After two aerial missions (11 and 28 March), detailed maps of the polluted areas could be drawn up. Sedimentationists boarded reconnaissance planes and confirmed that the extent of the pollution was very large and included the islands bordering the Côtes d’Armor.
131 research stations were chosen between Guisseny and Saint-Brieuc in order to determine the impact of the pollution. Samples were taken and analysed in 15 of these stations. Researchers noticed that the effect of this new oil spill added up to the remaining effect of the Amoco Cadiz incident.
Scientists reconstituted the events of the pollution and tried to determine the role played by natural elements. They distinguished three types of areas with the help of a vulnerability index, which took into account the geomorphology and sedimentology of each area. Out of 160 km of polluted areas:
- 50 km were heavily polluted, on Ile Grande, at Trégastel and at Ploumanac’h deposits were continuous and thick
- 35 km were fairly polluted, showing numerous discontinuous oil patches
- 75 km remained polluted to a small extent by scattered patches of thin films.
80 % of the damaged coasts were rocky.
By mid-April almost all the spilled oil had reached the shoreline.
Toxicological analyses were implemented by laboratories from the medicine faculty of Brest. The aim was to determine whether the oil had a potential effect on swimmers. But these studies were limited and the results were not very representative.
The evolution of fuel retained in the sediments was followed to check the spreading of the pollution and to measure the degree of water pollution on several sites. Data from four research campaigns of CNEXO’s ships, from March to June, asserted that pollution was significant off the Morlaix-Lannion zone, in the Sept-Iles area and off Le Trieux.
A fine proportioning method facilitated the creation of pollution cartography in the western part of the Channel, the Aber’s coastal area, the bays of Morlaix and Lannion and the area between Sept-Iles and Le Trieux. It allowed responders to establish almost instantaneously whether a zone was polluted or not.
The seabed was explored to check that there was no contamination. From 25 to 30 March, the CNEXO’s ship the Thalia carried out a first measurement assignment. Samples were taken at different depths in the water column. From 24 to 26 March, the Roscoff biological station's vessel the Pluteus asserted that there was no effect on deep marine sediments between Triagoz and Sept-Iles.
Impact studies were carried out on seaweed, plankton, bivalves, crustaceans.
- Giant seaweed was oiled to a greater or lesser extent depending on their location. Pollution did not disturb their photosynthetic activity, whereas cleaning operations seemed to have more noticeable consequences. High and medium level seaweed were little affected. Even if Ascophyllum were affected in some areas, overall losses were limited. Laminarias, which represent the main part of seaweed biomass, were also little affected.
- Global impact on plankton was low as the plankton cycle is short. Some studies on copepods showed that certain areas were polluted.
- Death of cockles and clams was recorded on Grande Island and periwinkles on polluted rocks suffered.
- Lobster larvae living at the sea surface were affected. But, on the whole, death of crustaceans due to the pollution was relatively rare. In Trégastel young bibs were found dead, their digestive tract gorged with oil. This fauna, which lived on rocks, suffered 80 % losses in Trégastel and Ploumanac’h (mid-April). Sand fleas which fed on beached seaweed survived.
Onshore studies about the pollution of intertidal sediments lasted 16 months. The effects of the oil spill that were directly linked to the nature of the fuel were measured. The Tanio’s fuel biodegraded relatively slowly, in comparison to crude oil. Along the coast the interbedding of levels of pollution was frequent with a thickness of up to 30 cm. These levels were discontinuous and mixed with polluted seaweed on many of the sandy beaches. In fine sediments the percolation was low because of the product’s viscosity, while on coarse-sand beaches it reached 40 cm. The most affected area included numerous beaches and cobble furrows, which had been seriously polluted. In these areas oil hardened and formed crusts.
The Ministry of the Environment contacted university and research institutes for a follow-up programme.
The impact of the pollution on the environment depended considerably on the degree of the pollution of the area, on the dwelling place (in sediments, on beaches, on rocks or in seaweed) and on human intervention (use of detergents, mechanical operations...). The presence of fuel on beaches, even in small quantities, altered the populations, mainly those fed on kelp. On a smaller scale, as oil accumulated, fuel was less biodegraded by bacteria.
The Institute for Marine Studies (IEM, University of Western Brittany) estimated the overall losses in the coastal marine biomass. It assessed the mortality and the settling back process on the beaches of Plougrescan and Grève Blanche (located in Trégastel), where samples had been taken to serve as references before the arrival of oil. Researchers assessed the local fauna populations at different depths. The studies on herbivorous mollusc survival gave an idea of the impact on the fixed populations living on the foreshore.
The first estimates concerning bird mortality were dramatic. There were almost no birds left on the Sept-Iles. According to the reserve keeper, alcidae (razorbills, guillemots) were the most affected. Rock birds were soon to arrive and he thought it was already too late to organise their protection. 80 % of the 4,000 pairs of northern gannets forming the Sept-Iles colony were oiled. Their eggs, covered with hydrocarbons, had no chance of hatching.
Despite the intervention of volunteers from the SPNB (“Société de Protection de la Nature en Bretagne”, Society for nature protection in Brittany), the fuel of the Tanio killed nearly 40,000 birds, twice as much as for the Amoco Cadiz incident. The extent of this mortality was also due to the fact that birds lived on the sea surface (pollution zone estimated at 1,000 square kilometres). Moreover the smell of the Tanio’s oil was too weak to repel the birds.
The sea industry under watch
The most affected area, representing 45 km of coasts from Trégastel to Ploumanac’h, was made up of a series of pink granite headlands. In this region, the variety of landscapes and the ecological wealth helped the development of various sea oriented economic activities: tourism, coastal fishing, oyster-farming, fish-farming. As a consequence, pollution led to important economic repercussions.
The Scientific and Technical Institute for Maritime Fishing monitored the exploited species, such as seaweed, cultivated oysters and mussels. From Perros-Guirec to Ile Grande, coastal seaweed was contaminated. However scallops and flat fish did not reveal any anomaly (at the end of April).