Sperm whales are the loudest animals on Earth and rely on sound to find food in the sprawling darkness of the deep sea. MBARI technology allows us to listen in, gaining new insight into the mysterious lives of these animals.

By reviewing 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 Sentinels have discovered sperm whales are more common offshore of California than previously believed.

The researchers also learned that sperm whales are found in the Monterey Bay area more frequently during the winter, providing strong evidence for seasonal migrations in this species in the Northeast Pacific Ocean.

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

“Animals give us a window into their lives through the sounds that they make,” said Postdoctoral Fellow William Oestreich, who led this research. “Collecting acoustic data allows us to observe animal behavior, deepening our understanding of cryptic animals like sperm whales.

“Our findings provide new insight into sperm whale behavior and, by extension, seasonality in the deep sea, which can help inform protections for this endangered marine mammal and the ecosystems in which it feeds.”

Sperm whales (Physeter macrocephalus) can reach 16 meters (52 feet) in length and weigh up to 41 metric tons (45 tons). Despite their size, the lives of these important predators remain shrouded in mystery. Sperm whales dive hundreds to thousands of meters below the surface to feed on squid and fishes.

Much like bats echolocating in the night sky, sperm whales produce clicks to locate prey in the dark deep ocean. These loud and distinctive clicks give scientists the opportunity to study their behavior just by listening.

Sperm whale vocalizations contain rich information about who these animals are and what they are doing. Scientists can determine the age and sex of individuals from the interval between consecutive echolocation clicks. The sounds the whales make also provide clues about their behavior, like if they are searching for food or have successfully caught a meal.

MBARI has the unique capacity to collect continuous high-quality sound recordings in the deep sea over a long period of time. The institute’s cabled observatory, the Monterey Accelerated Research System (MARS), is located on the continental slope just outside Monterey Bay.

MARS allows researchers to test and deploy innovative new technology for studying the ocean and provides a platform for monitoring the ocean soundscape. A hydrophone, or underwater microphone, on the observatory records around-the-clock acoustic data from the heart of the Monterey Bay National Marine Sanctuary.

“To see a sperm whale or its unique sideways spout, we must be nearby on a boat. But underwater, we can hear the unique sound of a sperm whale’s echolocation from a hundred miles away,” explained biological oceanographer John Ryan, who leads MBARI’s Ocean Soundscape Team and coauthored the recent study.

“Because sound travels so powerfully underwater, listening greatly expands the reach of our senses. This reach enabled our first key discovery—that sperm whales, which are rarely seen in Monterey Bay National Marine Sanctuary, are continuously part of the region’s rich biodiversity.”

MBARI researchers developed an algorithm to detect the distinctive vocalizations of sperm whales in the trove of acoustic data recorded by the deep-sea hydrophone. Acoustic detection revealed that off the California coast, sperm whale vocalizations peak in the winter.

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

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

The team determined that the sperm whale acoustic patterns detected across different regions of the Northeast Pacific likely represent seasonal migratory movements. Previously, sperm whales were believed to be wandering nomads that opportunistically encountered food.

Sperm whale seasonality aligns with the latitude of the North Pacific Transition Zone (NPTZ). The NPTZ forms where cool subpolar waters meet warmer subtropical waters. A wide range of marine life feeds in this zone. The NPTZ shifts seasonally—it is farther south in the winter and farther north in the summer—mirroring sperm whale movements.

The seasonal peaks in sperm whale vocalizations are not as strong as surface-dwelling migratory animals, such as blue whales (Balaenoptera musculus). Without light and wind, deep-sea processes were historically thought to remain static throughout the year. However, biological connections link the surface to the deep.

The rain of organic material that feeds deep-sea animals and ecosystems changes with the seasons and annual blooms of productivity at the surface that trickle down to the depths below.

MBARI’s new research on sperm whales presents the strongest evidence yet that this top deep-sea predator undergoes seasonal migrations. The more subtle signal of sperm whale migrations reflects the overall dampened seasonality of the deep sea.

“The deep sea is challenging to study, yet we know the animals that live there play a vital role in the health of the planet. Whales store carbon in their bodies and transport nutrients deep in the water column, playing important roles in marine food webs and carbon transport.

“By listening to one of the deep ocean’s largest predators, we can learn about bigger patterns in deep-sea ecosystems,” said Senior Scientist Kelly Benoit-Bird, who leads MBARI’s Acoustical Ocean Ecology Team and was a co-author on the recent sperm whale study.

