Killer Whales and Ship Noise Frequencies Are Now Same, Making Whale-Foraging Difficult
Underwater noise from large cargo ships and oil tankers may drown out communications between endangered kill whales of the Pacific Northwest, ultimately making it more difficult for them to find food they need to survive.
Using underwater microphones and sophisticated sound analysis, a team of researchers -- led by Scott Veirs of the Beam Reach Marine Science and Sustainability School -- measured the noise created by 1,582 different large ships-mostly commercial vessels-on 2,812 trips through Haro Strait, according to a news release.
The Haro Strain is a waterway just west of Lime Kiln State Park on Washington State's San Juan Island and is considered a critical foraging habitat for a population of approximately 84 critically endangered Southern Resident killer whales. Using Coast Guard tracking data, researchers were able to match individual ships to the different recordings.
"These ships are not only prevalent but quite loud compared to other sources of noise in the ocean," Veirs said in a statement. "Ships are dominating the soundscape."
Killer whales, also known as orcas, rely on echolocation to find food. This means that they send out clicks and listen for their echoes to figure out the size and location of prey, such as Chinook salmon. Therefore, these noise disturbances could greatly impact their survival.
While the low rumble of passing ships has long been connected to the disturbance of large whales, the growth in commercial shipping has raised the intensity of low-frequency noise almost 10-fold since the 1960s, researchers say. What's worse is their study found ships are responsible for elevated background noise levels not only at low frequencies as expected, but also at medium and higher frequencies -- including 20,000Hz where killer whales hear best.
What's unique about the recent study, is that it examines a broad range of large ships. Overall, researchers found container ships exhibited the highest median source levels, while military vessels where among the quietest. This, researchers say, could help conservationists find a solution for the underwater noise pollution problem. For example, if ships were to reduce their speed by six knots they could decrease noise intensity by half.
Their study was recently published in the journal PeerJ.
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