Toxic cocktail threatens to wipe out killer whales.
Overfishing and man-made noise may also affect the health of the animals, but PCBs particularly can have a dramatic effect on the reproduction and immune system of the killer whales, said a team of researchers Aarhus University, who found that the number of Orca or killer whales is rapidly declining in 10 out of the 19 killer whale populations investigated.
They warn that the species may disappear entirely from several areas within a few decades.
The research group, which includes participants from the United States, Canada, England, Greenland, Iceland and Denmark, reviewed all the existing literature and compared all data with their own most recent results.
This provided information about PCB levels in more than 350 individual killer whales around the globe - the largest number of killer whales ever studied.
"The findings are surprising. We see that over half of the studied killer whales' populations around the globe are severely affected by PCBs" said postdoc Jean-Pierre Desforges from Aarhus University, who led the investigations.
"Based on the weight of evidence from a couple of decades of research, PCBs remain the number one pollutant of concern at the top of the food chain for wildlife in the northern hemisphere," Peter Ross, one of Desforges' co-authors and a marine mammal toxicologist at Ocean Wise, the research arm of the Vancouver Aquarium in British Columbia, told National Geographic.
According to a press release by the research team, the killer whale is one of the most widespread mammals on Earth and is found in all of the world's oceans from pole to pole. But today, only the populations living in the least polluted areas possess a large number of individuals.
Killer whales are particularly threatened in heavily contaminated areas like the waters near Brazil, the Strait of Gibraltar and around the UK. Around the British Isles, the researchers estimate that the remaining population counts less than 10 killer whales. Also along the east coast of Greenland, killer whales are effected due to the high consumption of sea mammals like seals.
In the oceans around the Faroe Islands, Iceland, Norway, Pacific Northwest, the Antarctic, the prospects are not so gloomy. Here, killer whale populations grow and the models predict that they will continue to do so throughout the next century.
Recently, on the West-coast of Canada, three incidents involving resident Orca whales have garnered headlines around the world.
During the summer, J35, a 20-year-old orca nicknamed Tahlequah, lost a calf after giving birth and swam more than 1,000 miles for about 17 days with her dead off spring.
As the world followed the whale's sad ritual, scientists were monitoring another orca, three-year-old J50, which appeared to be slowly starving to death. She finally disappeared in mid-September.
More recently scientists have been photographing another animal, K25, that has lost significant weight.
National Geographic reported while Puget Sound's resident whale numbers are plummeting, nearby transient whales, which eat seals and sea lions, are stable --even though their PCB levels are often higher.
"Killer whale numbers in Canada and Alaska are actually increasing," National Geographic reported.
But Ross of Ocean Wise cautioned in the same article that the numbers may not reflect the full seriousness of the issue in the Pacific Northwest.
He explained that some of the killer whales out there today have been around during the heyday of PCB use during and after World War II.
These are slow-acting contaminants, which means adults can still see impacts from exposure as calves or while they were in utero. That means even populations that seem healthy may actually be at risk, Ross explained.
Caption: A pod of Killer Whales in the Pacific Northwest.
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