# Penguin Numbers Plummeting—Whales Partly to Blame?

- Link: https://greenlivingguy.com/2011/05/penguin-numbers-plummeting-whales-partly-to-blame/
- Published: 2011-05-03T19:33:08-04:00
- Author: greenlivingguy

for [National Geographic News](https://web.archive.org/web/20181201122616/https://www.nationalgeographic.com/latest-stories/)
Brian Handwerk

Published April 11, 2011

Penguin populations have plunged by as much as 50 percent during the past three 
decades in the West Antarctic Peninsula and Scotia Sea, scientists report.

The problem appears to be a shortage of [krill](https://web.archive.org/web/20180307065934/https://www.nationalgeographic.com/animals/invertebrates/group/krill/),
the seabirds’ primary fare, caused by rising regional air temperatures and rebounding
populations of hungry whales.

Fisheries biologist [Wayne Z. Trivelpiece](https://www.pewtrusts.org/en/search?topic=Oceans,Land,Environment%20Science&sortBy=date&sortOrder=desc&page=1)
of the National Marine Fisheries Service in La Jolla, California, has been monitoring
colonies of chinstrap and [Adélie penguins](https://web.archive.org/web/20181017083654/https://www.nationalgeographic.com/animals/)
since the mid-1970s.

Because Trivelpiece regularly bands and monitors individual penguins, he’s been 
able to uncover a key factor in the collapse: Far fewer young penguins are surviving
their first winter on their own, because they’re having a hard time finding krill.
Chinstrap penguins gather on the beach at Port Foster on Deception Island, Antarctica.
Photograph by Bob Smith, National Geographic

“It’s gone from about half of the chicks surviving in the 1970s and mid-1980s to
only about one tenth now,” Trivelpiece said.

“And we see from direct measurements of krill that there’s about 80 percent less
out here than there was just 20 years ago. So the probability of young penguins 
finding it often enough to survive during those first months of independence is 
much reduced.”

(See [“Adélie Penguins Extinct in a Decade in Some Areas?”](https://web.archive.org/web/20171101083502/https://news.nationalgeographic.com/news/2007/12/071228-penguins-extinct.html))
Penguins at Risk as

Krill VanishKrill are tiny, shrimplike animals that live in enormous numbers and
represent a large part of the Antarctic food web. Like flocks of herbivores on land,
krill feed on single-celled plants called phytoplankton and are in turn gobbled 
up by many marine predators, including penguins.

The local krill collapse is probably due to a pair of factors, Trivelpiece said.

One is regional air temperatures, which are some 10 degrees Fahrenheit (5 or 6 degrees
Celsius) higher than they were in the 1940s and 1950s. Those temperatures drive 
how much ice forms at the sea surface.

“If the ice no longer forms, phytoplankton [growing on the bottom of] that sea ice
aren’t available to provide a winter food source for the young krill that spawned
the summer before,” Trivelpiece said. “Without that food, the young krill don’t 
survive.”

(Related: [“‘Crazy Green’ Algae Pools Seen in Antarctic Sea.”](https://www.nationalgeographic.com/news/2011/3/110228-antarctica-green-algae-bloom-global-warming-science-environment/))

The second krill killer is actually a conservation success story—rebounding populations
of baleen whales, such as [humpbacks](https://web.archive.org/web/20190109050545/https://www.nationalgeographic.com/animals/mammals/h/humpback-whale/).

“From what information is available, stocks of krill-eating whales are beginning
to return, and their numbers are growing,” Trivelpiece said. (Related: [“Whale Hunting to Continue in Antarctic Sanctuary.”](https://www.nationalgeographic.com/news/2010/6/100625-whaling-whales-ban-iwc-japan-hunting/))

Nineteenth- and 20th-century whale hunts, which severely impacted populations of
the giant marine mammals, appear to have ushered in a penguin heyday.

“We don’t have good data prior to the 1930s, but it appears that at least the 1930s
to the 1970s were a real boom time for penguins, primarily because of the removal
of competition in the form of whales.”

“Population data from that period is largely anecdotal and provided by the rough
counts of British Antarctic workers. But even if you’re counting by the seat of 
your pants, the difference between 100,000 penguins in the 1930s and 500,000 or 
600,000 in the 1970s is enormous.”

Marine ornithologist Steve Emslie also provided valuable evidence of the boom with
his studies of historic penguin colonies. Chemical analyses of old tissue sources,
such as eggshells, found that Adélie penguins actually had been fish-eaters before
whale numbers dropped.

“Only in the last hundred years or so did krill come into their diet, when the whales
were taken out of the system and there was a krill surplus,” Trivelpiece said.

(See [“Penguins Changed Diet Due to Whaling, Study Suggests.”](https://web.archive.org/web/20171101094721/https://news.nationalgeographic.com/news/2007/07/070720-penguins-whales.html))

Can Penguins Survive Without Krill?

With krill now dwindling, the previous shift in penguin behavior begs a question:
Can the birds simply switch back to eating fish?

“From everything we’ve seen over a 30-year period, while krill has declined 80 percent,
we haven’t seen an increase of fish in [penguin] diets,” Trivelpiece said.

“But the fish stocks have also been heavily fished out by Russian trawlers, so we
don’t even know how much of that prey is available to them at this point.”

The penguin-decline study appears in this week’s issue of the [Proceedings of the National Academy of Sciences](https://www.pnas.org/).

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