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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.
Parks Canada will continue to monitor brook trout through other methods, like its angler diaries program and an annual program deploying fyke nets in various Kejimkujik waterbodies to track native fish populations.
Donnelly said conservationists should move their focus away from the park to other areas where chain pickerel have not been introduced.
“If there is anything that can be done, it will be in the early days of an invasion, not later,” he said.
Trevor Avery, an Acadia University biology and mathematics professor, has tracked chain pickerel in Kejimkujik since their introduction.
His university team studies chain pickerel caught in the park, analyzing the contents of their stomachs. Chain pickerel are ambush predators, and Avery said they will quickly devour anything that fits in their mouth.
“They’re really good at what they do,” he said.
Avery said population management options range from extremes like the use of rotenone, a naturally occurring fish pesticide, to more moderate targeted fishing.
“Humans are really good at getting rid of things,” he said, adding that consistent fishing could help keep the bigger chain pickerel out of the water, though not completely get rid of them.
Recreational fishing
Nova Scotia is known for world-class brook trout fisheries, said Andrew Lowles, resource manager at the Nova Scotia Department of Fisheries and Aquaculture.
He said that history can be traced back to The Tent Dwellers, a book published in 1908 that tells the story of a group of friends on a weeks-long fishing trip through the area that is now Kejimkujik National Park.
But Lowles said chain pickerel, known for their hard-fighting abilities, also present an opportunity for anglers.
“They’re easy to catch throughout the summer when folks are on summer vacations, when they’re cottaging,” he said.
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