A meeting to solve the mystery of the largest ever recorded die-off of over 300 southern right whales, including young calves is underway. The whales have been found dead in the last five years in the waters off Argentina's Patagonian coast - one of the most important breeding grounds for the species.

Possible causes being examined include bio toxins, - disease, environmental factors, and lack of prey, particularly the tiny krill which make up the bulk of the southern right's diet. The main evidence that will be examined is tests on samples taken from beached whale calves, which have shown "unusually thin" blubber. Southern right whales are one of three species of right whales, so called because fishermen considered them the "right whale" to hunt, because they are slow swimmers, easy to approach, live close to shore and float when dead.

In the first half of the 1800s about 45,000 right whales were killed, driving them close to extinction, before they became protected in 1937. Since then the southern right whale which weighs up to 90 tonnes when fully grown has been a conservation success, numbers rebounding to about 7,500, in populations off South America, South Africa, Australia and some oceanic islands. Numbers of the Northern Atlantic right whale and Northern Pacific right whale have recovered less well, to a few hundred each. Part of the concern about the recent die-off is that the dead whales have been found around the Peninsula Valdes, where one third of the global population of southern right whales is thought to use the protected bays for calving and nursing between the months of June and December. Peninsula Valdes is one of the most important calving and nursing grounds for the species found throughout the southern hemisphere,

The workshop meeting is sponsored by the International Whaling Commission, which last year declared the die-off as a management priority. Globally the southern right whale is one of 86 recognised species of cetaceans - porpoises, dolphins and whales - listed as being of "least concern" by the IUCN World Conservation Union.