The captain and first mate of a freighter that crashed into a coral reef off Mauritius, unleashing the Indian Ocean archipelago's worst environmental disaster, were sentenced on Monday to 20 months in jail.

"The court took into consideration the fact that both defendants pleaded guilty and apologized. The sentence handed down is 20 months in prison," said magistrate Ida Dookhy Rambarrun. 

The MV Wakashio, a Japanese-owned but Panamanian-flagged vessel, ran aground in July 2020, spilling more than 1,000 tonnes of toxic fuel into pristine waters, coating mangroves, corals and other fragile ecosystems.

The vessel's captain, Sunil Kumar Nandeshwar, who was convicted by a court in the capital Port Louis last week, admitted he had drunk alcohol during an onboard birthday party on the day in question. 

He and first officer, Hitihanillage Subhoda Janendra Tilakaratna, were found guilty of "endangering safe navigation."

"The captain and his second in command were irresponsible and did not deliver as they should on their 'navigational duties'," the magistrate said on Monday.  

The MV Wakashio was sailing from Singapore to Brazil with 3,800 tonnes of fuel oil and 200 tonnes of diesel onboard when it ran into the reef off the southeast coast of Mauritius.