Undersea noise from container ships, oil tankers, and cargo ships may be drowning out communications among the endangered orcas of the Pacific Northwest, making it harder for these rare whales to find the fish they need to survive.
“These ships are not only prevalent, but quite loud compared to other sources of noise in the ocean,” said oceanographer Scott Veirs, the lead author of a new study published Tuesday in the journal PeerJ. “Ships are dominating the soundscape.”
Using underwater microphones and sophisticated sound analysis, a team of scientists measured the noise created by 1,582 large ships—mostly commercial vessels—on 2,812 trips through Haro Strait, a waterway just west of Limekiln State Park on Washington state’s San Juan Island. They matched individual ships to the different recordings using Coast Guard tracking data.
Around 20 container, cargo, military, and other big ships pass through Haro Strait each day, most headed for the Port of Vancouver in British Columbia. In summer, the same area is a core habitat for the Southern Resident killer whales, around 88 critically endangered orcas that rely on chinook salmon as their main food source.
Along with expected low-frequency noise—which past studies have shown can affect the welfare of some whales—the team discovered that the ships created a lot of noise pollution at the higher frequencies that the killer whales use to detect salmon underwater, as well as find and communicate with one another.
“The most subtle sound they are probably trying to hear is the sound of their echolocation clicks bouncing off a salmon,” Veirs said. “Like bats, they’re listening for very faint echo from their prey.”
Since many chinook salmon runs in the region are also endangered, the findings suggest that noise from large ships could affect the Southern Residents’ survival by making it harder for them to locate salmon.
From an orca’s perspective, Veirs said, the ships create “a persistent source of loud noise, like highway noise in your neighborhood, or trying to have a conversation in a room with the vacuum cleaner on.”
Container ships were generally the loudest, while military vessels were among the quietest, although there was a wide variation in noise levels among all types of ships recorded in the study.
Both those findings hold the seeds of potential solutions to the noise pollution problem, said Veirs.
Container ships were the fastest-moving ships in the study, he said, and “the faster a ship goes, the louder it is. So just by slowing down, the ship could voluntarily lower its noise level.”
As for the low-noise military ships, “there’s an implication there that the military has employed ship-quieting technologies that could be useful in the commercial sector,” Veirs said. “I know NOAA”—the National Oceanic and Atmospheric Administration—“has had a couple conferences on this subject, of transferring ship-quieting technologies.”
The wide range of noise created by different ships within a single class “suggests that if you quieted the loudest 10 percent of the ships, you could reduce the median level of noise for the whole class of ships,” he explained. “From a fleet owners’ perspective, it might be the older ships, or the less well-maintained ships."
The next steps in the research will be to better understand how the noise levels documented in the study are impacting marine life in the Pacific Northwest, Veirs said.
“As an endangered species, the killer whales will be at the top of our list,” he noted. “But we also want to look at fish, invertebrates, and the many other marine mammals we have. Some of them are also high-frequency specialists, such as white-sided dolphins and Dall’s porpoise.”