A day after approximately 100 short-finned pilot whales washed up on the shore near Tuticorin in southern Tamil Nadu, rescuers on Tuesday were working to push the rest back into the sea.

“The stranding began late at night,” said JK Patterson Edward, director of the Suganthi Devadason Marine Research Institute based in Tuticorin. “By morning, we saw they had come in large numbers. Full efforts began at night to rescue them, with the support of local people.”

As reports of the stranding began to trickle in, the district administration moved into high gear. From the last account, everyone from the district collector and the superintendent of police to members of the forest department, fisheries and research organisations had been mobilised to participate in the mission.

Forty five of the 81 mammals that washed up on a five-kilometre stretch of shore have already died. Rescuers are working to push the rest back into the deep sea. This, however, might not be enough.

“Pilot whales move by sonar – that is they emit sound waves and move,” said G Sukumar, Dean of the Fisheries College and Research Institute in Tuticorin. “This kind of stranding is associated with sonar imbalance. If that is the case, even after taking them to safer waters, they again tend to come back to the shore.”

Sukumar’s team of two reached the shore along with other rescuers soon after midnight on Tuesday and returned for a brief rest only at five in the evening.

Dolphins or whales?

Short-finned pilot whales actually belong to the dolphin family, which might explain the confusion in reports that have been confidently asserting a mass stranding of either dolphins or whales.

Pilot whales frequently get stranded in huge numbers along coastlines across the world. New Zealand for instance regularly reports instances of such mass strandings. The last occurence was in February, when a pod of nearly 200 pilot whales washed up on the shores of the country’s South Island. Rescuers managed to refloat only 66 of them.

Pilot whales also travel in groups that can range anywhere from 60 to 1,000. Since they function as an extremely cohesive social group, if just a few members of the pod get stranded, the rest in the group soon follow.

Pilot whales might also be sensitive to changes in weather. After a strong El Niño in 1982-1983, they all but disappeared from the coast of southern California. Some link this to the decline in the population of squid at the time, but the reasons for their disappearance remain unclear.

A scientific mystery

Nobody knows why these whales get stranded in such large numbers.

“There are several theories for this, but nobody knows for sure, said Kumaran Sathasivam, coordinator of the Marine Mammal Conservation Network of India. “Pilot whales travel in large groups. There is a possibility that one or two individuals go to the shore for some reason – perhaps disease or infection – and the rest of the pod stays with them.”

This, he said, might be why even when pushed back into the sea through human intervention, pilot whales often return to the site of stranding. Another theory that is not yet proved says this stranding could be linked to geological activity.

“There have been tremors in Indonesia early this morning,” said Sathasivam. “We do not know whether this could be linked.”

Another reason they might have strayed near the shore, said Edward, is that the squid season has just begun, making the shore a more attractive proposition for feeding.

“These animals are purely oceanic,” said Edward. “They live in deep water and move in groups. When they search for food, if one has lost its way, the rest will follow.”

Looking at records

This is only the third recorded instance of a mass stranding of pilot whales on Indian shores.

The first was in July 1852, when several dozen washed up near Calcutta’s Salt Lake. British zoologist Edward Blyth incorrectly identified them as a new species that he called Globicephalus indicus. Later physiological examination showed that the cetaceans were simply short-finned pilot whales, also called Globicephala macrorhynchus.

The second stranding came a little more than a century later, coincidentally around the same time and place as the present one. On January 14, 1973, 147 pilot whales got beached on a three-kilometre stretch in Tuticorin. They did not live very long and are likely buried nearby.

“This phenomenon is not common and it is not uncommon,” said Sukumar. “Mass stranding is noticed among dolphins and whales and has been reported by other groups working on cetaceans.”