Just what is ailing the Southern Ocean penguins?
For a long time, the answer seemed to be that their icy habitat was being lost to global warming.
But as the BBC and others reported on Tuesday, a new study by the National Oceanic and Atmospheric Administration and the Scripps Institution of Oceanography suggests that isn’t the case.
According to the study, which appeared in the Proceedings of the National Academy of Sciences, one hypothesis guiding ecological interpretations of changes in top predator populations in this region, the “sea-ice hypothesis,” proposes that reductions in winter sea ice have led directly to declines in “ice-loving” species by eroding their winter habitat, while populations of “ice-avoiding” species have increased.
However, 30 years of field studies and recent surveys of penguins throughout the West Antarctic Peninsula and Scotia Sea demonstrate that populations of both ice-loving Adélie and ice-avoiding chinstrap penguins have declined significantly.
While the researchers say that ice loss does affect penguins, they say the more important problem appears to be a decline in the population of Antarctic krill (Euphausia superba), tiny shrimplike crustaceans that dwell
in vast schools.
Krill, the authors note, “is the dominant prey of nearly all vertebrates in this region, including Adélie and chinstrap penguins,” and changes in the amount of krill biomass provide the best explanation. Adélie and chinstrap penguin populations increased after competitors for the krill like whales and seals were heavily hunted in last century, but the birds have declined in number as climate change has affected krill and more seals and whales have been competing for the food.
In some areas, they say, a reduction in sea ice is associated with an 80 percent decline in the density of krill from the 1970s to the present.
As I reported last June, penguins, whales and seals are increasingly facing a new competitor in the battle for krill: man. Krill, it turns out, are an excellent source of omega-3 fatty acids, used in dietary supplements. They are also used to make animal feed and to nourish the world’s growing aquaculture industry.
The researchers say the krill catch around the WAP, South Shetland, South Orkney, and South Sandwich Islands has soared from 50,804 tons in 2002–3 to 202,346 tons in 2009–10. That is still a small share of the overall krill biomass, but it appears that demand is only going to keep growing.
Aker Biomarine, a Norwegian company that operates an Antarctic krill fishery from a single, technologically sophisticated factory ship, said last week that it had signed an agreement to furnish a Chinese dietary supplement maker with 230 tons of krill products over five years, and expressed confidence that more such deals would be coming.