25 March 2014

Adélie penguin population approaches a 30-year high

ANTARCTICA - The Adélie penguin population in Antarctica's Ross Sea is booming, with numbers looking to be the highest they've been for 30 years.

While exact results of the latest census of won't be available for two months, current trends indicate that there could have been over a million Adélie penguin pairs breeding in the western Ross Sea over this Southern Hemisphere summer.

The population from this area makes up approximately 38% of the entire circum-Antarctic Adélie penguin population.

Research showing Adélie population trends over the past three decades was published this month in the journal PLoS ONE. It is based on the count and ongoing research by Landcare Research scientists Dr Phil Lyver and Dr Mandy Barron, Antarctica New Zealand and Bartonk Solutions.

Dr Lyver said Adélie penguin colonies on Ross Island in the southern Ross Sea are counted every year. In the 1980s and 1990s, the population declined at about 2% per year, dropping to its lowest point in 2001, which coincided with the arrival of giant icebergs that altered the local sea ice and environmental conditions in McMurdo Sound. Since then, penguin numbers have steadily increased at about 6% each year.

There had only been sporadic counts of the colonies along the Victoria Land coast, a remote stretch of mainland Antarctica spanning 1000km. Before this summer's survey, the last full census of Victoria Land was back in 2006.

The summer's aerial survey was the first time the entire Ross Sea census had been conducted by helicopter and was made possible with the support of the Italian Antarctic Programme at Terra Nova Bay, who provided logistical support for the team.

''A large proportion of the birds along the Victoria Land coast forage over the deep continental slope ecosystem and often in quite different sea ice conditions to their counterparts on Ross Island to the south, so it is important to understand what is happening with this part of the population,'' Dr Lyver said.

"In an average year, there are around 850,000 pairs of Adelie penguins breeding in the Ross Sea each year. Having the Victoria Land census means we can assess whether the colonies in the northern sector of the Ross Sea have experienced the same level of growth as those in the south."

"If this has occurred, we could expect to get in excess of a million breeding pairs this season. And, our northern-most colony alone, Cape Adare, could have a quarter of those birds," he said.

Adélie penguins are a recognised indicator species, used by scientists and the Antarctic and Southern Oceans management organisation, Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR), to monitor possible changes in the marine ecosystem caused by perturbations, such as climate change, and also commercial fishing.

The long-term population records provide scientists with an understanding of the natural trends and variation in the Adélie penguin numbers. This gives them a greater ability to detect possible future changes from human-related influences.

The question now for scientists is what is driving the annual variation and increases they are seeing in the colonies. The high level of synchrony and correlation in annual growth rate among colonies suggests a common factor.

Adélie penguins generally do well in areas of intermediate sea ice concentration – around 15% ice coverage is ideal. The birds need ice for resting, but not so much ice that they have only a limited number of cracks close to the colony to forage through, or have to use extra energy walking great distances to get to open water. However, it's the loss of sea ice in some sectors of Antarctica that is concerning scientists.

Predictions indicate that 75% of Adélie penguin colonies (70% of the breeding population) in Antarctic will decrease or disappear by 2050 because of climate warming and the disappearance of sea ice. These declines will occur mostly at the colonies north of 70°S. All the Ross Island colonies observed in this study are south of 70°S.

Already scientists are seeing declines in Adélie penguin numbers in the West Antarctic Peninsula region where warming, loss of sea ice and reductions in the abundance of their primary prey, Antarctic krill, have occurred. The region's chinstrap penguins, a species which tend to avoid heavy sea ice conditions, have also experienced significant declines. This suggests the relationship between sea ice and krill is a major influence on penguin numbers.

In contrast to what is happening in the West Antarctic Peninsula, there has been an observed increase in sea extent of sea ice and duration of the sea ice season in the north-western Ross Sea region over the last three decades. This is where many of Ross Island penguins spend their time outside their breeding period. So the challenge for scientists is to understand the effect that the extra sea ice and other predicted environmental factors, such as increasing persistence of polynyas (expanses of water that remain ice free for large part of the year) or snowfall, are likely to have on penguin numbers.

It is also possible that, rather than being related to sea ice, the changes seen in the Adélie penguin population are linked to historical and recent changes in the number of other top predators (for example, minke whales and Antarctic toothfish) that compete with penguins for food. The removal of predators that eat krill and/or Antarctic silverfish could result in a greater amount of prey biomass available for penguins, thus supporting larger populations.

These are questions that will be addressed in the next phase of the study, said Dr Lyver.

Adelie penguin population approaches 30-year high [media release], 22 March 2014, Antarctica New Zealand

PLoS ONE citation
Lyver PO, Barron M, Barton KJ, Ainley DG, Pollard A, et al. (2014) Trends in the Breeding Population of Adélie Penguins in the Ross Sea, 1981–2012: A Coincidence of Climate and Resource Extraction Effects. PLoS ONE 9(3): e91188. doi:10.1371/journal.pone.0091188

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