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<br />(personal Communication, Owen Gonnan, U.S. Fish and Wildlife Service, 1993),
<br />
<br />Para.qites
<br />
<br />Fish in the upper basin (Valdez and Williams 1993) and in Grand Canyon (Valdez and Rye11997)
<br />are infected with an external parasitic copepod (Lernaea cy.prinacea.), Fish in Grand Canyon
<br />(Brouder and Hoffnagle 1997, Clarkson et al, 1997, Valdez and Rye11997) have also been found
<br />to carry the intestinal Asian tapewonn $othrioc~halus acheiloi"athi), Both parasites require
<br />>20.C for maturation of gametes and reproduction; in Grand Canyon, these conditions occur only
<br />in seasonally-warmed tributaries. The parasitic copepod has not been found to be lethal to the
<br />fish, but the Asian tapewonn has been recorded as lethal to fish during high population densities
<br />and/or high environmental stress,
<br />
<br />Effects of the Proposed Action on the Humpback Chub
<br />
<br />This determination evaluates the possible effects of a powerplant capacity release of 31, 000 cfs
<br />from Glen Canyon Dam on the endangered humpback chub in the Colorado River through Grand
<br />Canyon, This evaluation examines the proposed action for effects on the Grand Canyon
<br />agrigates, since the species is present in the affected area, and for adverse modification of critical
<br />habitat, since the affected area is designated as critical habitat for humpback chub,
<br />
<br />Effects To Critical Habitat
<br />
<br />The proposed action is likely to have adverse modification on primary constituent elements of
<br />critical habitat for the humpback chub in the Colorado River through Grand Canyon by modifying
<br />some of the primary constituent elements of water, physical habitat, and the biological
<br />environment, The increase in flow is not expected to significantly alter water quality (i, e"
<br />temperature, dissolved oxygen, conductivity, salinity, nutrients, pH), since the release would
<br />continue to be through the power plant and presumably from the same region oflake water as
<br />previous releases, However, the increase flow is expected to substantially increase suspended
<br />sediment load and hence, turbidity, for about the first 24-36 hours of the high release, This
<br />increase in turbidity is likely to benefit the native fish, since low water clarity appears to be one
<br />component of cover, This reduced water clarity may provide temporary protection from sight
<br />predators, such as brown trout and rainbow trout, during the first part of the high release,
<br />However, unless the young chubs are able to find suitable cover, they will continue to be
<br />susceptible to predation during the latter stages of the high release and after the release, This
<br />predation effect is likely to reduce overall survival and recruitment by the juvenile chubs.
<br />
<br />The primary effect to constituent elements will be from physical changes to shoreline habitat, A
<br />release of 31,000 cfs from Glen Canyon Dam will result in a vertical stage increase of the
<br />Colorado River at the confluence of the LCR (Le., 76 miles downstream of the dam) of about 2,9-
<br />4,7 feet, This calculated range in stage increase is based on present operational range of 17,000-
<br />23,000 cis; Le" an increase from 17,000 cfs to 33,200 cfs (when tributary inflow is included) will
<br />
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