Oceans of noise - Whale and Dolphin Conservation Society

haemorrhaging in the inner ears and cranial air spaces, consistent with impulsive trauma - i.e.
intense, loud sound, that did not come from a nearby explosion (Balcomb and Claridge 2001).
The levels of sound that would have been received by the whales were estimated to be between
140 dB and 160 dB. The researchers calculated that the frequencies produced by the midfrequency
sonar system employed, at that received level, could cause resonance in the cranial air
spaces of the cetaceans (Balcomb and Claridge 2001). This resonance could cause haemorrhaging
(as had been observed in the stranded animals), disorientation and an inability to navigate and
echolocate. However, this is only one theory. Other possible mechanisms to explain the injuries
observed include static or rectified diffusion in which intense acoustic exposure could cause a
type of compression sickness in whales (similar to the “bends”, as seen in human divers), and
perhaps especially the deep divers, by stimulating bubble formation or growth in the whales’
tissues (Houser et al. 2001). (This matter is considered in more detail later in this report.)
Two sonar systems are currently in the process of being introduced: in the US (SURTASS LFA)
and the UK (SONAR 2087). Both rely on low frequency sound to determine military targets.
Other countries already operate, or plan to operate, similar systems. There has, however, been
considerable concern over these proposed systems, because of:
i. the loudness of the sources;
ii. the distance that the sounds may travel, because of their low frequency nature; and
iii. tests that have demonstrated short-term behavioural changes in cetaceans in response to
the sonar. For example, blue and fin whales demonstrated possible vocal responses, gray
whales displayed avoidance of the noise during their migration, and humpback whales
temporarily stopped singing and lengthened the duration of their song. These responses
occurred when the whales received the source at levels of 155dB, and even as low as
115-125dB. The operational source level of the sonar system will, however, be well over
200dB (US Navy 2001), thus potentially exposing any whales in close proximity to much
louder levels than those which can induce these observed behavioural changes.
In addition to sonar, submarine-to-submarine communications systems are also a substantial
source of submarine sound: the systems produce sounds of 5-11 kHz at source levels of 180-200
dB (Richardson et al. 1995). Moreover, explosives used in military tests and exercises can be a
considerable source of underwater noise with source levels of 267 dB in a 0.45-7.07 kHz range
(Evans and Nice 1996; Perry 1998).
A recent victory for cetaceans came in a 2002 court decision to limit the use of the US Navy
LFAS. The area of operation has temporarily been reduced to a large part of the Pacific Ocean
focused around the remote Mariana Islands - an estimated area of one million square miles. While
this is a substantial area of ocean, it’s only about 10-15% of the area for which the U.S. regulators
originally proposed permits (NMFS, 2002).
As the military undertake activities in all the waters of the world, their potential encroachment of
cetacean habitats is considerable. Because public information on the exact nature and extent of
military activities is highly restricted, the total impact of the military’s ensonification of the
world’s oceans will be difficult to quantify.
3.8. Purposeful scaring of marine mammals
3.8.1 Acoustic Harassment Devices (AHDs)
The finfish aquaculture industry suffers predation by seals and other marine mammals and, in
response, acoustic harassment devices (AHDs) or ‘seal-scrammers’ have been developed to deter
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