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<br />
<br />;'~'fiij)rovin{! Habitats: ,', ,',., ' ,
<br />
<br />,\<~reating an environment on~e Gunnison River were sport and endangered fish thrive
<br />
<br />T" ' he U.S. Bureau ofRecIarnation
<br />, ' , has been changing the, opera-
<br />, tion of the Aspinall Unit dams
<br />to remove river sediment and maintain "
<br />a more naluml river environment.
<br />Dam releases are also varied each
<br />year, depending on the amount of wa-
<br />ter available, to study which," flows
<br />work best for endangered fish.
<br />Generally, releases mimic flow pat-
<br />, tems that eXisted before dams were
<br />coristructed, which means higher flows
<br />ill the spring and lower, more stable
<br />flows the rest of the year.
<br />In some cases, river flows needed
<br />for endangered fish may not be ideal
<br />for trout, however, generally the fish
<br />thrive., Observations include:
<br />~ High or '''flushing'' spring flows,
<br />and lower, more stable flows the
<br />rest of the year are beneficial to ,
<br />both endangered fISh and trout. '
<br />Higher flows flush out sediment,
<br />algae, vegetation and decaying
<br />material riom the river bottom,
<br />boost insect production and im-
<br />prove the habitat by helping to
<br />maintain, the natural state of both
<br />the riVer channel and flood plain
<br />habitats. . '
<br />~ Rapid changes in flow levels
<br />could harm 'trout popUlations if "
<br />their fry get trapped in outlying
<br />vegetation as water levelS recede.
<br />This becomes a bigger issue;f wa-
<br />, . ter has to be "spilled" over the top
<br />of the dam, rather than released
<br />through the generators -- this hap-
<br />pens about every other year on the
<br />Crystal dam. To avoid these sud-
<br />,den changes in flow.s; increases
<br />and decreases In water releases for
<br />endangered fish have been made
<br />gradually. '
<br />Additionally, the Service has
<br />worked Closely with the Colorado
<br />Division of Wildlife to regulate
<br />peak flows to accommodate the
<br />hatching periods of rainbow and
<br />brown trout fry when possible.
<br />~ Since 1992, water-release patterns
<br />from the Aspinall Unit dams have
<br />been aimed at benefitting endan-
<br />
<br />gered fish, yet overall rainbow'
<br />, and brown trout populations have
<br />increas'ed:
<br />~ However, the emergence' of
<br />,whirling disease, caused by
<br />'Myxobolus cerebralis" a micro-
<br />scopic,' spore-forming, amoeba
<br />that parasitizes the cartilage of,
<br />certain species of trout and
<br />salinon,could have a significant
<br />, impact rainbow trout and some ef- '
<br />feCt oti brown trout. 'It, isn't ex~
<br />pected to affe;:t trout or salmon in '
<br />the ,reservoit, but state hiologists
<br />will continue to study this:
<br />
<br />Impacts on trout' and kokanee in' Blue
<br />Mesa Reservoir "
<br />~ Adult kokanee have been growing
<br />, larger. Biologists believe this may
<br />be occurring because many young
<br />kokanee are, pulled through dam
<br />outlets during high spring re-
<br />leases, resulting in lower popula~
<br />, tions in the reservoir -- 'fewer fish
<br />can eat more and grow faster. An-
<br />gier's benefit because as the food
<br />
<br />base starts to drop, the fish he-
<br />come more aggressive and are
<br />easier to catch.
<br />~ Federal and state agencies are
<br />working to avoid the releasing
<br />'very large amounts of water from
<br />the reservoir in a short period of
<br />time.
<br />The high-voiume' discharge
<br />,could decrease plankton produc-
<br />tion, (fish food) and pull a large
<br />number of kokanee fry through
<br />the dam ,outlets.
<br />~ The, number of kokanee eggs col-
<br />lec\ed at the state's Roaring Judy
<br />Hatchery nearly doubled from 5.1
<br />million in 1992 to an all-time
<br />record of 9.2 million in 1993. In
<br />1994, biologists took 7.4 million
<br />eggs, 'making for another well-
<br />above-average year.
<br />~ Evaluation of protection policies
<br />, on kokanee populations will con-
<br />tinue through 1996 and will be
<br />considered in writing the biologi-
<br />cal opinion on Blue Mesa Dam.
<br />.
<br />
<br />
<br />BUru8U of Redamatlon photo
<br />Dam releases are varied each year, depending on the amount of water available,
<br />lostudy which flows weir\( best for endangered fish.
<br />
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