Sounds provide new information about the secret lives of sperm whales

Sperm whales are the noisiest animals on Earth, relying on sound to find food in the darkness of the ocean depths. MBARI’s technology allows us to listen and gain new insights into the mysterious lives of these animals.

By examining seven years of acoustic data recorded in the Monterey Bay National Marine Sanctuary, MBARI researchers and collaborators from the Naval Postgraduate School and the University of Washington’s Center for Ecosystem Monitoring discovered that sperm whales are more common off the coast of California than previously thought.

The researchers also found that sperm whales were more frequently seen in the Monterey Bay area during the winter, providing strong evidence of seasonal migration of the species in the northeast Pacific.

They published their findings on September 24 in the journal Movement Ecology.

“Animals provide us with insight into their lives through the songs they make,” said William Estrich, a postdoctoral researcher who led the study. “Collecting acoustic data allows us to observe animal behavior and improves our understanding of enigmatic animals like sperm whales.”

“Our findings provide new insight into sperm whale behaviour and therefore deep-sea seasonality, which may aid in the conservation of these endangered marine mammals and the ecosystems on which they feed.”

The sperm whale (Physeter macrocephalus) can reach lengths of up to 16 metres (52 feet) and weigh up to 41 tonnes (45 tons). Despite its size, the biology of this important predator remains mysterious. Sperm whales dive hundreds or even thousands of metres below the surface to feed on squid and fish.

Similar to how bats echolocate in the night sky, sperm whales emit clicking sounds to locate prey in the dark depths of the ocean. These loud and distinctive clicking sounds give scientists the opportunity to study the whales’ behavior just by listening.

Sperm whale songs contain a wealth of information about what the animals are and what they’re doing. Scientists can determine an individual’s age and sex from the time between successive echolocation clicks. Whale songs also provide clues about the whale’s behavior, such as whether it’s searching for food or has successfully caught food.

MBARI has the unique ability to continuously collect high-quality audio recordings in the deep ocean for long periods of time. The Institute’s cabled observatory, the Monterey Acceleration Research System (MARS), is located on the continental slope just outside Monterey Bay.

MARS enables researchers to test and deploy innovative new technologies for ocean research and provides a platform for monitoring the ocean’s acoustic environment. The observatory’s hydrophones record acoustic data around the clock from the heart of the Monterey Bay National Marine Sanctuary.

“You have to be close by boat to see sperm whales and their distinctive sideways spouts, but underwater, you can hear their unique echolocation sounds from up to 100 miles away,” explained biological oceanographer John Ryan, who leads MBARI’s marine acoustics team and is a co-author of the recent study.

“Sound travels very powerfully underwater, so hearing greatly expands the range of our senses. This range enabled the initial important discovery of the continued presence of rarely seen sperm whales in Monterey Bay National Marine Sanctuary as part of the region’s rich biodiversity.”

MBARI researchers developed an algorithm to detect the distinctive sperm whale calls in vast amounts of acoustic data recorded by deep-sea hydrophones, and acoustic detection revealed that sperm whale calls peak in winter off the coast of California.

This is the opposite of a summer peak in sperm whale songs previously reported by researchers in the Gulf of Alaska.

To understand the behavior underlying seasonal patterns of sperm whale vocalizations, MBARI researchers and their collaborators compared seven years of acoustic detections with state-of-the-art simulations that incorporated data on the well-understood migration strategies of other vertebrate species.

The team determined that the acoustic patterns of sperm whales detected in different regions of the northeast Pacific likely reflect seasonal migration of sperm whales, which were previously thought to be nomadic animals that encounter food opportunistically.

Sperm whale seasonality coincides with the latitude of the North Pacific Transition Zone (NPTZ). The NPTZ forms where cold subpolar waters meet warm subtropical waters, where a wide variety of marine life feeds. The NPTZ changes with the seasons, migrating south in winter and north in summer, reflecting the movements of sperm whales.

The seasonal peaks in sperm whale song are not as intense as those of migratory surface-dwelling animals such as the blue whale (Balaenoptera musculus). Without light and wind, deep-sea processes have historically been thought to remain stationary throughout the year. However, biological connections link the surface and deep oceans.

Organic rain, which nourishes deep-sea animals and ecosystems, changes with the seasonal and annual productivity of the ocean surface and washes down into the ocean depths.

MBARI’s new study of sperm whales provides the strongest evidence yet that this deep-sea apex predator undergoes seasonal migration. The more subtle signal of sperm whale migration reflects an overall weakening of deep-sea seasonality.

“The deep sea is difficult to study, but we know that the animals that live there play an important role in the health of the planet. Whales store carbon in their bodies and transport nutrients deep into the water column, playing a key role in the marine food web and carbon transport.”

“By listening to one of the deep ocean’s largest predators, we can learn about larger patterns in the deep-sea ecosystem,” said senior scientist Kelly Benoit Bird, who leads MBARI’s acoustic marine ecology team and is a co-author of the recent sperm whale study.

These findings may also help policymakers implement measures to protect endangered marine giants and the environments on which they depend.

“To manage human-wildlife interactions, we first need to understand where animals are and what they are doing. This study is an important first step, unlocking the mysteries of these predatory marine creatures and helping us to manage them responsibly,” Estrich said.

Many more opportunities for important discoveries lie hidden within the hundreds of terabytes of continuous audio data that MBARI has recorded since 2015. Through AWS Open Data projects, MBARI is sharing this unique data collection with a global community of researchers, policy makers, educators, and sound artists.