Warming temps, loss of sea ice linked to sharp drop in penguin numbers
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