Sustained disruption of narwhal habitat use and behavior in the presence of Arctic killer whales

“…A study on harbour porpoise ( Phocoena phocoena ) noted that individuals exhibited shallower diving following both an initial handling event as well as a measured noise dose-response experiment, but also showed that the same individuals appear to have recovered to baseline behaviour within 24 hours or less ( van Beest et al , 2018 ). Similar shallow diving has been noted in narwhal in response to predation events and the presence of predators ( Laidre et al , 2006 ; Breed et al , 2017 ), though these events resulted in longer disruptions of behaviour than measured here. Acoustically-tagged narwhal exhibited a period of silence (no vocalizations) after tagging in East Greenland, ranging from 9 to 37 hours after release ( Blackwell et al , 2018 ).…”

“…The most immediate response was the change in swimming direction in which the whales tried to avoid the sound source by changing the horizontal swimming direction and move close to the shore. Studies in Canada on the reaction of narwhals to the presence of killer whales (Orcinus orca) have shown that narwhals move within 500 m of the shore when killer whales are present (Laidre et al, 2006;Breed et al, 2017). This is in good agreement with the observations of movements in this study, and it was therefore natural to use "movements towards the coast" as a metric for the evasive response to exposure from ship or airgun noise.…”

“…In two previous studies in this same region, the first found bowheads selected moderate to heavy ice in summer, which was believed to reduce killer whale predation risk while also providing access to enhanced foraging (30), and the second assumed bowheads foraged in moderate ice presumed to aggregate zooplankton (78). The explicit incorporation of predation risk in the analyses presented here, however, supports the hypothesis that bowhead selection of sea ice in summer is strongly predator mediated, reinforcing the need to incorporate predation risk in analyses of animal space use (4,15). The large change in prey space use in response to a relatively small number of wideranging predators also illustrates that predator distribution and density, unlike resource distribution, may not be a straightforward predictor of prey distribution (79), because prey responses to predation risk are often disproportionate or nonlinear (1,80).…”

“…A study on harbour porpoise ( Phocoena phocoena ) noted that individuals exhibited shallower diving following both an initial handling event as well as a measured noise dose-response experiment, but also showed that the same individuals appear to have recovered to baseline behaviour within 24 hours or less ( van Beest et al , 2018 ). Similar shallow diving has been noted in narwhal in response to predation events and the presence of predators ( Laidre et al , 2006 ; Breed et al , 2017 ), though these events resulted in longer disruptions of behaviour than measured here. Acoustically-tagged narwhal exhibited a period of silence (no vocalizations) after tagging in East Greenland, ranging from 9 to 37 hours after release ( Blackwell et al , 2018 ).…”

“…The most immediate response was the change in swimming direction in which the whales tried to avoid the sound source by changing the horizontal swimming direction and move close to the shore. Studies in Canada on the reaction of narwhals to the presence of killer whales (Orcinus orca) have shown that narwhals move within 500 m of the shore when killer whales are present (Laidre et al, 2006;Breed et al, 2017). This is in good agreement with the observations of movements in this study, and it was therefore natural to use "movements towards the coast" as a metric for the evasive response to exposure from ship or airgun noise.…”

“…In two previous studies in this same region, the first found bowheads selected moderate to heavy ice in summer, which was believed to reduce killer whale predation risk while also providing access to enhanced foraging (30), and the second assumed bowheads foraged in moderate ice presumed to aggregate zooplankton (78). The explicit incorporation of predation risk in the analyses presented here, however, supports the hypothesis that bowhead selection of sea ice in summer is strongly predator mediated, reinforcing the need to incorporate predation risk in analyses of animal space use (4,15). The large change in prey space use in response to a relatively small number of wideranging predators also illustrates that predator distribution and density, unlike resource distribution, may not be a straightforward predictor of prey distribution (79), because prey responses to predation risk are often disproportionate or nonlinear (1,80).…”

“…A study on harbour porpoise ( Phocoena phocoena ) noted that individuals exhibited shallower diving following both an initial handling event as well as a measured noise dose-response experiment, but also showed that the same individuals appear to have recovered to baseline behaviour within 24 hours or less ( van Beest et al , 2018 ). Similar shallow diving has been noted in narwhal in response to predation events and the presence of predators ( Laidre et al , 2006 ; Breed et al , 2017 ), though these events resulted in longer disruptions of behaviour than measured here. Acoustically-tagged narwhal exhibited a period of silence (no vocalizations) after tagging in East Greenland, ranging from 9 to 37 hours after release ( Blackwell et al , 2018 ).…”

“…The most immediate response was the change in swimming direction in which the whales tried to avoid the sound source by changing the horizontal swimming direction and move close to the shore. Studies in Canada on the reaction of narwhals to the presence of killer whales (Orcinus orca) have shown that narwhals move within 500 m of the shore when killer whales are present (Laidre et al, 2006;Breed et al, 2017). This is in good agreement with the observations of movements in this study, and it was therefore natural to use "movements towards the coast" as a metric for the evasive response to exposure from ship or airgun noise.…”

“…In two previous studies in this same region, the first found bowheads selected moderate to heavy ice in summer, which was believed to reduce killer whale predation risk while also providing access to enhanced foraging (30), and the second assumed bowheads foraged in moderate ice presumed to aggregate zooplankton (78). The explicit incorporation of predation risk in the analyses presented here, however, supports the hypothesis that bowhead selection of sea ice in summer is strongly predator mediated, reinforcing the need to incorporate predation risk in analyses of animal space use (4,15). The large change in prey space use in response to a relatively small number of wideranging predators also illustrates that predator distribution and density, unlike resource distribution, may not be a straightforward predictor of prey distribution (79), because prey responses to predation risk are often disproportionate or nonlinear (1,80).…”