(Reuters) – Mauritius has arrested the captain of a Japanese bulk carrier that ran aground off its coast, causing a devastating oil spill in one of the world’s most pristine maritime environments, police said on Tuesday.

“We have arrested the captain of the vessel and another member of the crew. After having been heard by the court they have been denied bail and are still in detention,” Inspector Siva Coothen told Reuters.

The MV Wakashio struck a coral reef off the Indian Ocean island nation on July 25 and began spilling oil on Aug. 6, prompting the government to announced a state of “environmental emergency” the next day.

The oil spill spread over a vast area of endangered corals, fish and other marine life in what some scientists called the country’s worst ecological disaster. Emergency crews managed to remove most of the remaining oil before the carrier split in two on Saturday.

The Mauritius coastguard had repeatedly tried to reach the ship to warn that its course was dangerous but had received no reply, a maritime official with knowledge of the incident who asked not to be named told Reuters.

“The route set five days before the crash was wrong and the boat navigation system should have signaled that to the crew and it seems the crew ignored it. The boat did also fail to send out an SOS (when it ran aground), and did not respond to attempts by the coast guard to get in touch,” the official said.

Local media have reported that the crew were having a birthday party on board. Coothen and the official declined to comment on the reports but the official said an examination of the ship’s black box might reveal whether that was true.

Scientists say the full impact of the spill is still unfolding, but the damage could affect Mauritius and its tourism-dependent economy for decades. Removing the ship is likely to take months.