A question currently garnering significant attention in the field of salmon management is whether salmon can be reintroduced above dams, giving them access to historic habitats that are currently blocked off. Determining the feasibility of such an effort requires understanding the current state and suitability of the river habitats where salmon reintroduction is proposed. To inform such evaluations, FISHBIO conducted surveys of the upper Tuolumne River to characterize the distribution, abundance, and quality of fish habitat. This information is critical for assessing the feasibility of anadromous salmonid reintroduction, estimating the population size that the habitat could potentially support, and developing engineering alternatives such fish ladders or collection facilities for the upper Tuolumne River.

FISHBIO staff rafted through 25 miles of river to document the number, size and distribution of various salmon habitat types. These habitats included pools, runs, boulder gardens, cascades, and high- and low-gradient riffles. We collected detailed data on a number of habitat attributes, such as length, width, depth, large woody debris counts, substrate composition, and the percent of vegetation and canopy cover. In particular, we looked carefully at pools, and their potential for providing holding habitat for adult Chinook salmon during the summer. We also used drift nets and collected substrate samples to survey aquatic insects and other macroinvertebrates that serve as important salmon prey. Data from this survey will be used to create habitat maps of the area and, along with other studies, will be used evaluate the potential for supporting a salmon and steelhead population in this reach of river.