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 (Grus americana), 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).

Changing landscape and ecological conditions well beyond the Platte River 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,



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Endangered and Threatened Species of the Platte River 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 (Grus americana), 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). Changing landscape and ecological conditions well beyond the Platte River 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,

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Endangered and Threatened Species of the Platte River FIGURE S-1 General location and features of Platte River Basin, including its position across 100th meridian. Source: Adapted from DOI 2003.

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Endangered and Threatened Species of the Platte River 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 system of large dams with storage reservoirs and diversion works with canals provides such benefits as water supply, flood control, electrical power generation, and recreation; it also has substantially altered the river’s hydrology and geomorphology. Additional hydrological alterations occur with additions to groundwater through seepage from canals and irrigation and subtractions from wells. The geomorphic and hydrological alterations have caused changes in wildlife habitat and may affect species that depend on particular types of habitat. For example, altered stream flow has resulted in the expansion of woodlands and narrowing of river channels, but the endangered and threatened birds that breed or stop over in the central Platte River appear to prefer sparsely vegetated, open, sandy areas near shallow water. Protection of federally listed species has been in tension with water management in the Platte River Basin for more than 25 years. Dam construction, new diversions, and federal relicensing of power projects have all

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Endangered and Threatened Species of the Platte River been complicated by conflicts with the perceived needs of endangered and threatened species. The conflicts were sharpened by the ongoing litigation among the basin states over division of the waters of the North Platte River, which is not governed by an interstate compact. In 1997, in an effort to find a nonadversarial means of resolving listed-species disputes in the Platte River Basin, the basin states and the federal government entered into a cooperative agreement that established a Governance Committee representing state, federal, environmental, and water-user interests. The committee was charged with developing and implementing a recovery program for the listed species of the basin. Progress toward a recovery program proved slower than the parties had hoped. Meanwhile, implementation of the ESA in the Platte River Basin was increasingly controversial as the U.S. Fish and Wildlife Service (USFWS) issued a series of “jeopardy opinions,” finding that any new depletions of the Platte River would have to be compensated by mitigation measures, and a lawsuit forced the designation of “critical habitat” for the northern Great Plains population of the piping plover. Members of the Governance Committee, the interests they represent, and others whose interests would be affected by any recovery program began to question the science supporting current management of the basin’s listed species and sought an outside review of the science before the recovery program was made final. In 2003, the U.S. Department of the Interior (DOI) asked the National Academies to direct its investigative arm, the National Research Council, to evaluate independently the habitat requirements for the whooping crane, piping plover, interior least tern, and pallid sturgeon; to examine the scientific aspects of USFWS’s instream-flow recommendations and habitat suitability guidelines; and to assess the scientific support for the connections among the physical systems of the river related to the habitat as explained and modeled by the U.S. Bureau of Reclamation (USBR) (Box S-1). To help focus the National Research Council’s task, the Governance Committee offered 10 specific questions related to science and policy for the four threatened and endangered species (Box S-2). The National Research Council formed the Committee on Endangered and Threatened Species in the Platte River Basin to address the charge described in Boxes S-1 and S-2. The 14-member committee includes biologists specializing in the study of cranes, plovers, terns, and sturgeon; ecologists; engineers specializing in hydraulics, hydrology, and civil-environmental topics; a geomorphologist; a geographer; legal, economic, and water-policy experts; and a farmer. The committee met three times. Its first two meetings (held in Kearney and Grand Island, Nebraska) were open to the public and included invited presentations from researchers and decision makers and a public-comment session. During those two meetings, the committee participated

