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How Does Sonar Affect Marine Life?

Abhijit Naik Feb 17, 2020
Off late, there has been a lot of hue and cry about the negative effects of sonar on marine life. We will try to figure out whether active sonar affects marine species, the cetaceans in particular, and if yes, how?

The Bahamas Incident

In 2000, fourteen beaked whales were found stranded on the beaches of the Bahamas following a routine training exercise by US Navy destroyers. It was this incident that put sonar in the spotlight, despite the fact that the evidence implicating it was far from conclusive.
The connection between naval exercises―the use of sonar in particular―and the increasing instances of mass stranding of whales and dolphins around the world has baffled marine researchers. There is no concrete evidence to suggest that sonar kills whales, dolphins, and porpoises ... or any other marine species for that matter.
However, it's worth noting that it triggers physiological and behavioral changes in some species; some of which can eventually result in death. Also, there exists anecdotal evidence which suggests that the mass stranding of species has been on the rise since the introduction of this technology.

Sonar Basics

Sonar detects the presence of an object by bouncing sound waves on it, and calculating the time its takes for these waves to return. Military ships use sonar to sweep hundreds of miles of ocean floor for possible threats.
In fact, it's an integral part of the US Navy's anti-submarine warfare, wherein, it is used to detect and track enemy submarines. Besides military ships, it is also used by commercial and fishing vessels.
Intensity: Some sonar systems have an intensity of 235 decibels (dB). To put that into perspective, the noise a jet makes during its take off has an intensity of 150 dB at a distance of 25 meters. The data put forth by the US Navy suggests that, their long range surveillance sonar, the Low Frequency Active Sonar (LFAS) retains an intensity of 140 dB over a distance of 300 miles.

How Does Sonar Affect Marine Life?

Most marine mammals rely on sound for a host of life functions, including communication, foraging, and even movement. Some species even use echolocation―their inbuilt biosonar system to locate predators and prey. In such circumstances, the introduction of a foreign sound in the marine environment can no doubt interfere with basic functions of marine species.
Researchers studying the direct effects of sonar on marine species have observed that the exposure altered their behavior to a certain extent. The moment the whales were exposed to sonar pings, they would stop feeding or swimming, and then swim away from the noise.
At this juncture, their swimming was typically characterized by long, deep dives, as if they were trying to get rid of some threat on their tail. On the basis of their findings, researchers hypothesized that the noise caused the species to surface rapidly, which, in turn, made them vulnerable to decompression sickness.

Sonar and Beaked Whales

When it comes to mass stranding of species as a result of sonar activity, the beaked whale comes across as the most affected species. That might have something to do with the fact that it is the world's deepest-diving whale species.
As such, it is found at depths which is common for submarines. Another theory attributes this to their reclusive nature, further adding that it's likely that they confuse sonar pings for killer whale sounds.
There is another hypothetical explanation for the stranding of beaked whales. When beaked whales dive, their lungs collapse as they reach a specific depth. This prevents the infiltration of nitrogen in their bloodstream.
However, when they are exposed to sonar, their diving pattern is significantly altered. Instead of diving to greater depths, they make a series of shallow dives, as a result which their lungs fail to collapse, and that results in formation of nitrogen bubbles in their tissues, making them vulnerable to decompression sickness.
Besides beaked whales, even minke and killer whales are believed to be vulnerable to this hazard. Experts are of the opinion that sonar pings bring about a series of behavioral changes in these species, and the disorientation resulting from it provokes them to beach themselves. It's not just about small species though.
Even blue whales undergo a significant behavioral change when they are exposed to sonar waves. Other than disrupting their feeding behavior, sonar pings also mask their communication patterns, making it difficult for them to communicate with their kind.
Sonar is an essential tool when it comes to naval operations, and there is no way the navy can do away with it in the near future.
The good thing is that, they have acknowledged the effects of sonar testing on marine life, and are taking precautionary measures, like conducting aerial surveys to spot whales, and turning sonar off when whales are seen in the vicinity to ensure that no species are harmed.