Bentley: Over the weekend, the Australian government disclosed an incident where navy divers sustained minor injuries, believed to be caused by 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 international signals from HMAS Toowoomba, the Chinese vessel approached and activated its sonar, compelling the Australian divers to exit the water. This prompted a strong reaction from the Australian government, condemning the encounter as unsafe and unprofessional. This report delves into the nature of sonar and explores its potential effects on divers and marine life.
Sonar, an acronym for sound navigation and ranging, is a technology that utilises sound waves to navigate underwater and gather information about the underwater environment. In contrast to light, sound travels efficiently through water due to its higher density. Ships, from small boats to large tankers, commonly use sonar. The equipment emits acoustic pulses or pings, analysing the returning echoes to determine underwater features such as the seafloor, canyon walls, marine life, and other vessels. While sonar is widely used, military-grade sonars are significantly more powerful than commercial counterparts.
Effects of Sonar on Divers:
Studying the impact of sonar on divers is challenging due to ethical considerations, but anecdotal evidence and accidental exposures provide some insights. Human divers have reported unpleasant to severe experiences with naval sonars at levels around 150dB re 1 Pa (A Pascal (symbol Pa) is equal to a force of one newton per square meter. 1 Pa will equal an SPL (Sound Pressure Level) of 94 dB), approximately 10km away from the source. However, the tolerance limits for humans are around 180dB re 1 Pa, suggesting potential adverse effects, such as dizziness, disorientation, temporary memory and concentration impacts, or temporary hearing loss, at closer ranges. The specific levels the Australian divers were exposed to remain undisclosed, but their injuries were described as minor. Higher levels, closer proximity, or prolonged exposure can lead to more severe health impacts.
Impact on Marine Animals:
The effects of sonar extend beyond human divers to marine animals, particularly marine mammals and fishes. Marine mammals, despite lacking outer ears, have inner ears that function similarly to humans, making them susceptible to hearing damage from loud noises. Toothed whales and dolphins, reliant on echolocation for critical behaviours, may experience disruptions to navigation, hunting, communication, and mate-finding due to interference with their sounds. Additionally, non-mammalian fauna, such as fishes, which heavily rely on acoustics for various life functions, may also be impacted by sonar.
The recent incident involving Australian navy divers and a Chinese navy vessel highlights the potential dangers associated with sonar use in international waters. The Australian government's condemnation of the encounter raises questions about the safety protocols and professionalism in naval operations. Understanding the effects of sonar on both human divers and marine life is crucial for ensuring the responsible and secure use of this technology in our oceans. As nations continue to navigate international waters, it becomes imperative to strike a balance between military activities and the protection of the marine environment and its inhabitants.