Passage of Native Cutthroat Trout Through Small Culverts on Steep Slopes: What Are the Limits?

State and federal fish passage assessments often assume that culverts of even modest slopes and velocities are barriers to upstream passage of salmonids.  Preliminary research under controlled conditions demonstrate that native coastal cutthroat trout can move upstream through conditions that would be judged complete barriers using widely applied and accepted fish passage criteria.  Our work suggests that the fish are exploiting boundary layers within the culvert that provide more favorable hydraulic conditions than average bulk velocity calculations presume.  This presentation provides a preliminary summary of research from a detailed set of passage trials designed to test the ability of native cutthroat trout to move through culverts typical of those used on forest roads.  Research is ongoing and trials are expected to be complete in 2011.