Philippine fishermen, volunteers and authorities with dozens of fishing boats have joined hands in guiding back to sea about 500 disorientated melon-headed whales that were stranded in the shallow waters near the mouth of Manila Bay delta in the Bataan Peninsula.

The gentle mammals were first spotted swimming back and forth and straying very dangerously close (about a mile or 1.6 kilometers) to the shores of the coastal towns of Pilar, Orion and Abucay 135 kilometers northwest of Manila at around at around 4:00 am on Tuesday, said Philippine Coast Guard (PCG) Commodore Luis Tuazon and Bataan Governor Enrique Garcia Jr.

The Philippines Bureau of Fisheries and Aquatic Resources (BFAR) said its has responded to the reported mass "stranding" of whales off Pilar coastal waters in the province of Bataan where the famous and historic Corregidor Island is located.

Using dozens of fishing boats with machines shut down and bare hands, more than 100 village fishermen and volunteers along with BFAR, local police and Philippine Coast Guard personnel have joined the massive rescue. With great difficulty, the emergency team has waded into the chest-deep water, clapping their hands and hitting the surface to guide and drive the whales farther away from the coastal shore to deeper waters.

"The mammals were at first thought to have been dolphins, but experts then identified them as melon-headed whales," local veterinarian Mariel Flores said. "This type of whale can be easily mistaken for dolphins because of their size and their teeth, which resemble those of dolphins. The mammals have ears that are sensitive to large changes in pressure underwater," she added.

"It looked like they never wanted to leave. They looked sad,” said Rodolfo Joson, a village councilor. Joson and his son, Joey, a fisherman like him, have rushed home at about 4 a.m. to report the pod sighting. “It was still dark when we waded into the water. The whales were about 200 meters from the shore. The water was up to my neck. We first checked their conditions by playing with them. They did not repel us or leave. They were making hooting sounds,” Joson explained the mass beaching. “It seemed they were running away from waters that they didn’t like. Dolphins are happy and strong creatures. They raced with ships,” he added.

A post-mortem examination has revealed that four dead whales found beached farther up north in Abucay, Bataan, include two adult females, one of which was pregnant, while the other gave birth to a calf that also died, said Dr. Lemnuel Aragones of Ocean Adventure in Subic Freeport who did the necropsy at the Bataan fisheries office in Balanga City.

This is the first time that such large numbers of dolphins had been stranded in the Philippines. "We are trying to come up with a possible explanation to this unusual occurrence. It could be that the dolphins had lost their bearings and inadvertently ended up on the shallow portion of the coast unable to extricate themselves," said Dr Lemuel Aragones, Associate Professor at the UP Institute of Environmental Science and Meteorology.

Dr Aragones, who holds a PhD on Tropical Environmental Studies (Marine Ecology) from Australia's James Cook University, explained that "the melon-headed whales of the dolphin family have sophisticated navigation systems that operate on a principle similar to sonar instruments used in submarines. Like humans, dolphins also follow a 'leader' of their pod. It is possible that the leader of this dolphin [pod] had somehow lost its way. In turn, the leader’s acoustic system, which serves as its guidance system, might have been impaired," the marine expert elaborated.

Dr Aragones said "BFAR, UPIESM, and the Ocean Adventure Marine Park in Subic started the Philippine Marine Mammals Stranding Network (PMMSN) in 2005 as a response to cetacean strandings or beachings." She cited the PMMSN training received by BFAR officers in Bataan during Tuesday's mass beaching. She has asked the government to release funds for marine mammal studies.

The two adults had damaged eardrums, Alberto Venturina, the provincial veterinarian, said. "Dolphins with injured eardrums become disoriented, cannot dive for food and are too weak to swim and just flow with the current. If it's a sick leader, the animal needs to be identified and taken out of sight of the rest of the pod so the healthy dolphins could be prodded back to sea," he added."The two animals were identified as melon-headed dolphins, weighing about 250 to 300 kilograms (550 to 660 pounds)," explained Venturina, adding "the third dolphin was only a month old and measured barely a meter long. Its gender had not yet been determined."