Understanding the sources of ocean noise pollution
The three most significant sources of ocean noise pollution are ship noise, oil and gas exploration and military sonar.
Large international cargo vessels, supertankers and cruise ships are constantly in motion, producing noises from their engines, propellers, generators and bearings.
The problem with this noise is that it dominates the frequency ranges of 20-300Hz, the same range used by many species of whale. This makes it hard for them to communicate and, more dangerously, to distinguish ship noise from natural sounds. The consequence of this is accidental collisions, one of the leading causes of death for right whales around the world.
Ship noise, particularly where it becomes too constant, may also be a cause of some whales abandoning their habitats. The problem is greatest in coastal areas and around busy ports.
Noise from Oil and Gas Exploration and Mining
The oil and gas industry generates loud and continuous sounds through seismic-survey operations, pipeline and platform construction and removal and drilling. This problem is especially bad in the Gulf of Mexico, off the California coast, the Persian Gulf, the North Sea and off the coast of Brazil.
- Exploration noise
So-called ‘airgun arrays’ used to detect oil or natural gas beneath the seafloor use incredibly loud sound pulses directed at geological structures. These are some of the loudest man-made noises in the oceans. Blasted every 10-60 seconds for days or months at a time, these extreme bursts of sound can drive whales away from the area.
- Noise from drilling and extraction
The noise generated by drilling and extraction may not be as loud as the ‘airgun arrays’, but they last much longer. Over time, exposure to these noises can cause whales and other marine species to abandon their habitats.
- Military Sonar
In order to detect submarines over long distances, military sonar systems transmit some of the most powerful underwater noises.
High-energy acoustic pulses are emitted and their echo recaptured as a part of weapon and counterweapon targeting. These high frequency systems (over 10kHz) can transmit pulses of sound for thousands of metres.
So powerful are these noises that whole groups of whales and dolphins can beach themselves to escape the auditory assault. They can also disrupt communication and feeding behaviours and cause temporary hearing loss and permanent tissue damage. As a result, marine mammals are often forced to abandon their preferred habitats.
Cold War-era sonar systems were less dangerous, because they primarily focused on deep-water environments. But today’s sonar systems not only employ new, more powerful technologies but are frequently tested in shallow coastal waters, the same environments that are home to many endangered whales and marine creatures.
Not all manmade underwater noises are a bad thing.
To help prevent whales, dolphins and porpoises becoming tangled in fishing gear, some fisheries use underwater noisemakers, known as pingers, to warn of the location of fishing gear.
This new technique has already had some remarkable successes. For example, pingers have significantly reduced the number of harbour porpoise entanglements in the Gulf of Maine.
But while pingers are one source of underwater noise that is meant to be good for whales, we must carefully monitor their use, and be sure they never harm whales or drive them away from their critical habitats.