Use and Importance of Tributaries to Sustain Native Fish Communities in the San Juan River

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The recipients propose to conduct seasonal surveys of major tributaries of the San Juan River to evaluate their importance in sustaining native fish populations. The project has four main research objectives: (1) What is the fish community composition in tributaries of the San Juan River and how does that vary over space and time? (2) Describe habitat conditions that occur in each tributary including flow statistics, temperature, turbidity, overhead cover, stream width and depth. (3) Are movements into, out of, and within tributaries associated with environmental conditions (e.g., temperature, flow, resource availability) and species reproductive ecology? (4) Identify any potential barriers to fish movement in tributaries. Sample reaches will be distributed along longitudinal gradients within three main tributaries to evaluate the exchange of fishes between mainstem and tributary habitats. Standard sampling of fishes using backpack electrofishing gear and seines will be used to estimate population densities. Habitat measurements will be made at each sample reach to test if specific habitat features within tributaries that are favored by native and nonnative fishes. All fishes > 150mm captured at sampling sites will be marked with passive integrated transponder (PIT) tags to monitor movements within tributaries. This research will be coordinated with current monitoring programs on the mainstem San Juan River and tagging studies by Colorado Division of Wildlife (CDOW). Both of these programs will have the capacity to tag and scan fishes, thus the efforts can be leveraged to further evaluate dispersal of fishes between our sites in tributaries and the mainstem reaches. The proposed studies will provide critical information that can be used to guide management decisions in this system. First, the surveys of tributaries will evaluate the status of native fishes in these habitats. Tributary habitats might be particularly important for roundtail chub (Gila robusta), which has virtually disappeared from mainstem habitats, as well as recovering populations of federally listed species. Second, our surveys and fish movement data will quantify seasonal use of these systems. It is possible access to tributary habitats on a seasonal basis might help augment mainstem populations of native fishes. Third, tributary habitats may provide sources for nonnative fishes that negatively interact with native species. Fourth, our research will explicitly evaluate the role of potential barriers to movement of fishes within these tributaries.

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