These findings can also help decision-makers implement protections for these endangered ocean giants and the environments they depend on.

“In order to manage human-wildlife interactions, we first need to understand where animals are and what they are doing. This study provides that important first step, unraveling the mysteries of this elusive ocean predator and helping to inform responsible stewardship,” said Oestreich.

Buried in hundreds of terabytes of continuous audio data that MBARI has recorded since 2015 are many more opportunities for important discoveries. MBARI shares this unique collection of data with a global community of researchers, policymakers, educators, and sound artists through its Open Data project on AWS.

To avoid being caught, murderers often attempt to hide bodies using various methods. This can include shallow or deep burials, submersion in water, encasing in concrete or even disposing of remains in rubbish bins and suitcases.

Finding the body is a key part of any murder investigation, as it helps to identify, prosecute and charge the killer. Unfortunately, the task can be immensely difficult.

To help tackle the problem of locating hidden graves, we have trialed two innovative techniques for searching underground: ground-penetrating radar and electrical resistivity tomography, or ERT. Our results are now published in the journal Remote Sensing.

Borrowing tools from geology

The tools we used are known as geophysical methods because they measure the physical properties of materials in the soil under the surface.

The use of geophysical techniques for peering under Earth’s surface is not new—engineers, geologists and archaeologists have used the tools we tested for decades.

But geophysical techniques are not typically used for forensic investigations because directly finding a body with these methods is very difficult.

However, both of the tools we tested can help to locate a grave indirectly—by looking at the differences between the disturbed soil of the grave and the undisturbed soil around it. When the techniques encounter disturbed soil and/or the presence of body fluids, the resulting data will show as an anomaly—something different to the areas surrounding it.

To figure out whether the identified anomaly is a grave, researchers can then consider the size, shape and depth of the anomaly to make sure it correlates with a human body.

Pigs at the ‘body farm’

At the Australian Facility for Taphonomic Experimental Research (AFTER), Australia’s only “body farm”—a facility that uses donated bodies for forensic research—we buried five pigs in various configurations to mimic clandestine graves.

This included two single graves (a “shallow” grave of just half a meter, and a “deep” grave of almost two meters) and a mass grave with three pigs at one meter deep. We used pigs as they are a good body analog in terms of size and mass to humans.

We surveyed the graves with ground-penetrating radar and ERT before and directly after burial, and then one, eight, 14, and 20 months later.

Our findings revealed that geophysical imaging of hidden graves can work, but with varying results. This depended on the size, depth and age of the burial, and the amount of rainfall before the survey.

The grave containing the three pig cadavers was the easiest to observe due to its larger size and volume. This indicates geophysical techniques may be particularly useful in humanitarian investigations that involve searching for mass graves.

A shallow single grave was the next most observable. This is also an encouraging finding because most graves of hidden victims are only around half a meter deep. For both techniques, the two-meter-deep single grave was the most difficult to image.

Although both tools could detect some graves on some occasions, neither located all of the graves during the entire length of our survey. This was likely due to a combination of factors, including the soil type at the site and unprecedented weather conditions during the research period—La Niña flooded the research site multiple times.

We did, however, confirm that pig cadaver graves are good proxies to human donor graves when investigating geophysical techniques for finding them.

To do this, we compared the ground-penetrating radar and the ERT responses of the pig burials to those of human burials (all part of existing research projects at AFTER). We found no obvious differences between the two.

This is a very important result, because it means we can further test these tools in Australia and worldwide without being constrained by highly limited access to human donors.

More work needed

Similar studies have been done in the United Kingdom, the United States and South America. However, ours is the first systematic, multi-technique, geophysical survey of covert graves in an Australian environment. The only other similar Australian study was in 2004, however, it only used ground-penetrating radar and didn’t check back on the graves at multiple time points.

Our results clearly demonstrate that geophysical methods can be effective for locating unmarked graves under some circumstances, but don’t always work. To try and work out why, we will continue our research using the latest geophysical instruments and monitoring the moisture conditions inside the graves.

Ultimately, we believe using these tools can increase the chances of locating missing and murdered victims. Then, we can finally provide answers to their families and loved ones, and increase the chances of prosecuting their killers.

This article is republished from The Conversation under a Creative Commons license. Read the original article.