Green Crabs: Nothing Yet

Terri J Bell, CHN Marine Planning —

Lurking along coastal shores, with five spines on the side of its head and razor sharp claws- eating nearly everything and anything in sight is the European green crab, Carcinus maenas.

The influx of Green crabs, which are not native to Haida Gwaii, have damaged the ecology and economy along the Atlantic and Pacific coasts and are considered one of the “ten worst alien invasive species in the world” by the Department of Fisheries and Oceans.

A European green crab can vary in color from a yellow-red to dark-spotted green. Distinguishing this crab from others can be difficult, so look for the five spines or teeth on each side of the shell. Photo: Department of Oceans and Fisheries.

“They are quite disruptive when they arrive, if you catch them quickly, then you might be able to stop them, but once they are established you cannot get rid of them,” explains Stu Crawford, Haida Oceans Technical Team Ecosystem-based Management Coordinator. As the Green crabs hunt for food, they dig up eelgrass beds, destroying a place of shelter for juvenile fish to grow and smolt. They also damage clam beds and other shellfish populations. In extreme circumstances, the crab out-competes native crabs for food and space.

First spotted on and then detected on the west coast of Vancouver Island in 1999, the crabs are now a concern locally as they were recently found at Gale Passage near Bella Bella.

“They may eventually spread to Haida Gwaii from the central coast by ocean currents because the larva is free-floating. But they can also be moved to new areas by people, which is probably how they got to the central coast.  Juveniles can be hidden in fishing gear or larva can arrive in a ship’s ballast water,” explains Crawford.

The Haida Oceans Technical Team and Gwaii Haanas are actively preparing to prevent the crabs from establishing themselves in local waters by taking training that will enable them to effectively monitor and identify this invasive species. In June of this year, Tom Therriault, a research scientist with the DFO invasive species program travelled from Nanaimo, BC, to provide assessment training.

As part of their training, the team traveled to Naden Harbour to sample three different locations considered by Therriault to be most suitable for Green crab to establish. His areas of choice is based on stream location, floor sediments, and ocean salinity. Thankfully, no crabs were found in any of the traps the following day!

Clint Johnson and Niisii Guujaaw will be training other Gwaii Haanas staff, and HOTT will train the Haida Watchmen. In addition to monitoring local waters for early detection, HOTT is developing a management plan to try and prevent crabs from arriving and a rapid response plan should they be detected.

(l-r): Stuart Crawford, Ecosystem-based Management Coordinator, Haida Oceans Technical Team; Niisii Guujaaw, Resource Technician, Gwaii Haanas; Clint Johnson, Resource Conservation Officer, Gwaii Haanas; and Tom Therriault, Research Scientist, DFO set off to test their traps for capturing Green crabs. Photo: Terri J Bell, CHN Marine Planning

 

Stuart Crawford and Tom Therriaul note the species, size and sex of crabs caught in their traps. The monitoring results will also serve as a baseline for the current crab population in Naden Harbour. Photo: Terri J. Bell, CHN Marine Planning
An abundance of Red rock and Dungeness crab were found in the traps set in Naden Harbour. If Green crabs become established here they will radically alter the ecosystem. Photo: Terri J. Bell, CHN Marine Planning

PROTECT THE OCEAN

If you see a Green crab DO NOT put it back into the ocean! Notify CHN and DFO (contacts below). If possible take a photograph and then freeze the crab – CHN and DFO will want the specimen to confirm the invasion.

Please do your part and consider taking these precautions while fishing:

  • Clean, drain and dry off your boat and other equipment before heading into a new area. This will help stop the spread of Green crabs in their larvae and early juvenile stage.
  • Inspection your boat including the propeller, rudder, niche areas and boat trailer.

Please contact Stuart Crawford (CHN) < stuart.crawford@haidanation.com > or 250-626-3302 and DFO at 1-888-356-525.

Be the first to comment

Leave a Reply

Your email address will not be published.


*