Endangered and Threatened Species of the Platte River (2005)

The 100th meridian is a defining geographic feature in the United States that marks important transitions for land, water, and life. In the Great Plains, this north-south line (immediately east of Cozad, Nebraska) transects the corridor of the central Platte River Valley of Nebraska, the subject of this report. The river is emblematic of the human and ecological complexities of policy, science, and management for a dryland river (Figure 1-1). The river was named the Platte River, French for “flat river,” on June 2, 1739, by two French explorers who were searching for a route from Illinois to Santa Fe, New Mexico (Sheldon 1913).

The Platte River’s two great branches, the North Platte and the South Platte, rise in the Rocky Mountains in the West and join in western Nebraska to the west of the 100th meridian (Figure 1-2). The river flows 310 mi (about 500 km) through Nebraska across the meridian to a confluence with the Missouri River. The Platte River delivers the runoff of its 86,000-mi² (223,000-km²) drainage area, largely the result of precipitation in the high western mountains, to an extensive system of water control for the highly productive agricultural area in the plains. The river is more than a conduit for water, however; along its course, it creates an aquatic and riparian ecosystem that provides wildlife habitat unlike habitats found outside the river valley. The river corridor, within the Central Flyway of North America, provides habitat for migratory and breeding birds, including three endangered or threatened species: the whooping crane (Grus americana), the piping plover (Charadrius melodus), and the interior least tern (Sterna

FIGURE 1-1 South channel of central Platte River at Rowe Sanctuary near Kearney. Channel is periodically dry, as in this view. Riparian vegetation includes cottonwood-dominated forests and more open areas. Source: Photograph by W.L. Graf, August 2003.

antillarum athalassos). The broad shallow waters of the Platte near its confluence with the Missouri River constitute an important habitat for at least one endangered species of fish: the pallid sturgeon (Scaphirhynchus albus).

The infrastructure investments that made irrigated agriculture and urban water supply possible in the Platte River Basin have substantially altered the hydrologic regime of the Platte River. During the twentieth century in the Platte River Basin, construction of storage reservoirs and diversion dams and installation of wells to tap groundwater supported the economic vitality of the region. The structures continue to provide flood reduction, water supply, hydroelectricity, and recreational benefits. By controlling and diverting water flows, however, the dams altered the stream flows, and that caused widespread environmental changes. A major habitat change involved the expansion of woodland and the narrowing of river channels. Whooping cranes, piping plovers, and interior least terns, whose populations were already declining because of other factors, prefer more sparsely vegetated, open, sandy areas near shallow water.

Between 1967 and 1990, the whooping crane, piping plover, interior least tern, and pallid sturgeon were listed under federal legislation related to threatened and endangered species. Rather than address the individual species in isolation from each other, Nebraska, Colorado, Wyoming, and agencies of the U.S. Department of the Interior (DOI) signed the Platte River Cooperative Agreement in July 1997 to provide Endangered Species Act (ESA) compliance for all four species simultaneously. The signatories created the Platte River Endangered Species Partnership—which includes water users, environmental groups, and others—to implement the cooperative agreement. The agreement seeks to develop a recovery implementation program to improve and conserve habitat for the four listed species and seeks to enable existing and new water uses in the basin to proceed without additional regulatory actions related to the species. In 2003, DOI, with input from the Governance Committee of the state-federal partnership, asked the National Research Council to evaluate the scientific validity of the instream flow recommendations, habitat requirements for the species, and connections among the physical systems of the river related to the habitat as specified by the U.S. Fish and Wildlife Service (USFWS). The present volume is the final report of the committee.

This chapter provides a brief overview of the Platte River Basin, the primary management issues that are related to the river and the endangered and threatened species, and the governing policies that define potential approaches to these issues. It also explains the specific charge given to the Research Council’s Committee on Endangered and Threatened Species in the Platte River Basin.

Among the consequences of extensive economic development of the river resources and the associated changes in hydrology, geomorphology, and riparian vegetation were the changes brought about in wildlife populations. The physical changes in the river are reflected in habitat changes. In the central Platte River, more than 40 mi² (104 km²) of river channel has been altered. Declines in the populations of piping plovers and interior least terns have been particularly notable. The whooping crane declined to a low of 15 birds in the late 1800s and early 1900s and is now rebounding. Nationally, the pallid sturgeon also has become very rare. All three bird species prefer open, sandy areas near shallow water. Such areas are precisely the type of habitat that has shrunk in response to the hydrological, geomorphic, and vegetation changes. Continent-wide impacts caused the four species to become listed. Whooping crane populations were substantially decreased by overhunting and habitat degradation. Piping plovers and interior least tern populations were greatly reduced by dam and reservoir

construction and human interference during nesting. Pallid sturgeon populations were adversely affected by large dams and channel works built on the mainstem Missouri River. Ecological changes in the central Platte River also have had habitat implications for other species, such as neotropical migrant birds that have been favored by expansion of riparian woodlands.

