At least 40 dolphins have died in an area off Mauritius affected by an oil spill from a Japanese boat, officials said on Friday, as witnesses described the deaths of one mother dolphin and her baby. Environmentalists have demanded an investigation into whether the dolphins were killed as a result of the spill from a Japanese ship, which was scuttled on Monday after running aground in July and leaking oil. The death toll may rise: fisherman Yasfeer Heenaye said he saw between 25 and 30 apparently dead dolphins floating in the lagoon on Friday morning, among scores of the animals that fishermen were trying to herd away from the pollution. “There was a mother and her baby,” he said. “He was very tired, he didn’t swim well. But the mum stayed alongside him, she didn’t leave her baby to go with the group. All the way she stayed with him. She was trying to protect him.” He filmed as the calf wallowed on its side and died in front of them, floating on the waves. Mr Heenaye, his boat running low on fuel, motioned to Reuben Pillay, who tracked the mother dolphin. She initially looked normal, he said. “But in a few minutes she went on her side, one fin in the water, and one out of the water, and then she started flapping her tail really really rapidly,” said Mr Pillay, a professional drone operator and environmentalist. “She swam in circles in front of the boat, she moved her tail very violently and after about five minutes she just stopped moving, and she sank ... We heard cries, I thought it was a woman on the boat – but they told me, no – it was the dolphin.” The mother dolphin stopped moving and eventually slowly sank, tail first, beneath the waves. The dead baby floated on the surface. “We didn’t know what to do. It was heartwrenching,” Pillay said. Earlier in the day, Jasvin Sok Appadu from the Mauritius fisheries ministry told Reuters that 38 carcasses had washed up on the beaches so far. Autopsy results on 25 dolphins that washed ashore Wednesday and Thursday are expected in the coming days, he said. So far, veterinary surgeons have examined only two of the dolphins, which bore signs of injury but no trace of hydrocarbons in their bodies, according to preliminary investigations. Postmortem examinations on the first two were conducted by the government-run Albion Fisheries Research Centre. The dolphins have been dying in an area affected by an oil spill caused when the Japanese ship, the <em>MV Wakashio</em>, struck a coral reef last month. On Thursday, Greenpeace called on the government of Mauritius to launch an “urgent investigation to determine the cause of the deaths and any ties to the Wakashio oil spill”.