The Japanese-owned bulk carrier that ran aground off Mauritius and spilled oil over pristine waters and fragile coral reefs diverted from a regular shipping lane more than 100 kilometres from impact, data from a maritime analysis firm showed.

The MV Wakashio struck a coral reef on Mauritius's southeast coast on July 25 and later began leaking oil. Reuters reported that two of the ship's officers have since been arrested on charges of endangering safe navigation.

The iron-ore carrier was using a well-traveled shipping lane that goes past Mauritius when the accident happened, according to maritime analysis firm Windward and shipping sources. It appears to have deviated from that lane about 55 nautical miles (102 km) from Mauritius and headed straight for the Indian Ocean island, the data showed. 

The data shows the ship's track during the last few hours of its journey, including a minor turn after crossing into Mauritius’territorial waters.

"It was on a very bad trajectory," Omer Primor, Windward's head of marketing, told Reuters. It was not immediately clear why the ship appeared to deviate from its course. 

Tracking data for other cargo vessels passing close to Mauritius recently show them all sticking to the shipping lane.

Some corals have lived for centuries at the fringes of Mauritius. Now they are smothered in heavy fuel oil spilled from the wrecked tanker.

The full impact of the toxic spill is still unfolding, scientists say. As the Indian Ocean island's residents scramble to mop up the oil slicks and clumps, they are seeing dead eels and fish floating in the water, and fuel-soaked seabirds limping onto shore.

Oil began gushing from the cracked MV Wakashio about a week after it hit the reef. Around 1,000 tonnes of oil were spilled in total.

(With input from agencies)