During the first six months of the COVID-19 pandemic, as shipping traffic dropped by about 40% off the coast of California, the level of underwater noise that can be harmful to whales and other marine life also decreased by about 40%, according to the findings of a research team that included members of the National Oceanic and Atmospheric Administration (NOAA) National Ocean Service (NOS).
The research, published June 2 in the journal Frontiers in Marine Science, used undersea microphones to detect noise in the waters of the Monterey Bay National Marine Sanctuary — a rich expanse of ocean that stretches across 270 miles from the Marin Headlands to Hearst Castle. The study was a joint project between the Monterey Bay Aquarium Research Institute (MBARI), UC Santa Cruz, the Naval Postgraduate School in Monterey, Moss Landing Marine Labs, the Scripps Institution of Oceanography and NOAA. Funding sources included the National Science Foundation (NSF) and the SanctSound project, which is co-led by NOAA and the U.S. Navy.
“We’ve known for a very long time there is a relationship between shipping and noise,” said John Ryan, a biological oceanographer at MBARI, who helped lead the study. “We heard the economic slowdown very clearly.”
Ryan used a device called a hydrophone, which sits 2,900 feet below the ocean in waters 15 miles northwest of Monterey, to record the ocean sounds. The device, which has been there for six years, records sound 256,000 times a second, picking up everything from whale songs to the low-frequency rumblings of huge cargo ships, which can be heard from dozens of miles away.
“It’s about as big as a bottle of soda,” Ryan said. “Little instrument. Big data.”
Just as the pandemic reduced aircraft noise around airports, as well as air pollution and auto traffic temporarily in cities, the shipping slowdown provided a once-in-a-lifetime opportunity for scientists to study oceans with a much smaller human imprint. Ari Friedlaender turned his focus on humpback whales.
In April 2020, Friedlaender, a researcher at the UC Santa Cruz Institute of Marine Sciences, set out in an 18-foot inflatable boat to study the effects on humpback whales. Friedlander took small blubber samples, about half an inch long, from 44 humpbacks off Monterey and Moss Landing. His goal: to discover if levels of a stress hormone called cortisol in the whales changed as the often cacophonous background noise in the ocean suddenly decreased after the world locked down.
“It was very clear the ocean was a very different-looking and different-sounding place,” Friedlaender said. “My colleagues and I thought this is a unique time and we had an opportunity to understand the impact on animals that we otherwise could never get.”
Friedlaender took more samples last October after shipping traffic had begun to rebound, then more again last month. He plans one more round of sampling this fall, then will compare all the results.
The findings, said scientists involved in the research, could help inform ways to reduce the impacts of loud noises from ships, sonar and other sources on whales, dolphins and other marine animals that rely on sound to survive.
Researchers have known for years that loud noises can disrupt ocean wildlife. In one extreme case, 17 beaked whales washed up on beaches in the Caribbean with blood coming from their ears. The U.S. Navy concluded later that the animals died after military exercises in the area using high-intensity sound waves. Friedlaender also has done studies with the Navy in Southern California showing that blue whales have changed their feeding patterns on krill in the deep ocean in response to loud noises.
Friedlaender and Ryan said that learning more about noise pollution could help affect how the shipping industry, the Navy and others could reduce loud sounds, from slowing ships in certain areas to timing sonar exercises differently, to using engines that run more quietly.
“The goal of this is not to tell a group of people how to behave or point a finger,” Friedlaender said. “The idea is to show that if we do certain things, we might have the opportunity to minimize the impacts.”
Until 50 years ago, whales were hunted in the United States, their meat used to make dog food. Then laws banned whaling. They also were threatened by oil spills. But after the Exxon Valdez spill in 1989, new laws required double-hulled oil tankers, more alcohol and drug testing of captains, and more oil cleanup drills, leading to a dramatic reduction in spills from ships. Populations of most whale species have been slowly increasing in the U.S. and much of the world. With global ship traffic growing, noise pollution is the next frontier.
“It hasn’t been very long that we left these animals alone,” Friedlaender. “One thing is very clear. If we leave them alone, they will thrive.”