BLM Colorado

BLM Colorado

Thursday, November 16, 2017

BLM Colorado-Southwest District Surveying the Gunnison Gorge NCA……The Final Blog Chapter

BLM FISHERIES COLORADO
 
BLM Colorado-Southwest District Surveying the Gunnison Gorge NCA……The Final Blog Chapter
Over the last year we have shared two blogs on rainbow trout in the BLM Gunnison Gorge National Conservation Area in Southwestern Colorado.  Over the last several years there has been a large project by Colorado Parks and Wildlife (CPW) to spawn and stock rainbow trout in the Gorge after whirling disease nearly wiped them out in the 90’s.  This year BLM assisted CPW with both the spawn-take and the population survey within the Gorge.
If you haven’t seen them yet, start with “Black Canyon Rainbow Trout Spawn-take”:
Then see “Bringing Back Rainbow Trout in the Gunnison Gorge NCA”:
In order to determine if the intense stocking over the past years has been successful, population surveys must be performed.  The most efficient way to determine population and size class is performing a two pass mark recapture shocking survey on a section of the river.  With this method, on the first pass fish are shocked, netted, and marked with a hole punch in the top of the caudal fin.  Then the stretch is surveyed again 48 hours later and based on the number of fish along with the number of recaptures, a population model is used to determine fish per mile and also pounds per acre.  This survey stretch is two river miles in length.
With access and length of stretches, raft shockers would not work on this section of river because you would have to drag them up each stretch several times to fully survey the entire width of the river along with getting the boat up several sections of river with rapids.  Instead, the surveys are completed using a jet boat which must be airlifted into the canyon due to no access along the rugged canyon walls.
The helicopter brings in the jet boat
BLM Fisheries Biologist Russ Japuntich reaches out for a brown trout as BLM Fisheries Technician Josh Ryan waits for the next fish to surface.
An example of the caudal fin mark. These holes regrow within 30 days.
Fish are kept in large holding pens waiting to be measured, weighed, and marked before being released.
With increased stocking efforts the past couple of years and flows that have affected age 1 brown trout, there have been increases in rainbow trout in the Gunnison Gorge.  Estimates of 173 rainbows per mile in 2014 jumped to 480 per mile in 2016.  These are the strongest age classes seen since whirling disease in 1995.
Data courtesy of Colorado Parks and Wildlife
There has also been an increase in size class of rainbow trout from 2014 to 2016.  We hope this trend continues with the results of this year’s surveys.
Data courtesy of Colorado Parks and Wildlife
Fisheries Biologist Russ Japuntich with one of the adult rainbows one can expect to catch in the Gunnison Gorge NCA.
One of the beautiful brown trout found in the Gunnison Gorge NCA.