Local rivers and streams getting too hot for trout
Trout vulnerable as temperatures rise in Alberta’s rivers and streams
As the province closes streams and lakes in southern Alberta to fishing, scientists say the high temperatures in the waterways could still be deadly for some species — particularly trout.
Officials with Alberta Environment and Parks have closed more than 18 fisheries in the past week to protect fish populations in areas with water temperatures rising as high as 24 Celsius from the normal 15- 18 C.
It’s the first time in recent memory that streams and rivers have been closed for temperature- related reasons.
“Considering some of the extremely hot temperatures that we’ve seen this summer, combined with extremely low flows of our flowing waters, we’ve taken the step of closing angling in some streams where we think the impact of even catch- and- release fishing on fish populations could be problematic,” said Paul Christensen, senior fisheries biologist with Alberta Environment and Parks.
Closures include the Bow and Elbow rivers through Calgary, parts of the Castle River, the Sheep and Highwood River, as well as parts of the Oldman and Belly rivers.
The closures have already started to affect Alberta’s fishing guides and outfitters, but many realize it’s necessary to ensure the longer term sustainability of fish populations.
Not only can fish die off in hotter waterways, but Christensen said temperatures can also negatively affect how they feed, grow, breathe and reproduce.
“A lot of these factors would be contributing to the poor health of fish,” he said.
“If you combine that with the stress that angling could cause, even on caught- and- released fish, we felt the appropriate action to take was to close fishing temporarily until water temperatures recovered to a point that additional stress from angling won’t be problematic for the population.”
Some fish, such as bull trout and westslope cutthroat trout, both threatened species in Alberta, are extremely sensitive to high water temperatures, particularly above 24 C.
“That’s nearly lethal for some trout,” said Lorne Fitch, an adjunct professor at the University of Calgary, who spent 35 years as a leading provincial biologist. “Warmer water contains less dissolved oxygen. It’s just like putting a plastic bag over our heads. It creates a bit of stress.
“You can imagine the same process for trout — with less oxygen in the water, they are struggling to breathe.”
In addition, he said, high water temperatures pose a higher risk of bacterial or fungal infection for fish and limits their ability to find food and shelter, setting up even more stress as fish crowd cooler waters.
Trout will also move upstream in search of cold waters, he said, but they often run into obstructions like dams.
Fitch said it’s a cumulative effect for the cold water fish.
“The impact on the population can be quite severe,” he said, noting it ranges from immediate death for some fish to reproductive impacts for others.
He suggested the closures, however, are a knee- jerk reaction dealing with the symptoms rather than the ultimate cause: climate change.
“We need to deal more quickly with riparian vegetation revival,” said Fitch, noting it can provide a shading effect to prevent the water from heating even more.
In addition, he said, beavers can help regulate water temperatures.
“A good portion of the water that beaver dams store isn’t the surface water, but the water that’s stored as shallow groundwater,” he said.
“That water is stored and it slowly leaks out over a three- month period, re- entering the streams, and it comes out three to four degrees colder than when it went in.”
In the meantime, the fisheries’ closures are expected to last throughout this week — although it will all depend on whether the water temperatures are brought down by precipitation or cooler temperatures.
Officials are also monitoring the rivers and streams in the eastern slopes of the Rockies for similar concerns.