Off the Patagonian coast of Argentina, southern right whales have been dying off. Since 2005, over 300 dead right whales have been found in the area – making up a third of all sightings. While right whales in other areas of the southern hemisphere have not seen any abnormal die-off, this area has seen more than its share of dead whales. The majority of the carcasses found have been calves under three months old.

The southern right whale is a type of baleen whale and has been considered endangered since the 1930s when they were among favorite targets of whalers. A whaling ban helped the population of these creatures to rebound, but it was still far short of the 60,000+ population this species once held.

Causes for this die-off have been narrowed down to a few probabilities, though these are not the only possible factors: environmental concerns at the nursing grounds, biotoxins released by algae or related organisms, disease, and starvation. Some threats that are common for the northern right whale – a separate species – have been discounted including vessel strikes and entanglement in fishing nets.

Both in numbers and in proportion, this event is larger than the previous whale die-off of the gray whale which took place in the Pacific between Alaska and Mexico during 1999-2000. In that case, 250 whales – from a larger total population – died.