The term “occupants” is appropriate here because the whales of the Mediterranean are genetically different from their Atlantic cousins, which means that this group of mammals is unique in the world. “The conservation of marine mammals in the Mediterranean is a very particular problem”, explains Krishna Das. “There is very little transfer of genes with the species found in the Atlantic. This raises questions about their future, their exposure to pollutants at sea and their conservation and preservation. In addition, with regard to the Atlantic, there is less water renewal in the Mediterranean”. Also, beyond the question of the contamination, the objective of the study was to carry out a veritable ecotoxicological analysis of the pilot, sperm and fin whales in order to understand how the ecology particular to each of these species influences the contamination model. To do this, it is necessary to look at the individual characteristics of each of these cetaceans. “We sought to link the contamination profile of each of these three species with their ecosystem, their distribution in the Mediterranean and their diet. We did not have access to their stomachs so we needed to have a plan B, that is to say, to use food markers that can be analysed in the skin and which allow us to position the animal in the food web... We analysed these markers in the three species”, says Marianna Pinzone. How did we do this? By means of a crossbow (a tool used by the WWF) equipped with a hollow arrow which penetrates the blubber of the whale. This headpiece is connected to the biopsy equipment in the bow of the boat. The whale feels absolutely nothing when the arrow strikes. The sensation would be similar to that of a mosquito bite in humans. In order to ensure that several analyses are not carried out on the same animal, the researchers took several photographs during the operation. The photographer was careful to focus on the Right and left sides of the dorsal fin and the tail fin just as he took care to concentrate on the individual characteristics of each cetacean (specific marks and wounds etc.).

Higher levels of contamination

The place of mammals in the food chain is an important factor to identify because of the nature of the pollutants being examined. Indeed, persistent organic pollutants are lipophilic which means that they can only dissolve in body fat, therefore in organic matter including at great depths. “Even the animals of the Antarctic are contaminated by PCBs! The pollutants reach there by means of atmospheric and oceanic circulations. All areas of the Earth are affected, somewhat less in the Antarctic but the whales of the Antarctic are also contaminated”. Once they enter the sea water, the pollutants are first absorbed by plankton or other similar miniscule organisms. These polluted organisms are then ingested by bigger sea species. In accordance with the logic of the food chain, mammals are at the top of this pyramid and they accumulate fat reserves that are heavily contaminated by active toxic chemicals which are never dissolved. The pollutants end up in the blubber of the whale, a very dynamic tissue which breaks up during periods of hunger. When this happens, the pollutants are released into the blood, following the above pattern, the results obtained are not surprising. The fin whale, which feeds on plankton which are lower in the food chain is therefore less contaminated by PCBs, DDTs and others than the pilot and sperm whales. The pilot and sperm whales are heavily intoxicated. This can be explained by their pelagic diet because both of these mammals feed on cephalopods. The sperm whale in particular only eats a certain type of cephalopod and seems to have a very specific diet while the pilot whale may eat some kinds of fish as well as cephalopods. This probably explains why the pilot and sperm whales, animals which are higher in the food chain than the fin whale, are the worst affected by PCB-type pollutants. On the other hand, the results have revealed some surprises concerning the presence of DDTs in the tissues. The sperm whale shows a much higher level of contamination by DDTs than the pilot whale. “This is perhaps linked to the fact that the sperm whales (males in particular) move around more, they migrate to the coasts of the Mediterranean where these DDTs are still in use”.  It seems that the young males in particular have a tendency during seasonal migrations to head for the Eastern basin of the Mediterranean where large quantities of DDTs are still released into the marine environment. “In fact, we know very little about sperm whales because these animals live at great depths of up to 3,000 metres. They can bump into submarines at those depths! We are really just beginning to know something about sperm whales in the Mediterranean as elsewhere. The level of contamination in these animals should inspire researchers to study them more”, says Marianna Pinzone. More generally, it seems clear that these three mammals of the Mediterranean show higher levels of contamination than their Atlantic counterparts. Thus the pilot whale has a concentration of PCBs that is up to 95 times higher than the Tasmanian pilot whale. The same applies to the sperm whale which has twice the levels of PCB s found in the Atlantic sperm whales. As for the fin whale, it has a four times higher level of contamination than the Atlantic fin whale had twenty years ago!