Going on a diet
Penguins' primary prey reveals drastic changes in climate
Posted November 26, 2008
There’s an old saying: You are what you eat. But the krill-based diet of penguins breeding and living on King George Island off the northern end of the Antarctic Peninsula first tipped scientists off that food could provide an altogether different insight.
“It was the penguins that actually keyed us into to the global change scenario that has become the leading hypothesis about climate change in the peninsula region,” explained Wayne Trivelpiece, a scientist with the National Oceanic and Atmospheric Administration (NOAA) National Marine Fisheries Service whose research also receives support from the National Science Foundation (NSF).
Trivelpiece, along with his wife and co-principal investigator, Susan Trivelpiece, has compiled more than 30 years of continuous data on the three types of penguins at King George Island — Adélies, chinstraps and gentoos. During that time, atmospheric temperatures in the peninsula region have risen faster than anywhere on the planet, particularly in the winter, where the average has increased by 5 degrees Celsius.
“Studying all three [penguins] at once has given us some real insights into just what happens when we come across some major changes in environmental features and climate, which has certainly happened there,” Wayne Trivelpiece said.
Krill are shrimplike crustaceans that penguins, seals and other marine denizens feed on. Krill rely on sea ice in the winter as a habitat, grazing on algae that form underneath the ice. But the increasing temperatures have made the formation of sea ice, once predictable and reliable, uncertain from year to year, according to Wayne Trivelpiece.
That’s directly affected the abundance of krill and the survival rates of penguins.
In the 1970s and early 1980s, Trivelpiece explained, the researchers would find krill of many different sizes and age-classes (from juveniles to old adults) as they examined the contents of the penguins’ stomachs. But into the 1980s and ’90s, bird biologists were fascinated by what they no longer saw — variety.
The diets were now dominated by one age-class or size of krill each season, Trivelpiece explained. One year juveniles would dominate, and then each succeeding year the prey were a little bigger. The cycle would restart every four to six years.
“As we looked at this over time, there were very logical and predictable features to the size and age classes of the krill in the diets,” he explained. “The major thing that correlated with the krill size changes was having ice in wintertime or not having ice in wintertime.”
Krill were only being replenished every few years, in concert with winters that had heavy pack ice in the Antarctic Peninsula region, meaning lean sources of food for many marine predators in the intervening seasons. The Adélie and chinstrap populations, in particular, crashed by the late 1980s and early 1990s, according to Trivelpiece.
The Adélie population dropped by 50 percent at King George Island by 1990. Young penguins were no longer returning to the colony to breed as they had in previous years. The early years of the study found 40 to 60 percent survived to return to their breeding colonies; less than 10 percent survive today.
A krill survey in the Antarctic Peninsula region in 2000 estimated the krill population itself has dropped off by as much as 80 percent since the last survey in the early 1980s in the region.
“We had a vast change in the probability that young penguins fledgling off our beaches would be seen again in the colony two to five years later as breeders,” Trivelpiece said. “They were basically starving to death in much greater degree than ever before. That trend has continued to today.”
Unique collaboration of agencies
Wayne Trivelpiece began working on King George Island in 1976 for his PhD in zoology out of a tent camp that first season. Poland established a research station in Trivelpiece’s study area along Admiralty Bay in 1977, and until 1985, he and later Susan worked at the Henryk Arctowski Station as guests and visiting scientists of the Polish.
In 1985, NSF established a new camp (named Copacabana, or Copa) a few kilometers from Arctowski to continue the long-term study of the three Pygoscelis penguins. In 1997, NOAA incorporated the project into its Antarctic Marine Living Resources (AMLR) program established by the AMLR Convention Act of 1984, with the goal of managing the Southern Ocean resources through an ecosystem approach. Since that time, NSF and NOAA have been partners in supporting the research at Copa.
The United States passed the AMLR Act in response to an international treaty, the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR), established in 1982 over the concerns of krill commercial fishing. The treaty between 25 nations seeks to manage Antarctic fisheries to preserve species diversity and stabilize the entire Antarctic marine ecosystem.
About 10 years ago, NOAA invited Wayne Trivelpiece to supervise the seabird research at Copa and at the newly constructed NOAA camp on Livingston Island called Cape Shirreff. NSF and NOAA collaborate on supporting the camps, with the former opening the two facilities in October and November with its research vessel the ARSV Laurence M. Gould. NOAA’s RV Yuzhmorgeologiya, a Russian vessel, and staff then shutter the camps for the winter in March.