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Endangered and Threatened Species of the Platte River BOX S-1 Statement of Task for the National Research Council A multidisciplinary committee will be established to evaluate the central Platte River habitat needs of the federally listed whooping crane, Northern Great Plains breeding population of the piping plover, interior least tern, and the Lower Platte River habitat needs of the pallid sturgeon. The committee will review the government’s assessments of how current Platte River operations and resulting hydro-geomorphological and ecological habitat conditions affect the likelihood of survival of and/or limit the recovery of these species, and whether other Platte River habitats do or can provide the same values that are essential to the survival and/ or recovery of these species. The committee will consider the scientific foundations for the current federal designation of central Platte habitat as “critical habitat” for the whooping crane and Northern Great Plains breeding population of the piping plover. The study will also examine the scientific aspects of (1) the processes and methods used by the U.S. Fish and Wildlife Service in developing its Central Platte River instream-flow recommendations, taking the needs of the listed species into account (i.e., annual pulse flows, and peak flows); (2) characteristics described in the U.S. Fish and Wildlife Service habitat suitability guidelines for the central Platte River; and (3) the U.S. Department of Interior’s conclusions about the interrelationships among sediment movement, hydrologic flow, vegetation, and channel morphology in the central Platte River. in an observational flight over the Platte River from Lake McConaughy to Chapman, Nebraska, and visited the Rowe Sanctuary and Shelton Cottonwood Demography Site. The third meeting (held in Boulder, Colorado) was not open to the public, so the committee could complete its report. Members of the committee visited DOI researchers at their installations in Denver and Grand Island. The committee also reviewed documents describing the methods and procedures used by DOI investigators in reaching their determinations and other written documentation provided by experts and the public. The focus of the committee’s review is the habitat needs of the Platte River endangered and threatened species. The ESA protects critical habitat, defined as the specific areas that contain physical or biological features essential to the conservation of the species and that may require special management considerations or protection (ESA § 3(5)). This report uses the term only to refer to areas that have been formally designated under the ESA. Other key terms in the statement of task, defined by the committee for the purpose of this report, are limit, which was interpreted by the committee to mean adversely affect or influence; recovery, interpreted to mean improvement in the status of listed species to the point at which they would

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Endangered and Threatened Species of the Platte River BOX S-2 Governance Committee’s NAS Review Questions (October 31, 2002) The Governance Committee offers these questions to focus NAS in their scientific review. Not all members of the GC agree with all of the questions. However, we are unanimous that the NAS not review the Program, but stay focused on the science related to the questions. During the implementation of the review, individual GC members expect that they will have the opportunity to provide the NAS with their views on the specific issues and areas of concern to be reviewed. In reviewing the government’s assessments, the committee should consider how the following 10 questions apply to them. Do current Central Platte habitat conditions affect the likelihood of survival of the whooping crane? Do they limit its recovery? Is the current designation of Central Platte River habitat as “critical habitat” for the whooping crane supported by the existing science? Do current Central Platte habitat conditions affect the likelihood of survival of the piping plover? Do they limit its recovery? Is the current designation of Central Platte River habitat as “critical habitat” for the piping plover supported by the existing science? Do current Central Platte habitat conditions affect the likelihood of survival of the interior least tern? Do they limit its recovery? Do current habitat conditions in the Lower Platte (below the mouth of the Elkhorn River) affect the likelihood of survival of the pallid sturgeon? Do they limit its recovery? Were the processes and methodologies used by the USFWS in developing its Central Platte River Instream Flow Recommendations (i.e. species, annual pulse flows, & peak flows) scientifically valid? Are the characteristics described in the USFWS habitat suitability guidelines for the Central Platte River supported by the existing science and are they essential to the survival of the listed avian species? To the recovery of those species? Are there other Platte River habitats that provide the same values that are essential to the survival of the listed avian species and their recovery? Are the conclusions of the Department of the Interior about the interrelationship of sediment, flow, vegetation, and channel morphology in the Central Platte River supported by the existing science? What were the key information and data gaps that the NAS identified during their review? no longer be designated as endangered or threatened; and survival, interpreted to mean the persistence of the listed entity. This report represents the unanimous consensus of all members of the National Research Council committee. It is limited to the specific charge as agreed on by the Research Council, USFWS, USBR, and the Governance Committee (Box S-1). To address its charge, the committee considered the extent of the data available for each question and whether the data were generated according

