In Unprecedented Loss, Endangered Whales Die of Mysterious Cause - An estimated 500 North Atlantic right whales exist globally, making the recent deaths even more alarming.

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Although they seemed otherwise healthy, the North American right whales were all recently found dead in the Gulf of St. Lawrence in Canada. Now, Fisheries and Oceans Canada, the Marine Animal Response Society, the Canadian Coast Guard, and others are working together to find out why the whales died.

Right whales are considered the rarest of all whale species, and the International Union for the Conservation of Nature estimates that only about 350 individuals still exist in the Northwest Atlantic, which was once home to tens of thousands. The Department of Fisheries and Oceans Canada estimates 500 exist globally.

"For this species, even one animal is a hit to the population," said Tonya Wimmer, director of the Marine Animal Response Society. The species never fully recovered from 20th-century whaling practices that drastically reduced their numbers. They are recognized under the Canadian government's Species at Risk Act, and in the U.S., the animals are afforded protections under the Marine Mammal Protection Act.

A little over a week after the first whale was found, a second was found on June 19, and a third was found on June 20. According to Wimmer, the other three were found from June 20-23.

The waters around St. Lawrence are home to about a dozen cetacean species. Some, such as the beluga, have made the gulf their permanent summer home. But marine animals face a number of threats in the busy port area, from being struck by ships to contracting toxic infections.

A 2013 report found that water contaminants, high levels of noise, decline in prey availability, and global warming all negatively impacted the St. Lawrence beluga population, which shares habitat with right whales. And unlike belugas, the whales feed on zooplankton, which are also highly susceptible to changes in climate.

Wimmer and other local organizations are considering pulling one of the carcasses to shore to perform a necropsy to determine the exact cause of death. Wimmer could not provide an estimate of when results of the necropsy for these six whales would be available, but researchers have a small window of opportunity as the carcasses are already decomposing. Cause of death can sometimes be seen right away, while other fatalities are less immediately visible.

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