|
<br />KANAB AMBERSNAIL SPECIES ACCOUNT
<br />
<br />II
<br />
<br />:ij
<br />~
<br />~
<br />~
<br />:f
<br />.;
<br />,::1
<br />'i
<br />
<br />Distribution and Abundance
<br />
<br />>
<br />,
<br />
<br />Kanab ambersnail (KAS; Succineidae: Oxvloma havdeni kanahensis Pilsbry 1948) ,
<br />is a federally endangered landsnail that was proposed for emergency listing
<br />(England 1991a, 1991b) and officially listed in 1992 (England 1992). Fossil
<br />Oxvloma shells have been recovered from sediments in Grand Gulch (lower San
<br />Juan River) that date to 9,200 years ago (Kerns 1993). Living KAS were first
<br />collected by J.H. Ferriss in 1909 near Kanab, Utah in seep vegetation (Ferriss
<br />1910, Pilsbry and Ferriss 1911, Pilsbry 1948). Extant populations of KAS are
<br />presently known to occur at two southwestern springs: one at Three Lakes, near
<br />Kanab Utah, and the other at Vaseys Paradise, a spring at Colorado River Mile
<br />31.5R, in' Grand Canyon, Arizona (Spamer and Bogan 1993a, 1993b). Two
<br />populations formerly occurred in the Kanab area, but one population was
<br />extirpated by desiccation of its habitat. The remaining Utah population at
<br />Three Lakes occurs at several, small spring-fed ponds on cattail (~sp.;
<br />Clarke 1991). The Three Lakes site is privately-owned and the land owner is
<br />commercially developing the property.
<br />
<br />"
<br />
<br />~'~;,
<br />
<br />"
<br />r,;'
<br />~~:
<br />
<br />KAS were first collected at Vaseys Paradise in 1991 (Blinn et al., 1992,
<br />Spamer and Bogan, 1993), and an interagency team lead by the Bureau of
<br />Reclamation examined KAS ecology there in 1995 (Stevens et al., 1995). Vaseys
<br />Paradise is a popular water source and attraction site for Colorado River
<br />rafters; however access is limited by the dense cover of poison ivy
<br />(Toxicod~ndron rvdberaii) and the nearly vertical terrain (Stevens, at al.,
<br />1995). Within Grand Canyon, KAS is apparently restricted to Vaseys Paradise:
<br />no KAS were observed at 81 other Grand Canyon springs surveyed from 199,]' to
<br />1995. Rematched historic photographs of Vaseys Paradise (e.g. Turner and
<br />Karpiscak 1980:58-59) reveal that vegetative cover has increased greatly at
<br />lower stage elevations since completion of Glen Canyon Dam.
<br />
<br />,
<br />~~
<br />t~
<br />~~
<br />~~
<br />i~
<br />'I
<br />~
<br />
<br />).'
<br />
<br />~t~
<br />r;::
<br />~",~r-
<br />~;i
<br />
<br />",~;
<br />
<br />;.-;
<br />\\"
<br />
<br />Stevens, et al. defined primary habitat at Vaseys Paradise as crimson monkey-
<br />flower (Mimullls cardinalis) and non-native water-cress (Nasturtium
<br />officinale); and secondary, or marginal, habitat is defined as patches of
<br />other riparian vegetation that are not dominated by monkey-flower or water-
<br />cress, and not used by KAS. Land surveys in 1995 revealed rapid changes in
<br />vegetation cover over the growing season, with 5.9t to 9.3t of the primary
<br />habitat occurring below the 33,000 cfs stage, and 11.lt to 16.1t occurring
<br />below the 45,000 cfs stage. The total area of primary habitat was 0.22 acres,
<br />secondary habitat area was 0.22 acres, and the total vegetated area of the
<br />spring was 0.44 acres in June, ,1995.
<br />
<br />l;;:;'
<br />,'::
<br />~~::
<br />!x'
<br />t'-'.:;
<br />;~,
<br />
<br />~
<br />
<br />l<, !~
<br />[)IJ
<br />~~
<br />~
<br />J
<br />I
<br />f4~
<br />
<br />'~~?;':
<br />
<br />The total estimated Vaseys Paradise KAS population rose from 18,476 snails in
<br />March up to as many as 104,000 snails in September, 1995 as reproduction took
<br />place in mid-summer (Stevens et al., 1995). The proportion of the total
<br />estimated KAS population occurring below the 33,000 cfs stage rose from 1.0t
<br />in March to 7.3t in September, and that occurring below the 45,000 cfs stage
<br />was 3.3t in March, 11.4t in June and 16.4t in September, 1995.
<br />
<br />Life Requisites
<br />
<br />4
<br />
|