WSP04352

• File Number: 8220.101.10.E
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 4/1/1998
• Author: Sorensen/et al. - Ar
• Title: Monitoring and Habitat Surveys of the Endangered Kanab Ambersnail in Grand Canyon and Northern Arizona
• Water Supply Pro - Doc Type: Report/Study

MONITORING AND IlABITAT SURVEYS OF mE ENDANGERED
KANAB AMlIEBSNAIL IN GRAND CANYON AND NOJl.1BERN AIuzoNA

Jeff A. Sorensen and Dennis M. Kubly

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lNTRODUcnON

In 1992, the Kanab ambersnail (KAS; Succineidae: Oxy1011lD haydeni lcanabensis Pilsbry, 1948)
was federally listed as endangmlll by the U.S. Fish and Wildlife Service (USFWS 1992). Arizona
Game and Fish Department (AGFD) al30 RCOgnizes KAS in its draft Wildlife of Special CollCern
in Ari2DlIO (AGFD in prep.). Specific threats to KAS involve the loss and/or adverse modification
to wetland habitat and incidental take by dam releases (USFWS 1995).

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Only two populations of the KAS are known to exist currently in the American Southwest. An
extant population is fOUDd in southeastern Utah, on a private1y-owned wet meadow dominated by
ca""i1~ (TyphiJ domingensis) and sedges (Carex aqUlJlilus). This population (Three Lakes; 3L) is
threatened by habitat loss and possible extirpation by planned commercial development (USFWS
1995). The other population of this rare landsnail was discovered in 1991, at Vaseys Paradise
(VP) in Grand Canyoo National Park (Blinn et aI. 1992; Spamer and Bogan 1993). Located 75.3
Ian downstraun of Glen Canyon Dam, this site has a large, perennial spring with abyndant poison
ivy (Toxicodendron rydbergii), crimson monkeyflower (Mimulus cardinaJis), and watercress
(Nasturrium officinale). The VP population is threatened by habitat loss and incidental take from
controlled and uncontrolled high water rel-- from the dam. This population experienced habitat
loss and incidental take during an experimental 45,000 cfs (1275 m3/s) stage flow in March 1996
(Stevens et aI. 1991a). Both populations are geographically isolated (92.9 Ian distant), and are
believed to be relics from the Late Pleistocene glaciation, when wetland habitat was more
abundant (Spamer 1993; Spamer and Bogan 1993; Stevens et aI. 1997b).

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KASs are restricted to pemmially wet soil surfaces and decaying plant litter of springs and seep-
fed marshes near sandstone or limestone cliffs (USFWS 1995). A limiting factor in their
distribution may be the presence of cattails, monkeyflower, and watercress, which are identified
as the primary vegetation for KAS habitat. They are most abundant under fallen cattail stalks,
decadent monkeyflower litter, and young watercress (USFWS 1995; Stevens et aI. 1991b).

KASs have an approximately annuallifecycle, and reportedly live 12-15 months (Clarke 1991).
They emerge from winter hibernation in spring with the onset of wann weather, and begin
reproducing throughout the late spring and summer months. Peak reproduction typically occurs
in late summer, when densities of mature KASs are highest. A seasonal decline of KASs occurs
in autumn with mass die-offs of mature individuals, while young and immature KASs go into
winli:r dormancy (Blinn et aI. 1992; Stevens et aI. 1997b). KASs are hermaphroditic, possessing
both male and female reproductive tracts (Pilsbry 1948). Young snails develop from gelatinous
egg masses attached to wet plant litter. Fully mature KASs can have shell lengths up to 20 mm.

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