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Endangered and Threatened Species of the Platte River to standard scientific methods that included, when feasible, empirical testing. The committee also considered whether those methods were sufficiently documented and whether and to what extent they had been replicated, whether either the data or the methods used had been published and subject to public comment or been formally peer reviewed, whether the data were consistent with accepted understanding of how the systems function, and whether they were explained by a coherent theory or model of the system. To assess the scientific validity of the methods used to develop instream-flow recommendations, the committee applied the criteria listed above, but focused more directly on the methods. For example, the committee considered whether the methods used were in wide use or generally accepted in the relevant field and whether sources of potential error in the methods have been or can be identified and the extent of potential error estimated. The committee acknowledges that none of the above criteria is decisive, but taken together they provide a good sense of the extent to which any conclusion or decision is supported by science. Because some of the decisions in question were made many years ago, the committee felt that it was important to ask whether they were supported by the existing science at the time they were made. For that purpose, the committee asked, in addition to the questions above, whether the decision makers had access to and made use of state-of-the-art knowledge at the time of the decision. The study committee did not evaluate four items that are closely related to, but not part of, its charge: (1) USBR’s draft environmental impact statement, which was completed and released after the committee finished its deliberations on this report, (2) an advanced computer model, SEDVEG, to evaluate the interactions among hydrology, river hydraulics, sediment transport, and vegetation being developed, but not yet completed or tested, by USBR for application on the Platte River, (3) an evaluation of the models and data used by USFWS to set flow recommendations for whooping cranes being developed, but not yet completed, by USGS, and (4) the Central Platte River Recovery Implementation Program proposed in the cooperative agreement by the Governance Committee. Principal Findings of the Committee 1. Do current central Platte habitat conditions affect the likelihood of survival of the whooping crane? Do they limit (adversely affect) its recovery? The committee concluded that, given available knowledge, current central Platte habitat conditions adversely affect the likelihood of survival of the whooping crane, but to an unknown degree. The Platte River is important to whooping cranes: about 7% of the total whooping crane population

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Endangered and Threatened Species of the Platte River stop on the central Platte River in any one year, and many, if not all, cranes stop over on the central Platte at some point in their lifetimes. Population viability analyses show that if mortality were to increase by only 3%, the general population would likely become unstable. Thus, if the cranes using the Platte River were eliminated, population-wide effects would be likely. Resources acquired by whooping cranes during migratory stopovers contribute substantially to meeting nutrient needs and probably to ensuring survival and reproductive success. Because as much as 80% of crane mortality appears to occur during migration, and because the Platte River is in a central location for the birds’ migration, the river takes on considerable importance. The committee concluded that current habitat conditions depend on river management in the central Platte River, but the population also depends on events in other areas along the migratory corridor. If habitat conditions on the central Platte River—that is, the physical circumstances and food resources required by cranes—decline substantially, recovery could be slowed or reversed. The Platte River is a consistent source of relatively well-watered habitat for whooping cranes, with its water source in distant mountain watersheds that are not subject to drought cycles that are as severe as those of the Northern Plains. There are no equally useful habitats for whooping cranes nearby: the Rainwater Basin dries completely about once a decade, and the Sandhills are inconsistent as crane habitat, while the Niobrara and other local streams are subject to the same variability as the surrounding plains. Future climatic changes may exacerbate conflicts between habitat availability and management and human land use. If the quality or quantity of other important habitats becomes less available to whooping cranes, the importance of the central Platte River could increase. 2. Is the current designation of central Platte River habitat as “critical habitat” for the whooping crane supported by the existing science? An estimated 7% of the wild, migratory whooping crane population now uses the central Platte River on an annual basis and many, if not all, cranes stop over on the central Platte at some point in their lifetimes. The proportion of whooping cranes that use the central Platte River and the amount of time that they use it are increasing (with expected inter-annual variation). The designation of central Platte River migratory stopover habitat as critical to the species is therefore supported because the birds have specific requirements for roosting areas that include open grassy or sandy areas with few trees, separation from predators by water, and proximity to foraging areas such as wetlands or agricultural areas. The Platte River critical habitat area is the only area in Nebraska that satisfies these needs on a consistent basis. However, some habitats designated as critical in 1978 appear to be largely unused by whooping cranes in recent years, and the birds are using adjacent habitats that are not so designated.

