European Green Crab in Newfoundland Waters

The European green crab (Carcinus maenas) is native to several European coastal areas. It was found in North America in the early 1800's and recently arrived in Newfoundland waters, adapting and expanding rapidly in its new environment. Green crab is small to medium in size and reaches a maximum carapace width of 10 centimetres. It is distinguished from other crabs by the five pointed spines appearing on the outside of each eye and the three small rounded spines between the eyes. Other characteristics of green crab include slightly flattened back legs that aid in its rapid movement. Its colour can range from bright green, brown and orange to red, often depending on how recently the crab has molted.

One species often confused with the green crab is the rock crab (Cancer irroratus), due to the rock crab’s size and shape. A rock crab can be distinguished by its scallop-shaped carapace consisting of nine rounded teeth on either side of the eyes.

European green crab

European green crab

Rock crab (front) and green crab (back)

Rock crab (front) and green crab (back)

Environmental Impact of Green Crab

Environmental Impact of Green Crab Green crab primarily feeds on shellfish and other crustaceans, but has been observed eating small and juvenile finfish in eelgrass beds. It is a naturally aggressive and territorial crab species. There is also concern that green crab may damage eelgrass habitat: when digging for prey in the sediment or making burrows, green crab cut the roots of the eelgrass, which destroys this ecological habitat.

Unless controlled, this new aquatic invasive species will have a significant impact on biodiversity and habitat in the Newfoundland ecosystem.

Discovery and Survey Findings

In August 2007, European green crab was confirmed in the northern regions of Placentia Bay. This discovery raised significant concerns because of the potential negative impact of this species on biodiversity and habitat in these regions. Following the initial discovery of European green crab in North Harbour, Placentia Bay, the Science Branch of Fisheries and Oceans Canada in collaboration with Memorial University of Newfoundland and the provincial Department of Fisheries and Aquaculture, conducted several rapid assessment surveys for aquatic invasive species in Placentia Bay. The largest green crab population was observed in North Harbour. It was also found in smaller numbers in surrounding areas and along the west and southwest coasts of Placentia Bay. This raised concern as small populations may expand rapidly. Green crab was also found on the west coast of Newfoundland in St. George’s Bay near Stephenville in 2008.

Green Crab Distribution in Newfoundland Waters

AIS Survey / Stewardship Program Areas 2006-2009

  • Arnolds Cove: Placentia Bay
  • Baine Harbou:r Placentia Bay
  • Baker Cove: Placentia Bay
  • Bakers Cove: Placentia Bay
  • Beau Bois: Placentia Bay
  • Bests Harbour: Placentia Bay
  • Bittern Cove: Placentia Bay
  • Black River: Placentia Bay
  • Bloody Point: Placentia Bay
  • Boat Harbour: Placentia Bay
  • Browns Cove: Placentia Bay
  • Butlers Island: Placentia Bay
  • Civil East Cove: Placentia Bay
  • Clay Cove: Placentia Bay
  • Cocks and Hens Cove: Placentia Bay
  • Come by Chance: Placentia Bay
  • Cook Brook: Bay of Islands
  • Coopers Cove: Placentia Bay
  • Corner Brook: Bay of Islands
  • Crabbe Cove: Placentia Bay
  • Davis Cove: Placentia Bay
  • Deer Brook: Bonne Bay
  • Dog Harbour: Placentia Bay
  • Doting Hole: Placentia Bay
  • East of Placentia Mans Point: Placentia Bay
  • Fair Haven: Placentia Bay
  • Flat Island: St. Georges Bay
  • Fox Harbour: Placentia Bay
  • Garden Cove: Placentia Bay
  • Goose Arm: Bay of Islands
  • Great Brule: Placentia Bay
  • Great Sandy Harbour: Placentia Bay
  • Gulch: Placentia Bay
  • Hollets Cove: Placentia Bay
  • Hound Island: Placentia Bay
  • Jean Cove: Placentia Bay
  • Jeffery Cove: Placentia Bay
  • Kingwell: Placentia Bay
  • La Plante Cove: Placentia Bay
  • Lamaline: Placentia Bay
  • Lawn: Placentia Bay
  • Little Bay: Placentia Bay
  • Little Harbour East: Placentia Bay
  • Little Harbour West: Placentia Bay
  • Little Port Harmon: St. Georges Bay
  • Little Sandy Harbour: Placentia Bay
  • Little St. Lawrence: Placentia Bay
  • Lomond: Bonne Bay
  • Long Harbour: Placentia Bay
  • Maggotty Cove: Placentia Bay
  • Marystown: Placentia Bay
  • Mattis Point: St. Georges Bay
  • Mooneys Point: Placentia Bay
  • Muddy Hole: Placentia Bay
  • Northeast Arm Placentia: Placentia Bay
  • Neddies Harbour: Bonne Bay
  • North Arm: Western NL
  • North Harbour: Placentia Bay
  • North of Baker Cove: Placentia Bay
  • North of Brimstone: Point Placentia Bay
  • North Tilt Island: Placentia Bay
  • Old Cove: Placentia Bay
  • Penguin Arm: Bay of Islands
  • Piccadilly: Port au Port Peninsula
  • Pipers Hole: Placentia Bay
  • Placentia: Placentia Bay
  • Placentia Sound: Placentia Bay
  • Point au Mal: Port au Port Peninsula
  • Pools Cove: Fortune Bay
  • Port Harmon: St. Georges Bay
  • Port Saunders: Northern Peninsula West
  • Prowseton: Placentia Bay
  • Red Island: Placentia Bay
  • Rock Harbour: Placentia Bay
  • Rocky Cove: Placentia Bay
  • Rocky Harbour: Bonne Bay
  • Rose Blanche: Southwest Coast
  • Sandy Cove: St. Georges Bay
  • Sandy Harbour: Placentia Bay
  • Southeast Arm Placentia: Placentia Bay
  • Shallop Cove: St. Georges Bay
  • Ship Harbour: Placentia Bay
  • Southern Harbour: Placentia Bay
  • Spanish Room: Placentia Bay
  • Spencers Cove: Placentia Bay
  • St. Andrews: Southwest Coast
  • Staceys Point: Placentia Bay
  • Stephenville Crossing: St. Georges Bay
  • Swift Current: Placentia Bay
  • The Hole: Placentia Bay
  • Woods Island: Bay of Islands
  • Woody Island: Placentia Bay
  • York Harbour: Bay of Islands

Mitigation Methods to Control the Spread of Green Crab and Decrease its Impact

Ballast water is an identified source for the introduction of this aquatic invasive species and may be responsible for the introduction of European green crab in Newfoundland. Green crab has a long larval phase and can survive for extended periods in ballast water tanks. Adult green crab can also survive for long periods out of the water or in freshwater. Other pathways of introduction may include the movement of gear from one area to another and the unintentional release of by-catch species outside the area of capture. To control the spread of green crab, it is important to check and clean fishing gear and boats.

In 2008 and 2009, Fisheries and Oceans Canada worked with fish harvesters, the Fish, Food and Allied Workers Union, Memorial University of Newfoundland and the Department of Fisheries and Aquaculture to test various mitigation methods including trapping and removal. The results indicated that where sustained collection of green crab took place, the catch rate decreased significantly and the native species, rock crab, returned to the area.

References

© Her Majesty the Queen in Right of Canada, 2010
DFO/2010-1655
Cat. No.: Fs23-555/1-2010-PDF
ISBN: 978-1-100-14903-5

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