Behavioural Attributes of Entrainment Risk for Adult Bull Trout in a Hydropower Reservoir

Fish entrainment through turbine intakes is one of the major issues for operators of hydropower facilities because it causes injury and/or mortality and adversely affects population abundance. Here we used fine-scale acoustic biotelemetry and state-space modeling to investigate behavioural attributes associated with entrainment risk for adult bull trout (Salvelinus confluentus) in a large hydropower reservoir in British Columbia, Canada. We found that adult bull trout resided longer in the vicinity of the powerhouse and moved closer to the turbine intakes in the fall and particularly in the winter. Bull trout were more likely to engage in exploratory behavior (characteristic of foraging or reduced activity) during periods when their body temperature was < 2 °C. We also detected diel changes in behavioural attributes, with bull trout distance to intakes and probability of exploratory behaviour increasing slightly at night. We hypothesize that these behaviours are associated with foraging for kokanee (non-anadromous form of Oncorhynchus nerka), which have been shown to congregate near the dam of hydropower reservoirs in the winter. Study findings should be applicable to bull trout populations residing in other reservoirs and indicate that entrainment mitigation (e.g., use of deterrent devices) should be focused on the fall and winter.