Photo by mikebaird via Flickr Creative Commons
Peter Tyack is dedicated to studying how sound impacts marine mammals. As we know, whales and dolphins rely on vocalization to find food and one another. Many species are able to hear each other over vast distances, locating one another to breed and migrate to feeding grounds. Their sensitivity to sound means that the human activity in the ocean -- from the drone of ships engines to the sometimes lethal effects of military sonar -- is having disastrous effects. Just what kind of an impact are we having on cetaceans? Tyack took some time to talk with us and explain how our activities have changed over the last century and if there's hope for peace and quiet.
Photo by NOAA's National Ocean Service via Flickr Creative Commons
TH: In a TED talk you gave during Mission Blue, you noted that low frequency sound, such as that used by baleen whales, can travel globally and that this long-distance communication is vital for members of the same species in finding one another. What human activities also make these low frequency sounds that can interrupt or block out whale communication?
PT: Of all human activities, ships put the most low frequency noise into the ocean. We are all familiar with the noise that an engine makes, and the noise from ship's engines transmits right through the hull into the ocean. As the propellers rotate, they also generate loud noise that anyone who has been swimming near an outboard will recognize. Another important low frequency noise comes from the oil and gas industry as it prospects the ocean. They use very loud sound sources that direct pulses of low frequency sound energy into the ocean and then listen for echoes from oil or gas deposits below the seafloor.
Just to give an idea of how loud these pulses are, acoustic recorders placed in the middle of the Atlantic Ocean record these pulses every month of the year from places as far away as Nova Scotia, Brazil and Western Africa. Sometimes there are so many pulses that the recorders cannot be used to detect whales; this suggests that the pulses may interfere with long range communication by the whales themselves.
Photo by jurvetson via Flickr Creative Commons
TH: You point out that humans are a visual species so it is hard for us to understand the profound impact sounds play on marine life, particularly on mammals like whales and dolphins. Are there some resources you recommend for people to look at that helps us visualize this impact, such as sound maps?
It is really hard for us to understand how well and how far sound travels in the ocean and how important sound is for whales and dolphins. When a sound travels in the ocean free from interference from the land and sea surface, it can travel thousands of miles. For
example, the same sound broadcast from one ship west of Australia, could be heard off Bermuda nearly 10,000 miles away and off California over 11,000 miles the other direction.
Photo by LaPrimaDonna via Flickr Creative Commons
Whales and dolphins have evolved amazing acoustic sensitivities to take advantage of sound in the sea. If you have ever snorkeled or dived, you know that light does not carry far even in the clearest water, so it is hard to see very far. Sound is a much better distance sense for mobile animals at sea; dolphins and toothed whales have evolved their own sonar that allows them to find prey and avoid obstacles even as they dive into the deep black sea where sunlight never reaches. Baleen whales evolved low frequency calls that could be heard hundreds of miles away in the pre-industrial ocean. The problem today is that humans are changing the acoustic environment that marine mammals evolved to exploit. We have to be careful not to allow so much noise that marine mammals cannot meet their needs.
Photo by Shayan (USA) via Flickr Creative Commons
TH: How has human noise pollution in the oceans changed over the last century, and how are we seeing the impacts play out among marine mammals?
Over the past century, shipping noise has elevated the ambient noise by 10-100 times in the frequencies used by baleen whales to communicate. The pre-industrial world also saw fluctuations in noise as storms went by or earthquakes happened, and marine mammals have evolved sophisticated mechanisms to compensate for changes in noise. When it is noisy, some whales yell louder and others repeat their message several times. Another strategy is to give up and just wait until it is quieter. That may be OK for some messages, but waiting could be a problem if you want to warn your group about a predator sneaking up on them. If the noise is limited to a narrow frequency band, then whales can shift the frequency of their calls. For example, as shipping noise has become louder over the past 50 years, right whales have shifted the frequency of their calls upwards out of the ship noise band. It is as if the whole population changed from being bases to being tenors.
Photo by Just Taken Pics via Flickr Creative Commons
TH: Is there any hope of building marine preserves that regulate sound, so that there is, quite literally, a quiet space for marine mammals to talk with one another?
Unfortunately for marine life, sound does not pay attention to lines drawn on a map. If ships cannot enter a marine preserve, then animals will be spared the loud sound of a close passage, and the risk of collision, but most of the continuous low frequency noise
that interferes with communication comes from sources far from the preserve boundary. Physical barriers like land masses can block sound, so marine spatial planners may be able to locate industries and shipping lanes so as to reduce noise in some protected areas, but this will take careful analysis of how sound travels from an industrial development to important habitats.
Marine preserves may be more effective at regulating effects of sound in coastal areas than in the open ocean. In Sarasota Florida, dolphins have a boat pass within 100 yards about once every 6 minutes. As a boat approaches, the dolphins whistle to one another,
form a tighter group, and then go back to normal when the boat passes. By contrast, manatees call less when there is vessel noise. It is as if they give up when it is too noisy. Manatees like to feed in areas of seagrass, but when there is a lot of vessel noise, they leave these preferred foraging habitats. The sounds of boats in coastal waters do not carry as far as those of ships at sea, and boats make less noise when they move slowly. If motorboats were excluded from critical habitats for dolphins and manatees, or if they were required to slow down, even in relatively small areas, this could provide significant protection from the effects of noise.
Photo by Mike Johnston via Flickr Creative Commons
TH: Are there technological advancements that are helping to minimize our noise pollution, or is it up to regulating bodies to place restrictions on human noise pollution in the oceans?
This is not an either/or question. When a ship puts noise energy in the ocean, this represents inefficiency. Energy that could be going to propulsion is lost to noise. The owner of a luxury cruise ship may be willing to spend money to reduce vibration and noise, but it may cost more for the owner of an old ship to fix it up than to burn more fuel and live with the noise. The Navy has invested billions of dollars learning how to quiet ships, but some of the methods are expensive to build and may require extra maintenance. Regulators must decide what levels of noise pollution are tolerable for marine life, and then set standards to make sure those are not exceeded. This will stimulate use of the technological advancements that we already know about, and will likely lead to new technological innovation to reduce impacts of the global shipping trade. I am confident that if industry is given the correct incentives to protect marine life from the effects of noise, the technological solutions will be found.
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