Beaked Whales Respond to Simulated and Actual Navy Sonar

Abstract

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.

Effective beam pattern of the Blainville's beaked whale (Mesoplodon densirostris) and implications for passive acoustic monitoring

“…The capability to count and localize individuals within a foraging group is important for abundance studies (Marques et al, 2009) and studies of the behavioral impact of sound Tyack et al, 2011). The most straightforward way to localize an individual is to detect a click on multiple hydrophones (!3 for horizontal localization or !4 hydrophones for 3D localization) and use the time delays of arrival (TDOA) to estimate the source position (Vincent, 2001).…”

Description of the skeleton of the fossil beaked whale <i>Messapicetus gregarius</i>: searching potential proxies for deep-diving abilities

“…This strategy is already suspected in extant beaked whales based on several mass strandings of Mesoplodon densirostris and Ziphius cavirostris directly related to naval exercises involving mid-frequency active sonars (Amico et al, 2009;Cox et al, 2006;Filadelfo et al, 2009). It is generally accepted that the sound exposure forces beaked whales to alter their own diving behaviour, causing a decompression syndrome (Cox et al, 2006;Tyack et al, 2011). Zimmer and Tyack (2007) noticed the resemblance between the tonal mid-frequencies used and the calls of killer whales (Orcinus orca), suggesting that ziphiids try to avoid the latter.…”

The Challenges of Analyzing Behavioral Response Study Data: An Overview of the MOCHA (Multi-study OCean Acoustics Human Effects Analysis) Project

“…The first such BRS was conducted in 2007 and 2008 in the Bahamas (Tyack et al, 2011) with the aim of collecting baseline data on animal behavior, and conducting CEEs to measure responses to different sound stimuli. A major focus of the Bahamas work was beaked whales, which are thought to be some of the species most vulnerable to sounds from sonar exercises as they make up the majority of animals stranded in association with naval sonar exercises (D'Amico et al, 2009).…”

“…Many diverse analyses have been applied to data from each BRS, and we do not attempt to review them all here (although see Tyack et al, 2011;Miller et al, 2012;Curé et al, 2012, DeRuiter et al, 2013. Typically the first stage has been to synthesize the observational data for each individual to determine whether it responded, gauge the magnitude of any response and relate the onset of response to exposure intensity ("dose").…”