Cold enough for you?
Scientists study how Weddell seals regulate heat in the Antarctic
Posted February 1, 2013
Biologist Allyson Hindle hoists the VHF antenna high in the air, listening intently to the radio receiver for the telltale signal that her Weddell seal pup is somewhere close.
A thick blanket of clouds sits low across the sea ice that covers McMurdo Sound. The light is flat. The snowmobile ride out from McMurdo Station to a large black bump of a volcanic island called Big Razorback is difficult in the soupy conditions. The challenge of driving is compounded by the deteriorating conditions of the groomed snow road.
Summer is in full bloom in Antarctica, and that means melting ice, slush and small pools of water forming in the ephemeral ice cover. Hindle and the rest of the research team only have a few days left to locate a half-dozen seals that still carry the expensive instruments the team glued on them about a week ago.
The game of hide-and-seek with the Weddell seals has Jo-Ann Mellish a little anxious. The data loggers strapped to the pinnipeds carry valuable information that can make or break their field season. In this case, the researchers are asking a very fundamental question about the world’s southernmost mammal: Do seals get cold?
“You just sort of assume that if an animal lives in a certain habitat that they’re adapted to it — but nobody has actually looked,” said Mellish, a research associate professor at the University of Alaska Fairbanks who also works as a Steller sea lion scientist at the Alaska SeaLife Center in Seward.
“We need a baseline to understand how they may respond to environmental change, which is clearly going on at both poles,” she added.
Weddell seals (Leptonychotes weddellii) are endemic to the Antarctic, and are named after the British sealing captain James Weddell. The animals are among the super athletes of the Southern Ocean, capable of diving 750 meters or deeper into the frigid polar waters. Forays under water can last more than an hour.
On the surface, however, Weddell seals appear far less graceful, worming their blubber-cast bodies ever so slowly to and from their dive holes in the sea ice. The animals have set up home not far from McMurdo Station. Other researchers have studied the Erebus Bay colony now for more than 40 years, offering a rich dataset on each animal’s life history for Mellish’s team.
“For us, it’s the perfect outdoor lab where we can learn a lot about one species at a go,” explained Mellish, whose work on studying the physiology and ecology of Arctic marine mammals is far more logistically challenging.
And while chasing fast-swimming seals around the open ocean may sound like grand adventure, the accessibility of the Weddell seals is preferable for the kind of experiments designed by Mellish, Hindle and the project’s other co-principal investigator, Markus Horning, an associate professor at Oregon State University.
Horning is what Mellish calls “the gear head” of the scientific triumvirate. He is involved in helping develop the instruments the team uses to capture physiological measurements in data loggers attached to the animals.
“We work with manufacturers with the purpose of developing very specific devices that collect very specific types of data,” Horning said. “It’s not trivial to collect this kind of data. We’re talking about animals that are absent from our ability to directly observe them for most of their lives.”
To answer the question of whether seals get cold — or, in more formal science speak, quantifying the energetic requirements to thermoregulate in and out of the water — Horning came up with special heat flux sensors with Wildlife Computers president and chief engineer Roger Hill, who joined the field team in Antarctica.
The sensors are small discs glued to the seal’s fur with an epoxy. They measure the amount of heat transferred across the animal’s body to the air. Cables from the heat flux sensors plug into the data loggers, cell-phone sized instruments that also collect physical ocean properties like salinity and temperatures, as well as dive behavior such as depth and acceleration.
“We’re able to collect a lot of data about these animals and their thermoregulatory physiology that simply hasn’t been done or hasn’t been able to be done in the past,” noted Hindle, with the University of Colorado in Denver.
Her biggest task will come after this second field season is over: building a computer model from the field data and physiological assessments done for each animal to determine how much energy it expends in the course of a day.
“The cost of being a seal in air is different than the cost of being a seal in water,” Mellish noted. The animals swim in water that hovers just below the freezing point year-round, kept liquid thanks to the high salt content. Of course, water conducts heat away from the body 25 times faster than the air. Summer temperatures can be several degrees above freezing, but wind chill can send the temperature into double digits below zero.
