Recruiting the newest member of an Antarctic scientific expedition requires a unique touch. Ji-Yeon Cheon, a behavioral ecologist, had to approach her candidate with extreme caution, circling discreetly from the rear.
With slow, deliberate side-steps across the frozen sea ice, Ms. Cheon carefully avoided direct eye contact. Once in range, she raised a five-foot blowpipe and precisely delivered a sedative dart into the blubbery, speckled-gray flank of her target: a Weddell seal.
Over recent weeks, Ms. Cheon and her colleague, Hyunjae Chung, both doctoral candidates specializing in animal behavior from Seoul National University, have been meticulously tagging Weddell seals near Antarctica’s colossal Thwaites Glacier. These remarkable marine mammals will now carry small, head-mounted devices that record their underwater movements and the ocean’s characteristics. This crucial data will then be beamed via satellite whenever the seals surface, offering an unprecedented look into the sub-glacial environment.
The duo’s primary goal is to decipher how the rapidly warming ocean is influencing the seals’ diving and foraging patterns. Intriguingly, the same warm currents that erode the underside of Thwaites Glacier also churn up iron and other vital nutrients from the seabed, fueling a thriving ecosystem of fish and other marine life that these seals rely on for food. Scientists suspect similar ecological shifts might be occurring beneath the myriad of melting icebergs surrounding the glacier.
“The Amundsen Sea, particularly around the Thwaites Glacier, is experiencing swift environmental transformations,” noted Ms. Cheon. While Weddell seals aren’t currently classified as endangered, understanding their adaptation to these evolving conditions now and in the future is paramount for scientific research.
On the icy expanses of Antarctica, seals enjoy a relative freedom from predators, making them largely unafraid of human visitors, even those armed with blowpipes. However, this seemingly tranquil setting doesn’t diminish the inherent risks involved in the tagging process, for both the researchers and the seals.
The process begins with a careful aerial approach. As the helicopter carrying Ms. Cheon and Mr. Chung nears, the pilot skillfully uses its sound and motion to gently guide the target seal away from the ice floe’s edge, preventing an immediate retreat to safety. After landing, Mr. Chung performs a distracting sway, drawing the seal’s attention while Ms. Cheon stealthily advances from the opposite side.
A six-centimeter (2.4-inch) needle is then delivered, either via blowpipe or, for calmer individuals, directly by hand with a syringe. The seal might react with a flick of its tail, a gaping jaw, or a quick roll. Immediately afterward, Ms. Cheon and Mr. Chung retreat swiftly, maintaining a safe distance.
From a secure vantage point, the researchers patiently observe as the sedative takes effect, usually within 10 minutes or more. Once the seal is still, they gently place a tapered cloth bag over its head – snug enough to block its vision, yet open at both ends for clear breathing – to encourage deeper slumber. With the seal fully sedated, the team then carefully super-glues a small tracking device onto its head.
These compact devices, weighing around 600 grams (1.3 pounds) and roughly the size of three stacked smartphones, complete with a small antenna, appear to cause no discomfort to the seals. They will remain securely attached to the animals’ fur until the natural molting process next summer.
However, the act of tagging isn’t without its emotional toll on the scientists. Ms. Cheon admits that seeing a seal gaze up at her with large, ‘puppy-dog eyes’ during the injection often fills her with a profound desire to apologize.
Both Ms. Cheon and Mr. Chung concur that discussing the intricate and emotionally challenging nature of their work with friends back home is not a simple task.
The data gathered by these biological oceanographers extends beyond ecological interest; it provides an unparalleled window into Antarctic ocean physics, particularly during the harsh winter months when dense sea ice makes traditional ship-based research impossible.
Weddell seals, with their astonishing ability to dive up to 1,000 meters (two-thirds of a mile), can collect measurements at depths that would require human researchers to spend significant time and effort deploying and retrieving specialized instruments.
In the last decade, the sheer volume of data transmitted by seals about the Thwaites region has been “absolutely mind-boggling,” according to Lars Boehme, an animal-borne technology specialist at the University of St. Andrews in Scotland.
Dr. Boehme observed that seal-collected data has evolved from being a “laughingstock” in oceanography to such a ubiquitous and trusted resource that scientists now often use it without explicit mention in their publications. “I love that,” he remarked, emphasizing its value: “It’s good data, necessary data, that really helps you to understand the ocean and the climate.”
Following strict protocols, the Korea Polar Research Institute, spearheading this expedition, ensures the safety of both its human and animal participants. This includes rules against tagging pups, nursing mothers, or any seals deemed too large for the recovery bag. After sedation, researchers meticulously monitor the seal’s recovery for a minimum of 40 minutes, a critical period to prevent accidental drowning should the animal re-enter the water too soon.
Despite these careful measures, the tagging process isn’t always smooth. On occasion, seals have proven too aggressive, or the sedative less potent than expected, prompting Ms. Cheon and Mr. Chung to withdraw. A recent excursion saw their field guide, Seokju Woo, sustain a bite to the arm from a seal, resulting in a bruise, scratches, and a torn jacket sleeve, even with the recovery bag already in place.
In light of such incidents, the Korean institute promptly updated its safety protocols. Now, only highly experienced scientists are authorized to participate in the bagging and tagging procedure, and only once absolute certainty of sufficient tranquilization is established.
Ms. Cheon also suggested practical improvements, such as providing scientists with protective Kevlar sleeves and designing the recovery bag with a rigid handle, allowing for safer deployment from a greater distance, similar to a dogcatcher’s net.
For Yixi Zheng, a postdoctoral oceanography researcher at the British Antarctic Survey, the tagging experience, despite its risks, stress, and inherent feeling of intrusion, offers an unparalleled connection.
Working in the harsh Antarctic outdoors rarely affords scientists the chance to encounter anything warm or soft, a stark contrast to the abundant warmth and softness of the seals. Dr. Zheng explained that this close proximity ignites a profound sense of mammalian kinship, a feeling often missing in the vast, desolate icy landscape.
“They have fingers, they have hands,” Dr. Zheng mused, adding, “So when you touch them, it’s like, ‘Wow, we are similar.’”