While the ecology and evolution of partial migratory systems (defined broadly to include skip spawning) have been well studied, we are only beginning to under- stand how partial migratory populations are responding to ongoing environmen- tal change. Environmental change can lead to differences in the fitness of residents and migrants, which could eventually lead to changes in the frequency of the strategies in the overall population. Here, we address questions concerning the life history of the endangered Gila cypha (humpback chub) in the regulated Colorado River and the unregulated tributary and primary spawning area, the Little Colorado River. We develop eight multistate models for the population based on three movement hypotheses, in which states are defined in terms of fish size classes and river locations. We fit these models to mark–recapture data col- lected in 2009–2012. We compare survival and growth estimates between the Col- orado River and Little Colorado River and calculate abundances for all size classes. The best model supports the hypotheses that larger adults spawn more frequently than smaller adults, that there are residents in the spawning grounds, and that juveniles move out of the Little Colorado River in large numbers during the monsoon season (July–September). Monthly survival rates for G. cypha in the Colorado River are higher than in the Little Colorado River in all size classes; however, growth is slower. While the hypothetical life histories of life-long resi- dents in the Little Colorado River and partial migrants spending most of its time in the Colorado River are very different, they lead to roughly similar fitness expectations when we used expected number of spawns as a proxy. However, more research is needed because our study period covers a period of years when conditions in the Colorado River for G. cypha are likely to have been better than has been typical over the last few decades.

The Grand Canyon Monitoring and Research Center began long-term planning at its inception and, in May 1997, produced a Long-Term Monitoring and Research Strategic Plan that was adopted by stakeholder groups (the Adaptive Management Work Group and the Technical Work Group) later that year. The Center then requested the National Research Council's (NRC) Water Science and Technology Board to evaluate this plan.

Federal management of water is undergoing a change that involves a drastic reduction in the number of new water projects and an increase in emphasis on the quality of water management. This book summarizes and analyzes environmental research conducted in the lower Colorado River below the Glen Canyon Dam under the leadership of the Bureau of Reclamation. It reviews alternative dam operations to mitigate impacts in the lower Colorado riverine environment and the strengths and weaknesses of large federal agencies dealing with broad environmental issues and hydropower production. While many problems remain to be solved, the Bureau of Reclamation through the Glen Canyon area. The lessons of GCES are transferable to other locations and could be the basis for a new era in the management of western waters.