“The two agencies recognized the scientific and applied values of the long-term study and that it was unique in that respect. It appealed to both of them,” Wayne Trivelpiece says of the agreement. “We couldn’t do our program at all without NSF’s help. We couldn’t get anyone in to our field camps early in the year because we don’t have our own ship until January. I think this is a really great marriage for both of the agencies.”
More signs of climate change
For many years, however, the Trivelpieces were NSF grantees. Much has changed in the last four decades, and there are more visible signs of climate change in the Antarctic Peninsula region than what scientists are finding in the bellies of penguins.
The researchers spend many of their days hiking to penguin colonies and skua nests. Two big chinstrap colonies about 15 kilometers away used to require crossing a pair of glaciers. Two large lakes now sit in front of the glaciers.
“Those glaciers have receded so much that one has become quite dangerous to cross,” noted Susan Trivelpiece, who arrives on the island each year in October. “NSF has given us canoes to transit in front. That’s worked out well.”
Wayne Trivelpiece said the melting glaciers should be physical proof to many climate skeptics that the world is warming on a grand scale. “We are now canoeing across these mile-wide lakes where 80-foot glacier cliffs used to stand,” he said.
A better strategy for survival
It’s not all bad news on King George Island. While the Adélies and chinstrap penguins struggle for survival, the gentoos, recognized by the wide white stripe extending like a bonnet across the top of its head, are thriving. Other researchers in the region, including Bill Fraser and Ron Naveen, have identified similar trends.
Wayne Trivelpiece said the gentoos, larger than the Adélies and chinstraps, enjoy a more varied diet, relying less on krill than its smaller cousins do.
“These animals have done well,” he said. “They’ve hung in there, and seemingly increasing in numbers now, taking up some of the slack, if you will, of the Adélies and chinstraps.”
Diet alone doesn’t explain the gentoos’ success. They’re also the only species that doesn’t migrate in the winter to distant oceanic or pack ice habitats. Instead, as homebodies, they remain in the same hunting grounds but in much smaller colonies, usually with only a few hundred birds. Adélies and chinstraps can congregate in the hundreds of thousands.
The birds also mature differently, with Adélie and chinstrap chicks expected to forage on their own at about seven weeks of age. In contrast, gentoo adults support their young for up to 12 weeks, including the final couple of weeks when chicks go to sea where they can feed with adults.
“This may allow young gentoos to learn a little bit about what’s going on out there, and still be sustained by being fed at night at their colonies,” Trivelpiece said.
Keeping krill in stock
The data on the penguins are important for managing commercial krill fisheries, one of the primary goals of CCAMLR and AMLR. At this point, Wayne Trivelpiece said, climate change is the primary cause in the decline of krill due to the reduction of sea ice.
A June 2008 article by news agency Reuters said the annual commercial krill catch is only about 100,000 tons, well within what CCAMLR considers sustainable. That’s down significantly from the 1980s peak of 500,000 to 600,000 tons when the former Soviet Union fished the waters, according to Trivelpiece.
But there are signs the fishery could see more intense activity in the next few years. Krilloil is rich in omega-3 fatty acids, a popular dietary supplement found in not only pills but also milk and other foods. Fisheries also harvest the small crustaceans for special enzymes that can be used by surgeons to clean wounds, according to Reuters, while the pinkish remains after processing can be used as meal for salmon fish farms.
“The potential of the krill story is that the competition for protein of whatever form is becoming more and more acute,” Denzil Miller, Executive Secretary of CCAMLR, based in Hobart in southern Australia, told Reuters.
“I think in the next two to three years we are going to see a lot of changes in the way governments and the international community addresses problems of expectation around food security,” he added.
In addition, a Norwegian company has created a new way to harvest and process krill continuously, Reuters reported. Previously, it was hard to catch and then later process large amounts of krill because the enzymes inside them break down quickly, spoiling much of the catch.
CCAMLR currently has a 4 million-ton catch limit for Scotia Sea. Trivelpiece said one of the key pieces of conservation CCAMLR is working on is to divide that up into smaller management areas based on the four main island groups in the region. That will help ensure that the entire quota is not taken within the area adjacent to the islands where the penguins and seals would compete with humans for the krill.
“The fishery can’t concentrate their fishing in all in one area, where everybody believes if they were to do that it would adversely affect the predators,” he explained. “We’re trying to get all of this in place now, while the krill fishery is what all of us consider pretty modest.”
NSF-funded research in this story: Wayne and Susan Trivelpiece, have been funded for more than 30 years by NSF (Award No. 0443751), and by the Antarctic Ecosystem Research Division of NOAA’s National Marine Fisheries Service.
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