Ship noise extends to frequencies used for echolocation by endangered killer whalesAmy Walsh (Author) Published Date : Feb 03, 2016 12:37 IST
Noise pollution from ships have disrupted quiet of lot of things for Orcas and killer whales. And yes, they too like it peaceful around. One of the threats faced by today's oceans is underwater noise pollution from ships. Scientists have stated that too much noise is disrupting marine life. To find out scientists measured underwater noise as ships passed their study site 3,000 times.
There have been earlier studies that have called for stricter measures in order to control noise pollution to protect marine life. Conservation ecologists Douglas Nowacek at the Duke University Marine Laboratory in Beaufort, North Carolina, and Howard Rosenbaum at the Wildlife Conservation Society in New York City, had earlier told Nature that one concern is hearing damage in animals. That can happen either with very loud sounds or over longer periods of exposure to lower levels of noise. Also, with air guns, the reverberations raise the background noise level and so risk masking animals communication and navigation signals. A final concern is stress. Short-term stress is not that big a deal, but long-term stress is really detrimental. It causes physiological and reproductive problems; and we don t know a lot about how sensitive marine animals are to it.
In order to understand the nature of ship noise, particularly in coastal areas where ships access ports, scientists measured approximately 1,600 unique ships as they passed through Haro Strait, in Washington State. This area is the core critical habitat for the endangered Southern Resident killer whales salmon-eating orcas which are iconic in the Pacific Northwest and which support a multi-million dollar ecotourism industry in the U.S. and Canada.
Amazingly, the growth in commercial shipping has raised the intensity of low-frequency noise almost 10-fold since the 1960s. Because this noise occurs at the low frequencies used by baleen whales there is growing evidence it may impact their ability to communicate, and therefore their survival.
Southern Resident killer whales represent an endangered toothed whale species that inhabits an urban estuary in which shipping traffic is common and is very well characterized bioacoustically. Their auditory sensitivity, extrapolated from captive killer whales peaks at 15,000 20,000 Hz a frequency range that overlaps with the upper range of their vocalizations and the lower range of their echolocation clicks.
Behavioral responses to boat noise have been documented in toothed whales, including SRKWs. For example, bottlenose dolphins whistle less when exposed to boat noise and Indo-Pacific bottlenose dolphins lower their 5,000 10,000 Hz whistle frequencies when noise is increased by boats in a band from 5,000 to 18,000 Hz.
While the frequencies used by toothed whales are well above the peak power frequencies of ships, multiple lines of evidence suggest that ship noise spectra extend or should be expected to extend to higher frequencies. Laboratory experiments with cavitation and previous studies of submarines, torpedoes, and ships indicate that ship noise may extend as high as 160,000 Hz at the source.
The study shows that another potential way to reduce noise pollution is to simply slow down. The data suggest that, on average, each reduction in a ship's speed by 1 knot could reduce broadband noise levels by 1 dB.
Ship noise extends to frequencies used for echolocation by endangered killer whales