Whooping cranes, federally listed in 1967 under the Endangered Species Preservation Act, are the rarest species of crane in the world (Figure 1-3). Although exact numbers are not known, historical accounts indicate that the central Platte River was a stopping area for whooping cranes, which prefer its long vistas, shallow waters, and food sources in adjacent meadows and grasslands; sightings have been documented since 1820. Piping plovers, federally listed as threatened in 1986 under the ESA, are small migratory shorebirds that breed in three regions of North America: the Atlantic Coast, the Great Lakes, and the northern Great Plains (Figure 1-4). About 1% of the northern Great Plains breeding population uses the central Platte River as an area for nesting sites—almost exclusively the bare sandy areas associated with the active channel and in some cases alternative sites with open sandy areas, such as sand and gravel mines. In 2001, the population was estimated at about 85 nesting pairs on the Platte River (J. Dinan, Nebraska Game and Parks Commission, pers. comm., 2003). Interior least terns, federally listed as endangered under the ESA in 1985, are also small migratory birds that use open sandy islands, bars, and beaches

FIGURE 1-3 Whooping crane. Source: Photograph by George Archibald, International Crane Foundation, 1997. Reprinted with permission; copyright 1997, International Crane Foundation.

FIGURE 1-4 Piping plover. Source: USFWS 2004a.

on inland rivers for breeding sites (Figure 1-5). By the 1980s, the range for the interior least tern in the central Platte River had shrunk to include only a portion of the Platte River Valley between Kearney and Grand Island, and the bird was a rare migrant and an infrequent nester. The estimated total number of birds in the lower Platte River area is now lower than 500 (Kirsch and Sidle 1999). The pallid sturgeon was federally listed in 1990 under the ESA as endangered on the lower Platte River (Figure 1-6). The

FIGURE 1-5 Interior least tern. Source: USFWS 2004b.

FIGURE 1-6 Pallid sturgeon. Source: Photograph by Jason Olnes, University of Nebraska, May 2, 2001.

fish favors warm, turbid waters with annually variable flows and firm sandy channel bottoms with dunes and pockets, where it feeds on small fish and aquatic insects. Its population has declined throughout its range over recent decades; 500 observations per year in the 1960s declined to about seven per year in the 1980s (Fed. Regist. 55 (173): 36641 [1990]).

Nationwide declines in the populations of whooping cranes, interior least terns, piping plovers, and pallid sturgeon led to the listing of each under the provisions of the ESA or, in the case of the cranes, a prior act. By 1990, all four species had been listed (Table 1-1), and there was a continuing series of consultations and opinions by USFWS related to projects in the Platte River Basin. Water withdrawals were especially at issue because of the importance of water and flow regimes to the habitat of the species. Since 1978, the history of public decision making for water projects along the Platte River has been littered with lawsuits, negotiations, contentious debates over jeopardy opinions, and occasional agreements that allowed some projects to move forward with mitigation strategies. An example of the complications is the relicensing of hydroelectric projects by the Federal Energy Regulatory Commission. The applications of the Central Nebraska

Public Power and Irrigation District and the Nebraska Public Power District required 15 years for the approval of their licenses for their water and power operations. The USFWS recommendations for instream flows were also problematic for water managers. The instream flows, peak discharges, and pulses that USFWS determined to be essential to maintaining habitat for at-risk species restricted withdrawals and limited the use of river flow for other purposes.

Many of the data and nearly all the explanations of causal connections among the physical aspects of the Platte River, the ecology of habitats, and the biology of the four listed species have been questioned by commentators outside USFWS. In particular, the data related to whooping cranes, their use of the riverine habitats, and the importance of the Platte River in their ecology have attracted critical comment (G. Lingle, University of Nebraska, unpublished material, March 22, 2000). M.M. Czaplewski, J.J. Shadle, J.J. Jenniges, and M.M. Peyton (unpublished material, June 12, 2003) also have raised important questions about the science supporting the designation of the species as threatened or endangered and the science used to define instream flow requirements. The National Research Council committee has explored those and other criticisms of USFWS’s scientific work and has considered them with agency replies.

The complex nature of water-resource development and endangered-species management in the Platte River Basin became an increasingly difficult issue beginning in 1994 when six water-related projects in the Colorado Front Range became the subject of negotiations between project proponents and USFWS. The settlement of the negotiations included permission for the projects to continue and support for a recovery effort that encompassed areas downstream along the Platte River. During the 1990s, recovery efforts included work by the Whooping Crane Trust and the National Audubon Society to modify habitat in the river corridor. In recognition of the complicated policy issues involving Wyoming, Colorado, Nebraska, and the federal government (represented by DOI agencies, such as USFWS and the U.S. Bureau of Reclamation [USBR]), a new cooperative agreement was created among these entities. On July 1, 1997, the governors of the three states and the secretary of the interior signed a cooperative agreement defining a Central Platte River Recovery Implementation Program (DOI 1997). The agreement established a 10-member Governance Committee whose members represented the full array of participants and were charged with designing and implementing the recovery program. The success of the recovery program depends on a sound understanding of the relationships among water flows, channels, control structures, vegetation, and wildlife and on decisions by the Governance Committee that are founded on the scientific explanations of those relationships. Discussions among the Governance Committee members and the various publics they

represent revealed important questions about the scientific underpinnings of recovery plans for the species in question and of the explanations of environmental changes along the river that have affected wildlife habitat.

