Even without a great deal of evidence, logic suggests that whales and dolphins are highly susceptible to noise. Living in a world of sound, they rely heavily on their hearing for communication, finding their way around, locating prey and avoiding predators.

As perhaps the most acoustically-dependant animals on Earth, it is not surprising, therefore, that extraneous noise from underwater explosions and high-powered sonar (from seismic exploration and military activities, for example) can be lethal to them. As well as interfering directly with their day-to-day activities, such acoustic assault may cause the animals high levels of stress, hearing impairments, and perhaps even irreversible barotrauma.

In recent years, much concern has been expressed over the potential impact of anthropogenic sound upon cetaceans (particularly odontocetes, like beaked whales). Indeed, post mortem studies of mass stranded animals in the Bahamas and, most recently, in the Canaries have revealed evicence of multifocal haemorrhaging and ear damage as a direct result of naval activities..

Whales and dolphins have a complex system of air sacs and sinuses in their head - derived as out-pushings of the Eustachian tube (the passage with the basic function of equalising pressure on both sides of the eardrum). Whilst at the surface, a mixture of air and a fine foam (gas bubbles in an oil-mucus emulsion) fills these sinuses. This mixture compresses as the animal dives, thereby creating a vacuum inside the sinus cavities that must not be allowed to reach any appreciable negative value. When the animal returns to the surface, the mixture expands back to its original volume building positive pressure unless whatever was done to relieve the vacuum is reversed.

Acute auditory trauma -- in the air sinuses and middle ear cavities -- and the intense pain associated with such an injury could actually prevent an injured animal from diving. A diving-related injury of this kind would inevitably disrupt feeding at the depth of a whales normal prey, subsequently leading to malnutrition and dehydration in the animal. The thick layer of blubber on a pelagic odontocete contains less than 10% adipose tissue, which is not for the store of energy as in man. Instead, the blubber serves the more important function of thermal insulation, and if lost in a crisis would result in rapid death of the animal due to hypothermia.

Coastal cetaceans rarely "mass strand", due to the looseness of their social groups and familiarity with near shore waters. However, the loss of navigation abilities as the direct result of auditory impairments, deafness, and other injuries resulting from increased noise pollution in the marine environment, might concievably result in an individual travelling into less familiar habitats; and consequently running the risk of stranding and/or further injury. A large whale that can no longer navigate will be directed by ocean currents in the path of least resistance, and may have travelled up to 5,000 miles where it may be spotted, apparently healthy, to the observer.

It goes without saying, that the existing evidence for strandings as the direct result of extraneous noise pollution needs to be objectively reviewed and, where detrimental effects are implicated, measures for mitigation taken. If possible, a standardised protocol for dealing with potential future strandings needs to be developed. The CRRU aims to be at the forefront of this work.