Invasive green crab has continued to expand its foothold in Newfoundland and Labrador and the Department of Fisheries and Oceans (DFO) is expanding its invasive species program in response.
Lynn Lush has been DFO’s Aquatic Invasive Species Coordinator for the N.L. region since 2019, in which time she’s seen green crab extend its reach from the first foothold in the province in Placentia Bay, where it established itself in 2007. Green crab first came to Massachusetts from Europe, having stowed away in the ballast waters of merchant ships in the early 1800s.
“Since that time, we’ve seen an expansion into Fortune Bay,” said Lush. “2019, we saw the first detection in St. Mary’s Bay. We are seeing green crab continue to expand along the south and west coast of the province. The furthest north along the Great Northern Peninsula that we’ve received notification of is Plum Point, so they’re quite northern.”
Lush not only categorized green crab as “exceptionally invasive,” but pointed out the unique strain of green crab that inhabits Atlantic Canada. Two different “strains” of this population moved their way north from the Eastern Seaboard of the U.S. and interbred along the way. This hybridization, according to Lush, created a more aggressive and cold-tolerant variety of green crab.
The biggest danger this aggressive variations of green crab presents to the ecosystem of Newfoundland and Labrador is their propensity for destroying eelgrass beds while foraging for food.
“The important part of the eelgrass is that it serves as a nursery area for juvenile species; some of them commercial species like Atlantic cod and lobsters, for example,” said Lush. “Eelgrass also serves as a carbon sink, so it helps reduce pressures on the ecosystem from carbon, which is part of the climate change issues we see. It also helps keep the shoreline stable, so without eelgrass, erosion of the shoreline is a bigger problem.”
Outside of anecdotal stories of species preying on green crab, DFO has no evidence that the invasive species has any natural predators within the province.
Lush posited that there are species that could eat crab, but they have not yet registered them as food due to their outsider status in the local ecosystem.
With natural predation out of the picture for now, DFO is left to slow the spread of this voracious species. By 2020, DFO began distributing control licenses to harvesters and citizen scientists to allow for the capture and destruction of the species.
As of 2024, there are 60 license holders within the province.
In 2023, the federal government implemented the Aquatic Invasive Species Fund, which provided $8.75 million nationwide to control issues like the one DFO is having with green crab. With this funding, Lush and her colleagues are using this funding to control their populations along the south and west of the province, as well as working with other environmental non-governmental organizations (ENGOs) to do concentrated trapping efforts in St. Mary’s Bay and Placentia Bay. Lush noted, however, that these efforts are focused on control, not eradication.
“Eradication of green crab once they establish, I would say is near-impossible. You can always hope, but eradication of this species would be exceptionally difficult, so the goal is to control the populations so the ecosystem can be protected and rebound in the presence of this invasive species,” said Lush. “Our purpose and our hope is that we contain it in the areas that they are now and we work together with partners and citizens to ensure that populations are kept at the lowest level possible to ensure the ecosystem copes with green crab being present.”
Once green crabs have established themselves in an area, Lush said they spread rapidly. As a species, they reproduce twice a year, with each female capable of laying 185,000 eggs. With this in mind, DFO has laid out a set of practices for anyone in or around the water, whether commercially or recreationally, to mitigate their spread.
To aid in mitigation, DFO recommends practicing the clean, drain, dry method. Any boat that is in a body of water should be cleaned off, drained of all water and be allowed to fully dry before being transported, especially if the vessel in question is bound to a separate body of water.
Lush also identified the importance of identifying green crab to report their presence to DFO representatives.
“A lot of them do have that green colour, but we’ve seen them red and my colleague on the Northern Peninsula saw one that was almost a beige colour. So, the colouration is not the only definition for green crab,” said Lush. “There are five spines along each side of the eye, and between the eyes there is three little lumps that are identified against our native species.”
To report a green crab sighting in Newfoundland and Labrador, call 1-855-862-1815 or email DFO.NLAIS-EAETNL.MPO@dfo-mpo.gc.ca.
