Culvert Hydraulics and Passage Performance of Brook Trout: Challenging Existing Models

Under specific hydraulic conditions, culverts may constitute velocity barriers impeding fish upstream movements. The prediction of fish passage success is strongly linked to the knowledge of species swimming performance. Here, we present data from wild brook trout (Salvelinus fontinalis) volitionally entering culverts and swimming against moderate to high velocity flows. Fixed Passive Integrated Transponder (PIT-tag) systems allowed for determination of passage attempts and success of individual fish as well as their swimming speed throughout the culvert. The experiments were conducted in 13 culverts (length 9 to 45 m) made of smooth material or corrugated metal. 1090 brook trout were tested under variable water temperature (1.4 to 19 ^◦C), mean flow depth (0.03 to 0.46 m) and velocity (0.39 to 1.99 m s^-1) conditions. Fish swimming speeds, maximal ascent distances and passage success observed in the experiments are compared with predictions from existing models based on swimming capacity data obtained in laboratory studies. The results indicate a tendency for the predictive models to underestimate the passage success of smaller fish (< 120 mm) and to overestimate that of larger fish (> 150 mm). The results from this project challenge thinking about how swimming performance may limit the ability of brook trout to negotiate velocity barriers such as culverts. These findings may have important implications for culvert design and fish passage issues.