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Endangered and Threatened Species of the Platte River Habitat selection (to the extent that it can be measured) on multiple geographic scales strongly suggests that Nebraska provides important habitat for whooping cranes during their spring migration. Riverine, palustrine, and wetland habitats serve as important foraging and roosting sites for whooping cranes that stop over on the central Platte River. Whooping cranes appear to be using parts of the central Platte River that have little woodland and long, open vistas, including such areas outside the zone classified as critical habitat. In some cases the cranes appear to be using areas that have been cleared of riparian woodland, perhaps partly explaining their distribution outside the critical habitat area. 3. Do current central Platte habitat conditions affect the likelihood of survival of the piping plover? Do they limit (adversely affect) its recovery? Reliable data indicate that the northern Great Plains population of the piping plover declined by 15% from 1991 to 2001. The census population in Nebraska declined by 25% during the same period. Resident piping plovers have been virtually eliminated from natural riverine habitat on the central Platte River. No recruitment (addition of new individuals to the population by reproduction) has occurred there since 1999. The disappearance of the piping plover on the central Platte can be attributed to harassment caused by human activities, increased predation of nests, and losses of suitable habitat due to the encroachment of vegetation on previously unvegetated shorelines and gravel bars. The committee concluded that current central Platte River habitat conditions adversely affect the likelihood of survival of the piping plover, and, on the basis of available understanding, those conditions have adversely affected the recovery of the piping plover. Changes in habitat along the river—including reductions in open, sandy areas that are not subject to flooding during crucial nesting periods—have been documented through aerial photography since the late 1930s and probably have adversely affected populations of the piping plover. Sandpits and reservoir edges with beaches may, under some circumstances, mitigate the reduction in riverine habitat areas. Because piping plovers are mobile and able to find alternative nesting sites, changes in habitat may not be as severe as they would be otherwise, but no studies have been conducted to support or reject this hypothesis. 4. Is the current designation of central Platte River habitat as “critical habitat” for the piping plover supported by the existing science? The designation of central Platte habitat as critical habitat for the piping plover is scientifically supportable. Until the last several years, the central Platte supported substantial suitable habitat for the piping plover,

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Endangered and Threatened Species of the Platte River including all “primary constituent elements” required for successful reproduction by the species. Accordingly, the central Platte River contributed an average of more than 2 dozen nesting pairs of plovers to the average of more than 100 pairs that nested each year in the Platte River Basin during the 1980s and 1990s. The critical habitat designation for the species explicitly recognizes that not all areas so designated will provide all necessary resources in all years and be continuously suitable for the species. It is also now understood that off-stream sand mines and reservoir beaches are not an adequate substitute for natural riverine habitat. 5. Do current central Platte habitat conditions affect the likelihood of survival of the interior least tern? Do they limit (adversely affect) its recovery? The committee concluded that current habitat conditions on the central Platte River adversely affect the likelihood of survival of the interior least tern—in much the same fashion as they affect the likelihood of survival of the piping plover—and that on the basis of available information, current habitat conditions on the central Platte River adversely affect the likelihood of recovery of the interior least tern. Reliable population estimates indicate that the total (regional) population of interior least terns was at the recovery goal of 7,000 in 1995, but some breeding areas, including the central Platte River, were not at identified recovery levels. The central Platte subpopulation of least terns declined from 1991 to 2001. The number of terns using the Platte River is about two-thirds of the number needed to reach the interior least tern recovery goal for the Platte. The interior tern is nesting in substantial numbers on the adjacent lower Platte River, but numbers continue to decline on the central Platte, reflecting declining habitat conditions there. The decline in the tern population on the central Platte River has been coincidental with the loss of numerous bare sandbars and beaches along the river. Control of flows and diversion of water from the channel are the causes of these geomorphic changes. Woodland vegetation, unsuitable as tern habitat, has colonized some parts of the central Platte River. Alternative habitats, such as abandoned sand mines or sandy shores of Lake McConaughy, are not suitable substitutes for Platte River habitat because they are susceptible to disturbance by humans and natural predators. The shores of Lake McConaughy are available only at lower stages of the reservoir, and they disappear at high stages. 6. Do current habitat conditions in the lower Platte (below the mouth of the Elkhorn River) affect the likelihood of survival of the pallid sturgeon? Do they limit (adversely affect) its recovery?

