Thousands protested in the capital of Mauritius on Saturday (August 29) to demand an investigation into an oil spill from a Japanese ship and the mysterious death of at least 40 dolphins.
Demonstrators packed the square of St Louis Cathedral after the carcasses washed ashore in recent days.
The government has said it will carry out autopsies on all the dead dolphins and has set up a commission to look into the oil spill.
So far two of the dolphins have been examined at a government run research center; they showed signs of injury but no trace of oil, according to preliminary autopsy results.
The results from 25 dolphins that washed ashore on Wednesday (August 26) and Thursday (August 27) are expected in the coming days.
Local environmental group Eco-Sud, which took part in Saturday's protest, said representatives from civil society should be present during the autopsies and called for a second opinion from independent specialists.