Noise and boat traffic in UK waters
Sound is a whale, dolphin or porpoise’s primary sense and they are largely reliant on sound for the detection of prey, exploration of their environment, navigation and communication.
Sound travels approximately five times faster in water than in air, and levels of noise in the marine environment have increased greatly in recent decades. Anthropogenic (man-made) noise therefore poses a problem for whales and dolphins, especially noise of a frequency that could mask sounds that are biologically important to the animals. One of the most ubiquitous producers of noise in the marine environment is shipping traffic, though other sources of noise that may impact whales and dolphins include: air guns used during oil and gas exploration; predator deterrent devices used in fish farms; offshore windfarms and military activity.
Noise from ships dominates marine waters and is produced by the ship’s propellers, machinery and the movement of the hull through the water. In general, older vessels produce more noise than newer ones and larger vessels produce more noise than smaller ones. Most shipping has a low frequency range, i.e. less than 1kHz, which coincides with the frequencies used by baleen whales for communication and other biologically important activities.
The distant shipping noise adds to the constant ambient noise level in the marine environment and, as mentioned previously, this has increased dramatically in recent years, particularly in the Northern Hemisphere. This has implications for large whales such as the blue whale, which has been observed to vary the intensity of sound production levels in response to varying ambient noise levels.
Whilst large shipping typically produces sounds below 1kHz, smaller leisure craft generate sounds from 1kHz to 50kHz, which has the potential to impact toothed whales and dolphins. These frequencies overlap with the peak hearing frequencies of bottlenose dolphins, whose predominantly coastal distribution exposes them to such increases in underwater noise. For example, bottlenose dolphins in Cardigan Bay, Wales exhibited negative responses to pleasure boat traffic, including changes of dive times and the avoidance of approaching vessels. The authors also found that quieter, faster boats caused more disturbance than slower, larger boats. Noise emitted by high-speed boats rises above ambient levels (and thus becomes detectable by the dolphin) only a short time before closest contact, thereby provoking a startle reaction in the animal.
Another study on the south coast of the UK discovered that the increase in underwater noise over the summer months, caused by a dramatic increase in pleasure craft, is sufficient to impair communication between bottlenose dolphins and to reduce their echolocation performance. For this reason, the effects of increases in pleasure boat traffic may result in whales and dolphins temporarily or permanently leaving areas important for their survival.
The significance of vessel collisions has become much greater in recent years with the development of larger and faster vessels using waters inhabited by declining whale and dolphin populations.
Whale mortality from ship collisions is still underreported. To date, there are few conclusive reports of large whale being killed in UK waters as a result of collisions with marine traffic. In 2005, a minke whale calf was reported to have been struck by a small speedboat near Portsoy, Scotland and a high-speed ferry was involved in a collision with what may have been a whale off the Holyhead coast, Wales in 2006. The outcome of these collisions remains unknown.
Small cetaceans are susceptible to collisions with vessels in increasingly busy coastal waters. The increase in solitary, sociable dolphins (predominantly bottlenose dolphins) serves to amplify this risk. Several small cetaceans have been observed with badly damaged dorsal fins that may be attributable to propeller damage. Jet, a friendly bottlenose dolphin around the coasts of Hampshire and the Isle of Wight, UK, was also killed following a collision with a tug-boat propeller during the previous month.
Dave, another solitary bottlenose dolphin off the Kent coast, UK, had a significant part of her tail cut off, in what was almost certainly a collision with a boat propeller in October 2007. Georges or Randy, the solitary bottlenose, typically found either off the southern British or northern French coasts, has a distinctive dorsal fin bearing scars from a propeller wound. Jean Floc’h is a solitary bottlenose dolphin which lives primarily on the French Brittany coast, and has developed a particular fondness for boat oars and propellers, thus increasing the likelihood of a collision.
Whale-watching vessels have caused several whale and dolphin mortalities through collisions and can be a particular threat as they target areas of high whale and dolphin abundance. The trend for larger and faster vessels is of particular concern as this is likely to reduce the amount of time for operators (and cetaceans) to take evasive action when necessary. The impact of the collision will also be greater for faster and larger vessels and it has been suggested that speeds over 13knots are more likely to result in fatal collisions. Concerns over the in the number of whalewatching boats in some parts of the UK led to suggestions that speed restrictions (of 10 knots or less) be imposed in known areas of high whale abundance. Other management options include capping the number of boats in an area and providing a strict code of conduct that must be adhered to at all times. Recreational as well as commercial operators should abide by guidance.
A number of whale and dolphin watching codes of conduct exist for various areas around the UK, with the intention of promoting responsible wildlife watching and reducing collisions with cetaceans and boats. However, these are voluntary codes and, as such, cannot be enforced except in extreme cases that are taken forward legally.