Drought could threaten salmon returning to N.S. rivers to spawn, say conservationists

Some conservationists say they are concerned the prolonged drought in Nova Scotia may cause long-term harm to salmon stocks.

Atlantic salmon return each fall from ocean feeding grounds to the rivers where they were born, looking for an ideal place to spawn. But with spawning season in October and November, critically low water levels are threatening how this important step in their life cycle plays out.

“I’m pretty worried about how this generation of salmon will survive,” says Amy Weston, managing director of the Nova Scotia Salmon Association.

Female salmon lay and incubate their eggs in a nest or gravel bed known as a redd. Weston said the fish are picky in where they choose to build a nest and require favourable water temperatures and water flow, two factors that drought conditions have affected.

Salmon prefer cold, oxygen-rich water, and the warmer the water gets, the less oxygen it contains. Low water levels also mean a reduction in habitat for fish and impede their movement, making them more vulnerable to predators.

While recent rainfall has helped to replenish some of the main watersheds where salmon spawn, Weston fears that if the drought persists, it could lead to other problems in the winter.

“When we have shallow conditions and should we get a cold winter, ice forms in the river. And if it's too shallow, it will form and freeze to the bottom of the rivers,” she said. “That then pulls up the gravel when it breaks up, and you can risk losing those redds.”

Fish in the province were already under mounting stress due to low water levels and a dramatic increase in the water temperature. In the St. Marys River, one of Nova Scotia’s largest and most significant salmon rivers, the drought’s effects have been especially severe. 

“Feeder brooks that keep the main branch flowing completely dried up. Gone, nothing in them,” said Scott Beaver, president of the St. Mary’s River Association.

He said the lack of flow left small trout and salmon parr trapped in shrinking pools of warm water, making them easier prey for natural predators. Low water levels can also hinder the migration efforts of adult salmon and expose them to predation.

Beaver said he'd feared at one point during the drought that “we might lose the 2025 spawning season altogether.”

But he said late October rains have likely provided a reprieve for the fish and offered hope to people working to ensure the survival of the species. 

Nevertheless, both Beaver and Weston said long-term solutions to restore natural buffers such as riparian forests are required to provide shade to help keep rivers cool. 

As extreme weather becomes more common due to climate change, Weston said, it is important that communities strive to take care of fish habitat.