Listening for Whale Sounds 1,000 feet Deep in the Antarctic Ocean

GERLACHE STRAIT, Antarctica—The steel gray sea mirrored the overcast sky as Heidi Ahonen buckled her life jacket over her red waterproof coat. In just a few minutes she would jet out on a small inflatable zodiac boat in search of an underwater recording device she hoped to retrieve from more than 1,000 feet below the water’s surface. She had waited nearly a year for this moment. Thankfully the weather was cooperating, she thought. Too much wind or wave action in the strait could have jeopardized her mission on this mid-January morning.  Still, she said, “I’m nervous,” as she prepared to board the zodiac from the tender pit of the MS Roald Amundsen, an 11-deck hybrid-powered cruise ship named after the Norwegian explorer who became the first person to cross Antarctica and reach the South Pole. “What if the recorder flooded, or its batteries died?” said Ahonen, a research scientist from Finland who specializes in bioacoustics, a scientific field that examines animal behavior by the sounds they make. It had been 10 months since the device was released into the Gerlache Strait, a 120-mile-long waterway in the Southern Ocean—also known as the Antarctic Ocean—that separates a group of islands known as the Palmer Archipelago from the northwest coast of the Antarctic Peninsula. Theoretically, she knew, it should have stayed close to where it was originally sunk along with a 50-pound weight attached to a mooring line near to where the ship now idled, deep enough to avoid getting snagged on icebergs. But it wasn’t out of the question that strong currents could have forced it to drift. What if she couldn’t find it?  It was her first time leading a project in Antarctica and she felt pressure to succeed.  “Relax,” said her partner, Andrew Lowther, a marine mammal ecologist from Australia who’s conducted field research in Antarctica for more than a decade. “We’ll either find it or we won’t.” Uncertainty was a given working in one of the most extreme environments on Earth.  Last year, Ahonen launched a project through the Norwegian Polar Institute based in Tromsø, Norway, where she’s a senior researcher, to monitor the year-round presence of baleen whales in the strait that feed on reddish shrimp-like crustaceans called krill. There are 15 species of baleen whales, including the humpback, fin and the Antarctic minke whale that use comb-like plates of baleen instead of teeth to filter tiny prey out of the water. Some can eat more than 3,000 pounds of krill in a day.

Little information exists about the marine mammals that traverse this remote channel, which is a known hotspot for krill fishing, a legal and growing industry that has sparked global debate as it continues to supply an international demand for products made from the zooplankton including pet food and fish feed for farm-raised salmon, as well as Omega-3 supplements made of krill oil, sometimes referred to as “red gold.” “We don’t know anything about the year-round presence of species in this area,” Ahonen said with a Finnish accent, a braid of her multicolored burgundy and blonde hair draped over her shoulder.  The main international body charged with protecting marine life and managing fisheries in the Southern Ocean, known as CCAMLR (the Commission for the Conservation of Antarctic Marine Living Resources), doesn’t monitor whales. Ahonen partnered with HX Expeditions to carry out her research. The global cruise line, also known as HX, has headquarters in London and owns the MS Roald Amundsen. It offers guest scientists free cabin space and logistical support on their voyages to the southernmost continent—something Ahonen said was nearly impossible to find elsewhere when funding for national research vessels was being slashed.  “There is no Norwegian research vessel that would come here,” she said. 

She wanted to know if whales were overlapping with krill fishing vessels in the area, especially during winter in Antarctica, which runs from April to October, when there was hardly any other human presence.  “If they are not there when the fishery is there, that’s not a big problem,” she said. “But if they are there at exactly the same time, then there could be a competition.”  Last month, about 400 miles northeast of the Antarctic Peninsula, scientists and crew aboard a Sea Shepherd vessel campaigning against the krill fishing industry in the Southern Ocean documented eight fishing vessels trawling for krill amidst a group of humpbacks foraging for their prey in the South Orkney Islands. The next day, one humpback allegedly died after getting caught in one of the fishing vessel’s nets, according to the international marine conservation nonprofit. Ahonen hoped she might gain insights into the kinds of interactions happening between the animals and fishing vessels in the Gerlache Strait—if she could find the recorder.

