The first two papers (Sanderson et al., 2023a) and (Sanderson et al., 2023b) serve as building blocks for the third paper, included here. Specifically, having demonstrated the detection efficiency of HR acoustic tags and shown that drifters carrying these tags will be reliably detected as they pass an array of acoustic receivers in Minas Passage, this paper develops and applies a method by which acoustic tag detections by the HR2 acoustic receiver array can be used to estimate the expected number of times an Inner Bay of Fundy (IBoF) Atlantic salmon post-smolt would encounter a single near-surface tidal energy device at the FORCE site during its seaward migration.

IBoF Atlantic salmon are a federally endangered species protected by Canada’s Species at Risk Act; they are known to occupy the upper water column during various life history stages, and there is concern about harm from encounters with floating tidal energy technologies deployed at FORCE.

The method developed in Sanderson et al. (2023c) uses acoustic detections of tagged IBoF Atlantic salmon post-smolts from the Gaspereau River (2019, 2022) and Stewiacke River (2021) by HR2 acoustic receivers in Minas Passage and builds upon the approach used by Sanderson et al. (2021) to calculate the probability that drifters would collide with a tidal turbine installed in Minas Passage. Specifically, the method calculates the probability of encounter from an ensemble averaged estimate of detection efficiency, with a small empirical correction for fluctuations about the typical value at a given range and modelled tidal current speed.

Here, probability of encounter is defined as the probability that a tagged fish passes within the width of a floating tidal energy device (e.g., PLAT-I; 38 m) of a receiver location. Estimation of probability of encounter in the absence of a turbine was deliberate as turbine presence has been shown to elicit behavioural responses in fish in both laboratory and field conditions (e.g., Mülleret al. 2023; Bender et al. 2023).

As such, probability of encounter in this paper can only be considered as an upper limit on the probability of harm, because it does not take into account fish behavioural responses like avoidance or evasion that have been shown elsewhere and that could reduce the probability of encounter in Minas Passage.