Apr 12

Penguins in western Antarctica have undergone significant population declines, largely due to a reduction in the availability of their main food source, krill.

Photo of chinstrap penguins walking along beach

The chinstrap penguin, which breeds exclusively in the West Antarctic Peninsula and the Scotia Sea, has suffered declines in excess of 50% throughout its breeding range.

As the dominant prey for nearly all vertebrates in the Antarctic region, Antarctic krill (Euphausia superba) is one of the most important species in the Antarctic ecosystem.

However, in the past 40 years, the population of krill in the Southern Ocean surrounding Antarctica has fallen by around 80%.

Climate-driven changes, such as warming waters and less sea ice cover, as well as increasing whale and seal numbers, have been cited as some of the reasons behind the krill decline.

The Antarctic region is among the fastest warming areas on the planet, with increases of 5 to 6 ºC in mean winter air temperatures, and associated decreases in winter sea ice cover. Krill are dependent on sea ice during their larval stages, and the shrinking sea ice has contributed directly to a decline in breeding success.

Close up photo of Antarctic krill

The abundance of krill has rapidly declined in recent decades, with knock-on effects for vertebrate predators in the Antarctic.

Dr Wayne Trivelpiece, lead author of a new paper published in the Proceedings of the National Academy of Sciences, warns that “as warming continues, the loss of krill will have a profound effect throughout the Antarctic ecosystem.”

According to the study, the reduction in krill abundance has caused numbers of both the chinstrap penguin (Pygoscelis antarcticus) and the Adelie penguin (Pygoscelis adeliae) to fall steadily since 1986.

The team found that linking trends in penguin abundance with trends in krill biomass explains why populations of Adelie and chinstrap penguins increased after competitors, such as fur seals and baleen whales, declined due to hunting by humans in the 19th to mid-20th Centuries, as well as why they are currently decreasing in response to climate change.

The new findings challenge the current leading theory behind penguin declines in Antarctica, known as the ‘sea ice hypothesis’.

The sea ice hypothesis proposes that reductions in winter sea ice leads directly to declines in species which depend on sea ice for breeding and other activities by decreasing their winter habitat, while populations of species which do not depend on sea ice will increase.

However, the new findings show that populations have declined in the Adelie penguin, which depends on sea ice, and the chinstrap penguin which does not. Populations in both species have fallen by up to 50% since the mid-1980s, suggesting that the declines were instead linked to the abundance of their main food source.

Photo of Adelie penguin walking

The Adelie penguin has also undergone a population decline in recent decades, linked to declines in food availability and shrinking sea ice habitat.

Over the past 10 years, chinstrap penguin populations have fallen by 4.3% annually, while Adelie penguin populations have fallen by 2.9% annually over the last decade.

The researchers, a team from the National Oceanic and Atmospheric Administration (NOAA) and the Scripps Institution of Oceanography in the US, concluded that penguin numbers and krill abundance are both likely to fall further if the unprecedented warming trend in the Antarctic region continues.

Read the paper in the Proceedings of the National Academy of Sciences.

Find out more about Antarctic species on ARKive.

Explore other species affected by climate change on ARKive’s climate change pages.

Helen Roddis, ARKive Species Text Author

  • logan olsen (April 21st, 2011 at 3:16 am):

    the pianguans are marching

  • Chris Butler-Stroud (May 5th, 2011 at 5:17 pm):

    Reading the original paper and the cetacean paper that it quotes as a reference I would note that whilst the Academy of Sciences paper tests the hypothesis that the reduction of whaling is removing fewer whales from the Antarctic ecosystem and they are eating more krill, the significant conclusion is that the major impact on the penguins is climate change.

    When discussing whales the original paper references ‘Reilly, S., Hedley, S.L., Borberg, J., Hewitt, R., Thiele, D., Watkins, J., Naganobu, M. 2004. Biomass and energy transfer to baleen whales in the South Atlantic sector of the Southern Ocean. Deep Sea Research II 51, 1397-1409’ (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VGC-4DD934J-2&_user=10&_coverDate=06%2F01%2F2004&_rdoc=1&_fmt=high&_orig=gateway&_origin=gateway&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=523082b582d1666c3287ee0945e21345&searchtype=a) which states that the amount of krill consumed by whales estimated from a 2000 Antarctic survey amounted to some ‘4–6% of the estimated krill biomass in the region (and probably less than this percentage of the total annual krill production).’

    The Reilly et al. paper does not appear to set out to blame whales for low krill population numbers but indeed, seems to say that any future krill fishery should be managed so as to allow for recovery of whales, – it states that, ‘the depleted numbers of baleen whales resulting from past or current whaling activities should be taken into account when setting quotas for the commercial exploitation of krill if there is to be a recovery to pre-exploitation biomass levels of baleen whales’.

    Again, we should always be careful not to confuse the hypothesis tested and the conclusion that the papers arrive at. In this case that the dramatic man-made reduction in numbers of whales caused the penguins to switch diet to krill and now over fishing and climate change are affecting the penguins. As the Reilly et. al paper shows, the whales are, unfortunately thanks to whaling, very small players in this debate.