Invasive snail creeps up on Nova Scotia lakes, ponds

At seven centimetres, the Chinese mystery snail, also known as the trapdoor snail, may look big for an aquatic snail. But it's fairly unassuming.

However, Ken Donnelly of the Nova Scotia Invasive Species Council says this species can quickly outcompete other snails and change the water quality of ponds and lakes, making it a concern for Nova Scotian ecosystems. 

Donnelly says they are being seen more often over the past month. He said even his organization was surprised when it found several of the snails in its fishnets on a recent trip.

"It would be hard to count them all, but they are definitely prevalent," said Donnelly. "The growth in reports is pretty significant. We're getting more and more of them. So we're concerned that there may be many more than we know about."

They were first reported in Ontario more than 90 years ago and have been slowly making their way around the country, Donnelly said. 

They seem to be mostly in the Halifax and Dartmouth areas, he said, but some have been observed near Annapolis Royal and as far as Sydney. 

Donnelly said the snails are sold in pet stores, which may be how they got into the ecosystem.

Jerry Wang, owner of Shrimp Lover & Tropical Fish in Dartmouth, says anyone purchasing snails, or any imported species for that matter, should not release them into the wild — even if they are dead. 

Some aquarium keepers can end up with too many of the snails. Wang said that leads some to consider getting rid of them by any means necessary. A single female can produce as many as 130 babies at once. 

He warns owners about disposal methods that could lead to their introduction into the wild.

"Please, if you don't like it, don't dispose of it in the river or flushing the toilet," said Wang. "Bring to the closest local fish store.

"Their lifespan is not that long. So if you have a fish store, they will keep them until they peacefully die off."

Other provinces deal with this snail differently from Nova Scotia. It's illegal to possess, release, sell or transport the snail in Alberta. 

Once the snail becomes established in an ecosystem, it is hard to get rid of them. 

According to the Canadian Invasive Species Centre, molluscicides used to manage similar species have shown to be ineffective in the control of the Chinese mystery snails. Donnelly says the chemicals could also affect other native species, so their use is not recommended. 

Instead, Donnelly says containment is the best practice when the snail has already been established in an ecosystem. 

"It's possible that a Chinese mystery snail might attach to their fishing boots or their equipment," he said. "So they should look at them, clean their equipment, and make sure there's nothing that's hitching a ride."

He encourages people to stay alert when fishing, kayaking or swimming at your local pond or lake. Nova Scotians who believe they might have spotted these aquatic snails should take a photo, note the location where they found them and call the Maritime division of Fisheries and Oceans Canada (DFO).

In a statement, DFO said the introduction of an aquatic species into a body of water where it's not native is illegal under the Aquatic Invasive Species Regulations.