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CX2SA > INFO 17.04.11 17:58l 87 Lines 4146 Bytes #999 (0) @ WW
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Subj: Antarctic Penguin Population Declines with Krill
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Antarctic Penguin Population Declines with Krill
By Jim Lobe
WASHINGTON, Apr 11, 2011 (IPS) - Two species of Antarctic penguins have
declined sharply over the past 30 years as their chief food source has been
devastated by a combination of other predators, over-fishing, and rapidly
melting sea ice caused by global warming, according to a new study released
here Monday by the National Academy of Sciences.
Based on studies of Adelie and chinstrap penguins and the ecosystems that
have sustained them dating back to the 1970s, the report found that dramatic
declines in krill, the shrimp-like creatures that depend on sea ice for
reproduction, are chiefly responsible for the more than 50- percent plunge
in the flightless birds' populations in the South Shetland Islands.
The Adelie penguins, which favour sea-ice habitat during the winter, have
declined at a 2.9 percent rate a year over the last decade, while chinstrap
penguins, which favour open water, have declined by an even greater 4.3
percent annual rate over the same period, according to the study.
Some scientists had predicted that the decline in sea-ice habitat in the
Antarctic caused by warming air and water temperatures would have a more
negative impact on the Adelie penguin populations given their greater
dependence on sea ice as a habitat.
Under that so-called "sea-ice hypothesis", the chinstrap penguins were
expected to increase their population, at least relative to their Adelie
cousins.
But the study found that the abundance - or lack - of krill appears to be
playing a greater role in reducing the two species' populations.
Krill feed on photoplankton that thrive under sea ice. According to other
recent studies, the krill population in the Southern Ocean has declined by
as much as 80 percent since the 1970s.
"For penguins and other species, krill is the linchpin in the food web,"
according to Dr. Wayne Trivelpiece, the lead author and a seabird researcher
with the National Oceanic and Atmospheric Administration's (NOAA) Antarctic
Ecosystem Research Division.
"Regardless of their environmental preferences, we see a connection between
climate change and penguin populations through the loss of habitat for their
main food source," he said. "As warming continues, the loss of krill will
have a profound effect throughout the Antarctic ecosystem."
The Antarctic is among the fastest warming ecosystems on Earth. Mean winter
air temperatures have increased by five to six degrees Centigrade since the
1970s.
The warming has reduced both the extent and duration of winter sea ice on
which photoplankton and thus krill - and ultimately penguins - depend.
"If warming continues, winter sea-ice may disappear from much of this region
and exacerbate krill and penguin declines," according to the study.
The decline in krill, however, is not due to the disappearance of sea-ice
alone, according to the report, which also cited commercial fishing for
krill by specialised trawlers beginning nearly 40 years ago and growing
competition for krill by recovering whale and fur seal populations.
Indeed, populations of both Adelie and chinstrap penguins grew steadily
between the 1930s and the 1970s as a result of the losses sustained by the
two sea mammals hunted by humans.
"Penguins are excellent indicators of changes to the biological and
environmental health of the broader ecosystem because they are easily
accessible while breeding on land, yet they depend entirely on food
resources from the sea," according to Trivelpiece.
"In addition, unlike many other krill-eating top predators in the Antarctic,
such as whales and fur seals, they were not hunted by humans," he said.
"When we see steep declines in populations, as we have been documenting with
both chinstrap and Adelie penguins, we know there's a much larger ecological
problem."
Juveniles in both the Adelie and chinstrap penguins have proved the most
vulnerable to the loss of krill biomass, according to the report.
While in the mid-1970s, about 50 percent of young penguins would survive
their first year, only 10 percent survive now.
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