Photograph by Gerard Soury, Getty Images

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A southern right whale breaching off of Peninsula Valdes, Argentina.

Photograph by Gerard Soury, Getty Images

Mysterious Deaths Threaten a Population of Southern Right Whales

The "mass mortality" of hundreds of southern right whale calves mystify scientists.

Surprisingly large numbers of southern right whale calves are dying off the coast of Argentina, sparking concerns among marine scientists and conservation officials.

Overall, southern right whales are doing much better than their endangered brethren to the north. But for one group of southern right whales that gives birth off Peninsula Valdés, Argentina (map), fate has not been so kind.

Hundreds of the Peninsula Valdés whales have died since monitoring of their population size began in 1971, researchers report in a study published this month in the journal Marine Ecology Progress Series. From 1971 to 2011, 630 of the right whales died—adults and young ones combined.

But 77 percent of those deaths occurred between 2003 and 2011. And of those recent deaths, 89 percent have occurred in the calves. Scientists are still struggling to understand why.