Competing for Krill 

There’s an estimated 62 million tons of krill in the area where the fishery operates near the Antarctic Peninsula. Only around one percent of this biomass—620,000 tons—can be legally caught in this place, known as “area 48,” according to the Antarctic marine commission. This “trigger limit” was established by the organization in 1991 to try to maintain a sustainable fishery and avoid disrupting the rest of the marine ecosystem. But Lowther, Ahonen’s partner, who is also a research scientist at the Norwegian Polar Institute and has been studying marine predators for nearly 20 years said, “The level of sustainability is questionable.”  It depends on where the krill is caught, he said. If too much krill are taken from an area where predators depend on their presence, there could be negative impacts.  Suffering penguin populations have already been linked to a decline in krill in some areas along the peninsula, mostly due to climate change. Other research suggests pregnancy rates amongst humpback whales may also be connected to changing krill populations. As ocean temperatures rise, much of the sea ice krill depend on for food and shelter, especially as juveniles, is melting, forcing some of the tiny creatures to move south toward colder waters.  The Gerlache Strait, which is known to be an important area for larval krill, is becoming increasingly ice free, for example. 

To avoid depleting krill populations in known foraging areas for penguins and other wildlife, CCAMLR had strict limits for many years on how much krill could be caught in certain fishing zones within area 48. For instance, until last year, a maximum of 155,000 tons of krill could be fished on an annual basis in one of the sub areas known as 48.1. However, at the last annual CCAMLR meeting held in October in Hobart, Australia, representatives from the 26 countries plus the European Union that are part of the organization could not reach a consensus to renew this fishing regulation and let it expire.  Without it, there are no restrictions on where the total catch limit of 620,000 tons of krill can be caught. In theory, they can all be fished in one location.  In response to this change, the Association of Responsible Krill Harvesting Companies (ARK) issued a statement declaring it will explore voluntary options to spread out its total catch. 

“We’re still using monitoring techniques from 1982 to try and solve a 2025 problem.” — Andrew Lowther, Norwegian Polar Institute

But, voluntary measures are not sufficient, said Lowther, who keeps a trimmed salt and pepper beard and mustache and has long brown hair he pulls back into a ponytail most days.  Since 2014, he’s been actively involved in CCAMLR discussions on krill fishing, pushing for the organization to update their fisheries management strategy and environmental monitoring mechanisms to take into account both climate change and whales, which he said they have not done to date. “We’re still using monitoring techniques from 1982 to try and solve a 2025 problem,” he said.“People need to have confidence that the monitoring system in place is capable of detecting changes.” When the commission first established a mechanism to track how fishing and other environmental variables were impacting wildlife in Antarctica in the 1980s, CCAMLR hadn’t considered whales. There were hardly any left. After almost a century of being hunted and harvested commercially for their oil, whales had been nearly driven to extinction.  In recent decades, however, some species like humpbacks have experienced remarkable resurgences since the International Whaling Commission banned commercial hunting of the animals in 1986. Some of these whales travel more than 6,000 miles from their warmer breeding and calving grounds along the west coast of South America or the Great Barrier Reef in Australia to feed on Antarctic krill each year.  Now, as whales re-establish themselves as the largest air-breathing krill predators in the region, Ahonen and Lowther both say it’s essential to monitor their populations and obtain concrete data that can offer a better understanding of how the cetaceans’ renewed presence is affecting the overall ecosystem and if they are competing with the fishing industry for food. 

There are a number of scientists looking into this and asking a series of important questions, said Ahonen: “Is it a real competition, or is there still enough for both of them? You need to understand the consumption rates for the animals, how much the animal needs, and how much krill is available in the area, and how much the fishery takes.” Some, like Lowther, have been helping coordinate visual surveys of the animals from aboard cruise ships like the MS Roald Amundsen to monitor their distribution and abundance during the summer season in Antarctica.  Ahonen had decided to build upon these efforts as part of her project by partnering with Norwegian members of the Association of Responsible Krill Harvesting Companies and embedding several marine mammal observers on their fishing vessels to survey whales in winter.  “I really think it’s important to work with industry because it’s a topic that interests them too. And you get the best perspective when you have everyone on board,” she said.  But sighting whales is limited even in good weather. Whales surface sporadically to breathe, breach or lunge for gulps of krill. In fog, rain, snow or windy weather they can easily be missed.  Ahonen wanted to help fill in part of the information gap by doing something that she said had never been done before in the Gerlache Strait: listen to the whales and record them over long periods of time. 

Recording Polar Soundscapes

As a bioacoustician, Ahonen is intrigued by how much can be learned by studying the diverse sounds wildlife makes.  “I’m fascinated,” she said. “I’ve always been interested in how animals communicate.”  Many cetaceans, which include whales, dolphins and porpoises, produce unique calls, whistles and songs through which they recognize one another, summon their young, attract mates, hunt and navigate.  Their vocally active nature makes them perfect candidates to study through passive acoustic monitoring, a scientific method of observing marine ecosystems over time by using underwater microphones called hydrophones to detect not only animal sounds, but also noise created by human activity. 

