9570

• UCREFRP Catalog Number: 9570
• Author: U.S. Department of the Interior.
• Title: Preliminary Analysis
• USFW Year: 2000.
• USFW - Doc Type: Wayne N. Aspinall Unit Operations and the Federal Water Right Claim, Black Canyon of the Gunnison National Park.
• Copyright Material: NO

Fish and Wildlife
Fish and wildlife resources related to the operation of the Aspinall Unit include the fishery in
Blue Mesa Reservoir, the Gold Medal trout fishery downstream from the Unit, and the riparian
corridor along the river. A further analysis of these resources and impacts should be
accomplished by the Colorado Division of Wildlife.
Blue Mesa Reservoir is a major fishery in Colorado with kokanee salmon, rainbow trout, and
lake trout being the dominant recreation species. Changes in reservoir operations can affect loss
of fish through reservoir outlets, the thermal regime of the reservoir, and the overall productivity
of the reservoir. Summer reservoir levels would average 2-3 feet lower under the NPS desired
flows. In dry to average water years, operating to meet the NPS desired flows can result in Blue
Mesa storing 30,000 to 100,000 acre-feet less than with the base run. This would have a negative
effect on reservoir fisheries, but the significance has not been studied. Higher releases may
increase loss of fish, particularly schools of kokanee salmon, from Blue Mesa. This loss is of
significant concern to the Colorado Division of Wildlife due to the value of the kokanee fishery.
With storage of water in Blue Mesa Reservoir, the river downstream developed into a Gold
Medal trout fishery, dominated by naturally reproducing rainbow and brown trout. Rainbow
trout reproduction has been reduced greatly by whirling disease in recent years but the river
retains a Gold Medal quality fishery. Trout populations have been monitored for nearly 20 years
by the Colorado Division of Wildlife under a variety of flows. Significant problems occur to the
fishery under several flow conditions. Dewatering of brown trout eggs can occur when flows
drop after the fall spawning period, and both rainbow and brown larval fish have a poor survival
rate during high, fluctuating flow periods in the spring and early summer. Peak flows, if
gradually ramped and if occurring in the mid-May to June i range, should not significantly affect
the young fish.
Optimum adult fish habitat flows are probably around 800-1000 cfs, while the 300 cfs minimum
flow has been shown to support the fishery over short time periods. Anchor ice, potentially
damaging to fish and aquatic insects, develops in the river as far upstream as the Park when the
minimum flows are maintained in winter months. Elevated temperatures can occur in summer
months under minimum flow conditions.
Spring peaks in May, with appropriate ramping, as described in model runs B, C, and D, should
not be detrimental to the trout fishery and would help maintain river channel habitat conditions
for both trout and aquatic insects. Long-term impacts of peak flows on habitats such as
overhanging banks have not been addressed. The June spring peaks (E, F, and G) have more
potential for damaging rainbow trout recruitment. NPS desired flows would increase the number
of days flows are reduced to the minimum of 300 cfs from approximately 800 days to 1,600 days
(or from an average of 33 days per year to 66 days per year) during the 24-year study period, thus
having an adverse effect on the trout fishery. Table B-4 in Attachment B shows average monthly
flows in the trout fishery for the alternative model runs. Increased use of spillways under the
model runs would result in increased maintenance of Unit structures, and this would increase the
frequency of flow interruptions or fluctuations.

9