In January 2003, DOI, with the concurrence of and input from the Governance Committee, asked the National Academies to direct its investigative arm, the National Research Council, to assess the science underlying many of the decisions reached by agencies of the federal government related to endangered and threatened species in the Platte River Basin. Specifically, the Governance Committee asked for an evaluation of the habitat requirements of the listed species of the central and lower Platte River and for an evaluation of the scientific basis of USFWS’s instream-flow recommendations and habitat-suitability guidelines and of DOI’s conclusions about the relationships among sediment movement, hydrologic flow, vegetation, and channel morphology. See Boxes 1-1 and 1-2 for details of the charge to the committee and Box 1-3 for the committee’s definition of terms included in the statement of task. In early 2003, the Research Council formed the

Committee on Endangered and Threatened Species in the Platte River Basin, a panel of 13 members (later expanded to 14) that included a specialist for each listed species in the charge; two ecologists; engineers specializing in hydraulics, hydrology, and civil-environmental topics; a geomorphologist; a geographer; legal, economic, and water-policy experts; and a farmer (see Appendix A for details).

The committee held two public meetings in Nebraska—one in Kearney and the other in Grand Island—to collect information, meet with researchers and decision makers, and accept testimony from the public. The meetings included an extensive flight over the Platte River from Lake McConaughy to Chapman and visits to the Rowe Sanctuary and Shelton Cottonwood Demography Site. The committee met a third time, in executive session, in Boulder, Colorado, to complete its report. Subcommittees visited DOI researchers at their installations in Denver and Grand Island. The committee reviewed documents describing the methods and procedures used by DOI investigators in reaching their determinations.

The committee evaluated the literature relied on by the DOI agencies in formulating their decisions on threatened and endangered species and their understanding of the connections among water, sediment, river morphology, and habitat. The committee found that much of the literature pertaining to the Platte River for these applications was not in the refereed journal literature, the most common highly reliable sources. The refereed literature is significant because it represents the results of rigorous review and examination before publication, and it is the intellectual currency in the environmental sciences. Much of the literature of importance in dealing with threatened and endangered species along with the dynamics of the Platte River is in the “gray literature,” publications that are products of governmental agencies and private foundations. Although these publications are sometimes reviewed, they are not as widely available nor are they as highly regarded in the scientific community as refereed journal articles. Nonetheless, the gray literature is an important conduit of scientific information, and in the absence of extensive journal literature it represents the only viable substitute. When judging whether or not DOI agencies relied on the best available science, the committee assessed the availability of background literature and determined whether or not DOI agencies relied on all the available sources, regardless of the type. In many instances, the committee found that at the time of their decisions, DOI agencies were forced to rely on in-house investigations, agency reports, and conference or working-group reports. The committee assessed these sources in reaching its conclusions. The committee did not evaluate four items that are closely related to but not part of its charge: (1) USBR’s draft Environmental Impact Statement for the Platte River Recovery Program, which was completed and released when the committee had finished its deliberations and was close to finalizing its report; (2) an advanced computer model, SEDVEG, to evaluate the interactions among hydrology, river hydraulics, sediment transport, and vegetation for the Platte River—the model is being developed by USFWS but has not yet been completed or tested; (3) an evaluation of the models and data used by USFWS to set flow recommendations for whooping cranes that is being developed, but has not yet been completed, by USGS; and

(4) the Central Platte River Recovery Implementation Program proposed in the cooperative agreement by the Governance Committee, which, as stated in Box 1-2, was excluded from the committee’s charge.

The present report is the product of the efforts of the entire Research Council committee and underwent extensive, independent external review overseen by the Research Council’s Report Review Committee. It specifically addresses the statement of task as agreed on by the Research Council, USFWS, USBR, and the Governance Committee. The report is limited to that formal statement and to addressing 10 questions that the Governance Committee provided as guidance.

The remaining chapters of this report constitute the findings of the committee on Endangered and Threatened Species in the Platte River Basin. Chapter 2 provides a descriptive overview of the Platte River Basin and the historical background of the issues, including reviews of human, hydrological, and ecological history. Chapter 3 provides the foundation for understanding policy and science issues connected with the ESA. Chapter 4 evaluates the science behind decisions related to the physical systems of the Platte River. Chapters 5, 6, and 7 evaluate the validity of the biological science of the whooping crane, the piping plover and interior least tern, and the pallid sturgeon, respectively. Chapter 8 summarizes the committee’s conclusions and recommendations and presents succinct answers to the specific questions outlined by the Governance Committee.

In the 1870s, John Wesley Powell correctly predicted the high degree of variability of water resource supplies along and west of the 100th meridian, but he could not foresee the changes that have occurred in general climate, land use, and land cover and in the fundamental physical and biological characteristics of the Platte River in the vicinity of the meridian. Powell’s emphasis on change applies to all the components of the ecological systems in the central and lower Platte, but it is left to modern researchers to understand how those changes in water, land, and life interact with and influence each other. The primary underlying question that is a thread throughout the following pages is this: Are resource managers using the best available valid scientific information to support their decisions?