, 2007). This seems to be the case, for example, Hildebrand (2005, p. 286) estimated that beaked whales in the Bahamas incident were Src inhibitor not exposed to levels of sound higher than “160–170 dB re1 lPa @ 1 m for 10–30 s”. Much attention has been focused on mass stranding events. However, early evidence of less drastic, but perhaps equally important, disruption of normal behavior suggests, as expected, that disturbance is likely to be much more wide spread. Indeed, a small sample size of beaked whales exposed to mid-frequency active sonar during

foraging dives in the US Navy’s Atlantic Underwater Test and Evaluation Center (AUTEC) range in the Bahamas showed behavioral responses within a narrow range of exposure levels that is well below the current threshold used by regulators in the US as criteria for determining behavioral disruption in cetaceans (Tyack et al., 2011). The risk function used to assess the probability of behavioral harassment of cetaceans from sonar Ipilimumab purchase currently assumes a very low risk of harassment

at exposure levels near 140 dB; levels at which most beaked whales apparently stopped foraging and moved more than 10 km away from the AUTEC range for 2–3 days (Tyack et al., 2011). This supports a lower acoustic threshold for disturbance than is currently applied for these whales. A decline in vocal activity associated with foraging beaked whales acetylcholine was also documented during multi-ship exercises using mid-frequency active sonar (McCarthy et al., 2011). Although the majority of recent research has focused on beaked whales, active sonar has, as mentioned above,

been linked to strandings, disturbance and unusual behaviors in other species too. For example, the Bahamas mass stranding event included several northern minke whales (Balcomb and Claridge, 2001), as did the mass stranding in North Carolina in 2005, which also involved pilot whales and dwarf sperm whales (Hohn et al., 2006). Significant decreases in abundance of northern minke whales (e.g. Parsons et al., 2000), as well as anomalous behavior (e.g. porpoising; Dolman and Hodgins, 2009), have also been reported during naval exercises in Scotland. Other species reported to react strongly to sonar exposure include melon-headed whales (Peponocephala electra: Southall et al., 2006). Thus exposure to high intensity sound sources, including active sonar, is likely to be a threat to more than just beaked whale populations.