Scientists are listening to Blue Whales off California's coast. Here’s what their songs reveal

“We know that sound is vital to the lives and survival of these animals,” said Will Oestreich, a postdoctoral fellow at the Monterey Bay Aquarium Research Institute. Oestreich and his advisor, John Ryan, have been studying whales by using remote sound recording equipment in the Monterey Bay. Research shows that whales use sound for all essential life functions, including mating, migration, finding food and communication.

Top of story: A remotely operated vehicle on the docks by the Monterey Bay Aquarium Research Institute in Moss Landing (Monterey County).

Above: Marine ecologist Will Oestreich (left) and biological oceanographer John Ryan at the docks near the Monterey Bay Aquarium Research Institute in Moss Landing.

Santiago Mejia/The Chronicle

Studying the sounds of marine animals and their habitats, a field called acoustic ecology, is relatively new on the California coast, and it’s yielding exciting new insights. This growing discipline allows for more accurate detection of when animals are around and how they are communicating.

San Francisco Chronicle data team · Monterey Bay Aquarium Research Institute MARS hydrophone recordings

In recent years, the endangered blue whales’ presence in Monterey Bay has been detected by sound most robustly between August and December. This year, the Monterey Bay scientists have been picking up blue whale signals since July.

“These animals are super flexible (about) when they decide to migrate and feed,” Oestreich said. “They time that migration really in line with what’s happening with the seasonality of the ocean environment that controls the availability of the krill — food that they depend on.”

That flexibility is an example of how blue whales, like other migratory animals, are adapting to climate change, which impacts when and how much food is available, and in turn, can play a role in determining when they leave feeding grounds to reproduce, said Lindsey Peavey Reeves, a scientist with National Marine Sanctuary Foundation who collaborates with Ryan and Oestereich on whale research.

There are three listening sites in the Monterey Bay area — one west of Moss Landing, another one closer to the shore near the Monterey Peninsula, and the third site is farthest out, at roughly 20 miles off the coast.

Since commercial whaling was banned in the 1980s, climate change has been one of the main threats to blue whales, according to the International Union for Conservation of Nature, in part because it can cause a decline in krill, their primary food source, as warmer temperatures and ocean acidification can affect its availability. An estimated 2,000 blue whales summer off the California coast out of about 15,000 worldwide. While still endangered, California’s blue whale population has been recovering in the last decade.

Blue whales spend most of their time below the ocean’s surface and farther offshore than other species, making it harder for researchers to study them by sight — despite the fact that they grow up to 90 feet long and can weigh over 100,000 pounds. But the whales emit low-frequency sounds that can be tracked from hundreds of miles away, which is why scientists say these underwater microphones, called hydrophones, are a groundbreaking way to study them.

“A lot of species are a lot easier to hear or detect acoustically than they are to see,” said Anne Simonis, an acoustic ecologist and affiliate with National Marine Fisheries Service who studies marine mammals on the West Coast, including in the Greater Farallones National Marine Sanctuary near the Bay Area.

Studying when blue whales leave foraging grounds and when they stay provides insight into how the ocean is doing, which is especially important with climate change.

“They’re really an ecosystem indicator in a lot of ways,” said Peavey Reeves. “When we hear blue whales and we can categorize their different vocalizations into links to their behavior, we can glean understanding of the health of the ecosystem or what’s happening in the habitats that they’re in.”

The sound data on blue whales in Monterey Bay was collected from a hydrophone on the sea floor connected by a 32-mile cable — one that anyone can tune into live from what the Monterey Bay Aquarium Research Institute calls a Soundcape Listening Room. There are only 12 other such fixed devices on the West Coast, and none of those provide live sound, so Simonis, Peavey Reeves and their colleagues use different tactics to collect data elsewhere in California.

Sanctuary Soundscape Monitoring project scientist Anastasia Kunz (left) and Sanctuary Soundscape Monitoring project lead Lindsey Peavey Reeves gear up before deploying a hydrophone device in a kelp forest during a research trip off the coast of Morro Bay.

Jessica Christian/The Chronicle

In some cases, they drop a hydrophone to the sea floor, attached to weight and a buoy, and leave it for several months to record sounds in a specific area. When they are ready to retrieve it, they use a radio signal that will release the anchor so the instrument bobs to the surface.

Other times, they deploy hydrophones attached to floating buoys for several days to get snapshots of sounds in a larger area.

“We want to learn more about blue whales in particular, because we have stretches of the coastline, such as Greater Farallones, where we don’t have much information at all about these amazing creatures, and they’re in places where we really do need to increase their protection,” said Peavey Reeves.

Blue whales are back near California.

William Oestreich / Monterey Bay Aquarium Research Institute

Deciphering blue whales’ songs and what they’re talking about involves tons of data collection and looking for patterns, the Monterey Bay scientists say.

As scientists listened to a congregation of about 40 whales feeding on a massive concentration of krill in the Monterey Bay in 2017, they noticed something unusual. Rather than just keeping the good eats to themselves, the whales, which are known to be solitary, were bellowing to others, letting them know where the abundant feed was located.

Scientists call these bellows “D” type calls, which, when sped up for human ears. sound like low, repetitive hums or moans. “If we see them making a certain sound in association with a certain behavior, we interpret that it serves a function in that behavior,” Ryan, the Monterey Bay oceanographer, explained.

They, along with other researchers studying these sounds, have connected these loud bellows with foraging behavior. They’re also able to identify the different blue whale songs by examining the sound signals and their patterns.

Blue whale song Video: Monterey Bay Aquarium Research Institute

Listening to the songs of just one blue whale is a powerful experience, but listening to a whole group of dozens of blue whales, who are most often found swimming alone or in pairs, is even more striking, Oestreich and Ryan said.

“That’s a pretty visceral physiological experience to feel and hear such a dense aggregation of calls,” Oestreich said.

But blue whale sounds, at their normal speed, can’t really be heard using average computer speakers unless they’re enhanced, Ryan explained. Labs like the Monterey Bay research institute use subwoofers to listen, and when the blue whales sing, their low frequency rumble shakes the room.

“These are huge aggregations of whales, all feeding on the same swarm of krill in the same location and up to 40 blue whales in a very small area, if you can picture that many large animals all feeding together,” Oestreich said. “It’s kind of mind-boggling that there could be that much food available for that many of the largest animal ever to live,” he added.

There are other animal species that forage together in areas with abundant food, but what’s remarkable about blue whales is that they are calling to their friends tens of miles away to alert them about these bountiful spots, especially as climate change threatens the availability of krill.

Perhaps blue whales aren’t such solitary creatures after all. Because hydrophones have not been widely used by researchers until recently, records don’t go far back enough for scientists to compare how these deep-sea mammals socialized and shared information in a distant past. “We’re increasingly building longer-term records, though,” Oestreich added.

“The jury is still out on how flexible they can be if we continue to see climate-driven changes to ecosystems,” he said. “But it does appear that they’re more flexible than we once believed to be for quite a while.”

Tara Duggan and Yoohyun Jung are San Francisco Chronicle staff writers. Email: This email address is being protected from spambots. You need JavaScript enabled to view it., This email address is being protected from spambots. You need JavaScript enabled to view it.