An acoustic study of the underwater soundscape of Cordell Bank National Marine Sanctuary found that sound from shipping lanes in and out of the Bay Area overlaps with whale vocalizations. Data analysis from the recordings also found that whales, previously thought to be seasonal
inhabitants of the sanctuary, are present year-round. Both findings have implications for conservation
efforts.
“Cordell Bank is a highly connected marine ecosystem with highly mobile species, and what we hear and learn in this sanctuary is relevant over a much greater range,” said John Ryan, a senior research specialist at the Monterey Bay Aquarium Research Institute and one of the study’s co-authors.
Cordell Bank and the adjacent Greater Farallones National Marine Sanctuary are feeding grounds for blue and humpback whales and are part of a major migration route for gray whales. As human-generated noise has increased on the California coast, the impacts of ocean noise pollution on marine organisms and animals has become an important area of study. Gathering acoustic data is key.
Light doesn’t travel far in water, so in a dark ocean most marine mammals have evolved to use sound as their primary sense. The natural underwater soundscape is complex, and whales rely on sound for communication, foraging, navigation and even predator detection.
Sound, although dependent on temperature and pressure, can travel thousands of miles underwater, and whales have been known to communicate over great distances. Dr. Samara Haver, a post-doctoral scholar with Oregon State University and the study’s lead author, said the whales in the study—those with low-frequency vocalizations—can hear each other over incredibly long distances.
In 2015, a team of researchers deployed a hydrophone, a microphone that can function as a continuous underwater acoustic monitor, to collect ambient soundscapes for two years in Cordell Bank, a 1,200-square-mile area offshore from Point Reyes. The range of the hydrophone extended to the Greater Farallones, which wraps around Cordell Bank as it hugs the coast from San Francisco north to Point Arena.
Around the country there are 12 such hydrophone recorders, four of which are in marine sanctuaries. The device in Cordell Bank is part of a larger network that the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory has created with help from partners, said Danielle Lipinski, the research coordinator for Cordell Bank.
An analysis of the resulting acoustic data was published in the Journal of the Acoustical Society of America in 2020. It revealed that both large vessels and vocalizing baleen whales—fins, blues and humpbacks—contribute to the low-frequency ambient soundscape of Cordell Bank. In other words, acoustical niches inhabited by whales are cluttered by sound from the shipping lanes.
“Their communication is being compromised,” said Michael Stocker, executive director of Ocean Conservation Research, a West Marin nonprofit that explores solutions to noise pollution in marine environments. “Shipping noise is the most ubiquitous sound in the ocean. When it’s loud, you raise your voice, up to a point, and when it’s too loud, you just give up,” he said.
Conservative estimates showed the hydrophone was able to pick up sound from its location to the shipping lanes or a ship anywhere in the sanctuary, but more research is needed to understand how the ambient sound levels might be impacting the whales. Shipping noises could be fundamentally altering or overwhelming their communication, or the whales may be adapting—scientists don’t know, Dr. Haver said, but it’s clear that Cordell Bank does not provide refuge from vessel traffic.
The study also found blue and fin whales were present in the fall, winter and spring, and humpback whales were present throughout the year.
The unique features of Cordell Bank, including its depth, small size and close proximity to ship traffic, increase ambient sound levels. Dr. Haver said the sanctuary is more exposed to the Pacific Ocean than are other research sites, and that magnifies the way sound from fishing vessels is propagated.
Noise from large commercial vessels and other human activities is not specifically regulated in the two sanctuaries, but there are other rules in place. Large vessels are limited to defined shipping routes, and discharging material and disturbing the seafloor is prohibited.
Currently Cordell Bank and the Greater Farallones request voluntary shipping slowdowns from May 1 to Nov. 15. Sanctuary officials have observed up to 100 whales feeding within shipping lanes; slowing ship speeds not only reduces strikes, but also lowers noise pollution. “We do know that when ships slow down, they’re quieter,” Dr. Haver said.
The new findings could help sanctuary officials create stronger guidelines for vessel traffic, potentially redefining shipping lanes and adjusting dates for voluntary slowdowns.
Careful rerouting of shipping lanes and reductions in vessel speeds have helped reduce ship strikes in California, where there were 70 recorded incidents of ship strikes between 2007 and 2020, many related to Bay Area ports. Researchers believe those numbers represent a small fraction of the total, since many incidents go unnoticed and most whales sink after they die.
According to Cordell Bank’s outreach and education coordinator, Jennifer Stock, the lack of population recovery among blue whales is a prime concern for sanctuary officials.
Although shipping traffic in the Bay Area is expected to increase, Mr. Stocker says newer ships are being built with greater attention to noise pollution. Low-noise propulsion systems and vibration-isolated mounting systems can tone down the clamor of large ships.
“Currently the guidelines are only recommendations,” Mr. Stocker said, but “there is a bit of a shift in this direction because it’s more energy-efficient.” He and other researchers say the public can help reduce ocean noise pollution by buying local and reaching out to policymakers.
Researchers at Cordell Bank—from the National Oceanic and Atmospheric Association, the National Park Service, Point Blue Conservation Science, Oregon State University, Stanford University and the Monterey Bay Aquarium—are now working to better understand whales’ responses to noise levels and where and how often different species are present. Future studies will likely incorporate species that use higher-frequency vocalizations.
Piecing together the puzzle involves both monitoring and research projects that bring together current and long-term visual and acoustic data.
“We’re integrating what we learn from analysis of sound in the ocean with other forms of observation,” Dr. Ryan said. “This helps us understand how the ecosystem is changing, and how that might affect the marine mammals that rely on it.”