The Department of Fisheries and Oceans (DFO) is exploring control and containment options after trapping more than 70 live red swamp crayfish in a Halifax area lake.

The invasive freshwater species is indigenous to the southern U.S. and eastern Mexico. Over the summer, DFO and Saint Mary’s University researchers trapped and removed 70 live red swamp crayfish from Three Mile Lake, located next to Windsor Junction. 

During a media presentation along the Cobequid Road shore of the lake on Thursday, DFO aquatic invasive species biologist Sarah Kingsbury told reporters this type of crayfish has “severe or potentially severe” impacts on ecosystems. It preys on fish eggs, competes with native species for available resources, space, and calcium in the water. It can also alter the physical habitat structure and impact other species through its burrowing.

In addition, Kingsbury said homeowners with waterfront property on the lake could be impacted by bank erosion and destabilization. DFO is urging people to not move their traps or equipment in the lake. They’re also warning them to leave the crayfish alone.

“Please don’t move crayfish away from the lake or pick it up or interact with the crayfish. That can impact our trapping operations on the lake and you could accidentally introduce it elsewhere, which we want to avoid,” Kingsbury said. 

“This type of crayfish can host multiple types of parasites, and so that’s one more reason to not move the crayfish and interact with it. But also it’s another risk to our native species here.”

‘We are very concerned’

Current efforts are focused on determining the distribution of crayfish in the lake. Kingsbury said they’re trying to establish how many crayfish they can capture per trap over various points in time.

“Another thing we’re looking at is when do the crayfish stop going into the traps? So a lot of species will migrate into deeper water as it gets colder,” Kingsbury explained. “We want to know what is that cut-off point? When can we no longer trap them, and then when are we going to start again.”

While there’s no way to know exactly how the crayfish ended up in the lake, Kingsbury said as with most non-indigenous species, it occurs as a result of accidental or intentional human activity. She said this species is available through the live organism trade and is used for food, in aquariums, and as bait.

“We are very concerned because we don’t have native crayfish, so our species here are not accustomed to preying on crayfish. So that really changes the dynamics in that food web,” she said. 

“And also we’re not sure what the burrowing intensity will be because we haven’t had this type of species.”

Kingsbury described the crayfish as eating “basically anything it comes across.” The creatures tend to be more carnivorous when they’re younger and in need of more protein. As adults, they tend to be herbivores.

The shores of a lake in the autumn dotted with orange and yellow trees with a grey sky and a few white clouds dotting the horizon.
Three Mile Lake as seen from Cobequid Road on Oct. 19, 2023. Credit: Yvette d'Entremont

First official find of its kind in Canada

Although there have been reports of red swamp crayfish through the open source reporting platform iNaturalist, this marks the first time the species has been confirmed by DFO in Canada. Kingsbury said that means they can’t draw on past experience for more information about what to expect. 

“This is our first year of really doing an intensive study on the lake, so we’re not sure if we can categorize it as a thriving population,” Kingsbury said. “I’m not sure even what would be considered thriving versus not, but certainly established.”

Native species at risk from the crayfish include freshwater mussels, indigenous snail species, and juvenile fish. The largest crayfish recorded in research literature was found to have 500 eggs. 

Researchers were first alerted to the crayfish in Three Mile Lake in September of 2022 through a Facebook post in a local fishing group. Kingsbury said trapping yielded one living crayfish they were unfortunately unable to capture. They then returned this summer to research, monitor, trap, and remove the crayfish. Those efforts are ongoing.

“Clearly the crayfish that we saw last year survived the winter because we are now finding crayfish here this year,” Kingsbury said. 

“But from what we’ve read in the literature, crayfish make burrows and they stay in their burrows during the winter time. And if that burrow water doesn’t freeze, then they have a higher chance of survival.”

Concerns crayfish could move elsewhere

No crayfish have been found through trapping and monitoring of adjacent Third Lake and Powdermill Lake or in wetlands in between. But there are concerns they could move elsewhere, and so DFO is looking at ways to contain the crayfish.

“We are concerned that it could move beyond the water body,” Kingsbury said. 

“Part of the trapping is to figure out where exactly it is and how close it would be to an outlet to a lake, for example. And we are exploring options for putting in barriers.”

Kingsbury said DFO is working with provincial and federal partners and considering different options to control the Three Mile Lake crayfish population. 

At this time we’re not sure what the options are,” she said. “We’re still researching it. At this point, we’re really in the information gathering stage.”

There is one population of invasive crayfish in the province. Spinycheek crayfish have become established in Freshwater Lake in Cape Breton Highlands National Park. 

Saint Mary’s University researchers are urging anyone who spies a crayfish in Nova Scotia to contact them here

Yvette d’Entremont is a bilingual (English/French) journalist and editor who enjoys covering health, science, research, and education.

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