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Endangered and Threatened Species of the Platte River Current habitat conditions on the lower Platte River (downstream of the mouth of the Elkhorn River) do not adversely affect the likelihood of survival and recovery of the pallid sturgeon because that reach of the river appears to retain several habitat characteristics apparently preferred by the species: a braided channel of shifting sandbars and islands; a sandy substrate; relatively warm, turbid waters; and a flow regime that is similar to conditions that were found in the upper Missouri River and its tributaries before the installation of large dams on the Missouri. Alterations of discharge patterns or channel features that modify those characteristics might irreparably alter this habitat for pallid sturgeon use. In addition, the lower Platte River is connected with a long undammed reach of the Missouri River, which allows access of the pallid sturgeon in the Platte River to other segments of the existing population. Channelization and damming of the Missouri River have depleted pallid sturgeon habitats throughout its former range, so the lower Platte may be even more important for its survival and recovery. The population of pallid sturgeon is so low in numbers, and habitat such as the lower Platte River that replicates the original undisturbed habitat of the species is so rare that the lower Platte River is pivotal in the management and recovery of the species. 7. Were the processes and methodologies used by the USFWS in developing its central Platte River instream-flow recommendations (i.e., species, annual pulse flows, and peak flows) scientifically valid? USFWS used methods described in an extensive body of scientific and engineering literature. Reports of interagency working groups that addressed instream-flow recommendations cite more than 80 references that were in wide use and generally accepted in the river science and engineering community. The committee reviewed that information, as well as oral and written testimony critical of the research conducted by DOI agencies, and it concluded that the methods used during the calculations in the early 1990s were the most widely accepted at that time. Revisions were made as improved knowledge became available. Although the Instream Flow Incremental Method (IFIM) and Physical Habitat Simulation System (PHABSIM) were the best available science when DOI agencies reached their recommendations regarding instream flows, there are newer developments and approaches, and they should be internalized in DOI’s decision processes for determining instream flows. The new approaches, centered on the river as an ecosystem rather than focused on individual species, are embodied in the concepts of the normative flow regime. Continued credibility of DOI instream-flow recommendations will depend on including the new approach.

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Endangered and Threatened Species of the Platte River The instream-flow recommendations rely on empirical and model-based approaches. Surveyed cross sections along the river provided DOI investigators with specific information on the morphology of the river and vegetation associated with the river’s landforms. The portions of the cross sections likely to be inundated by flows of various depths were directly observed. Model calculations to simulate the dynamic interaction of water, geomorphology, and vegetation that formed habitat for species were handled with the prevailing standard software PHABSIM, which has seen wide use in other cases and has been accepted by the scientific community. The software was used by DOI researchers in a specific standard method, IFIM, which permits observations of the results as flow depths are incrementally increased. The continuing DOI model developments, including the emerging SEDVEG model, are needed because of the braided, complex nature of the Platte River—a configuration that is unlike other streams to which existing models are often applied. The committee did not assess the newer models, because they have not yet been completed or tested, but it recommends that they be explored for their ability to improve decision making. The committee also recognizes that there has been no substantial testing of the predictions resulting from DOI’s previous modeling work,1 and it recommends that calibration of the models be improved. Monitoring of the effects of recommended flows should be built into a continuing program of adaptive management to help to determine whether the recommendations are valid and to indicate further adjustments to the recommendations based on observations. 8. Are the characteristics described in the USFWS habitat suitability guidelines for the central Platte River supported by the existing science and are they (i.e., the habitat characteristics) essential to the survival of the listed avian species? To the recovery of those species? Are there other Platte River habitats that provide the same values that are essential to the survival of the listed avian species and their recovery? The committee concluded that the habitat characteristics described in USFWS’s habitat suitability guidelines for the central Platte River were supported by the science of the time of the original habitat description during the 1970s and 1980s. New ecological knowledge has since been developed. The new knowledge, largely from information gathered over the last 20 years, has not been systematically applied to the processes of designating or revising critical habitat, and the committee recommends that it be done. 1   The committee did not consider USGS’s in-progress evaluation of the models and data used by USFWS to set flow recommendations for whooping cranes.

