Although it sounds like another big fish story, Great Big Nature’s naturalist, Brian Keating, recently snorkelled with about 100 big mature Bull trout out near Banff, Alberta., Canada! The Bull trout is Alberta’s official Provincial fish. Its populations have been in serious decline for decades and are now a threatened species. “It was tricky ‘sneaking’ up to the fish to observe them (they were easily spooked), but we found the best way was to swim up-wind, and allow the breeze to gently blow us into position”, Brian said. Bull trout are what fisheries biologists call ‘fall spawners’. The fish will migrate up a chosen creek, find the perfect gravel bed, & dig out what is called a ‘redd’ where they lay & fertilize their eggs they then leave them hidden in the gravel for the winter. Biologists count fish redds to monitor the population health. There were an incredible 1,403 Bull trout redds counted in a survey in one very productive drainage in Kananaskis the years ago! This is a good news population-increase story for our Kananaskis Bull trout. This has not always the case. The population decreased considerably in decades past, causing Alberta Environmental Protection to implement a ‘catch & release-only’ fishery for Bull trout in the spring of 1992. Their numbers have increased dramatically since, with one study showing a 20-fold increase in the 8 years following the zero bag limit changes. Making these changes back then allowed the population to go from a 48% mortality in 1991, to 5% the following year. It was mostly overfishing that caused the population decline, but there were a few other factors. Unstable habitat due to fluctuating water levels (it’s a controlled lake, utilized for power production), with an average 12.5m drawdown every winter, affecting some of their spawning areas. Hybridization and competition with populations of stocked non-native eastern brook trout has also been implicated. Another important factor is that there is mortality from stress after the fish has been caught & released. That’s called ‘hook mortality’, and that can be up to 15%. Incredibly, it may be the desire to create that perfect social media posting that increases that mortality. To increase Bull trout populations, biologists are working now on what’s called ‘recovery stocking’, done to recover the original wild population in traditional habitats. University of Calgary students and Provincial biologists carefully catch fish & harvest eggs from appropriate females, who lay up to 2,400 eggs each, and the milt from the males. They then fertilize the eggs with milt in a shallow plastic dish. The eggs are placed in small plastic in-stream incubator capsules that look like a small hockey puck with holes through it. These are planted in the creek bottom as deep as what a female bull trout would do, to overwinter, and then retrieved in the spring to see the success rate. Once perfecting this process, it’s hoped that our native Bull trout can be re-introduced into streams where they have disappeared completely or where the population needs bolstering.Photo and Video: Brian Keating.
I was glad to hear this. I remember when they were vermin. I caught a little one in Calgary once. That was well outside its usual locations in the mountains.