Division of Wildlife
KOKANEE KILL AT VALLECITO RESERVOIR
The Colorado Division of Wildlife’s (DOW) kokanee salmon spawning operation
suffered a major blow earlier this month due to a fish kill at Vallecito
Reservoir. The kill, affecting only kokanee is due to a variety of
conditions perpetuated by the ongoing drought conditions in Southwest
The first reports of dead kokanee being found at the reservoir were taken in
late August. A conservative estimate of dead fish numbers in the thousands.
Vallecito is one of the major contributors to kokanee spawning operations
that help provide kokanee for 25 lakes and reservoirs across the state.
The good news for anglers who frequent the reservoir is that the other sport
fish species that inhabit the shallower waters of the reservoir were not
affected by the die-off.
“The fish kill primarily affected kokanee salmon and it was not a complete
kill,” said Mike Japhet, DOW aquatic biologist in the Durango office.
“Catchable rainbow trout, brown trout and northern pike are also present in
Vallecito and have not been affected by the depleted oxygen conditions found
in the deeper part of the lake.”
The life cycle of the Kokanee salmon is relatively short. Depending upon
conditions, kokanee spend three to five years in a lake or reservoir before
swimming upstream to spawn at the same location from where they were
released as fry. The egg-swollen females and the brick-red hook-jawed males
average 16 to 18 inches. Kokanee die after spawning. Some of Colorado’s
better kokanee reservoirs include Blue Mesa, Elevenmile, Granby, Green
Mountain and Vallecito.
At Vallecito, spawning kokanee head to Vallecito Creek to do their yearly
ritual. The DOW builds a fish trap to catch the spawning kokanee. Eggs and
milt are extracted from mature salmon fertilized eggs are transferred to the
Durango Hatchery where they are hatched and reared to 2 inches in length.
Kokanee salmon fry are released back into the creek the following spring as
the next year class of fish. Over the last 34 years, Vallecito has produced
1.2 million kokanee eggs on average. Even with the kokanee kill, the
operation will continue in hopes of making the most from the remaining fish.
“We have low expectations,” said Japhet.
The die off is due to low dissolved oxygen content in the deep water that is
inhabited by kokanee. It was a natural phenomenon, which could not have been
“This is the first instance of a mass fish kill in the history of Vallecito
Reservoir,” said Japhet. “Kokanee are known to inhabit deep water just below
the thermocline, which at Vallecito presently contains only 3.8 parts per
million dissolved oxygen.”
The ongoing drought in Southwest Colorado and continuing effects from last
summer’s Missionary Ridge fire led to extreme reservoir draw down, warmer
than normal water temperatures and lower than normal dissolved oxygen
content of the water.
“High amounts of organic debris that washed into Vallecito from last year’s
fire probably contributed to high biological oxygen demand, leading to
oxygen depletion in the deeper parts of the reservoir,” said Japhet.
The conditions have been hard on bodies of water throughout the region. A
fish kill was also recently reported at Lower Four-mile Lake--a high
mountain lake home to cutthroat trout.
The fishery can be, and will be re-established. With help from other kokanee
spawning operations, DOW officials are optimistic that loss due to the kill
at Vallecito can be covered. The stocking of Vallecito with kokanee will
take place next spring in hopes for better conditions.
“If we see more snowpack and more overall precipitation this winter things
will change for the better,” said Japhet. “In this business, just like a
farmer, you have to be an optimist and the only way to guarantee that there
wont be kokanee in the lake is to not put them there.”
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