Wednesday, May 28, 2014

Growth in penguin numbers cold comfort

Adelie penguins number are booming in the chilly western Ross Sea.  

Last updated  24/05/2014


BELLWEATHER: Adelie penguins number are booming in the chilly western Ross Sea.
Penguin numbers in Antarctica are plummeting, but in the western Ross Sea - part of New Zealand's territory - there are more adelie penguins than at any time in the past 30 years. Deidre Mussen explores the reasons - and why we need to care.
Freezing air bursts into the helicopter as Peter McCarthy leans out on its skid to photograph adelie penguins breeding below on Antarctica's Ross Island. "It gets pretty cold," admits a ruddy-checked McCarthy, Antarctica New Zealand's programme support supervisor, who is roped to the chopper for safety.

From the air, the birds appear as regularly spaced black blobs that dot the icy terrain, where they snuggle eggs on rocky nests. Over the course of a week, McCarthy aerially photographs 21 of the 22 adelie penguin breeding colonies in the western Ross Sea area, including along Victoria Land's remote coastline and some offshore islands, such as Ross Island, home to New Zealand's Scott Base.
Back in New Zealand, his shots are later fed into a computer, which has a specialised programme to count the black blobs, although human counters double-check penguin numbers visually.

The just-released final tally for last summer's census is a whopping 1.3 million adelie pairs, or 2.6m breeding birds, the most since the joint Antarctica New Zealand and Landcare Research penguin census project started 30 years ago. 

That includes the Cape Adare colony, home to the largest adelie colony in Antarctica, with 428,516 breeding pairs. "That's a real huge boost, considering continent-wide there are about 4 million breeding pairs," Landcare Research scientist Phil Lyver says.

Yet-to-be-published American research indicates the western Ross Sea has about a third of the world's adelies, based on a census across the entire Antarctic continent. The population has averaged about 855,000 breeding pairs over the past three decades.

Penguin research, says Lyver, isn't all about cute fluffy animals. "We're trying to use the penguins as what we call sort of a bellwether, an indicator species for the ecosystem, and so, to do that, we need to understand well how does the ecosystem or the changes in the ecosystem actually influence the birds here."

Scientists believe changes in penguin numbers can alert the world about Antarctica's health as global warming and fishing affect its icy environment.

New Zealand needs to worry about such changes because Antarctica drives our weather and directly affects our primary production-focused nation, Lyver says.

Fishing in Antarctica is also big business, and has been implicated in changes to penguin numbers elsewhere on the continent.

When New Zealand's adelie census began in the 1980s, population numbers were high in Ross Sea colonies but started declining in the 1990s.

In 2000, the world's largest iceberg, B-15, broke off the Ross Ice Shelf and part of it grounded to the north of Ross Island, near a large adelie colony at Cape Bird, where it stayed for several years.
It had a major impact on penguin breeding because it forced them to travel too far to find food for their chicks, causing breeding success to plummet.

However, population numbers started increasing again once the iceberg floated away.
The penguin story is vastly different on the more northerly Antarctic Peninsula and Scotia Sea, where populations have dramatically reduced during the same period, according to international research.
That has been blamed on a combination of reducing levels of sea ice because of rising temperatures and lower levels of krill, on which the penguins feed. These factors may be driving the surge in penguins in the Ross Sea area, Lyver says.

While sea ice extent and duration have decreased significantly around the peninsula over the past three decades, it covers a much larger area in the Ross Sea and lasts three months longer than 30 years ago. "Sea ice is important in food productions and also as a platform that allows the penguins to rest. It also gives security as the sea is calmer within sea ice areas," he says. It is also vital as a krill creche, where baby krill develop into penguin's favourite food. Studies clearly show krill abundance decreases in direct proportion to sea ice vanishing.

Ultimately, Lyver says, more research is needed to link biological sciences, such as New Zealand's adelie census, with physical studies of factors like sea ice and climate, to truly understand what is going on in the part of Antarctica nearest and dearest to New Zealand.

Scientists working at Cape Bird colony on Ross Island noted that early snowfall and high winds probably had an impact on the birds' breeding last summer, which had a success rate about half that of "normal" years.  Warmer weather means more snow will fall in Antarctica, and that directly affects the adelies' breeding success, he says.

They breed on land in nests made of rocks, unlike emperor penguins, which lay in midwinter then balance their eggs and chicks on their feet to keep them warm. More snow affects adelies' ability to keep their eggs warm. "It chills the embryo and kills the developing chick." Once the weather warms, snow melts and causes more problems for the colony as the freezing water also cools eggs and can wash away eggs and drown chicks.

Ironically, catching toothfish may help penguins because toothfish are the top predator and their decrease means fewer silverfish are eaten, which penguins also enjoy. However, krill fisheries may be impacting on penguin numbers in other parts of Antarctica because they remove an important penguin food.

Lyver warns that booming adelie numbers may be deceptive. "An ecosystem where adelie penguins are going well is not necessarily a healthy one. It's not wise to assume that increases in numbers means that it is healthy. "It's easy to think everyone is Happy Feet down there. OK, adelie penguins are a bellwether, but a bellwether of what?"

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