Can “pingers” and other acoustic deterrents help reduce the risk of collision between ships and cetaceans?

Each year, thousands of cetaceans die as a result of collisions with ships. Although many protective measures have been put in place, they have not always been proven effective, as is the case of “pingers”, acoustic deterrents whose effects on animals and the rest of the marine ecosystem are unknown.

This year, the Vendée Globe organisers asked competitors to avoid sailing in protected areas to reduce the risk of collisions with cetaceans - including sperm whales, humpback whales and grey whales. Some boats were even equipped with “pingers”, acoustic deterrent devices designed to keep animals away from ships. These devices are used by some fishing boats, particularly in the Bay of Biscay, to prevent cetaceans from accidentally getting caught in their nets, but there is less documentation on their use in preventing collisions with ships.

Research has not yet proven the effectiveness of pingers. The idea may sound good, but it raises a number of questions. Are pingers just a new form of human “pressure” on cetaceans? Do all 90 species react in the same way? Could the animals become accustomed to these underwater pings over time, thereby reducing their effectiveness as a deterrent?

Used in combination with other maritime traffic management measures, such as speed limits in areas where cetaceans are particularly abundant, and optimised to limit their harmful impact on the animals and the marine environment, pingers could help reduce collisions between ships and cetaceans, which kill thousands of cetaceans every year and are thought to be responsible for almost 30% of deaths in certain threatened species, such as the North Atlantic right whale.

How collisions are currently avoided

The risk of collisions is greater in areas with high cetacean densities and heavy shipping traffic. Besides fatal accidents, collisions cause serious injuries, stress and behavioural disturbances, all of which contribute to the overall decline of cetacean populations.

Solutions to avoid collisions must be developed immediately, such as training for captains and merchant navy personnel, as well as measures to bypass protected areas and reduce ship speeds. New technologies such as real-time visual and acoustic detection tools must also be developed.

Scientific studies have also identified sensitive areas where there is a high risk of collision.

Ambient noise can prevent whales from hearing an approaching vessel

While acoustics are the primary sensory modality used by cetaceans, the underwater hubbub generated by human activities, including maritime traffic, partially masks the sounds these marine mammals produce. This reduces their ability to communicate with their congeners, to find their prey, to detect the presence of predators, and to identify other dangers, such as approaching ships. For example, baleen whales have a low-frequency hearing sensitivity of 15Hz-20kHz, broadly corresponding to our own hearing range but with better performance in infrasound. This performance should normally enable them to hear large ships

However, it would appear that these large cetaceans have difficulty detecting and anticipating the approach of a ship and are often unable to avoid them. We see several reasons for this.

In areas where there is heavy maritime traffic, the ability to detect acoustic signals from a single vessel among the noise of others is reduced. But other factors seem to exacerbate the problem, particularly the speed at which ships travel, which is much higher than that of these large whales. Humpback whales, for example, move around their breeding grounds at an average speed of 2 knots. Not to mention the time they spend in a static position, such as during resting periods.

In addition, the variation in the properties of acoustic propagation in the water column (especially near the surface) and the directionality of boat noise (which tends to be directed towards the stern) could make it difficult to locate the vesse, and potential habituation to the continuous noise of maritime traffic could reduce the whales' vigilance when approaching ships.

In a bid to reduce noise pollution generated by human activity at sea, the development of quieter boats is aimed at reducing the impact of noise. However, one might wonder whether this will not have the unfortunate side effect of increasing the risk of whales failing to detect ships, therefore increasing collisions.

This led to the idea of using “pingers”: devices that emit sound signals to repel or warn animals, initially designed to prevent accidental capture of cetaceans in fishing nets and more recently proposed as a potential preventive measure to keep animals away from areas at high risk of impact, such as wind farms, or to reduce collisions with ships.

The pingers would be deployed on the hulls of ships or on buoys in areas of heavy maritime traffic; they would generate audible signals to scare the animals away or alert them to the presence of a ship, prompting them to change direction to avoid a collision. These pingers could be activated remotely or automatically when a ship enters a high-risk area identified by the maritime authorities.

There is a lack of data to determine whether pingers are effective in avoiding collisions

The considerable lack of research aimed at experimentally testing the effectiveness of pingers means that it is not yet possible to decide whether or not they should be used.

Considered by some to be like car horns that add to the ambient noise, and by others to be a miracle solution,the use of pingers and other audible warning devices is hotly debated.

While there have been some encouraging scientific results (cetaceans changing course to move away from ships) others have found no beneficial effect and sometimes even an increased risk of collision (attraction to the source of the sound, cetaceans suddenly surfacing).

Questions also remain about their environmental impact, with noise having potentially harmful effects on many species, in addition to repercussions at the ecosystem level, and their large-scale implementation.

Pingers appeared on the market very (too) early and have not been tested sufficiently to demonstrate their effectiveness. Furthermore, they are often manufactured and used generically, whereas their design should be considered on an almost case-by-case basis, according to the auditory sensitivity of the target species, its behaviour, the ecological context (feeding or breeding areas), social context (presence of young, group size), the properties of sound propagation in the environment and natural and anthropogenic environmental pressures (level and bandwidth of ambient noise). From a scientific point of view, a universal acoustic deterrent for all cetacean species seems difficult to conceive.

One way to improve the effectiveness of pingers while limiting their impact would be to replace or combine the synthetic signals traditionally used with natural signals (such as sounds produced by the species itself), which are potentially more informative and may have less of an impact on the environment. This requires extensive preliminary research to decode the acoustic communication systems of the different species of cetaceans.

In partnership with the company Greenov, we are currently conducting a pilot study involving experimental field testing of the effectiveness of an acoustic signal as a warning to humpback whales in a breeding area, ahead of the company’s development of a prototype acoustic deterrent device to be attached to the hull of ships. These experiments at sea are complex and require strict protocols that must be overseen by scientific experts. To this end, we carry out controlled sound exposure experiments, commonly known as "playback", and measure the behavioural responses of humpback whales previously equipped with multi-sensor tags non-invasively deployed on their backs using suction cups.

The United Nations Ocean Conference to be held in Nice from 9 to 13 June 2025, followed by the conference on collisions between ships and cetaceans on 16 June 2025 in Brest, will be two opportunities to bring together maritime authorities, engineers and scientists to collectively discuss research priorities and the regulatory solutions and measures to be adopted.