Mussel movement: How'd these giant aquatic visitors get into an Alberta stormwater pond?

·3 min read
Hanna Wheatley, 9, shows off the shells she found in a Sherwood Park stormwater pond. (Submitted by Kimberly Wheatley - image credit)
Hanna Wheatley, 9, shows off the shells she found in a Sherwood Park stormwater pond. (Submitted by Kimberly Wheatley - image credit)
Hanna Wheatley, 9, shows off the shells she found in a Sherwood Park stormwater pond.
Hanna Wheatley, 9, shows off the shells she found in a Sherwood Park stormwater pond.(Submitted by Kimberly Wheatley)

The big shells found in a stormwater pond were a mystery to the Sherwood Park children who found them, but some experts are equally puzzled about how they got there.

"It kind of looked like an oyster," said nine-year-old older Hanna Wheatley, who made the discovery with brother Blake, 7, near their home in Sherwood Park's south end. "I think they're pretty cool."

They'd seen something similar at the ocean but never in landlocked Alberta. Whatever had been living in the shells was long gone.

The kids did a little more research (poking around with a stick) and turned up about a half-dozen empty shells in the man-made pond, part of the Upper Nottingham Stormwater Management Facility.

Their mom, Kimberly Wheatley, got caught up in the mystery of the shells, which were about the size of a hand and pearly-white on the inside.

A photo posted to a local Facebook page elicited a few thoughts, including a comment from one person who had boiled up about 50 of them and was "not impressed with the taste."

"Clams is what the consensus was, but I can't imagine it," Wheatley said.

In fact, they are most likely clams or mussels, said Alberta Environment and Parks aquatic scientist Ron Zurawell after studying a photo.

"Anglers do periodically pull one up on a fishing line," he said. "More frequently we see evidence of them by witnessing the shells after the clams die off — we'll find the dead shells washed up on shore."

The shells found by Hanna Wheatley and her brother Blake were likely from a mussel that is native to Alberta.
The shells found by Hanna Wheatley and her brother Blake were likely from a mussel that is native to Alberta. (Submitted by Kimberly Wheatley)

Zurawell said the solitary organisms, which have been in Alberta for thousands of years, are typically found in lakes and slow-moving rivers. They can flow from one body of water to another or be distributed by wildlife, he said.

But Zurawell was surprised to learn where these were discovered.

"I personally haven't had ... anyone showing this size of mussel from a stormwater pond, so I find that kind of interesting," he said.

Heather Proctor, a biological sciences professor at the University of Alberta, said it would have taken years for them to get that big.

"How they got to a stormwater pond is a good question," Proctor said in an email. "If the pond has no connection to a natural water body, a human would likely have had to move them."

Proctor suggested someone may have been keeping the shells as a decoration and dumped them into the pond.

A University of Alberta professor suspects people likely put the shells in the pond, which isn't connected to any natural waterways.
A University of Alberta professor suspects people likely put the shells in the pond, which isn't connected to any natural waterways.(Google Maps)

According to Zurawell, Alberta has more than two dozen species of bivalves that can be as small as a pinhead or as large as the ones found by the Wheatley children.

Those particular shells, he said, likely were Pyganodon grandis, a species of freshwater mussels commonly known as a giant or northern floater.

"That's by far the largest one that we would see in Alberta," he said. "They'll grow to about that five-inch size, which is quite large."

Zurawell said mussels are good for the ecosystem, filtering the water and providing a food source for animals like muskrats.

They're also edible for humans but Zurawell offers a word of caution given Alberta's proclivity to toxin-producing blue-green algae blooms. "These mussels and clams do filter-feed rather indiscriminately," he said.

Hanna Wheatley has no arguments with that advice.

"I think that'd be pretty gross."