DURANGO, Colo. – Colorado Parks and Wildlife aquatic biologists went electrofishing this week to take a population estimate of fish species on the Animas River through downtown Durango using a mark and recapture method.
Early indications revealed positive steps in the recovery of the Gold Medal water following the 416 Fire of 2018, which resulted in an estimated 80% fish die-off because of ash and debris flows in the Animas River.
Fish recorded during the survey included brown and rainbow trout, bluehead suckers, flannelmouth suckers, white suckers, dace and sculpin. Official results of the population survey will be available before the end of the year.
CPW aquatic biologist Jim White said it was the best population of bluehead sucker, a native species, in the Animas River in the last 10 years. He was also happy with the number of stocked rainbow trout recaptured, particularly the Gunnison River rainbow trout, which has been stocked because it has shown to be highly resistant to whirling disease.
“The bluehead sucker abundance was incredible, the best we have seen in years,” White said. “We have also seen a rainbow trout population really rebound – the best rainbow trout we have seen in the Animas for years. We also saw some real quality brown trout of good size.”
Tuesday and Wednesday, fish were collected by electrofishing, which does not harm the fish but momentarily stuns them so they can be easily netted from a raft. It is a common scientific survey method for sampling fish populations.
Netted fish were placed into an oxygenated tank and measured, with some marked on the caudal fin.
CPW repeated the process Thursday and Friday, starting from 32nd Street and working downstream. Aquatic biologists made special note of recaptured fish that had been marked the previous days. Retrieving marked fish helps CPW get a more accurate population estimate.
CPW conducts this type of survey work on the Animas River every two years to make a record of species composition and survival of stocked fish. CPW also looks for the abundance of native fish.