Mystery killer behind tragic right whale deaths likely identified

Right whale deaths
© Andrea Chirife/Southern Right Whale Health Monitoring Program

Deaths of the endangered whales, mostly young calves, leapt 10-fold from 2005 to 2014. No one knew why until possibly now.

In 2005, something dreadful and very unusual started happening around Peninsula Valdes, an important calving ground for southern right whales on the coast of Argentina. Dead whales started washing ashore, many of them small calves younger than three months old; especially troubling given that females do not become sexually mature until ten years old and give birth to a single calf after a year of gestation. The average number of right whale deaths per year at this spot leapt from fewer than six per year before to 65 per year from 2005 to 2014. When TreeHugger wrote about it in 2010, we called it one of the largest die-offs of great whales ever recorded.

But now scientists may have cornered a suspect. The potential perpetrator? Blooms of toxic algae.

New research by NOAA Fisheries and NOAA Ocean Service scientists and others from the United States and Argentina reveals that the incidence of whale deaths at Peninsula Valdes closely follow the concentrations of the toxic algae Pseudo-nitzschia – which can produce a strong neurotoxin known as domoic acid. When concentrations of Pseudo-nitzschia were high, the more young whales died; and conversely, when the algae density dropped, so did the number of deaths. While this isn’t definitive proof, it’s hard not to recognize it as strong circumstantial evidence.

"The numbers hinge at the same point and have the same pattern," said Cara Wilson, an oceanographer at NOAA Fisheries' Southwest Fisheries Science Center and lead author of the paper. "What's unusual about this is how long these bloom events continued to re-occur. You don't usually have deaths every year but the calves died in high numbers every year from 2007 to 2013."

Right whales haven't had an easy time of it. They were named by whalers who identified them as the "right" whale to kill while hunting, explains National Geographic. "These leviathans had enormous value for their plentiful oil and baleen, which were used for corsets, buggy whips, and other contrivances. Because of their thick blubber, right whales also float accommodatingly after they have been killed. Populations of these whales were decimated during the whaling heydays of the 17th, 18th, and 19th centuries," the magazine notes. During this period they came close to extinction.

The new research shines the spotlight on a specific time and place, but the findings are important beyond Argentina since they demonstrates that some of the largest creatures in the ocean can succumb to the kind of algal blooms that are expected to increase with climate change. Scientists are also studying whether harmful algae could have played a role in the recent rash of whale deaths in Alaska, which NOAA has declared an Unusual Mortality Event. You can read more about that tragedy here: The mystery of Alaska’s dead fin whales.

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