Protecting Atl’ka7tsem’s Marine Life
Monitoring for the invasive European Green Crab
The European Green Crab
The European Green Crab (Carcinus maenas) is an invasive species to British Columbia. The species has been introduced to our coasts via ship ballast water, where the crab larvae have hitched a ride from Europe and established in our waters.
These crabs pose a significant threat to marine ecosystems due to their aggressive behaviour, voracious appetite, and ability to adapt to their environment. The European Green Crabs (EGC) have few predators compared to native crab species, and will outcompete those native species for food and habitat. They poses a particular threat to sensitive eelgrass meadows, as their foraging behaviour involves cutting the eelgrass at the base.
The EGC was first detected in Canada in New Brunswick in the 1950’s and on the West Coast of Vancouver Island in 1998. Monitoring efforts are ongoing to track the spread of these invaders. The map on the right indicates locations of confirmed green crab sightings along Vancouver Island, Haida Gwaii, and other areas of the BC coast.
To date, there are no sightings of this invasive crab in Átl’ka7tsem!
Photos: Jeff Adams, sourced from https://ssisc.ca/green-crab
Key identification features
Distinctive Shell
The European green crab is recognizable by its 5 spines on either side of the eyes with three rounded lobes between the eyes and a pentagon shaped shell. Though they are called a green crab, as many can appear a mottled green-brown, they can come in many colours and should not be identified on colour alone!
Claws and Legs
Their pinchers – also called chelae – are different sizes. Walking legs are green and speckled with black.
The back leg tips are hairy and flattened to assist with swimming.
Size and Behaviour
Typically, the crab measures up to 10 centimeters across, with a broad, slightly flattened body. European Green Crabs are aggressive and territorial, outcompeting local species.
Photos: Sea to Sky Invasive Species Council https://ssisc.ca/green-crab
Though there have been no EGC sightings in Átl’ka7tsem (yet), they have been spotted nearby. In 2019, EGC were discovered in Boundary Bay, just east Tsawassen and south of Delta. Annual monitoring of that area is conducted by members, volunteers, and partners of the Friends of Semiahmoo Bay Society.
These invasive crabs can easily (accidentally) be trasported by huamns moving between these areas in ballast water, fishing gear, or on boats. The larvae also float in the water column for up to 90 days of their life, and could be naturally transported by currents into Átl’ka7tsem.
Due to the imminent threat and potential devastating impacts, local groups have coordinated monitoring efforts. In Átl’ka7tsem, EGC monitoring is conducted annually by the Sea to Sky Invasive Species Council, Bowen Island Municipality and Fish and Wildlife Club, and the Blue Act Marine Society and their many dedicated volunteers. Monitoring for these inadvertent invaders would not be possible without the time and hard work of these local organisations and their numerous volunteers.
To monitor for the EGC, baited crab traps are placed once a month from April to October in areas identified as suitable potential habitat for the crabs. These areas are often low profile, muddy, intertidal zones with vegetation for cover and foraging, for example the Squamish Estuary. The crab traps are baited with frozen fish and anchored in the water at low tide to prevent stranding anything caught in the trap. The traps are left for 24 hours then checked during the next low tide. Anything caught in the trap is identified and recorded, then safely released back into the ocean (except for EGC, which would be retained).
Monitoring efforts are supported and informed by Fisheries and Oceans Canada, and conducted under a Scientific License.
Current Monitoring Efforts
Tracking the European Green Crab
In Átl’ka7tsem, monitoring efforts have been underway to track the spread of the invasive European Green Crab. Researchers and volunteers have been conducting regular surveys to assess the distribution of this species. Data collected from these efforts are crucial for understanding the ecological impact and developing effective management strategies.
Monitoring sites include:
- Bowen Island
- Sunshine Coast (Williamsons Landing)
- Porteau Cove
- Furry Creek
- Squamish (Cattermole Slough, Mamquam Blind Channel, Central Estuary)
All monitoring locations in Átl’ka7tsem are noted on the Marine Reference Guide, our online interactive map.
If you think you have spotted a European Green Crab, please takea picture and report the sighting directly to Fisheries and Oceans Canada:
You can also help prevent the spread of EGC! Make sure to clean, drain, and dry all water vessels, sporting equipment, and other gear.
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