New Satellite Analysis Shows Mauritius Oil Slick Growing Ten Times In Size Over Past Five Days

This article was updated with the latest satellite imagery and analysis on the size of the oil slick over the course of the day.

The latest satellite data and analysis of the oil spill caused by the stricken Japanese bulk carrier, MV Wakashio off the coast of Mauritius, taken on Tuesday 11 August at 3.12pm Mauritian time, shows that the area directly impacted by the oil slick has expanded to almost ten times its original size since the vessel first started leaking heavy oil into the coastal waters five days ago.

The analysis reveals that the oil slick now stretches over 14 miles in length along the East Coast of Mauritius from Blue Bay Marine Park to the tourist island of Ile aux Cerfs.

Using Synthetic Aperture Radar (SAR) satellites from satellite company Iceye, which are specially calibrated to detect oil slicks, the US satellite analysis company, Ursa Space Systems, was able to estimate the size of the Southern portion of the oil slick up to Pointe du Diable as now covering an area of 27 square kilometers. 

This is in comparison to the size of the more concentrated oil slick on Thursday 6 August 2020, when it then covered an area estimated at 3.3 square kilometers, centered mainly around Ile aux Aigrettes and the Port of Mahebourg.

Size and location of Wakashio oil slick on 11 August 2020

Size and location of Wakashio oil slick on 6 August 2020

Other findings from the SAR satellite analysis reveals:

• Small amounts of oil film appear to be entering Blue Bay Marine Park
• Most of the Bay of Mahebourg has a thin covering of oil film
• The oil slick appears to stretch North, with traces of the oil slick seen slightly beyond the tourist island of Ile aux Cerfs and Ile aux Margenie

The supporting salvage operations can also be tracked using SAR satellites.

Blue Bay Marine Park

Using the false coloring of orange to highlight the extent of the reflective oil sheen, synthetic aperture radar is able to show the oil slick going around the oil protective boom and into Blue Bay Marine Park on the left of the image. The Wakashio is circled in white.

Oil sheen heads North

Satellite analysis using synthetic aperture radar shows the oil sheen moving Northward along the coast of Mauritius, and around the large aquaculture farms off the East Coast of Mauritius on 11 August 2020 at 3.12pm local time, five miles North of the Wakashio crash site.

Strong winds and currents from the South of the island have pushed traces of the oil sheen North past the small tourist islands of Ile aux Cerfs and Ile aux Margenie, 14 miles North of the crash site.

Understanding oil spills

To the naked eye, the ocean may appear clear, but the silky film of the heavy oil impacts the surface tension and other chemical properties of seawater, and this is what is detected by the SAR satellites. 

Oil floats on the surface of water and over time usually spreads out to a thin layer.  As the oil spreads, this layer becomes thinner and thinner and changes in color from black or brown to a rainbow of colors and finally to a silver of silver-grey, very thin layer called a sheen.

This rainbow-like sheen can be seen from high resolution satellite imagery around the Port City of Mahebourg on 9 August 2020.

Harmful to corals and marine life

Although a thin sheen may look almost transparent, it has long term consequences for the health of marine life.

It can impact the health of fragile coral reef ecosystems, mangroves, sea birds, fish, turtles, dolphins, whales and shellfish in several ways, impacting lungs, immune and reproductive functions and leading to multiple organ failure among marine mammals. This is particularly concerning for Mauritius, which is one of richest biodiversity hotspots in the Indian Ocean with unique fauna and flora not found anywhere else in the world, particularly in the location of the crash site.

According to the US National Oceanographic and Atmospheric Administration (NOAA), fish eggs and larvae can be especially sensitive to lethal and sublethal impacts, and can make seafood unsafe for humans to eat.

1600 tonnes of heavy oil left on board

Also on Tuesday 11 August, the Wakashio, experienced a widening gash along its side, that has been widely viewed.

A statement by the vessel owner Nagashiki Shipping Co. Ltd., revealed that as of Tuesday 11 August,  

• “Approximately 1,020 metric tons of Very Low Sulphur Fuel Oil (VLSFO) onboard had been pumped out and transferred onto small tankers. 
• Approximately 1,180 metric tons had leaked out from the vessel fuel tank, of which an estimated 1,000 metric tons had leaked outside of the vessel, and 460 metric tons is estimated to have been manually recovered from sea and coast.
• About 1,600 metric tons of VLSFO and about 200 metric tons of Diesel Oil remain on the ship, and transfer work will continue.”

This means that of the 3800 metric tons of heavy oil (VLSFO) on board the vessel on 25 July 2020, 720 metric tons has leaked into the ocean and has been unrecoverable so far, and 1600 metric tons remain at risk on board the vessel, 61% of the original amount. 

With ongoing cleanup efforts in the lagoon, less oil on board than the initial volume on 6 August when the leaks commenced, and calmer weather, it is hoped that the extent of the oil spill can stabilize in the upcoming days to aid cleanup and rehabilitation efforts.