It’s unlikely fat and healthy adult Weddells are much bothered by such conditions, with some sporting the beer-belly equivalent of eight centimeters of blubber. But what about nursing mothers or half-starved juveniles still honing their foraging skills?
“Smaller, leaner animals are going to be at a disadvantage for heat loss,” Hindle explained. “They’re more likely to lose heat to the environment, and therefore they’re going to have to ramp up heat production.”
The three-year grant from the National Science Foundation’s Division of Polar Programs included two summer seasons to collect data from the field. The team’s goal was to study 40 individual animals over that time in four different categories. The specimens ranged from the plumpest adults to haggard mothers who had just given birth and from doe-eyed pups to those skinny juveniles.
Mellish noted that studying the range of physical types among the Weddell seals served two purposes. One was to look specifically at how animals of different sizes and shapes use energy to retain or release heat. In addition, the Weddell seals can serve as proxies, like a stuntman stand-in, for the more elusive pinnipeds in the Arctic. For example, small Weddell pups are about the size of ringed seals, while adults roughly match bearded seals in stature.
“While it’s not exactly comparable, it’s the closest thing we’ve got, and it’s infinitely better than trying to model something based on random numbers,” Mellish said. “We have an enormous amount of variability [between individuals], which is really useful for us, because if you have the animals behave in the same way all the time, there’s no room for flexibility in the face of [climate] change.”
Even with a colony containing hundreds of seals only a half-hour snowmobile away from McMurdo Station, it took the scientists weeks to find the right specimens for each physical type.
“We did a lot of stalking and a lot searching,” Hindle said.
Finding the right animal is just the beginning of about a half-day operation. The team first takes a surface heat profile of the animal using infrared imaging — a snapshot of its hot and cold surface areas. Then a tripod scale with a winch is used to weigh the seal; females can bulk up to about 600 kilograms.
The scientists then set up a temporary shelter where team veterinarian Rachel Berngartt sedates the seal and monitors its health. Hindle and Mellish perform a medical physical, from doing an ultrasound to taking blood samples.
Meanwhile, Horning and other team members epoxy their instruments to the fur of the animal. The heat flux sensors, data loggers, instruments and cables make the Weddells appear a bit like cyborg seals.
The look is only temporary. The biologists will release each animal back to the wild for about a week, before they attempt to recover their data loggers and a blubber sample. After it molts, the seal will lose any sign that it has been involved in a scientific experiment.
A long-range, satellite-linked transmitter on the animal first alerts the team back in McMurdo Station that it has hauled out onto the ice after a week has passed. The satellite ping comes within about two hours when a seal pops back out of the water. Each seal also carries a very high frequency tag, a short-range radio transmitter, which Hindle’s VHF antenna can locate.
It still takes a bit of hunting around to locate the pup in the flat white afternoon on the sea ice this particular day. Eventually, the plump pup is found after a few more minutes of riding around the ice-locked islands where the seals tend to congregate. All four heat flux sensors — on the head, neck, under the flipper and across its flank — have come loose.
“It will be interesting to see how many days of data we have on this guy,” Hindle said with a sigh. Later in the day, the team would locate a feisty female before returning to McMurdo Station.
In the end, Mellish’s anxiety was unfounded: All of the seals were eventually found and the data loggers recovered with about a day to spare. It will still be another year before all the data are crunched and Hindle’s model completed.
Then they may get a detailed answer on that seemingly simple question: Do seals get cold?
“It’s really a ground-truthing program, because nobody really knows what it takes to be a seal in the wild in this sort of environment,” Mellish said. “You can guess, but nobody has directly measured it, so we’re pretty excited about that.”
NSF-funded research in this story: Jo-Ann Mellish, University of Alaska Fairbanks, Award No. 1043779; Markus Horning, Oregon State University, Award No. 1043497. All research was conducted under National Marine Fisheries Permit 15748 and Antarctic Conservation Act 2012-003.
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