The Spawn Must Go On

The broodstocks at Zimmerman Lake and the Leadville National Fish Hatchery represent the backbone of efforts to recover the Greenback Cutthroat Trout.
Video: Greenback cutthroat trout spawning operation

On June 30, Colorado Parks and Wildlife officials were met with a blizzard and 34-degree temperatures at Zimmerman Lake while conducting its greenback cutthroat trout spawning operation. This video from Senior Video Producer Jerry Neal highlights the dedication of CPW’s aquatics staff working in these winter-like conditions, even if it says summer on the calendar.

While teamed up with CPW Cutthroat Trout Research Scientist Kevin Rogers, the Northeast Aquatics team collected spawn and mark recapture data from the greenback cutthroat trout “broodstock” population at Zimmerman Lake. Aquatic Biologists are always prepared for variable weather when working at 10,000 feet, but they certainly were not expecting blizzard conditions when they arrived at the lake early in the morning on June 30.

team captures using live "trap" nets
Courtesy of Jerry Neal/CPW

The team captured the fish using live “trap” nets that were deployed the previous afternoon (when it was sunny and warm). Eggs were collected from females and mixed with milt (sperm) from males. The fertilized eggs were driven in small one-gallon coolers to CPW’s Salida Isolation Unit, operated by the Mt. Shavano Fish Hatchery, where they are either reared to fry to be stocked back out into the wild at other reintroduction sites, or raised to one year of age to be stocked back into the wild and replenish the broodstocks at Zimmerman Lake and the Leadville National Fish Hatchery.  

All of the fish that are stocked into Zimmerman Lake are given a Passive Integrated Transponder (PIT) tag, each with a unique alphanumeric code, and a color coded Visual Implant Elastomer (VIE) tag, with each color representing a different year class and family group. During the spawn operation at Zimmerman Lake, each fish was scanned for its PIT tag and visually checked for its VIE tag.  Additionally, aquatic biologists measured length and weight and identified sex of each fish. All of this information enables biologists to assess individual fish growth rates and estimate survival of the different year classes and family groups, and thus evaluate CPWs efforts to maximize genetic diversity in the broodstock.  

The broodstocks at Zimmerman Lake and the Leadville National Fish Hatchery, and associated hatchery operations, represent the backbone of efforts to recover the Federally Threatened State Fish of Colorado, the Greenback Cutthroat Trout.

“It is fun and rewarding work for the biologists, even though the weather isn’t always ideal,” said Boyd Wright, CPW Native Aquatic Species Biologist.


Written by Jason Clay. Clay is a public information officer for the Colorado Parks and Wildlife northeast region.

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