Do Planes and Helicopters Disturb Whales?

When sound produced in the air is transmitted to water, a large amount of sound energy is reflected off the water. Only waves that strike the water at a near-vertical angle are actually transmitted into the aquatic environment. In water, sound waves travel four to five times faster than in air.

At high altitudes, sound intensity is already reduced before it reaches the water’s surface. At low altitudes, noise is louder, but it decreases rapidly as the aircraft or helicopter moves away and changes the angle, which hinders the sound’s transmission into the water. In addition, sounds produced in the air would spread over a greater distance in shallow waters.

Aircraft mainly produce low- and mid-frequency sounds. Hence, baleen whales are theoretically more likely to be disturbed, since they communicate at those frequencies and their auditory system is adapted to hearing them.

A study conducted in the Beaufort Sea in northern Alaska compared the reactions of belugas and bowhead whales to aircraft and helicopter noise during spring migration to the feeding ground. In both species, the types of reactions, when present, were similar: reduced surface time, precipitous dives, sudden changes in direction or movement away from the noise source.

Researchers observed reactions in bowhead whales to only 15% of helicopter flights at altitudes below 150 metres. The available data does not indicate whether bowhead whales reacted less when the altitude was higher.

In both species, other studies have shown that behavioural changes were more common in resting whales than in whales that were actively feeding or breeding.

In a similar study, a group of sperm whales behaved unusually after an aircraft circled above them for several minutes: the 11 sperm whales gathered in a semicircle facing outwards. The largest male in the group positioned himself towards one end, while the only calf of the group stayed in the centre of the curve. This type of formation is sometimes observed during real threats, such as killer whales, sharks and whalers.

Most of the whales’ reactions to airborne noise seem short-lived. But the long-term effects of these disturbances are particularly difficult to assess. In most studies, whales’ behaviour in response to aircraft noise is recorded from the aircraft itself, which greatly limits the time of observation following the disturbance. Moreover, a lack of a change in behaviour does not necessarily mean that the sound had no physiological effect on the whale.

The sounds produced by planes and helicopters are generally louder than those produced by boats. Ship engines emit sound directly into the water, thus limiting the loss of sound energy. These sounds also go in all directions, so tend to propagate over long distances. In addition, since boats travel more slowly than aircraft, the noise disturbance lasts longer. Indeed, the noise produced by boats can sometimes be heard for hours, while that of planes and helicopters is only heard for a few dozen seconds.

Consequently, planes and helicopters can potentially affect whale behaviour. But do these behavioural changes have a long-term effect on the whales’ well-being? To what extent can the noise pollution problem be attributed to aviation? And how can we limit disturbances caused by planes and helicopters?

Further studies are needed to answer these questions. A better understanding of the effects of planes and helicopters would also reduce bias in whale research, which sometimes involves aerial surveys.

For now, it is prohibited to fly over the Saguenay–St. Lawrence Marine Park at less than 609.6 metres (2000 feet), to limit noise disturbance. According to the studies consulted, this distance seems sufficient to greatly reduce the impact of noise on whales.