Platte River Management Joint Study Final Report

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f 30 Spalding 1987). Although informat:ion on toxicity of these chemicals to Platte River forage fish (or closely related species) is available, these data have'-not been investigated for biological significance to the Platte River ecosystem. High water temperatures decrease solubility of dissolved oxygen and decrease its availability to f.orage fish. Elevated temperatures act directly on the fish, increasing metabolism, respiration, and oxygen consumption. There is a maximum temperature which a fish species can tolerate, regardless of the other effects of increased temperature in the stream. Informa- tion on lethal temperatures of Platte River forage fish species (Carlander 1969) suggests that several of the species found have thermal tolerances less than temperatures ineasured in the Platte Rive r . '. The phenomena which cause elevated summer temperatures in the Platte River are air temperature and solar radiation, and probably the stage of the river and-cross-sectional profile. Certain flows and cross-sectional profiles expose large expanses of shallow (3 to 6 cm (1 to 2 inches] deep) water on flats and bars in the river. High ambient air temperatures and high solar radiation can heat the water to temperatures fatal to forage fish. In laboratory studies, species found in the Platte River --(common carp, golden shiner;" emerald shiner, common shiner, --flathead minnow, white sucker, and channel catfish) and acclimated to high water temperatures (25-26°C E77-790F] die at temperatures less than those measured in the river during some summers. Time series analyses of temperatures in the Platte River are being conducted (K. Dinan, pers. comm.) but have not yet been applied to analyzing effects on forage fish. 4. Effects of chanQes in Platte River habitat conditions on endanQered and threatened snecies Are the chancres influencinQ species recoverv? Endangerment occurs for a variety of reasons. Section 4(a) (1) of the Endangered.Species Act (16 USC 1531 et seq.) states that determination of whether any species or population is endangered or threatened must be based on one or more of the five factors listed in that Section. Those factors include: (1) the present or threatened destruction*, madification, or curtailment of its habi:tat or range, (2) overutilization for commercial, . recreational, scientific, or educational purposes, (3) disease or predation, (4) the inadequacy of existing regulatory mechanisms, or (5) other natural or manmade factors affecting its continued existence. Some endangered species, sucYi.as the desert pupfish (Cyprinodon macularius) or the San Bruno elfin butterfl.y (Callophrys mossii bayensis), are largely sedent:ary. Accordirigly, those species can