The Australian government recently reported that its navy divers sustained minor injuries due to sonar pulses from a Chinese navy vessel. The incident occurred while the divers were clearing fishing nets from the propellers of HMAS Toowoomba in international waters off the coast of Japan. Despite using internationally recognized signals, the Chinese vessel approached the Australian ship and activated its sonar, forcing the divers to exit the water.
The Australian government condemned the incident as unsafe and unprofessional. However, it is important to understand what a sonar pulse is and the potential injuries it can cause to divers.
Sonar, which stands for sound navigation and ranging, is used by ships to navigate through water and detect objects underwater. Sonar equipment emits short acoustic pulses and analyzes the echoes to determine what is present underwater, such as the seafloor, canyon walls, coral, fish, ships, and submarines. While most vessels use sonar, navy sonars are stronger compared to commercial sonars used for fishing.
Studying the effects of sonar on divers is challenging due to ethical concerns about exposing humans to harmful levels of sound. However, there have been anecdotes from various navies and accidental exposures, as well as studies on human hearing underwater. Human divers have described naval sonar sounds as unpleasant to severe at levels around 150dB re 1 µPa. At this level, divers may experience dizziness, disorientation, temporary memory and concentration issues, or temporary hearing loss. The Australian divers in this incident sustained minor injuries, but the specific sound exposure levels are unknown.
At higher sound levels, closer ranges, or longer exposures, more severe physiological or health impacts may occur. In extreme cases, sudden sound can cause damage to tissues and organs.
Sonar also affects marine animals, particularly marine mammals with inner ears similar to humans. They can experience temporary or permanent hearing damage from noise exposure. Marine mammals rely on sound for navigation, hunting, communication, and finding mates. Interfering with their sounds or impacting their hearing can disrupt critical behaviors. Additionally, non-mammalian fauna like fish rely on acoustics for many life functions.
Overall, understanding the effects of sonar on divers and marine animals is crucial for mitigating potential harm and ensuring safe practices in underwater environments.