When ships are nearby, sperm whales change their calls

For sperm whales to live well, they must be heard. Whether diving to forage or chatting at the surface, or supporting each other through childbirth, they communicate through energetic, rhythmical sequences of clicks called codas. Scientists working to decode these enigmatic phrases have discovered that some even function like our vowels, with linguistic structures that closely mirror our own.  

But the ocean is no longer a quiet place for whales. The latest research to come from Project CETI, a multidisciplinary initiative aiming to translate sperm whale communication, suggests shipping noise is changing the messages sperm whales are sending and may even be altering the way they are received.  

“There were some really discrete features we could see in whale voices when ships are present,” says David Gruber, founder and CEO of Project CETI and a National Geographic Explorer, who co-authored the new study.  

Gruber says what these vocal changes mean is still unknown: “Are they talking about the boats, or is this more of an impact of the ship noise that they're changing their communication?” he says.  

By analyzing over a thousand sperm whale codas in the eastern Caribbean, the researchers found that when ship noise is present, the whales both shorten and switch the codas they use. In the presence of ships, the researchers also had a harder time deciphering the codas, leading them to theorize whales might struggle to hear each other too.  

“Imagine if I say something in a loud factory. You're going to know that I said something, but you're not going to know what exactly I said”, says Gašper Beguš, linguistics lead at CETI and an associate professor of linguistics at the University of California, Berkeley. 

The study is more evidence of the negative impacts of noise pollution for marine life, particularly marine mammals. One of CETI’s motivations for decoding sperm whale communication is to promote conservation efforts. They hope this new data could support efforts to regulate noise pollution in the ocean.  

“I think it really opens up a whole new chapter for protection,” says Beguš. 

A noisy sea 

Ocean soundscapes are filled with rumbling geological movements, creaking icebergs, and the clicks and calls of marine life. But in the past century, people have introduced noisy activities such as underwater drilling and seismic surveys. According to one study published in 2022, underwater noise from ships in particular had doubled in the 11 years prior. Earlier estimates suggest that global shipping has increased low-frequency noise by at least 32-fold across major shipping routes since the 1950s. 

All that human noise pollution has been shown to interfere with the communication systems of the group of marine mammals known as cetaceans, which includes whales and dolphins. Research has shown several species speak louder in noisy water, including orcas and humpback whales. Bottlenose dolphins have been found to whistle longer amid noise, and still face difficulty coordinating their behavior.  

To investigate the impact on sperm whale communication, researchers in the new study analyzed nearly 1,400 codas recorded with acoustic tags on 15 whales off the Caribbean island of Dominica. To identify the specific codas produced when ships were present, they studied both the recordings themselves and location data from an online database of vessel reports.  

Then they ran statistical modelling and machine-learning analyses to find out whether there were any variations in the codas, and if they could detect the presence of a ship based on these variations alone.  

How codas change when ships are around 

CETI scientists have identified two vowel-like codas in sperm whale communication, longer a-codas that resemble our a’s, and shorter i-codas analogous to ours. In their analysis, published July 22 in Ecological Informatics, the team found that in the presence of shipping noise, the whales were more likely to use a-codas. The authors suggest this pattern indicates a structural change in the way the whales are communicating in the presence of ships.  

“If they change their vowels when ships are around, maybe there's the first glimpse of meaning in those vowels,” says Beguš.  

This shift in acoustic behavior could also indicate increased resilience to vessel noise, says Michelle Fournet, an acoustic ecologist at the University of New Hampshire not involved in the study, as sperm whales have evolved in soundscapes with extreme properties, like earthquakes. Yet the speed of change is key, she adds.  

“Anthropogenic noise has emerged in the ocean on human timescales, not evolutionary timescales,” says Fournet. “So the question this study begs is: ‘Do the changes help the whale?’ Knowing that is the key to interpreting the results.” 

In addition to changing which vowels they used, the whales also shortened their codas amid shipping noise, the study found. In dolphins, researchers have observed shortened calls and some speculate this cadence is a way to ‘squeeze in’ communication into quiet periods. Whether this is also true for sperm whales is unclear. CETI has found that i-codas are shorter than a-codas, but the latter were more likely to be heard when ships were around, adding more complexity to the whales’ response.  

Clicks within a-codas and i-codas also tend to have distinct acoustic properties, which helps scientists—and potentially the whales, the CETI researchers think—distinguish between them. Most a-coda clicks are heard in a-codas, and most i-coda clicks are heard in i-codas.  

Yet when shipping noise was present, more codas appeared to have ‘mismatched’ clicks from the other type—indicating the ship noise may be distorting the sound of the original coda. In effect, this made it more difficult for the researchers to identify which coda the whales were emitting even at distances of just a few meters.  

“This is the best evidence suggesting that when a whale receives this in noise, it's probably also more difficult for the whale to distinguish what the other is saying,” says Beguš.  

Toward a quieter ocean  

For sperm whales, family units provide protection from predators and help raising young, so there could be potential knock-on effects of disrupting that, says Susan Parks, a behavioral ecologist at Syracuse University who was not involved in the study.  

“The fact that you can detect a subtle behavioral change, that could just be the tip of the iceberg of a more serious physiological disturbance that's not something we could measure directly externally,” she adds.  

The research shows that sperm whales, like other cetaceans, are not exempt from the impacts of our choices, says Fournet. “They join the ranks of whales and dolphins worldwide that humans ask to speak up, hurry up, and change, to accommodate our activities.” 

CETI’s scientists speculate that noise pollution may impact communication early, when juvenile sperm whales are learning these patterns.  

“We know from human babies, if they're growing up in noisy environments, it's more difficult for them to understand what the caregivers are saying—so we know this is learned vocalization,” says Beguš, and whale babies probably also have more trouble.  

The findings could support regulations aimed at limiting ocean noise, the researchers hope. 

“It's a real responsibility that we give them space to evolve, to develop, for their offspring to have a quiet environment so they can learn,” says Beguš. “I think we absolutely need to use this evidence in order to protect them.” 

The researchers also showed their machine-learning algorithm could detect the presence of the ships based on specific markers in the codas themselves, which could one day help to notify ships where whales are.  

“The future is really, how do we not hit them, and how could we manage our noise to allow them to continue to have really rich communal and cultural lives,” says Gruber.