Tyler Swarr, aquatic biologist for CPW, holds up a brown trout from Antero Reservoir on Wednesday, Oct. 6 when officials conducted the brown trout spawn there in South Park (photo by Jason Clay/CPW)
FAIRPLAY, Colo. – Each fall, brown trout spawn in the mountain creeks and rivers across Colorado. It is also when aquatic biologists, hatchery staff, wildlife officers and volunteers for Colorado Parks and Wildlife come together to conduct its annual brown trout spawning operation at North Delaney Butte Lake and Antero Reservoir.
A quota is set to collect the number of eggs necessary to meet the needs for hatchery production, which CPW uses to augment natural reproduction across Colorado’s creeks, rivers and reservoirs.
This year, that quota was 1.1 million brown trout eggs. It took just three working days at those two brood stock bodies of water to meet the quota of fertilized eggs that get sent to CPW’s Mt. Shavano Hatchery in Salida and its Poudre Rearing Hatchery in Larimer County.
The hatcheries will rear the fish to a fingerling size, around three inches, before being stocked out across Colorado in 2022. Those brown trout fingerlings will get stocked back into both Antero Reservoir and North Delaney Butte Lake to ensure a strong brood stock population, but also across many other reservoirs and rivers.
“Some of them will come back and be stocked into Antero and some will go to North Delaney as well, so we can come back in three or four years and still will have fish,” said Tyler Swarr, aquatic biologist leading the brown trout spawning operation at Antero Reservoir. “The rest of them will get stocked out across the state.”
CPW stocks more than 700,000 brown trout annually to provide exceptional fishing opportunities.
Crews at Antero Reservoir were able to collect and fertilize 227,026 brown trout eggs from 117 females during its lone spawning day on Wednesday, Oct. 6.
At North Delaney Butte Lake in North Park, CPW’s team needed just three days (Oct. 5-7) to gather 888,574 eggs to surpass the quota of 1.1 million fertilized brown trout eggs for the year.
“2021 was another good brown trout spawn year at North Delaney,” said Kyle Battige, aquatic biologist leading the brown trout spawning operation there. “We saw many year classes present, handled over 1,500 brown trout in three days and I’m happy overall with the current condition of the brood lake”
Brown trout spawn in the wild occurs over the months of October and November. It is temperature dependent.
“River fish spawn a little bit later since it is colder,” Swarr said. “Since reservoirs absorb a lot more solar radiation, they are warmer, so they’ll actually spawn earlier here than they will in rivers.”
In the reservoirs, the silt from the wave action can cover the eggs and prevent them from getting the fresh oxygen they need to grow and hatch. In a river setting, brown trout will lay eggs in the gravel on the river bottom. Those eggs typically get laid in places of upwelling where there is a crest of a riffle and you have a plunge that causes the water to travel through the gravel, slowly turning the eggs and delivering oxygen to them.
“Our spawning operation helps to sustain some of our brown trout fisheries in the state and provides a little bit more fishing diversity for anglers,” Swarr said.
Brown trout are a hard-fighting fish and have beautiful coloration that matches the autumn season. Brown trout are golden brown with vibrant black, red and orange spots.
“The cool thing about them in the state of Colorado is they are resistant to whirling disease since they evolved with that in Europe,” Swarr said. “So, they’ve become kind of the bread and butter of our wild trout fisheries, at least in our northeast region, because really most of the brown trout in the state of Colorado are naturally reproducing wild populations and we don’t have to stock them to the numbers we do with rainbows. Rainbow trout are still impacted heavily by whirling disease.”
You can learn more about whirling disease by visiting our website.
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