“I’ve always been interested in how animals communicate.” — Heidi Ahonen, Norwegian Polar Institute

As part of her previous research, for instance, at the Norwegian Polar Institute, which conducts scientific research and environmental monitoring in the Arctic and Antarctica, Ahonen had investigated the impact of underwater noise from shipping traffic and oil and gas exploration on marine mammals like narwhals in the Fram Strait, a passage in the Arctic Ocean, which runs between Greenland and Svalbard, Norway.  “These guys are my favorites,” she told a group of guests listening to her lecture on bioacoustics aboard the MS Roald Amundsen as she played them an audio clip of the long single-tusked cetaceans’ squeaks and clicks they make to detect their prey using echolocation. Natural phenomena can also be studied using this method to record wind, waves, rain and ice, one of the most dominant noises in polar soundscapes, she said.  Ice sizzles and pops when it melts on land. And in the ocean, sea ice creaks and groans as it expands and contracts. Thunderous booms erupt when icebergs collide. Ahonen reminded the guests that just the day before, some of them might have heard a glacier calving before they saw it. 

They had been visiting Stonington Island in Marguerite Bay. where the first U.S. scientific research station known as East Base was established in 1939, when a sudden roaring sound stopped them in their tracks before they spotted its source—shelves of ice were falling from a massive white glacier with swiss cheese-like pockets that glowed celestial blue. Only a narrow waterway separated the glacier from the guests’ gaze and gasps as they watched the ice hit the sea, sparking the formation of a wave with its force and another crescendoing roar as it surged, crested and broke on the small island’s shoreline.  For Ahonen’s current project, funded by the Antarctic Wildlife Research Fund, she planned to record two years’ worth of underwater sound from three different locations in the Gerlache Strait and another popular krill fishing area called the Bransfield Strait, which lies between the South Shetland Islands and the tip of the Antarctic Peninsula. If it worked, she said, she hoped to demonstrate to CCAMLR that passive acoustic monitoring could be an effective and low-cost way of monitoring whales and other vocalizing marine mammals going forward.  One of her colleagues and project partners from the Institute of Marine Research in Norway had originally deployed the three recorders called SoundTraps from the MS Roald Amundsen in March 2024 and named them Harry, Hermione and Ron after the main characters in the bestselling Harry Potter book series.  Ten months later, Ahonen and Lowther set out to retrieve them from the same ship. In January, they embarked on their journey, along with the rest of the ship’s crew and paying guests, from Ushuaia, Argentina, often referred to as “the end of the world.”  From there, they traveled through the infamous Drake Passage, known for being one of the most treacherous and sea-sickness-inducing ocean crossings. Over the next two weeks, they would sail to the Antarctic Circle, which lies on an invisible latitude line of 66.5 degrees south, and back north along the west coast of the Antarctic Peninsula, stopping at various sites along the way. During this voyage, Ahonen told the guests she would attempt to retrieve the recorders, which she referred to as “underwater ears,” to see if they’d accomplished what she’d hoped.

Searching for Soundtraps

Ten days into their journey, Ahonen pulled on her waterproof pants, thick rubber boots and red wind and rainproof jacket. She felt butterflies in her stomach as she prepared to head out on the zodiac that cloudy mid-January morning. “I don’t like being in the spotlight,” she said, pulling a woolen headband over her ears to protect them from the cold.  Yet, nearly 400 passengers aboard the ship were being invited to watch her.  Lowther used a wrist-mounted GPS navigator to direct the boat captain toward the coordinates where the first of the SoundTraps was supposedly deployed. Harry had intentionally been placed in the southern part of the Gerlache Strait where krill fishing did not typically take place, but was a popular tourism destination. The recordings collected in this location would serve as a sort of a baseline of data that Ahonen could later use to compare how whale behavior and distribution differed in places where the fishery operated and where it did not. They might also track the noise levels made by cruise vessels.  Understanding—and reducing when possible—the impact of cruise ships and the noise they make was a priority for the expedition cruise company, said Morgan.  “Marine noise is a massive issue,” he said. The cruise company had already tried to reduce this impact, as well as their carbon footprint, with the MS Roald Amundsen, the world’s first hybrid battery-powered cruise ship, which it had unveiled in 2019. “We can, in a really sensitive area, just run on batteries and be a silent ship.” In just a few minutes, Lowther signaled for the zodiac to slow down and come to a stop. They should be close, he said. Morgan swiftly let down a transponding hydrophone off the side of the boat into the water. Ahonen then used another communication device called a deck box to transmit a signal through the underwater microphone to locate the acoustic release attached to the SoundTrap. When triggered, this piece of equipment frees the recorder from its anchored hold on the seafloor so it can surface. Several minutes passed in silence, interrupted only by the sounds of a few humpbacks exhaling. “Look! Whale!” shouted Morgan, pointing toward a misty stream of water spouting from one of the animals’ blowholes about 40 feet away.

