Wednesday, October 28, 2009

Orcas: new studies show changes in killer whales

When discussions of Arctic or Antarctic species come up, they often focus on polar bears, penguins, and walruses - all animals worthy of our concern and whose populations are at risk from changes in their environment due to climate change, pollution, or oil drilling development.

Orcas - or, if you like, Killer Whales - are also being impacted by environmental changes, some good and some not so good.

In a report from Canadian scientists, there is evidence that orcas are able to manage changes in their ocean environment by moving more northward, extending their uppermost boundaries in the Arctic Circle. This is made possible by the reduction of sea ice, particularly in the summer months.

Orcas typically cruise the thinner edges of the Arctic ice but avoid the thicker ice where access to the surface for breathing would be more limited. The scientists reviewed data of orca sightings dating back centuries and saw a definite increase since 1900 in the Arctic region, including into the Hudson Bay, that coincides with the recorded reduction of the Arctic sea ice. It remains to be seen whether this will disrupt the marine ecosystem as the orcas possibly begin to prey more and more on northern Arctic species like bowhead whales, belugas, and narwhals.

In another study, orcas were cited as a probable cause for the decline of sea otters, seals, and sea lions along southwest Alaska over a period of several decades. Not to completely blame the orcas, the study points to a cause for this change in the orcas' diet as the result of industrialized whaling. Whaling decimated whale populations and deprived orcas of an important food source. Hence the shift to other marine mammals as prey.

Orcas are extremely social animals, living in family units or pods, that can exist for many years, complete with elaborate and close social hierarchies. External stressors (ie: changes in their environment and/or food source) that produced changes in populations have been cited in a recent report as a possible cause for changes in the social structure of orcas in Canadian/U.S. waters. It opens the door for more study as to the impact of habitat change on the social order and survivability of this highly social marine mammal.

And lastly, according to a scientific report, the population of orcas that inhabit the Antarctic's Ross Sea, has apparently been decreasing both in terms of frequency (when observed) and in numbers and the primary culprit is, once again, commercial overfishing. In this case, the overfishing of the Antarctic Toothfish, a primary food source for this particular orca population. Whether the orcas have declined or are moving on to better hunting grounds has yet to be determined. But it is another example of the struggle between man and nature over available marine resources. And if the ocean's animals keep losing - from the smallest feeder fish to large predators like orcas - then ultimately we lose.

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