Trout catch at Kejimkujik decimated by invasion of voracious predator

Kejimkujik National Park in Nova Scotia is pausing its annual brook trout census because an invasive species is devastating the local ecosystem.

The census started in the 1990s with volunteer fly fishers who would count, weigh and measure any brook trout they caught to help Parks Canada monitor the species. 

However, Parks Canada told CBC News in a statement that this year's census is being paused due to the impacts of chain pickerel, which it said accounted for nine of every 10 fish caught in 2025 in the national park in western Nova Scotia. 

“With the arrival of invasive chain pickerel, the number of brook trout reported in the creel census is not currently large enough to meet statistical power for this monitoring project,” said a spokesperson for the agency. 

Chain pickerel, illegally introduced to Nova Scotian waters in 1945, spread throughout the province and made their first appearance at the park in 2018. Once established in a water system, they quickly take over, eating everything they can — other fish, reptiles, frogs, dragonflies, even ducklings.

Data from the park's angler diary program shows that the voracious predator's catch rates skyrocketed from 18 per cent in 2020 to 66 per cent in 2021 and over 80 per cent the next year. 

Ken Donnelly, executive director of Invasives Canada, said once chain pickerel get established, it is nearly impossible to get rid of them. 

“It's sad that it's come to this, but I fully understand where they're coming from,” he said of Parks Canada's decision, adding that it feels “a little defeating.”

According to Parks Canada, Kejimkujik includes 46 lakes and ponds and more than 30 streams and rivers, most of them part of the Mersey River watershed, which originates north of the park and is the largest in Nova Scotia.

Due to that connectivity, permanently protecting all of Kejimkujik or the Mersey River system from chain pickerel is not possible, the agency says.

Kejimkujik staff tried creating fish barriers, but due to flooding, they were not effective in blocking the spread.

That does not mean they have given up on mitigation efforts. 

“With the help of volunteers, Parks Canada staff have removed more than 5,300 chain pickerel and counting,” said the agency. 

Chain pickerel remain under mandatory retention at Kejimkujik, meaning anglers who catch them can't release them back into the water. All native fish species, including trout, must be returned to the water.