Closer to the boat, gentoo penguins poked their orange beaks out of the water before diving back under, likely feeding on drifting gelatinous blobs called salp, which Lowther referred to as “penguin fast food.”  Morgan began summoning the SoundTrap to respond, singing “talk to me” to an indistinguishable tune until Ahonen suddenly shouted “found it!” She’d received a message on her deck box that the recorder had been located and triggered its release. “It should be on its way up,” she said.  “Bridge bridge,” the boat driver called to the captain of the cruise ship through his radio. “All guests and crew should look out for a lifejacket orange contraption floating at the surface,” he said. Without delay the captain responded. A guest on deck 10 had spotted it not far from the ship’s tender pit. “Weeeeee!” squealed Ahonen as the zodiac cruised toward the SoundTrap. When they reached it, Morgan swept it out of the water and passed it to the scientist. Ahonen hugged it gleefully. Upon returning to the ship, she hosed Harry off. Surprisingly, even after 10 months underwater the instrument was pretty clean. When she was done, Lowther carried the 15-pound instrument back to their cabin, which they had transformed into a cramped but workable makeshift lab. Ahonen couldn’t wait to open it and see what it had recorded.  There, they laid it on the floor atop a bathroom towel and began disassembling it one screw at a time until Ahonen could get to the memory cards she was after. As she plugged them into her computer on the bed, she chuckled. “I never thought I’d be using a bed to do this.”  She clicked on a sound file from March 2024 recorded just after the initial deployment. Almost instantly, she heard a series of grunts. “That could be a humpback,” she said. The audio was clear. “It’s really good quality,”she said, eyes wide, giddy with excitement.  “Now, we can say it can work 350 meters deep in Antarctica.” 

“Platforms of Opportunity”

Two days later, Ahonen successfully retrieved the second SoundTrap named Hermione, north of where she picked up Harry, and with much more confidence. When she got back to the ship, she and Lowther quickly deployed a refreshed Harry. They had prepared it with new batteries and clean memory cards so that it could take Hermione’s place and continue recording in the same spot for another year. Then they hurried Hermione to the ship’s science center, eager to give guests a chance to get an up-close view and learn how it works. It didn’t take long for a small crowd to gather around the rectangular flame-colored apparatus Ahonen laid on a table. She explained the orange frame they were inspecting served as a flotation device for the cylindrical hydrophone it encapsulated, which had been set to record five minutes of sound at the top of every hour for the last 10 months.  “Each of these units has over 7,000 files of five minutes from every hour. So that will be a fair amount of data to go through,” she said. It could take months before she could analyze them all with the help of colleagues and determine if any of the animal sounds recorded overlapped with those from fishing operations or cruise vessels. Ships like the MS Roald Amundsen provide a unique environment for both scientists and tourists to interact.  “They’re platforms of opportunity,” said Verena Meraldi, HX’s chief scientist, who oversees the scientific research projects the company supports. “Having access to a researcher who can give an answer to all of your questions is amazing. I mean, how many people can have that opportunity to see them work in real time?”  Last year, the company hosted 87 expert researchers from more than 10 institutions and universities. 

