Scripps scientists using underwater microphones to monitor the ocean ecosystem

There are numerous ways scientists measure the impacts of climate change. Sometimes it’s by what they see, or maybe even by what they smell. In a recent case, it’s by what they hear.

Whale calls. That’s not a sound the average person hears every day. However, for Natalie Posdaljian, a postdoctoral scholar at Scripps Institution of Oceanography at the University of California, San Diego, it’s a sound she’s become familiar with as she studied years’ worth of these sounds collected from 2003 to 2025.

“What’s interesting about this study is this type of time series is very novel, probably one of a kind across the Pacific Ocean, this really long time series,” Posdaljian said.

For 15 years, ocean sounds were collected along the Southern California Bight using a mooring, which included a hydrophone, a glass float, and a data logger. These instruments, which had weights attached to them to keep them below the surface, would sit at specific areas along the seafloor, collecting sounds from whales for one year.

"Once we’re on the vessel, we’re traveling all over the Southern California Bight, so it takes us a couple to complete our route of getting to all of these different sites," Posdaljian said. "Once we get there, we retrieve the instrument that was previously there. Once we send the code, it takes about 30 minutes up to the surface. We secure the instrument and then oftentimes we have the next instrument already ready to go, and we deploy it ideally in the same area, so we keep the long-term time series consistent."

Once the new instrument reaches the seafloor, researchers would head back to land and start analyzing the data from the year prior and repeat the cycle once a year.

"What we were able to do was find changes that were linked in the ocean’s soundscapes, so all the different sounds that were recorded in the ocean, and find these changes both biologically, we looked at fin whales and blue whales, but also anthropogenic shifts based on anthropogenic changes,” Posdaljian said.

Those changes started to paint a picture for scientists and how they were impacting whales, all while analyzing their calls.

"We were able to hear climate change in the sense of the marine heatwave that occurred in 2014 and 2016," Posdaljian said.

A similar pattern was recognized during what’s known as the Pacific Decadal Oscillation, or PDO for short. It’s like a longer version of El Nino that can last for 20-30 years and has warm and cool phases.

"For fin whales, we saw up to a 30% increase when the PDO was in a cool phase versus a warm phase,” Posdaljian said.

It wasn’t just the whales they were tracking, but the sounds from cargo ships, too.

"After the 2008 recession, there was a very steep decrease in the number of ships,” Posdaljian said. “And the number of ships hasn’t exceeded 2008 levels again.”

However, Posdaljian says the whales still compete with the sounds from these ships when communicating.

”Sound is everything to whales in the ocean; that’s how they survive," Posdaljian said.

These sounds give insight into when and where marine animals migrate and live as their surroundings could change.

“We were able to see potential shifts in the ranges of these animals, and that’s important because we’re starting to see animals change where they’re spending their time," Posdaljian said. "And when you think about an animals’ conservation, you understand an animal’s ecology, and you conserve based on that ecology — where they are, when they are, where their migration rates are.”