JOHANNESBURG (AP) — At least 14 dead dolphins have washed up on the coast of the Indian Ocean island of Mauritius, where a Japanese ship ran aground last month and spilled more than 1,000 tons of fuel, environmental groups and experts said Wednesday.

Other dolphins stranded on shore and appeared seriously ill, environmental consultant Sunil Dowarkasing said.

“This is a terrible day. We are seeing these dolphins swim up to the shore in distress and then die,” said Dowarkasing, a former member of parliament. “We have never seen deaths of these very intelligent marine mammals like this. Never.”

More dolphins may have died out at sea and tests will be done to determine the cause of death of those found on shore, he said.

“I think there are two possibilities: Either they died from tons of fuel spilled in the sea, or they were poisoned by the toxic materials on the bow of the ship that was sunk offshore,” Dowarkasing told The Associated Press.

“We've been worried about this. The oil spill and sinking of the bow are ruining what had been the best-preserved area of our island,” he said.

The Japanese bulk carrier MV Wakashio ran aground on a coral reef near the eastern coast of Mauritius on July 25. Pounded by the surf for days, the ship's hull cracked and on Aug. 6 it began leaking fuel into the waters of the Mahebourg Lagoon, fouling a protected wetlands area, mangroves and a small island that was a bird and wildlife sanctuary.

The ship later broke in two and the bow, the smaller of the two pieces, was towed out to sea and sunk.

The ship's captain and first officer have been charged with “endangering safe navigation.” It's not yet clear why the ship strayed miles off course.

The environmental group Greenpeace has called for an investigation.

“This is a deeply sad and alarming day for the people of Mauritius and for its singular biodiversity," said Happy Khambule, Greenpeace Africa's senior climate and energy campaign manager. The long-term impacts of the oil spill will likely affect whales, turtles, seabirds and much of the marine life in the area, Greenpeace warned.

Greenpeace Africa and Greenpeace Japan joined a Mauritius human rights organization, Dis Moi, in a letter to the government on Monday calling for greater transparency and accountability in its handling of the crisis and calling for wide-ranging investigations.

“The ocean is part of who we are. The whole country including coastal communities depend on its health," Vijay Naraidoo, co-director of Dis Moi, said.