Brook Trout Passage Performance through Culverts: The Importance of Motivation

Under specific environmental and hydraulic conditions, culverts become barriers to upstream movements of fish. Motivation to stage an attempt is the first step towards successful passage. However, motivation is challenging to quantify. Here, we use attempt rate to assess motivation of 450 wild brook trout (85-230 mm) volitionally entering 3 culverts and swimming against moderate to high velocity flows (0.39 to 1.99 m s^-1) at water temperatures ranging from 3 to 18°C. A Fixed Passive Integrated Transponder system allowed for the identification of passage attempts and success of individual fish. Attempt rate was quantified using time-to-event analysis techniques allowing for time-varying covariates and repeated events per individual. Model selection was based on minimization of the Akaike information criterion. Attempt rate was greatest during the spawning period, at elevated discharge, and at dusk. Attempt rate decreased with increasing number of conspecifics downstream of the culvert. The selected model suggests that attempt rate is a dynamic phenomenon, variable over time and among individuals. These findings provide a better understanding of factors influencing the species motivation to negotiate barriers such as culverts and have important implications for culvert design and fish passage issues.