Few people witness these mysterious creatures swimming in Monterey Bay, but if you listen closely, you’ll hear plenty of sperm whale sounds. The chatter of undersea creatures fills the soundscape, and the sounds of sperm whales pierce the background. Once thought to be a rare event, Monterey Bay Aquarium Research Institute (MBARI) researchers used underwater microphones to detect an unprecedented number of sperm whales in Monterey Bay.
Unlike humpback whales, which are ubiquitous in Monterey Bay and featured in Star Trek IV: Voyage Home (along with the Monterey Bay Aquarium as a cetacean research laboratory), sperm whales are often undiscovered. there is. According to Santa Cruz Whale Watching, their boats only spot sperm whales once every few years. These large, endangered predators briefly surface for air, then dive thousands of feet into the inky depths to hunt. To find prey, whales make loud clicks that last several seconds and listen for the echoes. This echolocation locates squid, sharks, skates, and fish far away in the darkness of the deep ocean.
Researching deep-sea organisms is difficult because the vast amount of water prevents light from reaching very far. However, according to MBARI, sperm whales are the loudest animals known, and water carries sound for miles. “It’s really interesting to go out into a really wild place,” said Will Oestreich, a National Science Foundation postdoctoral researcher on the MBARI acoustic marine ecology team. To observe the chatter of marine life, MBARI researchers installed microphones at a deep-sea cable observatory outside Monterey Bay. As the name suggests, the observatory is directly connected to MBARI via a cable, allowing the instruments to receive continuous power and transmit information to researchers.
An underwater microphone, or hydrophone, installed at MBARI’s wired deep-sea observatory, the Monterey Acceleration Research System (MARS), in the heart of the Monterey Bay National Marine Sanctuary. The treasure trove of acoustic data recorded by this hydrophone provides researchers with an important lens into marine life and ecosystems. (Photo provided by MBARI)
Since 2015, Mike has been continuously recording underwater soundscapes. Sperm whales are the noisiest animals known, but their sounds don’t last more than a second. To select sperm whale calls from seven years of recordings, Oestreich and his colleagues created an automated program to identify and analyze sperm whale calls.
Researchers were surprised by the sheer number of sperm whales in Monterey Bay. Until this study, sperm whales were thought to be extremely rare. “What was shocking to me was how regularly they came here,” Oestreich says. Sightings are rare, so the researchers were surprised to find that sperm whales lived in the bay in large numbers year-round.
Having discovered so many sperm whales, the research team decided to track the population’s demographics and movements. The interval between clicks is directly related to the animal’s body size, and female sperm whales are much smaller than males. They found that both males and females generally swim around the bay, as well as their young. All three populations were present year-round, so it’s not just a single population of sperm whales coming to the bay.
Like other whales, sperm whales migrate to different hunting and mating grounds throughout the year. The total number of sperm whales in Monterey Bay fluctuates seasonally, and this migration is offset by the well-studied Alaska migration. Whales hunt in the deep sea where sunlight does not reach, which shows that the deep sea ecosystem is connected to the seasons. “By studying one animal, you can learn about an entire ecosystem,” Oestreich says.
Like bats, sperm whales use short clicking sounds to perform echolocation and locate prey. As the clicks travel through the water, they bounce off harder objects, like the delicious squid that a sperm whale eats. When the whale hears this returning sound, it knows the location of the squid and zeroes in on its target. “When the sperm whale starts zeroing in on its prey, the clicks get very close and you start to hear what sounds like a stream,” Oestreich said. As the whale approaches, the time between the click and the echo becomes shorter and shorter, until it suddenly stops. This is when whales eat squid. By tracking this pattern, scientists tallied how often the whales preyed.
Monterey Bay contains National Marine Sanctuaries, and sperm whales frequent these protected areas. Now that MBARI scientists have learned that sperm whales frequent Monterey Bay, Oestreich said he wants to work with conservation groups to use that data to protect this endangered species. “Knowing when these animals are here and what they’re doing is an important part of informing animal conservation.”
For more information about sperm whales and the underwater soundscape, visit fisheries.noaa.gov/species/sperm-whale.