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Endangered and Threatened Species of the Platte River The committee also concluded that suitable habitat characteristics along the central Platte River are essential to the survival and recovery of the piping plover and the interior least tern. No alternative habitat exists in the central Platte that provides the same values essential to the survival and recovery of piping plovers and least terns. Although both species use artificial habitat (such as shoreline areas of Lake McConaughy and sandpits), the quality and availability of sites are unpredictable from year to year. The committee further concluded that suitable habitat for the whooping crane along the central Platte River is essential for its survival and recovery because such alternatives as the Rainwater Basin and other, smaller rivers are used only intermittently, are not dependable from one year to the next, and appear to be inferior to habitats offered by the central Platte River. 9. Are the conclusions of the U.S. Department of the Interior about the interrelationship of sediment, flow, vegetation, and channel morphology in the central Platte River supported by the existing science? The committee concluded that DOI conclusions about the interrelationships among sediment, flow, vegetation, and channel morphology in the central Platte River were supported by scientific theory, engineering practice, and data available at the time of those decisions. By the early 1990s, when DOI was reaching its conclusions, the community of geomor-phologists concerned with dryland rivers had a general understanding of the role of fluctuating discharges in arranging the land forms of the channel, and DOI included this understanding in its conclusions about the river. In the early 1990s, engineering practice, combined with geomorphology and hydrology, commonly used IFIM and PHABSIM to make predictions and recommendations for flow patterns that shaped channels, and this resulted in adjustments in vegetation and habitat. In fact, despite some criticisms, IFIM and PHABSIM are still widely used in the professional community of river restorationists in 2004. In applying scientific theory and engineering practice, the DOI agencies used the most current data and made additional measurements to bolster the calculations and recommendations. Since the early 1990s, more data have become available, and the USBR has conducted considerable cutting-edge research on a new model (SEDVEG) that should update earlier calculations but is not yet in full operation (and was not reviewed by this committee). Sediment data are obtained by sampling sediment concentrations and multiplying the concentrations by discharges and duration. For flow, gaging records on the Platte River are 50 years in duration or longer, and they are in greater density than on many American rivers; the gages provide quality data on water discharge for the Platte River. Murphy and Randle (2003) review the analyses and other sources of knowledge about the flows

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Endangered and Threatened Species of the Platte River that provide a sound basis for DOI decisions. In addition to the review by Murphy et al. (2001) concerning vegetation, several studies over the last 20 years have provided an explanation of vegetation dynamics that the committee found to be correct and that is the basis of DOI decisions. Early work by USFWS (1981a) and Currier (1982) set the stage for an evolution of understanding of vegetation change on the river that was later expanded by Johnson (1994). For channel morphology, there is a long history of widely respected research to draw on, including early geomorphologic investigations by Williams (1978) and Eschner et al. (1983), continuing with the reviews by Simons and Associates (2000), and culminating in recent work by Murphy and Randle (2003). 10. What were the key information and data gaps that the NAS identified in the review? The committee reached its conclusions for the preceding nine questions with reasonable confidence on the basis of the scientific evidence available. However, the committee identified the following gaps in key information related to threatened and endangered species on the central and lower Platte River, and it recommends that they be addressed to provide improved scientific support for decision making. A multiple-species perspective is missing from research and management of threatened and endangered species on the central and lower Platte River. The interactions of the protected species with each other and with unprotected species are poorly known. Efforts to enhance one species may be detrimental to another species, but these connections remain largely unknown because research has been focused on single species. One approach is to shift from the focus on single species to an ecosystem perspective that emphasizes the integration of biotic and abiotic processes supporting a natural assemblage of species and habitats. There is no systemwide, integrated operation plan or data-collection plan for the combined hydrological system in the North Platte, South Platte, and central Platte Rivers that can inform researchers and managers on issues that underlie threatened and endangered species conservation. Natural and engineered variations in flows in one part of the basin have unknown effects on other parts of the basin, especially with respect to reservoir storage, groundwater storage, and river flows. A lack of a full understanding of the geographic extent of the populations of imperiled species that inhabit the central Platte River and a lack of reliable information on their population sizes and dynamics limit our ability to use demographic models to predict accurately their fates under different land-management and water-use scenarios. Detailed population

