligan displays 10crabs on a folding table in his South Surrey garage, an alarminghaul trappeda 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-competesnative species anddestroyseelgrass 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.

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."

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, butclimate change is bringing them farther north, saidThomas Therriault, 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 biodegradableplastic alternative or even an appetizer.

Although numbers seem to be rising in Boundary Bay and nearby locations, Therriault said it may not be too late to intervene and stopthe 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."