The Internet of Elephant Seals
Move over, scientists. Intrepid seals and whales are collecting data where humans can't reach.
Image: Michael Fedak
Michael Fedak's favorite animal is the elephant seal, but not for the typical reasons. It's not their expressive faces or huge smiles that draw him in, nor their surprisingly violent territorial battles. For Fedak, it's the mystery of how they survive at sea for months at a time.
"They are a funny creature in a sense," he said. "They do all their foraging way out at sea for long periods of time, and they come to shore just twice a year to breed and to molt."
In the last decade, Fedak has glued satellite tags onto hundreds of southern elephant seals to collect data on ocean conditions like water temperature and salinity as the animals swim. He is part of a wave of marine scientists deploying marine mammals like narwhals, seals, and bowhead whales to map the undersea environment in areas where people can't reach.
Adapting the tag technology to work with animals is no small task, but it's helping biologists glean useful information about their favorite species, while oceanographers fill gaps in their knowledge necessary to predict the effects of climate change.
"These animals are occupying places where oceanographers can't really get to, and they dive a mile below the surface many times per day," said marine ecologist Kristin Laidre of the University of Washington, who has tagged narwhals and bowhead whales in the Arctic. "They are a really great sampling platform for remote ice-covered areas."
A biologist at the University of St. Andrews in Scotland, Fedak tracked the massive elephant seals as they migrated thousands of kilometers to Antarctica to feed in the early 1990s. At the time, he used satellite tags that recorded only the seals' location, speed, and velocity. But then he hit a dead end: while he knew how deep they were diving and in what parts of the ocean, he didn't know anything about the watery environments they preferred. When he asked oceanographers if they could help him out, they told him that they couldn't; the areas the seals preferred were too hard to access to survey, and where they did have data it wasn't detailed enough.
And so Fedak formed an unlikely partnership: he teamed up with an oceanographer "who was very keen to get information on the places the animals went," Fedak told me. "With him we hatched the idea of having the animals carry oceanographic instruments."
Fedak equipped 14 elephant seals with satellite tags—and from February to October, they collected 10,000 profiles over a wide area, dwarfing that of the so-called high-tech equipment
Oceanographers typically collect data in frozen areas by deploying a robotic glider or crushing ice with an icebreaker and dropping down a CTD profiler, which collects salinity, temperature, and depth readings as it's hauled up through the water column. But collecting data on a wide area, especially one covered in ice, requires moving the ship frequently, and there are many places that are unreachable.
Marine mammals, however, make pretty good oceanographic instruments. Elephant seals and narwhals can dive up to 2,000 meters to the seafloor, where they spend around 15 minutes foraging for food before returning to the surface to breathe. This path is almost identical to the Argo float program, a set of more than 3,000 oceanographic floats spread throughout the ice-free ocean. The floats drop to 2,000 meters, and then collect temperature, salinity and pressure data as they rise to the surface, where they transmit the data to a satellite.
"Elephant seals are animate Argo floats, and they go to the places that Argo floats don't get as often," said Fedak. "Our instrument is uniquely pre-adapted to do this kind of thing."
What they aren't pre-adapted to do is collect and transmit data, which is where the satellite tags come in. Fedak's one pound tags, about the size of his fist, collect data on temperature, salinity and depth, which are the "key measurements oceanographers need to understand water masses and predict how they will behave," he said.
However, data collection is limited by the amount of data that can be sent to the Argos satellite system, an international collaboration that collects data from many scientific projects. When the seals surface to breathe, the tag has only three minutes to transmit its data to the satellite before the seal dives back down. To add insult to injury, Argos accepts a maximum of 228 bits in a single message (plus 28 bits to identify the data source), "which by today's standards is nothing," said Fedak. The system accepts only one message every 40 seconds.
"You'd like to be collecting full-resolution depth and salinity and temperature data every second, but you'd never get the data back," he said. Instead, his tags run complex software that selects the 20 "most salient" readings for every six-hour period, favoring the deepest dives, series of rapidly changing conditions, and the minimum and maximum temperatures, among others.
It sends those data as frequently as possible in each six-hour period to make sure the data were received before resetting and collecting new profiles. "The real complexity in the tags is involved in the software," Fedak said.
The tags also have reliable, low-power electronics so that the single lithium battery lasts the 8-10 months needed to fully capture seasonal changes where the seals forage. Their physical casing resists the pressure of the deep sea, which reaches 200 atmospheres at 2,000 meters, and the damage that comes with being attached to an unwieldy elephant seal prone to banging itself on ice or a rock.
When Laidre followed bowhead whales through the Arctic, however, she took a different tack. Unlike elephant seals and narwhals, bowhead whales are too big to catch, so she would "drive up to them really fast and put a tag on them with a long pole, and then drive away," she said.
Instead of collecting oceanographic data, her tags included a fluorometer to track phytoplankton and a depth recorder so she could study the whales' feeding habits. These tags did not transmit to a satellite. A magnesium bolt attaching the tag to the whale corrodes after three or four days, after which time it floats to the surface—and then the scientists hope that it turns up.
"We get 50-70 percent of them back, although sometimes we get them back years later; one of our tags went from Greenland to Scotland," Laidre said. "It's kind of like throwing something that costs a lot of money into the ocean and hoping you find it."
It's a risk that's paid off for Laidre. In a different research project, her fleet of 14 CTD-equipped narwhals spent their winter diving deep in the ice-covered Baffin Bay, which connects the Arctic Ocean to the Atlantic Ocean. The unicorn-like whales collected data from the previously undocumented deep water, and confirmed that the area was warming. "There had been some previously documented warming of Baffin Bay, and we verified that with the narwhal data," she said. "They indicated that, on average, temperatures were about 0.9°C warmer in the deeper depths than had been previously estimated by models."
Fedak has seen his seals' efficiency firsthand. One year on an Antarctic mission, he watched the efforts of a ship, a large autonomous underwater vehicle, and a set of robotic gliders combine to collect only a few hundred CTD profiles. While he was there, he equipped 14 elephant seals with satellite tags—and from February to October, they collected 10,000 profiles over a wide area, dwarfing that of the so-called high-tech equipment.
As the data accumulate, oceanographers can use it to track patterns of warm water to predict the effects of climate change in the Antarctic, such as sea level rise from melting glaciers. "All the glaciologists think they're quite unstable, but no one knows how unstable," said Fedak. "So predicting what they're going to do is very important to understand how low-lying areas like New York City are going to respond in the next decades."
And he's been getting his biology fill too. Elephant seals sleep underwater at about 400 meters, where they drift for about 40 minutes before going up for air. Depth sensors from his tags showed that some of the seals slowly drifted up towards the surface while sleeping, while others slowly descended—an indicator of their health, as fatter, healthier seals are less dense than water and float. Fedak mapped the healthy, fat seals to the oceanographic conditions of areas where they were able to find good food in order to predict where else they might do well.
"It's really disconcerting to imagine these animals floating around sound asleep," he said. "We're learning all of these things from their behavior that suggests physiological capabilities that we don't understand."
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