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Endangered and Threatened Species of the Platte River viability analyses using the most recent data would improve understanding of the dynamics of the populations of at-risk bird species and would allow managers to explore a variety of options to learn about the probable outcomes of decisions. Continuation of population monitoring of at-risk species using the best available techniques, including color-banding of prefledged chicks and application of new telemetry techniques, is recommended. There is no larger regional context for the central and lower Platte River in research and management. Most of the research and decision making regarding threatened and endangered species in the Platte River Basin have restricted analysis to the basin itself, as though species used its habitats in isolation from other habitats outside the basin. There are substantial gaps in integrative scientific understanding of the connections between species that use the habitats of the central and lower Platte River and adjacent habitat areas, such as the Rainwater Basin of southern Nebraska and the Loup, Elkhorn, and Niobrara Rivers and other smaller northern Great Plains rivers. The committee is confident that the central Platte River and lower Platte River are essential for the survival and recovery of the listed bird species and pallid sturgeon. However, in light of the habitat it provides and the perilously low numbers of the species, there is not enough information to assess the exact degree to which the Platte contributes to their survival and recovery. Water-quality data are not integrated into knowledge about species responses to reservoir and groundwater management and are not integrated into habitat suitability guidelines. Different waters are not necessarily equal, either from a human or a wildlife perspective, but there is little integration of water-quality data with physical or biological understanding of the habitats along the Platte River. The cost effectiveness of conservation actions related to threatened and endangered species on the central and lower Platte River is not well known. Neither the cost effectiveness nor the equitable allocation of measures for the benefit of Platte River species has been evaluated. The ESA does not impose or allow the implementing agencies to impose a cost-benefit test. Listed species must be protected no matter what the cost, unless the Endangered Species Committee grants an exemption. Cost effectiveness, however, is another matter. The ESA permits consideration of relative costs and benefits when choosing recovery actions, for example. USFWS has adopted a policy that calls for minimizing the social and economic costs of recovery actions, that is, choosing actions that will provide the greatest benefit to the species at the lowest societal cost (Fed. Regist. 59:3472 [1994]). In addition, persons asked to make economic sacrifices for the sake of listed species understandably want assurances that their efforts will

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Endangered and Threatened Species of the Platte River provide some tangible benefit. In the Platte, the direct economic costs of measures taken for the benefit of species appear reasonably well understood. The biological benefits are another matter. For example, the costs of channel-clearing and other river-restoration measures are readily estimated. Their precise value for cranes is more difficult to estimate, although their general use is fairly well established. The allocation of conservation costs and responsibility also has not been systematically evaluated. USFWS has concentrated its efforts to protect listed species in the Platte system on federal actions, such as the operation of federal water projects. That focus is understandable. Water projects with a federal nexus account for a large and highly visible proportion of diversions from the system. In addition, those actions may be more readily susceptible to regulatory control than others because they are subject to ESA Section 7 consultation. But some nonfederal actions also affect the species. Water users that depend on irrigation water from the federal projects may well feel that they are being asked to bear an inordinate proportion of the costs of recovering the system. A systematic inventory of all actions contributing to the decline of the species could help the parties to the cooperative agreement channel their recovery efforts efficiently and equitably. The National Research Council committee charged with evaluating ESA actions in the Klamath River Basin recently reached a similar conclusion (NRC 2004a). The effects of prescribed flows on river morphology and riparian vegetation have not been assessed. Adaptive-management principles require that the outcomes of a management strategy be assessed and monitored and that the strategy be adjusted accordingly, but there has been no reporting of the outcomes of the 2002 prescribed flow, no analysis of vegetation effects of managed flows, no measurement of their geomorphic effects, and no assessment of their economic costs or benefits. The connections between surface water and groundwater are not well accounted for in research or decision making for the central and lower Platte River. The dynamics of and connections between surface water and groundwater remain poorly known, but they are important for understanding river behavior and economic development that uses the groundwater resource. The effects of groundwater pumping, recently accelerated, are unknown but important for understanding river flows. Some of the basic facts of issues regarding threatened and endangered species in the central and lower Platte River are in dispute because of unequal access to research sites. Free access to all data sources is a basic tenet of sound science, but DOI agencies and Nebraska corporations managing water and electric power do not enter discussions about threatened and endangered species on the central and lower Platte River with the same datasets for species and physical environmental characteristics. USFWS per-

