Noise Pollution

A whale, dolphin or porpoise’s primary sense is that of sound. Sound plays an integral part in many aspects of their daily activities. It is their main method of communication with each other, using a mixture of squeaks, whistles, clicks, moans and slapping to interact with one another. They also use sound to explore their environment, navigate and locate and feed on prey.

Sounds propagates (travels) in water approximately 5x faster than in air which may explain why cetaceans utilise this medium. The oceans are a noisy environment and there are many man-made sounds introduced to the marine environment that may pose a threat to cetacean populations. The two main areas of concern in the Hebrides have been highlighted on this page: seal scarers and military sonar.

Seal Scarer Noise

The Scottish fish farming industry suffers predation of fish stocks by seals. Various methods of predator deterrents have been developed. One of these methods is the use of Acoustic Deterrent Devices (ADD’s) or ‘seal scarers’. These seal scarers use sound to frighten or induce pain in seals in order to keep them away from fish cages. There is growing concern about the impact of seal scarers on non-target species such as cetaceans, as the hearing of many cetacean species is believed to be more sensitive than seals.

Fish farms are predominantly located in coastal areas such as Lochs and the Sounds between islands. Therefore coastal species such as bottlenose dolphins and harbour porpoise are at highest risk of exposure to ADD disturbance noise pollution.

Studies in British Columbia have suggested that harbour porpoises are excluded within 4000m of a seal scarer unit and abundance is significantly reduced within 3.5km of a farm using seal scarers.

Such noise pollution may have a range of impacts on cetaceans including the reduction of available habitat and creating barriers to movement through lochs and sounds.

HWDT are working with local fish farming companies to assess the extent of this threat on local harbour populations.

Military Noise

As a remote location the Hebrides is regularly used by the military for training purposes and there is concern that some of the equipment used may be introducing a high level of noise pollution to Hebridean waters which may have a deleterious effect on the cetaceans found here.

Of prime concern is the noise induced from the use of active sonar (Sound Navigation and Ranging). Active sonar is where sound is purposely generated by projector (underwater speaker). The sound waves generated reach a target and are returned as echoes to a hydrophone array (underwater microphones). Sonar’s include a range of devices from simple echo sounders and fish finders to complex military systems. The low frequency systems used by the military to detect submarines are extremely powerful and emit very loud sounds. The most powerful system is the Surveillance Towed Array Sensor System Low-frequency Active Sonar (SURTASS LFAS) system and emits extremely loud sound said to be equivalent to standing next to a jumbo jet during take off. Because these sounds are low frequency it means they can travel many hundreds of miles. In 2003, a US court has restricted the US Navy in its use of LFAS due to its impact on marine mammals

There is concern that the British military are testing these systems in the waters of western Scotland, in particular the northwest approaches.

Effects of sonar

Cetaceans are reliant on sound for feeding, communication and navigating and are especially vulnerable to noise disturbance. To date, four incidents of cetacean strandings have been documented and linked to military sonar activity (locations are Greece 1996, Bahamas 2000, Madeira 2000 and the Canary Islands, 2002). Observed impacts from exposure to such noise are:

Other issues of concern that have not been addressed in detail here are boat noise, seismic testing, and offshore developments such as wind farms.