BLM Colorado

BLM Colorado

Tuesday, May 2, 2017

Black Canyon Rainbow Trout Spawn-Take

Black Canyon Rainbow Trout Spawn-Take

Longer days, warmer temperatures, and the start of snow melt in the high country signifies the start of spring in the Colorado Rockies and the rest of the Western United States. It is also an important time for our recreational fisheries as rainbow trout begin to spawn. Some rainbow trout fisheries in the state are wild and free where the populations are self-sustained through successful reproduction and recruitment. However, there are some populations that require help in order revitalize once abundant populations that have been effected by disease. On several warm mid-April days, BLM Colorado’s Southwest District fisheries crew assisted Colorado Parks and Wildlife (CPW) with collecting rainbow trout in the Black Canyon of the Gunnison National Park at East Portal, located just below Crystal dam to spawn and collect fertilized eggs. 

CPW aquatic biologist Eric Gardunio motors back to the boat ramp after a successful day on the water.

Why is the BLM assisting Colorado Parks and Wildlife with work inside a National Park you might ask? Well to continue the process of a previous blog from the fall of 2016: ( The eggs that are collected at this location will be reared at a hatchery and once they have grown to 2” long fry, they will then be stocked in the BLM Gunnison Gorge NCA located downstream of the park.

Entrance to the Park

In the early 90’s, whirling disease hit the Gunnison River and virtually eliminated rainbow trout recruitment from 1994 to 2007; adversely affecting the rainbow trout population. Before whirling disease, the river was home to a robust wild rainbow and brown trout fishery. Rainbow trout during those years had densities of over 5,000 fish per mile and biomass greater than 200 lbs/acre. Since the disease struck, rainbow trout now roughly account for 10% of the biomass. Along with the disease, the brown trout in the river thrived as the rainbow populations declined. Brown trout numbers are still high, which has made the recovery a little difficult even with successful reproduction. Supplemental stocking of whirling disease resistant strains of rainbow trout, which is a cross between the Hofer strain and Colorado River rainbows; has helped the population slightly recover through reproduction and recruitment.

BLM Fisheries Technician Josh Ryan, holds a large male rainbow that was netted while electrofishing.

In order to collect eggs and milt from individuals, electrofishing via boat is used to capture fish. Several short sample reaches with multiple passes are completed to cover the entire width and length of the river at East Portal. Individuals identified as “reproductively ripe” are separated and placed in a holding pen to be spawned. Spawning occurs on Tuesdays and Fridays, with collection occurring Monday, Tuesday, Thursday, and Friday of every week during the spawn period. The fertilized eggs that are collected are transported to the CPW Pitkin Fish Hatchery in Pitkin, CO. 

Eric Gardunio showing the eggs from a female rainbow trout that was collected and will be sent to the holding pen.

Eric Gardunio spawns a female rainbow trout into a mixing bowl to be fertilized.

Over ripened eggs from a female, notice the oblong and inconsistent shape. In this instance these over ripened due to flow fluctuations out of Crystal dam that forced the female to delay spawning.

It is an ongoing process to restore the rainbow populations to what the river once held. High water years during spring runoff have helped keep brown trout numbers down in recent years. Hopefully later this year we will be back on the river in the Gunnison Gorge NCA (much like last fall) stocking fry back into the system. 

The Black Canyon of the Gunnison National Park and Gunnison Gorge National Conservation Area are MUST DO’S if you are ever spending some time in Southwest Colorado. There are many recreational opportunities to satisfy one’s need for adventure, along with amazing scenery created by fluvial and geological processes. If the opportunity rises during a long weekend, make the trip to the area and see it for yourself.

The Black Canyon of the Gunnison National Park.

CPW technician shows off a gorgeous colored up male rainbow trout that is ready to spawn.

CPW technician holding another fish collected and ready to spawn.