Factors influencing the decline of native fishes in the upper Verde River watershed and management options for their conservation

Native fish in streams throughout the American Southwest are declining. Many native fish species have been extirpated from the Verde River in Arizona in the past few decades. The introduction of non-native fish nearly a century ago, and stocking of non-native game fish have seriously impacted native fish. Increased groundwater pumping due to increasing urban populations, the threat of climate change, and the low priority of instream water rights compared to other water users' rights leave streamflow in the Verde River watershed in danger of decline. A decline in streamflow leads to loss of instream habitat for native fish, and crowding of native and non-native species.;The objectives of this study were 1) to compare native and non-native fish abundance and distribution with respect to habitat characteristics, 2) to describe factors currently threatening native fish, and 3) to explore management and policy options that can mitigate as many of the problems threatening native fish as possible.;The thesis is written with two stand-alone chapters because, though both are focused on native fish, they explore different questions using different methods. Chapter one is the report of an observational study examining native and non-native fish distribution and abundance, and differences in habitat utilization. In this study I collected microhabitat data associated with individual native and non-native fish and analyzed the data using Kruskal-Wallace and chi-squared analysis, and non-metric multidimensional scaling. Neither native nor non-native species showed strong affinity for particular habitat characteristics. Non-native fish were far more abundant in the entire study area than native fish, with only two sites predominately populated with native fish.;Chapter two is written as a review of the status of, and threats to, native fish of the Verde River, and various management options that could be used to conserve native fish populations. Of all of the possible factors affecting native fish, hydrologic alteration and the continued presence of non-native fish are the biggest threats. Arizona must redefine the legal relationship between surface and groundwater, and monitor groundwater usage to protect instream flows. In addition to protecting instream flows and habitat, native fish must be protected from non-native fish by controlling non-native numbers, and possibly by providing refuge habitat for native fish.