Decline of penguins recorded on subantarctic island
Above the Antarctic Convergence Line, the biological boundary of Antarctica, lies Macquarie Island. The Australian-administered island, much like South Georgia, has become a true wildlife paradise after whalers and sealers left the island and pests have since been eradicated. In particular, the four species of penguins native to the island have grown strongly again. Or at least they did until some time ago. Because the numbers are declining again and researchers are looking for the reasons.
A study by the University of Tasmania’s Institute of Marine and Antarctic Studies IMAS recorded a decline in chicks since 2007 in the census of king penguin populations on Macquarie. That’s when the Tasmania Park and Wildlife Service began systematically monitoring and conducting counts of the world’s second largest penguin species on Macca, as the island is affectionately known by Australians. “The decline either means that the island has reached its carrying capacity or that the population is actually declining,” explains Penny Pascoe, a doctoral student at IMAS who conducted this study on the topic. Carrying capacity determines the maximum number of living organisms that can find sufficient food and optimal living conditions (breeding sites, enemy pressure) in a given area, so that the population can grow to this number and stay on that size. However, if a population begins to decline, it means that one or more factors have changed negatively. What it is in Macquarie’s case is now under closer scrutiny.
King penguins on Macquarie account for about ten percent of the species’ total population worldwide, and the island is the species’ most significant breeding site in the Pacific Antarctic. After sealers on the island had brought elephant seals and other seals virtually to the brink of extinction, they turned their attention to king penguins and summarily processed the animals into oil for fuel. Thus, the penguins shared the fate of the seals. However, thanks to protective measures at the beginning of the 20th century, the population recovered and still by the beginning of 2000 the number increased rapidly again. This is also a starting point for further research on the decline. “Further work is needed to determine if the decline we are seeing is due to a decline in the overall adult breeding population or if it is a natural stabilization following the population’s rapid recovery from exploitation” Penny Pascoe continues.
However, the study by Pascoe and her colleagues also cites climatic changes as possible reasons. This is because the authors of the study, when comparing breeding numbers with weather data, found that years with low chick numbers were associated with high rainfall and very large wave heights on the beaches. In addition, the meteorological office also recorded more storms and higher water temperatures, all factors that can have a major negative impact on the breeding success of king penguins.
What speaks to the influence of climatic changes on the decline is a comparison with other penguin species living on Macquarie. Gentoo penguins in particular, which have been on the rise elsewhere, have experienced a massive decline. About half the population here has disappeared in the past twenty years, another study by Penny Pascoe showed. And rockhopper penguins, of which the southern species lives on Macquarie, are also declining globally. While no alarm bells need to be sounded yet for the closely related endemic royal penguins. But they, too, could quickly be put in an endangered position by the changes that climate change is bringing, especially to this corner of the Southern Ocean. The impact would then be felt on and around the island, as the penguins have an important ecological role. They fertilize the island and the surrounding ocean with their excrement. Julie McInnes, Ph.D., of IMAS, leader of the study reminds, “We must remember that the marine ecosystem is interconnected and the removal of one species can have an impact on other species.”
Dr Michael Wenger, PolarJournal
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