If you’ve ever been swimming in the ocean, you know that seeing underwater is a lot different than on land. Light isn’t able to penetrate into the depths of the ocean, so even on shallow dives everything looks darker and certain wavelengths of light are absorbed more by water, so colors are not as vibrant. On land, our vision can tell us a lot – in the water, it can really only tell us about our immediate surroundings.
Because of this, in most marine animals, vision is not relied upon as the primary sensory system, as it is in many terrestrial species. Instead, hearing is widely used by marine species to interpret the world around them. In fact, studies have shown that whales have 2-3 times as many fibers in their auditory nerve and 2-3 times fewer fibers in their optic nerve when compared to terrestrial animals. This represents a greater investment in audition than other sensory systems.
To learn more about how sound travels in the ocean and why this makes it a favored sensory method, check out this Kraken & Friends post.
All animals face similar problems in nature: reproducing, avoiding predators, finding food and navigation. Marine species are able to use sound for each of these purposes:
- Low frequency whale calls can travel hundreds to thousands of miles. This type of long-distance communication is essential for species that are dispersed over large areas – where finding a mate isn’t always easy.
- Social species use a variety of short-range calls to communicate within their social groups, including predator alarms and sexual advertisement.
- Many toothed whales use sound to aid in navigation and finding food through echolocation.
But animals are not the only ones using and producing sound in the world oceans. For decades, naval exercises have been implicated in mass-strandings of several species of whales. Last year, in response to a federal court case, the US Navy was ordered to limit the use of sonar testing in some sensitive whale habitats. While this was an important step in the protection of whales, there are other sources of anthropogenic noise in our oceans.
Marine traffic and oil and gas exploration of the ocean have also been implicated as substantial contributors to marine noise pollution. While 100 years ago, none of these sources of human-caused noise were present in the ocean, today our oceans are littered with sounds that are causing physiological and behavioral changes in a variety of marine species.
Check out the Discovery of Sound website to listen to other sources of human-caused marine noise pollution.
This has been a long-standing battle, however. In 2004, the International Union for the Conservation of Nature (IUCN), developed a resolution to address undersea noise pollution. This spurred interest in the matter by the US Congress, which directed the Marine Mammal Commission to investigate further.
Last year, a study of the impact of seismic surveys suggested that international treaties addressing maritime pollution should be amended to include noise pollution.
Keep your ears peeled. Partly in response to this study, the issue has been resurrected. Murmurings on Capitol Hill suggest that, in light of this study, we might be hearing more about this issue in the months to come.
For more information about marine noise pollution, check out this Scientific American article.