Fish Passage in Montana Culverts: Phase II -- Passage Goals

Abstract

Culverts have been shown to disrupt fish mobility in high-gradient mountain streams, and are of concern to transportation system planners, designers, and managers. However, there is still some uncertainty concerning the cumulative impact that culverts can have on a fishery. In this project, passive integrated transponders (PIT tags) were used, primarily on Yellowstone cutthroat trout, to examine fish passage in the roaded drainage of a high-gradient stream system. This project focuses on fish passage in the upstream direction through successive culverts over all portions of the hydrograph, including the high flows that Yellowstone cutthroat encounter during spawning runs. Results are presented in probabilistic terms in addition to the traditional passage/no-passage format. The results show that water velocity is a good indicator of the probability of fish passing a culvert. The probability of a fish passing a series of culverts is best predicted by combining the probability that fish will, in general, pass individual culverts.