Long-term monitoring has revealed a 43% decline in a large Adélie penguin population off the east coast of Antarctica, near Mawson Research Station, over the past decade.
The loss of some 154,000 breeding birds, breeding on 52 islands along the 100km coastline, contrasts sharply with other populations in East Antarctica, where there have been long-term increases or stable population trends. (see Penguin Heaven).
It also goes against the model’s predictions of a continued increase in this population after decades of sustained growth.
Australian Antarctic Division seabird ecologists Dr Louise Emmerson and Dr Colin Southwell said the rate of decline is similar to that of Adélie penguin populations on the Antarctic Peninsula, which are subject to external pressures from fishing, climate change and human activity.
However, Mawson’s population decline is thought to have been triggered by altered environmental conditions and then exacerbated by internal feedback processes within the population, rather than direct human pressures.
“We believe this population decline was initially triggered by five years of extensive summer sea ice adjacent to the colony in the mid-2000s, which impeded access to adult feeding areas and did not saw hardly any chicks survive,” Dr Emmerson said.
“The frequency of these unfavorable breeding conditions remained high thereafter, and nestling survival also began to decline. These two processes combined resulted in a faster population decline than would be expected if they had acted in isolation.
Safety in numbers
Dr Emmerson said it’s possible that the smaller a population gets, the harder it can be for individuals to survive, either because of an increased risk of predators, or because small groups aren’t as good for navigate, feed and locate their prey. This is especially important for young nestlings with limited life experience.
“It may be that the old adage of being safe in numbers is playing out for baby birds in the vast and harsh Southern Ocean, although the whys and wherefores need further investigation,” Dr Emmerson said.
“We estimate that this population has lost around 80,000 fledglings in a good breeding season, compared to the population peak in the early 2000s.
At the deepest
Young Adélie penguins are literally thrown into the deep end around two months of age, when they leave the colony and enter the Southern Ocean for the first time, without parental supervision.
“I remember seeing baby birds come into the water for the first time and they did this weird kind of breaststroke, like they were trying to use their flippers to stand up. It was a completely new experience for them,” Dr Emmerson said.
“When they first enter the water, they can’t swim, they don’t have any predator avoidance behavior, so they’re susceptible to being eaten by leopard seals and they’re not efficient at catching prey, they have no idea of their marine environment, and because there are no adults to help them, they must learn quickly or they won’t survive.
“So while we don’t know exactly what is causing the decline in nestling survival in the Mawson area, the fact that there are fewer of them may compromise their chances of survival.”
Long term monitoring
Dr Emmerson said the next step was to continue research to understand the drivers of nestling survival on their naive first winter voyage to sea after leaving the colony, and to ensure that any resumption of fishing activities in the region is carefully managed.
She said continued long-term monitoring across the environmental range where penguins breed was essential for early detection of population decline and for understanding population changes.
Australia’s long-term monitoring of Adélie penguins near Casey, Davis and Mawson research stations is also key to decisions made by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). , the management of krill fisheries and consideration of the protection of terrestrial and marine areas.
As this study shows, long-term monitoring allows scientists to uncover intrinsic factors involved in population decline that may be masked by population changes caused by year-to-year variability in environmental conditions. . This is essential to inform predictive demographic models that tend to focus on environmental drivers of demographic change.
“Model predictions based solely on external environmental factors may not accurately predict future population changes and/or underestimate the true impacts of climate change on species populations,” Dr Emmerson said.
“It remains to be seen whether this population of Mawson penguins stabilizes, continues to decline or recovers. However, it is clear from this study that, where possible, we would be better off preventing impacts in the first place, or trying to mitigate them before population declines are well established, or the processes causing the decline become confused and lead to a rapid decline in the population. ”
The research is published in Biology of global change today.