DiMarzio
Nancy A.
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Vessel noise affects beaked whale behavior : results of a dedicated acoustic response study
Beaked whales respond to simulated and actual navy sonar
DiMarzio
Nancy A.
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Article
Some beaked whale species are susceptible to the detrimental effects of anthropogenic noise. Most studies have
concentrated on the effects of military sonar, but other forms of acoustic disturbance (e.g. shipping noise) may disrupt
behavior. An experiment involving the exposure of target whale groups to intense vessel-generated noise tested how these
exposures influenced the foraging behavior of Blainville’s beaked whales (Mesoplodon densirostris) in the Tongue of the
Ocean (Bahamas). A military array of bottom-mounted hydrophones was used to measure the response based upon
changes in the spatial and temporal pattern of vocalizations. The archived acoustic data were used to compute metrics of
the echolocation-based foraging behavior for 16 targeted groups, 10 groups further away on the range, and 26 nonexposed
groups. The duration of foraging bouts was not significantly affected by the exposure. Changes in the hydrophone
over which the group was most frequently detected occurred as the animals moved around within a foraging bout, and
their number was significantly less the closer the whales were to the sound source. Non-exposed groups also had
significantly more changes in the primary hydrophone than exposed groups irrespective of distance. Our results suggested
that broadband ship noise caused a significant change in beaked whale behavior up to at least 5.2 kilometers away from
the vessel. The observed change could potentially correspond to a restriction in the movement of groups, a period of more
directional travel, a reduction in the number of individuals clicking within the group, or a response to changes in prey
movement.
Article
Beaked whales have mass stranded during some naval sonar exercises, but the cause is unknown. They are difficult to sight but can reliably be detected by listening for echolocation clicks produced during deep foraging dives. Listening for these clicks, we documented Blainville's beaked whales, Mesoplodon densirostris, in a naval underwater range where sonars are in regular use near Andros Island, Bahamas. An array of bottom-mounted hydrophones can detect beaked whales when they click anywhere within the range. We used two complementary methods to investigate behavioral responses of beaked whales to sonar: an opportunistic approach that monitored whale responses to multi-day naval exercises involving tactical mid-frequency sonars, and an experimental approach using playbacks of simulated sonar and control sounds to whales tagged with a device that records sound, movement, and orientation. Here we show that in both exposure conditions beaked whales stopped echolocating during deep foraging dives and moved away. During actual sonar exercises, beaked whales were primarily detected near the periphery of the range, on average 16 km away from the sonar transmissions. Once the exercise stopped, beaked whales gradually filled in the center of the range over 2–3 days. A satellite tagged whale moved outside the range during an exercise, returning over 2–3 days post-exercise. The experimental approach used tags to measure acoustic exposure and behavioral reactions of beaked whales to one controlled exposure each of simulated military sonar, killer whale calls, and band-limited noise. The beaked whales reacted to these three sound playbacks at sound pressure levels below 142 dB re 1 µPa by stopping echolocation followed by unusually long and slow ascents from their foraging dives. The combined results indicate similar disruption of foraging behavior and avoidance by beaked whales in the two different contexts, at exposures well below those used by regulators to define disturbance.