Paying guests can also collect data for various “citizen science” projects during each expedition. Some observe cloud coverage and upload their observations to the NASA GLOBE Observer app, which is used to track and better understand global weather events. Others collect samples of phytoplankton, which krill eat, for a project called FjordPhyto, led by the Scripps Institution of Oceanography in San Diego and Universidad Nacional de la Plata in Argentina to investigate how these microscopic plant-like organisms are being affected by glacier melt and climate change in the Southern Ocean.  In 2024, Meraldi said guests contributed more than 30,000 submissions to different citizen science projects.  In January, the science center served as a bustling hub for daily lectures on glaciology, geology, climate change, seabirds, the Antarctic food web and more. Posters of sea birds and illustrations of 18 species of penguins decorated the walls, along with life-size replicas of various marine mammals’ bones and teeth, including a narwhal’s unicorn-like tusk. Some guests got their first glimpse of live krill here using the center’s stereoscopes to magnify the tiny animals. Two other guest scientists on board had caught a few of them using a fine mesh net off the side of a zodiac earlier in the trip and named them Bonnie and Clyde. They were investigating how krill can be monitored from space as part of a joint project being led by the World Wide Fund for Nature, the University of Strathclyde in Scotland and the British Antarctic Survey (BAS).  The krill appeared translucent and reddish in color. Their feathery little legs fluttered about showcasing how they are used to swim and trap their food. Their beady black eyes seemed largely disproportionate to their two-inch bodies.  These zooplankton play a vital role in transferring excess carbon dioxide from the atmosphere to the deep ocean. When they eat phytoplankton, which absorb carbon from the atmosphere through photosynthesis, they absorb this into their bodily tissue. When they shed their exoskeletons or poop, this matter sinks to the deep ocean where the carbon is then stored for up to 100 years.  Without them, the guests learned, none of the animals they’d been marveling at throughout the expedition would be able to survive. Not the Adélie penguins they’d seen nesting at Red Rock Ridge, regurgitating partially digested krill into their fluffy chicks’ gaping beaks. Or the crabeater seals they’d seen lounging on pack ice. Despite their name, the seals eat krill, not crabs. 

One evening, around midnight just as the sun was setting, the scientists studying krill had watched several humpbacks corral their prey by swimming in circles beneath them while blowing air out of their blowholes, trapping the tiny creatures inside a net of their bubbles.  At 2:30 a.m. on the second-to-last morning of the expedition, Ahonen and Lowther readied themselves to attempt to retrieve the third SoundTrap, named Ron, as most guests were asleep.  Lowther wore his “lucky merman” hat. It was darker outside than it had been throughout the whole expedition and he was worried they might not be able to see the recorder when it surfaced. The sun had barely set in more southerly areas we had traveled. Now, the ship was entering the Bransfield Strait at the tip of the northern Antarctic Peninsula.  The seas were choppier, too. It took balance and coordination to step onto the zodiac being tossed by the waves and bumping against the side of the cruise ship’s tender pit.  “Let’s get some good data!” said Morgan, who had joined the first two searches. For this one, Meraldi joined too. 

As we motored out into the dark, Ahonen used her cell phone flashlight to illuminate the deck box and communicate with the SoundTrap’s acoustic release: It was time to come up. In less than a minute, she received confirmation that the recorder had been located.  All eyes began searching for a sign of the instrument floating in the darkness.  Suddenly, Meraldi exclaimed, “I see it!”  There in the distance, about 100 meters from the zodiac, was the orange SoundTrap bobbing in the surge.  As Morgan and Lowther hauled it out of the water onto the boat, Ahonen sighed with relief. “Mission accomplished,” she said. 

Listening to Whales

Later that morning, as the sky brightened and seas calmed, the MS Roald Amundsen made its last stop of the voyage in Whalers Bay, a former Norwegian whaling station located on the shores of Deception Island, an active volcano in the South Shetland Islands off the northwest coast of the Antarctic Peninsula.  Lowther and Ahonen had camped on the island for several months in 2018 monitoring chinstrap penguins, named for the narrow black band of feathers that underlines their beak. Over the years, Lowther said volcanic ash has hidden much of the evidence of the slaughter that took place here during the late 19th and early 20th century, when thousands of whales were killed and brought ashore here to strip them of their blubber used to produce lamp oil. “All through there is a lasagna of silt and whale carcasses,” Lowther said, walking along the shoreline, pointing toward the bay.  Still, some relics of the bloody era are evident.  Several rib bones poke through the ashen sediment. Vertebrae the size of car tires are scattered near dilapidated wooden boats the whalers used to tow the animals to shore. Tall cylindrical vats, now rusted from age and the elements, loom lopsided from where they once stood tall filled with whale oil.  Two days later, as the ship crossed the Drake passage again en route back to Ushuaia, Ahonen played some audio clips she’d pulled from the hydrophones for guests. The significance of being able to hear the recent recordings of the animals that were once nearly eradicated by humans was not lost on those listening.  “These ones here are from April 27th,” Ahonen said, playing sound files from the recorder named Hermione. For several minutes a diverse sequence of otherworldly sounds projected from her computer speakers, from low-frequency burping noises to high frequency trumpets that strongly resembled those of an elephant. “It’s most likely the same individual,” said the scientist. She hoped the haunting, mysterious sounds would prove useful in the next stages of whale conservation in the Southern Ocean. “We’re very, very lucky with the data we’re getting,” she said with a satisfied smile, knowing all three of her SoundTraps, Harry, Hermione and Ron, worked at icy depths in Antarctica.