Senegalese fishermen dragged dozens of stranded pilot whales back out to sea on Wednesday but at least 20 more died on the beach after mysteriously coming ashore.
More than 100 pilot whales, which have bulbous foreheads and can grow to over 4 meters long, beached themselves overnight at Yoff, a traditional Lebou fishing community on the Cap Vert peninsula, mainland Africa's most westerly point.
Local fishermen struggled through the night to drag the animals back to sea from the sloping sandy beach, using their brightly colored open wooden boats known as "pirogues" and attaching ropes around the animals' sleek, black bodies.
"No one slept last night because all the fishermen were called out to help save the whales," said Iba Dieye, a local fisherman from Yoff.
"About 100 of the big fish washed up on the beach last night at around 9 p.m.. We worked all night to try to drag them back into the ocean. We got about 80 back into the water with ropes, our pirogues and our hands. But the ones still here are dead now," said another fisherman, Elima Bah.
Nevertheless, hours after the mass stranding, local adults and children were still trying to haul some of the remaining live whales back into the waves.
During the day, curious crowds gathered around the carcasses of the dead animals. Some snapped photos with their mobile phones, while children played on the carcasses, dousing them with water to create a slippery slide.
Local fishermen said they would need government help to remove the dead whales from the beach. They said they feared the rotting carcasses could cause disease and infection.
"COLLECTIVE SUICIDE"
"All animal carcasses should be destroyed and shouldn't be eaten. But this is Africa, and if the area is not secured, people are tempted to cut off a piece of flesh, some for their animals, like their dogs, and some to eat themselves," said Kabore Alassi, a professor from Dakar's Veterinary School.
Witnesses said some residents dragged off whale carcasses.
Local experts said a similar mass beaching of whales had occurred at the same spot some 30 years ago. Some residents had fallen ill after eating meat from the dead whales.
They had no precise explanation for the mass stranding.
"It's like a collective suicide. Even when you push them out, they still keep coming back," said Ali Haidar, president of the Oceanium marine conservation organization in Dakar.
"It's something to do with their navigational and orientation systems getting disturbed," he added.
Haidar said that when around 250 whales beached on the shore in neighboring Mauritania two years ago, experts believed the animals had been disturbed by offshore seismic and sonar exploration by international oil companies.
The sonar systems of submarines patrolling or involved in military exercises could have a similar effect on whales.
It was also possible that the pilot whales at Yoff had been driven ashore by chemical pollution in the water, Haidar said.
(Additional reporting by Finbarr O'Reilly, Normand Blouin, Diadie Ba and Pascal Fletcher; writing by Pascal Fletcher; editing by Philippa Fletcher)