Sounding The Depths, How Noise Pollution is Changing Our Oceans

There are around 50,000 large ships travelling the world. This doesn’t include the multitude of smaller vessels in use everywhere, add to this about 10 million ferries and 4 million fishing boats and we have quite a flotilla of vessels ploughing our oceans. The noise generated from these vessels alone is enough to give anyone a headache. But now throw into the mix the noise from an unknown number of military equipment, seismic shipping and exploration rigs, drills, dredges and wind farms and it’s enough for anyone to reach for a headache pill.

Background noise, say scientists has increased by 15 decibels in past 60 years but is this enough to drown out and affect the day-to-day sounds of marine animals. Many marine biologists think it is. We are causing, say experts, acoustic smog in our ocean. And recent research is showing some unexpected casualties.

Sound Travels over Vast Distances

Marine mammals use sound in hunting, communicating with other members of their groups, in courtship and in navigating in an often dark and low visible environment. It is difficult to appreciate just how important sound is for marine mammals. Without interference, sound can travel thousands of miles underwater, and marine mammals have evolved remarkable sensitivities to take advantage of this. Baleen whales are without vocal cords in their larynxes but are able to generate the loudest sounds on earth from any biological organism. And how Humpback whales make their mysterious and haunting song without vocal chords still eludes researchers. Toothed whales such as dolphins and sperm whales use sounds to communicate amongst each other and to echolocate enabling detection of organisms and navigation. Perhaps the most well known use of sound in whales is in the famous humpback whale song. It was a remarkable discovery that humpbacks separated by 4500 km across the world sing the same song with slight variations in the song occurring each year.

Noise, the Culprit Of Whale Deaths

Over the past century, the noise from shipping activities has increased ambient noise to 10-100 times in the frequency range of baleen whales, say scientists. When there is a lot of noise some whales call louder, or repeat messages, other may wait until it is less noisy. This, say scientists, is okay but if you need to warn your group of danger, it’s a problem. Right whales have even shifted the frequency of their calls. Other impacts have been reported; Humpback whales have been found to change their “song” when forced to compete with low frequency sonar. Animals may be able to move from noisy areas but for those populations that are endemic to certain habitats, such as Hong Kong’s pink dolphins, here are grave concerns about increases in noise level on local populations. There has been particular concern over the effects of naval sonar on marine mammals. Since 1960, with the advent of powerful sonar there have been 40 known mass standings’ of Cuvier’s beaked whales worldwide, 28 were know to involve sonar or seismic activity. The discovery of dead whales with internal haemorrhaging and gas bubbles in their blood vessels is also linked to sonar and seismic surveys. As well as physical and behavioural disruptions, noise is likely to increase stress levels. Studying these animals is difficult at the best of times and we many never know the true extent of the impact.

Noise Pollution Casts Its Shadow Over All Marine Life

And it’s not just marine mammals that are affected by the unprecedented rise in ocean noise. Studies have already shown that many species of fish are sensitive to noise disruptions, suffering hearing damage and death after seismic surveys. Even moderate levels of seismic noise were shown to cause temporary hearing loss in fish. And noise can also cause a stress response, with studies showing a number of fish species secreting stress hormones in the presence of shipping noise. Increasing noise levels has been shown to affect behaviour directly, causing some species of fish to drop to depth, become less active or form tighter schools. Schools of Bluefin tuna are disrupted with vessel noise; this is a problem as tuna schools help the fish find suitable spawning and feeding grounds more accurately.

And the effects of noisy oceans seem to cast their shadow over other marine life. In 2004 and then again in 2008, hundreds of Humboldt squid died off the coast of Oregon in the US. Originally, biologists blamed a change in deep-sea currents for the mass death but new research has pointed the finger squarely at ocean noise causing physical trauma. And before death, says Michel Andre at The Technical University in Catalonia who conducted the study, there is severe damage affecting the squid behaviour, such as their ability to hunt and avoid predators.

And it’s not just the larger species that are affected by increases in ocean noise. Researchers at the University of Bristol in the UK, found that reef fish larvae, even a few days old, use sound to navigate their way from open water to coral reefs. Even more remarkable is their claim that coral larvae do the same. Further work has identified a number of other marine invertebrate larvae also responding to sound. For these tiny ocean babies, sound is used to indicate the presence of predators or unsuitable habitat. It helps them avoid areas with unsuitable noise. For some species, noise such as the cacophony produced by a coral reef may attract them. But the increase in sound in the world’s oceans may well be affecting how young marine life evade predators and find suitable places to settle.

Some scientists point out that many marine animals, marine mammals included, would have adapted to a certain amount of noise disruption through evolutionary time (from waves, rain, storms etc.) but these adaptations would be for natural background noise. And evolutionary adaptations to cope for such a rapid raise over what is recent geological time, is unlikely.

Carbon Emissions; a Double Whammy for Noise

And it seems even our deadly friend, carbon emissions, is altering sound in the oceans too. According to a report this year from University of Hawaii, as carbon dioxide from the world’s rising carbon emissions combine with seawater and make them more acidic, the way in which sound is absorbed is altered. Seas are less able to absorb low frequency sounds so the human made noise travels even further.

The report is highly significant. Previous studies have focussed on the effects of ocean acidification on shelled animals; this is the first to identify how it is changing the acoustics of the oceans too. According to lead author, Dr Tatiana Ilyina sound absorption for low frequency noise could fall by 60 percent by 2100 in high latitude, deep oceans if carbon emissions are not significantly reduced. Recent research on the hearing of clownfish showed that with increasing Co2 fish hearing is dramatically affected. Professor Philip Munday of James Cook University showed that under acidification levels predicted for 2050, clownfish do not respond to sound to enable them to evade predators.

There are of course detractors who maintain that ocean noise is localised and decreases rapidly away from the source. And while there have been many laboratory studies showing the effects of increases in sound on a variety of marine life, studying the effects of sound in the wild is problematic. To confound the issue, sound travels differently depending on the depth of water and the frequency of the sound. There is also a so-called sound channel at 1000m depth around the world that allows low frequency noise to travel for 1000 kilometres. And species are susceptible to different frequencies, for example toothed whales and dolphins are sensitive to high frequencies, whereas baleen are sensitive to low frequencies. Despite all this, there is now mounting evidence that noise does indeed cause dramatic and often devastating impacts on marine life.

Those taking up the mantle against ocean noise have found some international recognition. In 2004, The World Conservation Union adopted a resolution declaring noise as a form of ocean pollution, similar resolutions and agreements have developed but their effectiveness remains to be seen. Some conservation groups are calling for marine sanctuaries where all human activity is banned, including noise. But there is still no international law that controls noise pollution despite the issue being raised in many international meetings. With ocean noise crossing national boundaries across the world, it is time that nations took the issue seriously and work closely together.

Our oceans are the lungs of our planet providing half of all the oxygen in the atmosphere. As we clog them with acoustic smog, we are not only choking our marine life, but ourselves as well.

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