Endangered and Threatened Species of the Platte River

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• SUMMARY The North Platte River and the South Platte River rise in the Rocky Mountains of Colorado and flow through Wyoming and Colorado, respectively, to join in western Nebraska to form the Platte River, which continues eastward to its confluence with the Missouri River. The central Platte River and the lower Platte River are the focus of this report. The central Platte River (as defined in this report) includes the reach from Lexington to Columbus, Nebraska, and the lower Platte River is the segment from Columbus to the confluence with the Missouri River (Figure S -1). A portion of the Platte River corridor is within the North American Central Flyway and provides habitat for migratory and breeding birds, including three endangered or threatened species: the whooping crane (Gnus americans), the northern Great Plains population of the piping plover (Charadrius melodus), and the interior least tern (Sterna antillarum athalassos). Most of the interest related to habitat areas for these listed birds extends from Lexington to Chapman (Figure S -1). The broad, shallow waters of the lower Platte River provide important habitat for the endangered pallid sturgeon (Scaphirhynchus albus). Continentwide conditions are responsible for the declines in populations of those four species that resulted in their listings under the Endangered Species Act (ESA) or, in the case of the cranes, prior legislation. The decline in whooping crane populations began many years ago with overhunting and widespread habitat destruction. Whooping cranes, the rarest species of crane in the world, were federally listed as endangered in 1967 under the Endangered Species Preservation Act. Critical habitat for the whooping crane was designated in 1978. Only about 185 wild birds remain, and another 118 are in captivity. The northern Great Plains population of the piping plover was federally listed as threatened in 1986. Critical habitat for the piping plover was designated in 2002. The population on the Platte River was estimated in 2001 at about 85 nesting pairs. The number and extent of suitable nesting sites have declined with changes in magnitudes and frequency of river flows, flooding from local runoff, changes in vegetation, and human interference during nesting. Interior least terns were federally listed as endangered in 1985. Observations of the interior least tern are rare in the central Platte River. The estimated total number of birds in the lower Platte River area is now less than 500. Their population decline results from the loss of open sandy areas in and along rivers, a byproduct of inundation by reservoirs, channelization, large -scale changes in flow regimes, and replacement of open areas with woodlands, sand and gravel mines, housing, and roadways. The pallid sturgeon was federally listed as endangered in 1990 in the lower Platte River. Populations of pallid sturgeon have declined throughout its range; 500 observations per year in the 1960s declined to about seven per year in the 1980s. Pallid sturgeon seem to prefer warm, turbid waters with annually variable flows and firm, sandy channel bottoms; however, extensive damming has disrupted fish passage and resulted in cooler stream flows, less turbid waters, and inconsistent flow regimes. Commercial harvesting, now illegal, also contributed to the decline of the pallid sturgeon. The Platte River delivers water, mostly from precipitation in the Rocky Mountains, to an extensive water - control system for irrigated agriculture and urban water in all three states. This I