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Endangered and Threatened Species of the Platte River sonnel are not permitted to collect data on some privately owned lands. As a result, there are substantial gaps between data used by DOI and data used by the companies, and resolution is impossible without improved cooperation and equal access to measurement sites. Important environmental factors are not being monitored. Monitoring, consistent from time to time and place to place, supports good science and good decision making, but monitoring of many aspects of the issues regarding threatened and endangered species on the central and lower Platte River remains haphazard or absent. Important gaps in knowledge result from a lack of adequate monitoring of sediment mobility, the pallid sturgeon population, and movement of listed birds. Responses of channel morphology and vegetation communities to prescribed flows and vegetation removal remain poorly known because the same set of river cross sections is not sampled repeatedly. Groundwater may play an important role in flows, but groundwater pumping is not monitored. Long-term (multidecadal) analysis of climatic influences has not been used to generate a basis for interpretation of short-term change (change over just a few years). The exact interactions between climate and the system are poorly known because only short-term analyses of climate factors have been accomplished so far. In addition, the relative importance of human and climatic controls remains to be explicitly defined by researchers, even though such knowledge is important in planning river restoration for habitat purposes. Direct human influences are likely to be much more important than climate in determining conditions for the threatened and endangered species of the central and lower Platte River. Potentially important localized controls on habitat for threatened and endangered species on the central and lower Platte River are likely to be related to urbanization, particularly near freeway exits and small cities and towns where housing is replacing other land uses more useful to the species. Off-road vehicle use threatens the nesting sites of piping plovers and interior least terns in many of the sandy reaches of the river. Sandy beaches and bars are inviting to both birds and recreationists. Illegal harvesting has unknown effects on the small remaining population of pallid sturgeon. In each of those cases, additional data are required to define the threats to the listed species. Successful conservation in the Platte River Basin must begin with water management. The committee found that sufficient scientific knowledge and understanding exist and have been used to make informed decisions about the management of water resources, the Platte River, and the threatened and endangered species that use the river as habitat. Regarding the critical understanding and modeling that DOI has used to explain the connections among stream flow, sediment movement, vegetation, and habitats, the com-

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Endangered and Threatened Species of the Platte River mittee found that valid science was used when recommendations were made in the past but that future decisions must rely on the use of newer methods and perspectives, particularly the concept of normative flow regimes. The quality of the information upon which decisions are based could be further improved by publishing research findings in peer-reviewed journals or in externally reviewed synthesis volumes to increase accessibility and decrease the reliance on non-peer-reviewed literature. The committee found numerous gaps in knowledge. Addressing them could substantially improve science and management for the river, its human population, and its threatened and endangered species. Those gaps are mostly related to problems of integration of the various lines of scientific investigation, a focus on highly localized rather than more broadly based ecosystem perspectives, a lack of analysis of basinwide connections, a lack of standardized procedures for data collection among government and private agencies, and lack of understanding of the relative cost effectiveness and distributional consequences of alternative conservation measures.