WSPC12531 ‎(2)‎

• File Number: 8220.101.10
• Description: Colorado River Water Projects - Glen Canyon Dam-Lake Powell - Adaptive Management
• State: CO
• Basin: Colorado Mainstem
• Date: 3/1/1998
• Author: Unknown
• Title: Narrative for Biological Resources - Kanab Ambersnail - Distribution and Abundance - 03-01-98
• Water Supply Pro - Doc Type: Report/Study

002482

Narratives For Biological Resources
Kanab Ambersnail

Distribution and Abundance

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Kanab ambersnail (KAS; Succineidae: Oxvloma havdeni kanabensis Pilsbry 1948), is a landsnail
that was proposed for emergency listing (U.S. Fish and Wildlife Service 1991a, 1991b) and
officially listed and endangered in 1992 (U.S. Fish and Wildlife Service 1992). Fossil Oxvloma
shells have been recovered from sediments in Grand Gulch (lower San Juan River) that date to
9,200 years ago (Kerns 1993). Living KAS were fust collected by J.H. Ferriss in 1909 near
Kanab, Utah in seep vegetation (Ferriss 1910, Pilsbry and Ferriss 1911, Pilsbry 1948). Extant
populations of KAS are presently known to occur at two southwestern springs: one at Three
Lakes, near Kanab Utah, and the other at Vaseys Paradise, a spring at Colorado River Mile
31.5R, in Grand Canyon, Arizona (Spamer and Bogan 1993a, 1993b). Two popuiations formerly
occurred in the Kanab area, but one population was extirpated by desiccation of its habitat. The
remaining Utah population at Three Lakes occurs at several, small spring-fed ponds on cattail
(Tvpha sp.; Clarke 1991). The Three Lakes site is privately owned and the land owner is
commercially developing the property.

KAS wlire fust collected at Vaseys Paradise in 1991 (Blinn et al. 1992, Spamer and Bogan
1993), and an interagency team lead by the Bureau of Reclamation examined KAS ecology there
from 1995 through 1997 (Kanab Ambersnail Interagency Work Group 1997a). Vaseys Paradise
is a popplar water source and attraction site for Colorado River rafters; however, the dense cover
of poiso.n ivy (Toxicodendron rydbergii), and the nearly vertical terrain (Stevens et al. I 997b )
limit access. Within Grand Canyon, KAS is apparently restricted to Vaseys Paradise: more than
100 other Grand Canyon springs surveyed from 1991 through 1997 failed to detected the
presence of KAS (Stevens, pers. comm., Sorensen and Kubly 1997). Rematched historic
photographs ofVaseys Paradise (e.g. Turner and Karpiscak 1980:58-59) reveal that vegetative
cover has increased greatly at lower stage elevations since completion of Glen Canyon Dam.
Flow regulation by the dam has increased primary KAS habitat area at Vaseys Paradise by more
than 40%.

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Stevens et aI. (1997b) defined primary KAS habitat at Vaseys Paradise as that dominated by
crimson monkeyflower (Mimulus cardinalis), non-native watercress (Nasturtium officinale),
sedge (Carex aQuatilis) and smartweed (Polvgonum amphibium). Secondary, or marginal, habitat
has been defined as patches of other riparian vegetation that are not dominated by these species
and are not used extensively by KAS. Land surveys from 1995 through 1997 revealed rapid
changes in vegetation cover over the growing season, with 11.2% to 16.1 % of the estimated total
primary habitat occurring below the 45,000 cfs stage in 1995, and 7.0-12.0% of the estimated
total habitat occurring from 20 April 1996 through 3 October 1997. The total estimated area of
primary habitat was 905.7 m2 (0.22 acres), equivalent to the area of secondary habitat, and the
total vegetated area was 1811.4 m2 (0.44 acres) in June, 1995.

Life Requisites

KAS occurs on little-disturbed, saturated soil and associated wetland vegetation at Three Lakes,
near Kanab, Utah (Stevens, pers. commun.), where cattail and sedges are the predominant