Sonar, or SOund Navigation And Ranging, uses sound propagation to detect underwater objects. It is widely used for mapping the ocean floor, locating shipwrecks, and detecting marine life. A common concern is whether sonar’s sound waves can harm or kill fish.
Sonar and Fish Perception
Active sonar systems emit sound pulses, or “pings,” into the water, listening for echoes to detect underwater targets. Fish possess specialized sensory systems for sound and vibrations. Their primary auditory organs are internal inner ears, which contain dense calcium carbonate structures called otoliths. These otoliths move in response to sound waves, bending sensory hair cells and sending signals to the brain, enabling sound perception. Many fish species also have a swim bladder, a gas-filled organ that aids buoyancy and can amplify sound, enhancing hearing sensitivity. Additionally, fish have a lateral line system, a network of mechanoreceptors that detects movement, vibration, and pressure changes in the surrounding water.
Direct Physical Effects on Fish
High-intensity or prolonged sonar exposure can cause physical damage to fish. The gas-filled swim bladder is particularly vulnerable to rapid pressure changes or intense sound waves. This can lead to barotrauma, causing rupture or damage to the swim bladder, which affects the fish’s buoyancy control, hearing, and overall health. Beyond swim bladder trauma, other direct injuries from powerful sonar sources at very close proximity can include hemorrhaging, tissue damage, or internal organ damage. While immediate mortality is not common for many fish species, it can occur with high-intensity sonar and close proximity. Severe injuries may also lead to delayed death.
Behavioral Changes and Indirect Harm
Sonar can induce behavioral changes in fish, leading to indirect harm. Fish may avoid sonar-affected areas, displacing them from habitats for feeding, spawning, or resting. This displacement can disrupt their access to necessary resources. Sonar noise can also interfere with behaviors like schooling, foraging, and predator avoidance. Chronic exposure to anthropogenic noise, including sonar, increases stress levels in fish. This stress can negatively impact their growth, reproduction, immune function, and overall fitness, making them more susceptible to disease or predation. Such disturbances can also interfere with migratory patterns, potentially leading to long-term population impacts.
Factors Affecting Impact
The impact of sonar on fish is not uniform and depends on several interacting factors. Sonar characteristics, such as frequency, intensity, and duration, play a significant role. Lower frequency sounds travel farther and can affect a broader range of marine life, while higher frequencies are more localized and attenuate quickly. Louder sonar signals carry a greater potential for harm, and prolonged exposure increases impact severity.
Fish species vary in their susceptibility; those with swim bladders are generally more vulnerable to direct physical harm from intense sound pressure waves. Environmental conditions, including water depth, temperature, and salinity, influence how sound propagates, affecting sonar’s reach and potential impact. Proximity to the sonar source is also a key determinant, as the risk of injury or behavioral disturbance increases substantially the closer a fish is to the source.