Snake River - Biology

Biology

The World Wide Fund for Nature (WWF) divides the Snake River's watershed into two freshwater ecoregions: the "Columbia Unglaciated" ecoregion and the "Upper Snake" ecoregion. Shoshone Falls marks the boundary between the two. The WWF placed the ecoregion boundary about 50 kilometres (31 mi) downriver from Shoshone Falls in order to include the Big Wood River (the main tributary of the Malad River) in the Upper Snake ecoregion, because the Wood River is biologically distinct from the rest of the downriver Snake. Shoshone Falls has presented a total barrier to the upstream movement of fish for 30,000 to 60,000 years. As a result only 35% of the fish fauna above the falls, and 40% of the Wood River's fish fauna, are shared with the lower Snake River.

The Upper Snake freshwater ecoregion includes most of southeastern Idaho and extends into small portions of Wyoming, Utah, and Nevada, including major freshwater habitats such as Jackson Lake. Compared to the lower Snake River and the rest of the Columbia River's watershed, the Upper Snake ecoregion has a high level of endemism, especially among freshwater molluscs such as snails and clams. There are at least twenty-one snail and clam species of special concern, including fifteen which appear to exist only in single clusters. There are fourteen fish species found in the Upper Snake region that do not occur elsewhere in the Columbia's watershed, but which do occur in Bonneville freshwater ecoregion of western Utah, part of the Great Basin and related to the prehistoric Lake Bonneville. The Wood River sculpin (Cottus leiopomus) is endemic to the Wood River. The Shoshone sculpin (Cottus greenei) is endemic to the small portion of the Snake River between Shoshone Falls and the Wood River.

The Snake River below Shoshone Falls is home to thirty-five native fish species, of which twelve are also found in the Columbia River and four of which are endemic to the Snake: the relict sand roller (Percopsis transmontana) of the Percopsidae family, the shorthead sculpin (Cottus confusus), the maginated sculpin (Cottus marginatus), and the Oregon chub (Oregonichthys crameri). The Oregon chub is also found in the Umpqua River and nearby basins. The lower Snake River also supports seven species of salmon (Oncorhynchus). There are also high, often localized levels of mollusc endemism, especially in Hells Canyon and the basins of the Clearwater River, Salmon River, and middle Snake River. The mollusc richness extends into the lower Columbia River and tributaries such as the Deschutes River.