A female dolphin died after strenuous attempts to save her baby from death in the oil-polluted waters off the coast of Mauritius, and repeatedly tried to raise his head over the waves mixed with oil after he lay on his side, while environmental protection activists called for an investigation into the deaths of dozens of dolphins following the oil spill.

Footage obtained by Reuters from a fisherman trying to save the dolphin and its mother shows the desperate last moments of the mother and her baby before they died.

At least 40 dolphins have died in Mauritius, 38 of them washed ashore, since Monday when a Japanese ship sank after it ran aground last July and spilled oil from them.

Fisherman Yasfer Hinai, 31, who took pictures of the mother and her baby, said the number of dolphins could rise, indicating that he saw nearly 200 dolphins inside the reef on Friday morning, including between 25 and 30 who died. Fishermen tried to push the dolphins from shallow water into deeper waters.

"There is an oil slick on the surface of the water inside the coral reefs, and if they (dolphins) stayed there they might all die, but if they got out there might be a chance for survival. We were making noise in the boat in order to push the dolphins out of the reef," Hinai said.

He continued, "There was a mother and her baby, and the little boy was very frail. He could not swim well. But the mother did not abandon him and did not leave him to join the group. She kept with him to the end trying to save him and push him to catch up with the group of dolphins, but the little one turned on his side and died in front of her and floated in the waves."

"I could not hold back my tears as I saw this scene. I am the father of a little girl and it was very difficult for me to see the mother trying desperately and doing everything in her power to save her baby," Hinai added.