Rainbow trout in Bow River decline By 50 percent
Research suggests river saw decrease in population of up to 50 per cent
The Bow River’s rainbow trout population has dropped by up to 50 per cent in recent years, suggests research by the province and University of Calgary.
That’s led U of C researchers to push for a reduction in angling on the Bow, a world-renowned fishing stream that generates $24.5 million in tourism annually.
“It’s disconcerting, to say the least, to see such a rapid decline,” said Chris Cahill, a PhD student and lead author of the study, which has been published in the Canadian Journal of Fisheries and Aquatic Sciences.
“The challenge here is to support a fishery like this where you have multiple stressors. It is one of the highest-effort angling fisheries in Alberta.”
The researchers assessed provincial government studies on rainbow trout populations from 2003 to 2013, focusing on a 224-kilometre stretch of the Bow River from Calgary’s Bearspaw Dam to the Bassano Dam.
From those numbers, they concluded the species’ population had declined by 43 to 50 per cent over that time period.
What’s not so clear is the precise cause for the dramatic drop, said Cahill.
Severe flooding in 2005 and 2013 may have contributed, while whirling disease that attacks the nervous system of younger fish could be another.
“Numbers also declined in the non-flooding years,” said Cahill.
Climate change could play a role, he said, “but the other stressors are more immediate.”
He said the only controllable one is angling, which even in a catchand-release environment on the Bow could have a significant impact on rainbow trout numbers.
“The mortality rate for catchand-release is three to nine per cent,” said Cahill. “Imagine running a marathon and then having your head held under water.”
The river is so heavily fished that some trout can be caught up to six or seven times, he said.
Introducing a lottery system for fishing permits is a potential solution, said Cahill, adding the approach has met with good compliance in New Zealand. He noted that Alberta imposed fishing moratoriums as recently as last summer on several rivers due to lower flows and warmer water temperatures.
Limitations on fishing in rivers on the Rockies’ Eastern Slopes were proposed by biologists earlier this year, but ran into opposition from anglers and was ultimately rejected by the province whose officials insisted there wasn’t enough science to back the moves.
“There’s no available science until bold experiments are carried out,” said Cahill.
The U of C team and provincial biologists surveyed the river this fall for an update on fishery numbers, data that should be available next year.
A spokesperson for the province wasn’t available to comment Monday.
The mortality rate for catchand-release is three to nine per cent. Imagine running a marathon and then having your head held under water.