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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The timing of the one-time test flow may Occur at a sensltlve periods of a the Kanab
ambersnail's lifecycle. Although the one-time test flow is only scheduled for 7 days of high
flows, impacts from the flow may be manifested throughout the growing season and into the fall.
Substantial alterations to the lower habitat of the Kanab ambersnail habitat will occur as a result
of the proposed action. High flows are likely to eliminate most, if not all, of the vegetation
below the 1275 cms zone. In March, Kanab ambersnail numbers are at their lowest. The
species is just recovering from high winter mortality and lowest annual densities (Table 1). The
timing of the flood will likely occur during a period of dormant vegetation. The resumption of
spring growth will follow as a result of increased photoperiod and temperature. Following
completion of the project, the area will be allowed to naturally re-vegetate. The rate and pattern
of rejuvenation is not known. Some rejuvenation is expected during the ensuing two to six
month growing season. During the high flows of the 1983, Mimulus roots that were not eroded
survived inundation (Larry Stevens, GCES, personal communication). Nastunium is likely to
re-colonize by seed. Individual ambersnails that successfully ovetwinter should be large enough
to reproduce by June, with as mentioned earlier, the peak ofreproduction occurring in July and
August (Stevens et al. 1995a). In August and September 1995, Kanab ambersnail densities were
higher on Nastunium than MimuIus. Sand or other debris may be deposited at the lower
elevation at Vaseys which may affect the rate of vegetation rejuvenation, species composition,
or snail distribution.

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Kanab ambersnails which fall or migrate down to the water's edge after the flood before
vegetative rejuvenation, will not fInd habitat and may be lost to the river. During the 1995 field
season, three individuals were found on bare rock but always in close proximity to vegetation.
The likelihood of a higher percentage of individuals being impacted is increased if individuals
have migrated or have been washed down to the river's edge after a natural disturbance.
Conversely, if the habitat has undergone winter die-baclc or been scoured away from some
natural event, the loss of habitat or individuals may actually be less than the anticipated level.

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An unusually cold or later winter may fmd the Kanab ambersnail still in its winter state during
the test flow. During March of 1995, three of 48 snails, or 6.3 percent of the individual
examined retained the mucosal plug or seal indicative of the winter dormant state (Stevens et aI.
1995a). It is possible that those individuals may be successfully transplanted. Researchers in
New Y orlc State discovered that estivating Cerion sp. were able to survive several days of
transport with broken epiphrams. It was hypothesized that the seal serves as a culture for fungi
rather than a barrier to moisture (Paul Morris, University of Massachusetts, personal
communication). The variability in natural conditions (springflows, floods, and climate)
contributes to the large fluctuations in Kanab ambersnail population size and habitat.

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Southwestern Willow Flycatcher

The test flow is designed to be a release over powerplant capacity to test the ability to use now
as beach and habitat-building tool to return processes of the Colorado River in the Grand Canyon
similar to those provided under a natural hydrograph. As evaluated in this consultation. this is

Biological and Conference Opinions Glen Canyon BeachiHabilal-Building Flows 2116196

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