Collapse of the Adélie penguin population at Mawson in East Antarctica | Polarjournal
A decline in juvenile survival during their first winter has exacerbated the rate of decline of the Adélie penguin population at Mawson Station. As soon as they dive into the Southern Ocean for the first time, the young birds are on their own. Photo: Louise Emmerson

The Adélie penguins in East Antarctica have been doing extremely well in recent decades and their populations have increased tremendously. However, this is no longer true for the large population near Australia’s Mawson Research Station: over the past decade, population numbers have declined by a dramatic 43 percent, a new study now reports.

While Adélie populations elsewhere in East Antarctica continue to grow strongly or at least remain stable, the population near Mawson Station has lost 154,000 breeding birds in the last decade, breeding on 52 islands along the 100-kilometer coastline. The researchers had not expected such a strong downward trend. The model predictions, at least, have assumed that the population will continue to increase.

Dr. Louise Emmerson and Dr. Colin Southwell, the two authors of the current study published in the journal Global Change Biology, compare the decline to Adélie populations on the Antarctic Peninsula, where fisheries, climate change and human activities are having a negative impact on penguin development.

Adélie penguins need just the right amount of sea ice to raise their chicks. Too much sea ice means they have to expend a lot of energy to get across the ice to their feeding grounds; too little ice can affect the availability of their prey. Photo: Louise Emmerson

In contrast to the Antarctic Peninsula, changing environmental conditions likely led to the decline in the Mawson population, which was further exacerbated by feedback effects within the population, the authors said.

“We think this population decline was initially triggered by five years of extensive summer sea ice adjacent to the colony in the mid-2000s, which hampered access to the adults’ foraging areas and saw virtually no chicks survive,” Dr. Emmerson explains. “The frequency of these unfavourable breeding conditions subsequently remained high, and fledgling survival also began to decrease. These two processes together resulted in a more rapid population decline than would be expected if they had been acting in isolation.”

Penguins live in large colonies and forage together in larger groups, which gives them some protection from predators. In addition, young animals can take their cues from older ones when navigating. Such a dramatic drop in the population may therefore have caused difficulties especially for the young birds, which at only two months old are left to fend for themselves and find food on their own. The probability as a young, inexperienced Adélie penguin to fall prey to hungry leopard seals is much higher when the group is small and the experienced animals are missing.

Penguins have been monitored since the 1990s as part of the Australian CCAMLR ecosystem monitoring program on Béchervaise Island off Mawson Research Station. Photo: Louise Emmerson

“When they first enter the water they don’t know how to swim, they have no predator avoidance behaviour, so they are vulnerable to being eaten by leopard seals, and they’re not efficient at catching prey. They’re totally clueless about their marine environment, and because there are no adults to help them they have to learn quickly or they don’t survive,” Dr. Emmerson said. “It may be that the old adage of safety in numbers is playing out for the fledglings in the vast and harsh Southern Ocean, although exactly why and how needs further investigation.”

The authors do not yet know the exact reason for the decline of juveniles in the Mawson population, but they assume that their chances of survival are lower because there are fewer of them.

According to Dr. Emmerson, long-term monitoring of the Mawson population will continue to understand the factors that influence survival of fledglings during their first winter at sea after leaving the colony. It is possible that changes within the population are masked by year-to-year fluctuations in environmental conditions, and it is very important to uncover the intrinsic factors that exacerbate declines.

The graphic shows (a) the location of the study offshore near the Mawson Research Station, (b) the decline in occupied nests/breeding birds over 10 years; and (c) annual population counts on Béchervaise Island showing annual fluctuations (black line) and a dramatic decline (purple line). Graphic: Emmerson & Southwell 2022

“Model predictions based on external environmental factors alone may fail to accurately predict future population change and/or underestimate the real impacts of climate change on species’ populations,” Dr. Emmerson says.

Long-term monitoring of all Adélie populations near Casey, Davis, and Mawson stations is also critical for Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) decisions, krill fishery management, and terrestrial and marine conservation. In any case, the resumption of fishing in the area must be carefully managed.

“Whether this Mawson penguin population stabilises, continues to decline, or recovers, remains to be seen. It is clear from this study though that where possible, we are better off preventing impacts in the first place, or trying to alleviate them before population decline is well-established, or the processes causing the decline become confounding and result in rapid population declines,” Dr. Emmerson said.

Julia Hager, PolarJournal

Link to the study: Emmerson, L., & Southwell, C. (2022). Environment-triggered demographic changes cascade and compound to propel a dramatic decline of an Antarctic seabird metapopulation. Global Change Biology, 00, 1- 16. https://doi.org/10.1111/gcb.16437

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