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stocked, and litigation was considered. Today a major HMP involving state agencies, water supply and irrigation districts, Native American tribes, NGOs, and other groups is being de- veloped for the lower Colorado River. A few NGOs, however, plan to litigate if dissatisfied. In 1999, USFWS Region 2 asked several of the authors to formulate a plan to perpetuate fishes native to the lower basin. We accepted the assignment with trepidation, since a "common solution [for seemingly intractable situations) is to replace... uncertainty of resource issues with... certainty of a process, whether that process is a legal vehicle-such as a new policy, regulation, or lawsuit-or a new institution such as a technical oversight committee or science advisory committee" (Gunderson 1999; bracketed material and italics ours). In this instance, the committee was ad hoc and largely undirected, consisting of academic scientists advised by agency biologists. In the meantime, new definitions of recovery goals (USFWS 2002a, 2002b, 2002c, 2002d) for the four big-river fishes be- came an issue, which in part redirected the group's efforts. This article presents our recommendations for a science- based recovery strategy that could aid the recovery of the big-river fishes in the lower Colorado River. The recom- mendations are not new. They are based on our collective knowledge, published papers, and unpublished plans. We believe they offer important new perspectives that should be incorporated into criteria used by the RIP (USFWS 2002a, 2002b, 2002c, 2002d) to determine when a listed big-river species has "recovered' Rationale and approach Some workers dealing with the lower Colorado River advo- cate a return to conditions before the arrival of western Eu- ropeans, after which the ecosystem would be allowed to change without management. Others deem the river already so highly altered that it should he written off to save conser- vation dollars. Many view the first recommendation as too idealistic and unrealistic and the second as defeatist. Instead we choose to take the middle ground by advocating aggres- sive, ongoing management, because the lower Colorado River is one of only a few places in the American Southwest where surface water will persist into the foreseeable future. We expect management practices to evolve in concert with changing sociopolitical practices and cultural values. Until now, varying emphases have been placed on flood control, power generation, irrigation, recreation, municipal supply, and other uses. Today's trends include a shift from rural to urban water uses and increasing emphasis on promoting mainte- nance of biodiversity. Native fish management in the lower Colorado River has become an increasing responsibility for federal and state agencies over the past three decades. That re- sponsibility is likely to continue increasing, as is evident in the Lower Colorado River Multi-Species Conservation Program planning process currently under way. Herein lies an oppor- tunity to perpetuate native fishes. The key to success is to em- bed secure, exclusive native fish habitats and effective native fish management as part of daily river operations. We recognize that the Colorado River as now regulated dif- fers substantially from what it was, and we accept that it will not be the same again. We also recognize that regulation of discharge and flow patterns is not per se the principal threat to the persistence of the four species considered here. The fun- damental problem is that abundant, nonnative predatory species preclude recruitment of natives. We have no doubt that if nonnative species vanished, the big-river fishes world per- sist in today's modified habitats. But although all native species tested thus far reproduce to sustain themselves in predator-free habitats, few have succeeded in waters shared with nonnative species (Marsh and Pacey 2003). Nonnatives prey on the larvae and juveniles of native species. All nonnative species are actual or potential predators or competitors, and where they occur we believe reestablishing an original fauna is impossible. We recognize that nonnatives cannot be erad- icated everywhere, but at least we can provide local habitats from which nonnatives are excluded. If an original fauna is to persist, continuing management will be required. Our proposal deals with the concepts of, rationale for, and uncertainties about the numbers of individuals necessary to satisfy the goal of species maintenance. The need to maintain large effective population sizes makes it necessary to use space in the main stem, off-channel floodplain, and distrib- utaries (effective size is a term that relates a population in na- ture to an idealized population with certain genetic charac- teristics). The proposed solution involves translocation of native species between predator-free, off-channel habitats and the main channel, backwaters, and reservoirs (hereafter channel plus connectives). Reproduction and recruitment take place off-channel, and large, wide-ranging, and pan- mictic populations of adults maintain both population size and genetic variation there and in the channel plus connec- tivcs. The plan briefly addresses habitats that are needed to ac- complish such goals and anticipated problems in developing such habitats; it alsn suggests ways that the native fishes can be managed successfully over the long term. Dwindling populations. The last wild Colorado squawfish was caught in 1975 in the lower Colorado River (Minckley 1991). Bonytail persist only in Lake Mohave (in Arizona and Nevada) and perhaps in Lake Havasu (in Arizona and Cali- fornia) as a few wild fish that are augmented by hatchery reintroductions. Humpback chub are represented by one viable population in the Little Colorado River-Grand Canyon complex. Cold water from Glen Canyon Dam precludes humpback chub reproduction downstream in the Colorado River main stem, and most humpback chub live and spawn in the Little Colorado. Some young move into the main stem, mature, and reenter the tributary to spawn. The Little Col- orado population hovered near 10,000 adults into the early 1990s but recently is thought to have declined substantially. Perhaps 10% as many humpback chub occupy the adjacent Colorado River main stem (Valdez and Ryel 1995). 222 BioScience . March 2003 / Vol. 53 No. 3