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Warming temps, loss of sea ice linked to sharp drop in penguin numbers
Gentoo penguins face a dwindling food supply due to a loss of sea ice and competition for krill.
Decline in chinstrap penguin populations have been linked to global warming.
By Bob Berwyn
SUMMIT COUNTY — Populations of two penguin species living in western Antarctica are declining rapidly, most likely because the loss of sea ice is reducing the abundance of krill, their primary food source, as well as competition from whales and the pressure of commercial krill fishing.
The number of both Adelies and chinstrap penguins has dropped by half since the 1980s. In that same span, mean winter air temperatures in the region have climbed by up to 10 degrees, leading to a huge loss of sea ice.
A new study by the National Oceanic and Atmospheric Administration and the Scripps Institute of Oceanography suggests the drop in penguin populations is directly tied to drop in krill, which, in turn, is linked to the loss of sea ice.
Krill are shrimp-like animals that grow to about two inches long. They are one of the most abundant forms of life on the planet and form the basis of the food chain in Antarctica.
The findings contrast with other studies that link the decline of some Antarctic species to a loss of sea ice habitat. In this most recent study, both ice-loving adelies and ice-avoiding chinstraps were showing significant declines. The link, of course, is that krill is a primary food source for both.
“We hypothesize that the amount of krill available to penguins has declined because of the increased competition from recovering whale and fur seal populations, and from bottom-up, climate-driven changes that have altered this ecosystem significantly during the past two to three decades,” the scientists wrote in the study.
Krill densities have declined by up to 80 percent in the vicinity of the Antarctic Peninsula and the Scotia Sea, with that drop linked to the decline in sea ice. The melting ice adds fresh water to ocean, creating favorable conditions for krill. Without the sea ice in the mix, the ocean is not nearly as productive.
Krill and penguin numbers are likely to decline further if warming in the area continues, they said, suggesting that biologists should keep a close eye on the numbers. The chinstrap penguins are especially susceptible because they rely almost completely on habitat on the west Antarctic Peninsula and the surrounding Scotia Sea. Adelies may be buffered from the worst impacts by large populations in the Ross Sea and the Indian Ocean sectors of Antarctica.
The study explains that, since chinstrap and adelie penguins were never hunted directly by humans, their population numbers directly reflect other environmental factors. A surge in penguin populations between the 1930s and 1970s can probably be linked to whaling. When whales were nearly wiped out, krill numbers spiked.
In addition to the declining sea ice, increasing whale numbers and a growing krill fishing industry are other factors in the decline of krill, the researchers explained.
“Linking trends in penguin abundance with trends in krill biomass explains why populations of Adelie and chinstrap penguins increased after competitors (fur seals, baleen whales and some fish) were nearly extirpated in the 19th to mid-20th Centuries, and currently are decreasing in response to climate change,” they wrote.
The study is online at the Proceedings of the National Academy of Sciences.
Filed under: biodiversity, endangered species, Environment, global warming, Marine biology Tagged: | Antarctic sea ice loss, chinstrap penguins, Environment, gentoo penguins, global warming, penguins, Summit County News, West Antarctic Peninsula climate change
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The study which is being referred to is suspicious and I have previously questioned the following quote attributed to that study, “We hypothesize that the amount of krill available to penguins has declined because of the increased competition from recovering whale and fur seal populations, and from bottom-up, climate-driven changes that have altered this ecosystem significantly during the past two to three decades,” The flaw is that absolutely no mention is made of the ever increasing KRILL fishery that has evolved and continues to increase in and adjacent to the Southern Ocean. NOAA and Scripps Institute claim responsibility for this report, why are they inwilling to include the impact that man and his sophisticated krill fishing methods has had on the declining populations.
I read the study and it clearly refers to a combination of factors, including both recovering whale populations AND industrial krill fishing. I tried to make that clear in my reporting. We gotta save the whales and the penguins, and, especially, the krill. We’re all in this boat together.
Dear Bob
Thanks for highlighting this paper. I too have read the original paper and the cetacean paper that it quotes as a reference and 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 i 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.