When marbled crayfish were identified in a Burlington, Ont., pond last summer, experts were immediately on high alert. Though Canada is already home to various crayfish species, the marbled type has the ability to self-reproduce, meaning one alone can establish new populations by the hundreds.
Not only could the crayfish throw off the delicate balance of aquatic ecosystems by threatening food sources and habitat for other species, but they can also cause shoreline damage as they burrow holes into sand for protection.
“It’s quite frightening in the invasive species world to have something like this, and it’s very unique,” says Brook Schryer, assistant coordinator in the Invasive Species Awareness Program with the Ontario Federation of Anglers and Hunters. Schryer, along with his colleague Premek Hamr, a biologist and crayfish researcher, are part of a group of experts who were among the first to find and identify the species in Burlington’s City View Park.
The search for the little critters wasn’t an easy one, however. Despite the marbled crayfish being formally identified in July of last year, the species was actually first reported through iNaturalist—a global platform people use to identify and share information about plants, animals, and other biodiverse organisms in their environments—in October of 2021. Schryer, Premek, and the rest of their working group set out in the spring and summer of 2022 to locate the crayfish for further examination, but came up empty-handed both times. That’s with Environmental DNA (eDNA) technology showing positive results of the species in the area.
Finally, in July of 2023, a groundskeeper at City View Park flagged to the team that he had found one of the crayfish. Since then, the working group has collected over 50 marbled crayfish. The pond has now been drained twice in an effort to eradicate the species, but the team will test again in the spring to see if the draining was effective. Schryer says that the species typically cannot survive in temperatures under 4°C, so they are hopeful that, along with the draining, a stretch of colder temperatures will do its work.
“They’re still very small at this point, but when you’re talking about the possibility of two to 500 offspring per cycle and about two cycles a year, that’s exponential,” says Schryer.
The group has collaborated with partners from the City of Burlington and the provincial and federal governments to continue monitoring and controlling the crayfish. Schryer says they appear to be contained to one pond, and that it’s likely the crayfish was released by someone who owned it as a pet—which was recently prohibited in Ontario, for the very reasons it’s now a threat.
And not only are the crayfish a threat to natural species, they’re problematic for Ontario’s economy, too, says Schryer: “The fishing industry is huge and it provides so much money to our economy. When you have things that imperil that, like these crayfish, that could lead to reduced angling numbers and all sorts of different impacts.”
For Schryer, the case serves as an important reminder of the ripple effect in our ecosystems, where impacts can be hard to gauge. “There are just things we can’t predict, so I always think about the precautionary principle: ‘If you don’t know what’s gonna happen, don’t do it.’”
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