WSP03252

• File Number: 8220.101.09
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 2/16/1996
• Title: Biological Opinion Summary
• Water Supply Pro - Doc Type: Biological Opinion

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Proposed critical habitat for the southwestern willow t1ycatcher area includes the Colorado River
from RM 39 to RM 71.5 with the following description (U.S. Fish and Wildlife Service 1993):

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The boundaries include areas with surface water (main river channel and all associated side
channels, baclcwaters, pools and marshes) throughout the May-September breeding season, and
areas where such surface water no longer exists owing to habitat degradation but may be
recovered with habitat rehabilitation. The boundaries also include areas within 100 meters of
the edge of the surface water described above. This includes area with thickets of riparian
shrubs and trees, and areas where such riparian vegetation does not currently exist but may
become established with natural regeneration or habitat rehabilitation.

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This 52 kilometer reach represents 10 percent of the southwestern willow t1ycatcher habitat
proposed in Arizona.

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EFFECTS OF THE ACTION

Humpback Chub

The Service stated in the Reasonable and Prudent Alternative in the 1995 biological opinion that:
"Attainment of riverine conditions that support all life stages of endangered and native fish
species is essential to the Colorado River ecosystem," and that "Studies of high steady flows in
the spring may include studies of habitat building and habitat maintenance flows." As a common
element in the FEIS, beach/habitat-building flows were to restore downstream habitat conditions
that were the consequence of increase flood control. The Service identified that baclcwaters and
other nearshore habitats were used by larval and young-of-year fishes as refuge and nursery
areas. These areas are ephemeral in a riverine system, and maintenance of them by using flows
that historically created these areas was incorporated into the preferred alternative of the FEIS.

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Conducting the test flow in 1996, fOllowing a year of average humpback chub production in the
Little Colorado River, supports previous recommendations from fishery biologists that transport
of young-of-year fishes from preferred, productive habitats in the upper reaches of the Grand
Canyon should be avoided in years following exceptional production in the Little Colorado
River. This recognizes that some young-of-year or other small-sized humpbaclc chub in (he
mainstem during flood flows might be transported downstream. The amount or extent of this
transport is unknown and is the basis for some of the studies being conducted as part of. or In
conjunction with, the test flow (Persons 1995).

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Flood flows have the potential to displace nonnative fishes more than native, riverine Ii,hc:'
(Clarlcson et aI. 1994), and this would be beneficial to humpback chub and other native ti,hc:'
in the Grand Canyon. Investigatio_ns of fishes before and after the test flow will provide nc:c:dc:d
data to address this potential benefit.

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Biological and Conference Opinions Glen Canyon BeachlHabitat-Building Flows 2116196

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