Culvert Hydraulics and Passage Performance of Brook Trout: Understanding the Key to Success

Under specific hydraulic conditions, culverts may constitute velocity barriers impeding fish upstream movements. Motivation to stage attempts is the first step towards successful passage. However, once a fish entered a culvert, what is driving its success? Here, we present data from wild brook trout volitionally entering 13 culverts (length 9 to 45 m) made of smooth material or corrugated metal and swimming against moderate to high velocity flows (0.39 to 1.99 m s^-1). Fixed Passive Integrated Transponder systems allowed for the determination of passage attempts and success of individual fish. 857 brook trout from 85 to 230 mm were tested under variable water temperature conditions (1.4 to 19 ^◦C). Data from fish that staged attempts were analyzed using a logistic regression approach with model selection based on minimization of the Akaike information criterion. Best model includes water temperature, flow velocity and fish length, but also covariates such as depth of downstream pool, culvert type and hydraulic radius and allows quantification of the effect of these variables on probability of success. These findings provide a better understanding of factors influencing the species ability to negotiate velocity barriers such as culverts and have important implications for culvert design and fish passage issues.