Vocal count responses of narwhals to bulk carrier noise in Milne Inlet, Nunavut, Canada

Abstract

AbstractConcerns were raised about possible behavioral disturbance to narwhals (Monodon monoceros) when exposed to shipping noise in Milne Inlet, Baffin Island, Canada. We deployed passive acoustic recorders in August and September 2018 and 2019, along and adjacent to the nominal shipping corridor. We measured broadband (0.01–25 kHz) sound pressure levels (SPL) after correcting for the auditory weighting function of high frequency cetaceans. Received SPLs and counts of Whistles, Buzzes, and Knocks were compared in a before‐during‐after study of individual bulk carrier transits, relative to periods with no ships. Narwhal call counts were generally lower once bulk carriers were within line‐of‐sight, including when ship noise levels were just above ambient noise levels. Call counts varied both “before” and “after” individual bulk carriers passed by the recorders. There was no evidence of a behavioral threshold SPL below which a response did not occur. We did not observe call count reductions to the same extent in 2019 compared to 2018 as higher ambient noise levels in 2019 likely masked some individual ship noise. There was no evidence of habituation or sensitization to the bulk carrier noise within or between years. Continued acoustic monitoring is recommended, especially if bulk carrier transits increase.