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Biological Condition Index Development for the Lower Truckee River and Eastern Sierra Nevada Rivers: Fish Assemblage

This document describes a fish assemblage IBI for western Nevada rivers, and how it is applied it to the Truckee River.
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Written By

Robert M. Hughes and Thomas R. Whittier
Department of Fisheries and Wildlife
Oregon State University
200 SW 35th Street
Corvallis, Oregon 97333
Gregg A. Lomnicky
Dynamac Corporation
200 SW 35th Street
Corvallis, Oregon 97333

Prepared For
Pyramid Lake Paiute Tribe
Nevada Division of Environmental Protection
April 2005
We developed a fish assemblage IBI for western Nevada rivers and applied it to the Truckee River. Available state and federal fish assemblage data from the Carson, Walker, and upper Truckee rivers were analyzed to select and score metrics. Selected metrics included number of native species, % sculpin individuals, % mountain whitefish individuals, evidence of sculpin and whitefish reproduction, % cutthroat trout individuals, % sensitive individuals, % mountain sucker individuals, % omnivorous individuals, % highly tolerant individuals, % alien individuals, and % external anomalies. Metrics were scored continuously from 0-1 and the IBI was scored from 0-10 by summing the metrics. Those metrics and scoring criteria were then applied to existing fish assemblage data for the lower Truckee River. The IBI declined from the Nevada border to Wadsworth, with sharp declines at river miles 57 (Oxbow), 69 (Mustang), and 87 (Painted Rock). Revisits to the same sites indicated that IBI scores may vary by 1.0 as a result of temporal and sampling variation. We consider median IBI scores >7.5 as acceptable, 5.0-7.4 as marginally damaged, and <5.0 as damaged. However, these are only guidelines and 2.0 changes in IBI scores over space or time are probably biologically significant.

TruckeeRiver_Fish_IBI_FINAL_2006.pdf1.2 MB