| Summary: | Abstract Icebreaker vessels in the Canadian Arctic are used to monitor and maintain open shipping lanes during summer and fall. Icebreaker operating routes often overlap with important habitats of endemic Arctic marine mammals, leading to potential interactions and disturbance. In this study, we examined the frequency, proximity, and duration of encounter events between narwhals ( Monodon monoceros ) and icebreaker vessels in Tasiujaq (Eclipse Sound), Nunavut, an important summering area for this species. We combined tracking data from 25 narwhals equipped with satellite telemetry devices in Tasiujaq between 2016 and 2018 with automatic identification system (AIS) data for the same period from 7 icebreaker vessels. We defined an encounter event between a narwhal and an icebreaker as the total consecutive occurrences of an individual within 50 km of a vessel within 1 hour. For all years combined, 17 out of 25 narwhals had at least 1 encounter with an icebreaker and all 7 icebreakers were involved in at least 1 encounter. The closest distance (closest point of approach) recorded was <1 km and the longest cumulative duration of encounter events for 1 narwhal with 1 icebreaker was 121.6 hours ( n = 27 encounter events over 17 days). Proximity and continuous exposure of narwhals to high levels of noise are a key concern when considering short‐ and long‐term effects on behavior and fitness of this species.
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