Valvata utahensis

Subtle variation in shell morphology between Valvata utahensis and Valvata humeralis reflects a long-term evolutionary divergence based on a recent genetic study (Miller et al., 2006). Miller et al. (2006) showed that comparable levels of nuclear genetic variation exist within each of six locations examined, however, reduced mitochondrial sequence diversity was observed at Thousand Springs compared with the other locations examined. Miller et al. (2006) further illustrated that the species shows no genetic structure within locations over relatively small physical distances (up to 3 km) and suggest active dispersal of individuals (via crawling) and pssive dispersal (downstream displacement) may have produced this pattern.

The range was previously thought to have been reduced to only a handful of sites in Idaho with one of six sites having unique genetic structure; extirpated from former range in Utah; subfossil in California. The species has recently been found to be discontinuously distributed over 410 km of the Snake River and tributaries and occurs in a variety of habitats (including reservoirs). Threats such as competition from the New Zealand mudsnail, dewatering, hydropower projects, and degraded water quality, have been shown to have a much lower impact than was initially presumed.

Historically known from the Snake River in Idaho and from northern Utah. Known from fossils in Honey Lake, Lassen County, California (Taylor and Smith, 1981). Although it was formerly thought to be limited to a few springs and mainstem Snake River sites in the Hagerman Valley, Idaho, and a few sites above and below Minidoka Dam and immediately downstream of American Falls Dam (USFWS, 1992), it is now known to be discontinuously distributed in at least 410 km of the Snake River in Idaho and some associated tributary streams (increase of 196 km) (USFWS, 2010).

Although previously only known from a few sites in the Hagerman Valley and at a few sites below American Falls Dam in Idaho; extirpated in Utah (U.S. Fish and Wildlife Service, 1992; Hovingh, 2004); recent specimens were collected in 2002 from six locations within the Snake River mainstem ranging from Lower Walcott to American Falls Reservoir about 50 river km away as well as at Thousand Springs near Bliss and in the Big Wood River near Bliss, Idaho (Miller et al., 2006). Miller et al. (2006) noted of the six locations, the Thousand Springs population was genetically distinct from those at Snake River Vista, Coldwater, Lower Walcott, American Falls Reservoir, and north fork of Big Wood River. Current distribution includes the Snake River from RM 585 upstream to the confluence of the Henry's Fork with the Snake River (RM 837) with colonies near the towns of Firth (RM 777.5), Shelley (RM 784.6), Payne (RM 802.6), and Roberts (RM 815), and in the Henry's Fork 15 km upstream from the Snake River confluence (at RM 8342.3); as well as tributaries such as Box Canyon Creek (RM 588), and one location in the Big Wood River (USFWS, 2010).

In the laboratory, increasing densities of New Zealand mudsnails (Potomopyrgus antipodarum) limited the growth rate and absolute growth of this species (Lysne and Koetsier, 2008); however 10 years of coexistence has shown no evidence of local extirpations due to competition between the species (USFWS, 2010). Although dewatering of the Snake River has been considered a potential threat, the species is able to re-colonize most submerged zones during summer high flows (USFWS, 2010). Proposed hydropower projects discussed in USFWS (1992) are no longer moving forward plus recent studies have shown the snail is not as limited geographically or in regard to habitat as was once thought making it less susceptible to the threat from existing hydropower dams (USFWS, 2010). Similarly, the current known tolerance of wide habitat types and water quality no longer makes it as susceptible to degraded water quality than was once thought (USFWS, 2010).