In what could be bad news for many forms of marine life, researchers have learned that ship noise in coastal habitats extends to echolocation frequencies used by endangered Southern Resident killer whales (SRKW).
The study, which was conducted between March 2011 and October 2013, combined calibrated hydrophone measurements and ship location data to estimate subsurface sound pressure levels for 1,582 vessels traveling through the inland waters of Washington and British Columbia, also known as the Salish Sea. This same estuary hosts the Vancouver, Seattle, and Tacoma commercial shipping ports.
Because the Salish Sea is the killers whales’ core critical habitat where they use echolocation to hunt Chinook salmon populations in murky waters near Seattle, the researchers wanted to find out if noise from the nearby shipping lane interferes with the whales’ ability to hunt.
The killer whales use mid-range and high frequencies to communicate and locate prey, so the researchers measured a wide range of frequencies, from 10 Hz to 40,000 Hz.
The study shows that ships are responsible for elevated background noise levels at low, medium, and high frequencies — including at 20,000 Hz, the point at which killer whales’ hearing is at peak performance. The noise could interfere with both communication and echolocation, the researchers say.
While container ships exhibited the highest sound frequencies, vessels belonging to the armed forces had some of the lowest levels. This suggests the researchers note, that transferring the military’s sound-muffling technology to the commercial sector may be a good idea for the protection of marine life.
Underwater noise pollution is just one of the threats faced by denizens of the deep. Because of this, the team hopes its groundbreaking study of the way ship noise affects the SRKW population will increase understanding and awareness of the potential threat underwater noise pollution poses to other marine life. They also hope that their work will help in the development of mitigation strategies.