Americas Program Dissertation Enhancement: The Importance of Colorado River Flow to Endemic Fish of the Northern Gulf of California: Evidence from Stable Isotopes in Fish Otoliths

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0323139FlessaThis Americas Program thesis enhancement project will support thesis dissertation research by Kirsten Rowell under the supervision of Dr. Karl Flessa of the University of Arizona. The research, which will involve collaboration with Dr. Conal True of the Universidad Autonoma de Baja California, Ensenada, Mexico, aims to correlate oxygen and carbon content with water and food by studying their isotopic variation in small structures found in the head of most fish (otoliths). Before upstream dams and water diversion, the Colorado River was a major influence on northern Gulf of California habitats. River regulation and impoundment are hypothesized to have altered the estuarine habitat, negatively affecting two endemic fish types. Specific goals of this study include: 1) comparison of the pre-dam and post-dam environmental conditions recorded by the stable isotopes of oxygen and carbon in the otoliths; 2) comparison of growth rates in pre-dam and post-dam specimens of both fish species; and 3) comparison of the habitat, timing and frequency of spawning in pre-dam and post-dam specimens of the two species of fish. By using baseline data stored in fish otoliths in the forms of stable isotopes of oxygen and carbon, growth increments, and spawning frequencies, this study will significantly enhance the dissertation research of a female graduate student, initiate international collaboration with a Mexican colleague, and provide fisheries managers with techniques to detect and measure long-term historical changes in food webs and habitats. The Americas Program and the Geography and Regional Science Program of NSF are jointly supporting this thesis enhancement project.