Mass Beaching Of Dolphins In Philippines

This story was filed by CBS News' Barnaby Lo, reporting from Manila.

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Hundreds of dolphins were trapped in shallow waters near the coast of Bataan province in the Philippines early Tuesday morning. At least three dolphins, one of them pregnant, were found dead by residents in the seaside town of Pilar.

Local officials say although a mass beaching is not unprecedented, it is the first time such a huge number of dolphins have beached themselves — an estimated 400 to 500, according to the Philippine Coast Guard.

Fishermen and volunteers have been able to successfully guide most, if not all, of the dolphins back to the open sea, as search and rescue vessels of the Coast Guard continue to patrol the area.

Alberto Venturina, the provincial veterinarian, told French news wire AFP that they found water in the lungs of two of the dead dolphins, indicating that they had drowned.

"It's possible that they got lost. They came from the north and were headed towards the South China Sea," he said.

The third dead dolphin measured barely a meter long and was only a month old.

"We will try to determine the actual reason for the phenomenon. It is something unusual," said Malcolm Sarmiento, chief of the Bureau of Fisheries and Aquatic Resources (BFAR), in an interview with a local cable news network. "It is the first time that such a large pack [of dolphins] entered Manila Bay, and it’s acting strangely."

Sarmiento offered two possible reasons for the occurrence. He said a strong seaquake may have damaged the dolphins' eardrums while they were diving for food.

"Once their eardrums are injured, they would lose their sense of direction and they would become disoriented," explained Sarmiento. "They cannot dive for food anymore resulting in a situation where they become weak with hunger and they just go with the current."

Another possibility, according to Sarmiento, is that the school of dolphins was following a sick leader that may have beached itself.

Investigation into the mass beaching is ongoing. Authorities will continue to monitor coastal areas in the next 72 hours for similar occurrences.