meetings. The committee assessed the science used by DOI agencies as it existed when the agencies made their decisions. Since those decisions were made, there have been advances in science and engineering that may improve management.

This chapter evaluates the types, relevance, and quality of science used by DOI to understand and manage the individual endangered species and the ecosystem associated with the river, and it assesses the validity of the science for policy decisions. The scientific basis of listing a species and designating critical habitat is discussed in Chapters 5, 6, and 7. This chapter begins with a consideration of how science is connected with the goals of restoration of the Platte River for the benefit of threatened and endangered species. It then describes the basic connections that sustain the Platte River ecosystem (including its hydrology and geomorphology) and the habitats important for its threatened and endangered species. Next, it addresses specifically the validity of the science underlying DOI decisions related to instream flows and ecosystem connections that managers use to preserve and enhance habitat for threatened and endangered species. The chapter concludes with some special scientific considerations for decision makers that have not yet been fully explored.

SCIENCE AND MANAGEMENT TARGETS FOR SPECIES

Management of the Platte River for the benefit of threatened and endangered species entails a preliminary decision that deeply involves science and the state of our knowledge. It is likely to require restoration of the physical system of the river, its hydrology and geomorphology, to create habitats useful for sustaining the species. Restoration in this sense implies managed and designed changes to alter the existing river to some other target condition. The target of restoration in most applications is the presettlement condition because those arrangements supported in relative abundance the species that are now endangered or threatened. It is rarely possible to completely attain such a restoration because of human effects such as land-use changes in the watershed and water-control infrastructure, but as a general objective the presettlement conditions represent the end-point of a spectrum of possibilities. There are two fundamental approaches to restoration: first, through knowledge of the presettlement conditions, and second, through knowledge of the present connections among physical systems, habitats, and species. In the case of the Platte River, restoration of the river to its prehuman or pre-European-settlement condition is faced with three issues: first, knowledge about prehistoric systems is sparse; second, they were always changing; and third, it is not possible to reconstitute them. First, knowledge about the prehuman ecosystem of the Platte River is highly limited by the lack of direct observations. Proxy measures of the



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