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Invasion of the green crab: Intruder gobbles key species in Island waters

The invasive European green crab is proliferating at an alarming rate on the west and southern coasts of Vancouver Island, devouring smaller Dungeness crab and bivalves as well as the eelgrass that is critical to young salmon.

The invasive European green crab is proliferating at an alarming rate on the west and southern coasts of Vancouver Island, devouring smaller Dungeness crab and bivalves as well as the eelgrass that is critical to young salmon.

The Department of Fisheries and Oceans has identified hotspots around Sooke and Barkley Sound, but environmental groups and First Nations say the green crab’s infestation extends to Haida Gwaii and likely most parts of the B.C. coast.

They say “industrial trapping” of the green crab is essential before it wipes out local species and key habitats.

“An urgent coast-wide response is needed … we have to get them out of the water,” said Josh Temple, founder of the Coastal Restoration Society in Tofino. “It’s extremely concerning when we are trying to protect habitat, native species and save every last salmon we have.”

The European green crab is considered one of the world’s 100 most devastating invasive species, hitching rides on ships to establish big populations along the coasts of every continent except Antarctica. It was believed to be introduced in the San Fransisco area in 1989, and has moved north, where the species was first found in Barkley Sound in 1999.

Temple said that since 2016, the green crab has “exploded” on the west coast.

It is a voracious predator, eating other crabs and destroying critical habitat such as eelgrass, which acts as a nursery for small pelagic fish such as herring, anchovies and juvenile salmonids.

Fishermen are also concerned that increasing populations of seals in estuaries are already threatening young salmon populations, so destruction of key hiding areas is considered a serious threat to salmon stocks.

The Nature Conservancy of Canada said green crabs chop off the shoots of eelgrass at the base, which can “easily destroy an entire area.”

The Coastal Restoration Society hopes to start a pilot project with First Nations to trap green crabs on a large scale. Some modified prawn traps to avoid excessive by-catch are already in use near Tofino and Sooke.

Ryan Chamberland, who operates Vancouver Island Lodge in Sooke, is working with the T’Sou-ke First Nation to tackle the green-crab problem. He said a single trap off his dock in the Sooke Basin can capture between 25 and 50 a day.

Trapping this week by the Tlaoquiaht First Nation in Barkley Sound found 105 green crabs in less than an hour.

“I’ve been doing my own trapping program for about 18 months to see how bad it was,” said Chamberland. “The results are alarming.”

He is developing a community trapping program and a potential commercial trapping program with the T’Sou-ke First Nation. In the development stage with DFO, it’s awaiting final approvals and funding.

T’Sou-ke First Nation Chief Gordon Planes said the invasion of green crab in local waters is “massive” and a “rapid response” is needed to get populations under control.

He said green crabs are a direct threat to his nation’s food sources, such as Dungeness crab and salmon.

“We would like to see a collective response up and down the coast … the green crab isn’t going anywhere; we won’t get rid of it, but we have to control it,” said Planes. “This will all come at a cost. The [federal and provincial governments] have to understand the extent of this invasion and we have to decide quickly on how to control the numbers.”

Chamberland said DFO has determined the green crabs in the Sooke Basin have already developed a unique DNA structure, likely because the basin is considered a “closed system.”

The DFO will likely start new controlling programs there first, said Chamberland, and move to other areas once more is known. “The scary thing is, some of the crabs [from the Sooke Basin] have now been identified in the Burrard Inlet, the Gulf Islands and Washington state.”

Chamberland hopes increased efforts to trap green crabs can provide a silver lining for a new First Nations fishery.

Green crab meat is good to eat — perhaps not as good as a Dungeness, but edible nonetheless. Chamberland said it could be marketed on its own or as part of the imitation crab meat sector, which is made from pollock and other fillers.

The other silver lining to a potential green crab fishery is use of its shells in the biodegradeable plastics industry.

Associate professor Audrey Moores and a team at McGill University in Montreal have discovered a way to turn shell waste of green crabs into biodegradable plastics, which would break down under oceanic conditions.

The university started studying the problem after Atlantic Canada suffered severe infestations.

Moores said McGill is seeking financial support to use biochemical components of the European green crab to develop a marine biodegradable plastic, which would enhance recovery of deteriorated coastal ecosystems and provide a new industry to sustain coastal fishing communities.

DFO officials did not immediately return calls for comment. The department’s website says the European green crab has “the potential to upset the overall balance of the marine ecosystem. Unless controlled, this new aquatic invasive species will have a significant impact on biodiversity and habitat in the Canadian ecosystems.”

The DFO encourages anyone who finds them to report them at

Temple believes the crabs are everywhere.

“A lot more assessment has to be done in larger areas. European green crabs are likely up and down the coast and both sides of the Island and many started showing up in Haida Gwaii a few weeks ago,” said Temple, a commercial fisherman and diver for more than three decades.

“We really need to start a coast-wide industrial response. I think we have to go after every site. Get traps in the water in an industrial target trap program and work with DFO to equip and train First Nations to run the program in their territories.”

Temple said his society can provide training to reduce risk of COVID-19 exposure in First Nations communities.

“From 2016 to now, there have been massive outbreaks, and there are lots of gaps [in testing],” said Temple. “DFO has a very small department working on this. The [green crab] populations are exploding much faster than we can keep up.”

Temple said female green crabs can produce 200,000 eggs a year, and over a lifespan of five or six years can produce 1.2 million.

Chamberland said they can stay in the larval stage for four to six months, which allows them to survive in ships’ bilges for long periods and spread to other areas easily.

The Maritime provinces have been battling the green-crab invasion since the 1950s. Over time, it has severely endangered native species such as the rock crab, Jonah crab and lady crab.

In 2008 and 2009, Fisheries and Oceans Canada collaborated with fish harvesters and the provincial Department of Fisheries and Aquaculture to try various methods to fight the green crab, specifically trapping and removal. The results showed that, in areas where sustained removal of green crabs took place, the catch rate for the crabs decreased considerably and the native species, the Jonah crab, regained the territory.

“I think we can learn a lot about what happened on the East Coast, especially with the [green crab’s] movements, habits and what it does to eelgrass.” said Planes.

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The Global Invasive Species Database says the European Green Crab, or Carcinus maenas, is native to Europe and northern Africa. It is a voracious food generalist and in some locations it has caused the decline of other crab and bivalve species. The Nature Conservancy of Canada said the global fishing and shipping industries have helped the crab quickly broadened its range.

The species’ most distinctive feature is the greenish tinge on its shell. Although it can range from grey to red, it is primarily green in most regions. The shell has no bumps and extends to the eyes, giving it an almost saucer-like shape. On average, the crab is 60 millimetres long and 90 millimetres wide.