A big breath
Study tackles emperor penguin diving physiology, population dynamics and even leopard seals
Posted February 10, 2012
Leopard seals are sort of the Great White Sharks of the Southern Ocean — viciously effective and elusive predators that are notoriously difficult to study. Never mind all the sharp teeth.
Two years ago, Dr. Paul Ponganis and his research team moved their main base of operations from near McMurdo Station to Cape Washington, 300 kilometers away, where an emperor penguin colony goes to breed every Antarctic summer. They had hoped that during their ongoing research into emperor penguin physiology that one of the handful of leopard seals that prowl around the colony might be used for behavioral research.
But they never got close.
“They are a poorly studied animal. Not many people get access to them,” Ponganis said. “I knew it was going to take a lucky year at Cape Washington to do this leopard seal study.”
An anesthesiologist and marine biologist, Ponganis has studied Antarctica’s largest penguin species for more than 20 years, research first pioneered in the 1960s by his colleague at the University of California-San Diego’s Scripps Institution of Oceanography, Jerry Kooyman .
The researchers are particularly interested in the penguins for their innate diving abilities. Over the years, the scientists have collected plenty of data on how fast the emperors can swim, the number of strokes they take on a dive, and just about any other tangible detail imaginable.
They’ve learned the birds are regularly capable of going down to depths of 500 meters for five to 12 minutes at a time. They’ve been able to calculate the air volume in the birds’ lungs while they are diving. The deeper the birds go, the bigger the gulp of breath in their lungs. The oxygen from the lungs is then carried through the bloodstream to the animal’s muscles.
The latest question has to do with the deepest dives, which presumably require more oxygen to be extracted from the lungs and circulated through the body. In theory, that should require the heart to pick up the beat.
“Is the pattern during the deep dives different?” Ponganis said. “Is the overall heart rate for a deep dive of equivalent duration to a shallow dive lower, the same or higher?”
Much of the team’s previous research into emperor penguin diving physiology has taken place on the sea ice that covers McMurdo Sound through the early part of the Antarctic summer. Dubbed Penguin Ranch, the study site is located over an area where the water column is only about 100 meters deep.
The move to Cape Washington allowed the scientists to study swimming behavior five times as deep. For the last two years, working from a field camp on the coast of Victoria Land, they outfitted the birds with electrocardiogram recorders to monitor their heart rates as they plunged to great depths in search of food.
Ponganis and his team know from their work at Penguin Ranch that the birds hyperventilate before a dive, revving their heart rate as high as 220 beats per minute, before it slows down to about 60 beats.
“They’re really oxygenating themselves, storing things up to get ready for this dive. They’re really fired up. When they dive, it plunges back down,” he explained.
The heart rate on shallow dives can slow markedly, as time drags on. After 10 minutes or more, the heart drums out a beat 20 times a minute. On one dive, an emperor stayed under water for a record 27 minutes, possibly trapped from reaching the surface because a hole in the ice had closed or a leopard seal was prowling about.
“I wish we had a heart rate monitor on that one,” Ponganis said, estimating a heart rate of five beats a minute. “This animal is just eking things out. That’s an extreme situation, but they are capable of doing that.”
So, what does all this have to do with leopard seals? While a major focus of the study is on diving physiology, the scientists are also interested in colony population dynamics. The group monitors the seven emperor penguin colonies around the Ross Sea.
In the case of Cape Washington, home to between 15,000 and 20,000 breeding pairs, the researchers wondered if the leopard seals affect the Cape Washington colony through predation.
The plan had been to locate a seal, sedate it, and put a digital backpack camera on the animal capable of taking up to 10,000 images. A radio transmitter on the instrument package would help the scientists relocate the animal and recover the camera.
No one even knows how many penguins a leopard seal typically consumes in a day, Ponganis noted. “If we take one picture a minute, we would get every capture,” he said.
Ponganis said it is highly unlikely that the leopard seals alone could threaten a colony, but it is one of many factors that must be understood if scientists are to properly assess how the emperor penguins will respond to a changing climate.
The physiology work is also part of that assessment, he explained. Are the emperors already pushing the limits? If so, how would changes to the environment affect them? Some scientists believe the emperors are already being affected, calling for their protection.
But studying penguins isn’t just about helping save one species. Medical science can also learn a thing or two from the diving physiology of animals like the deep-diving emperor or some mammals like seals.
“The big thing in both emperors and seals is that they can tolerate levels of oxygen that are so low, and levels of blood flow that are so low, we would have serious tissue damages, strokes, all sorts of problems,” Ponganis explained.
In stroke victims, for example, a lot of tissue damage actually occurs when blood flow returns to an organ that had its supply temporarily cut off. Such oxidative stress can produce free radicals — sort of rogue molecules — that can damage cells. In recent years, there has been a big push in medical science to treat such conditions with antioxidants, molecules capable of “scavenging” free radicals.
Studies of emperors at Penguin Ranch and other research on seals have found that the animals have elevated antioxidant levels, particularly of a molecule known as glutathione, which is also important in recycling other antioxidants, according to Ponganis.
“Essentially, they have this system that as oxygen free radicals form, they can scavenge them and break them down and prevent any of the deleterious effects of any of these oxygen free radicals,” Ponganis explained.
“Research on penguins and marine mammals can provide insight into the processes that are going on in human patients, and eventually lead, even if it’s tangential, into some improved therapies,” he added.
NSF-funded research in this story: Paul Ponganis, University of California-San Diego’s Scripps Institution of Oceanography, Award No. 0944220 .