At the end of May, an orca was found dead in the Seine, between Rouen and Le Havre.
At the beginning of August, a very weakened beluga headed upriver, but did not survive the attempt by rescuers to bring it back to sea.
On Saturday, a seal was seen in the Seine, near Rouen.
Why do you think cetaceans swim up European rivers?
Do you think these are isolated acts or is there a dynamic that is taking place?
Gérard Mauger: “Today, we are back to normal.
It is a known fact that, at all times, cetaceans sometimes go up rivers.
I am thinking of the porpoise, which frequents the bay of the Seine and which went back to it, in the Middle Ages, as far as the bay of Jumièges, where we found this famous killer whale [in May].
For the beluga, it's the same, these are species that quite often frequent freshwater estuaries and sometimes go up rivers like the St. Lawrence [Canada].
It is a well-known population that has been studied for a long time.
What was very special here was that for both the killer whale and the beluga, we had to deal with two animals that arrived in a very weak state in the Seine estuary.
Why did they go up the river when they were tired?
I don't have an answer to give.
It is true that we can qualify this behavior as "aberrant", in the sense that they are not used to going so far up a river and, above all, that they have not sought to return to the sea. Quite often, there are animals that go up the rivers, but they go back to the sea after a while.
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According to Stéphane Lair (director of the Quebec Center for Wild Animal Health), this type of event is due to the degradation of natural habitats. Do you share this hypothesis?
GM: “There is no explanation, for the moment, which takes precedence over others.
What is certain is that when animals are not well and are in pain, their behavior is sometimes strange.
There, what is special with the two animals is that they are two individuals who, normally, should have been with their congeners, because they are gregarious species.
For undetermined reasons, for the moment, they are found isolated from their original group and have found themselves a little "lost", far from their usual living area.
On the reasons, there are tons… A problem of illness, perhaps: pathologies that mean that these two individuals could not follow their original group or that forced them to leave them.
Or they were separated for other reasons, such as disturbances in their echolocation system, which could be linked to parasites, or diseases of the inner ear, or explosions or other very loud sounds. .
We do not have an answer for the moment, we will have to wait to see a little more clearly on the result of the autopsy of the beluga and the killer whale.
The common point between these two individuals is that they arrived weakened, emaciated and that they stopped eating several weeks ago.
This does note that there was a problem even before they put the fins in the Seine.
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Do you think it is possible, by 2050, that we could find beluga whales and other species not endemic to French waters, such as sharks in the Mediterranean, permanently established near our shores? ?
GM: "What is obvious is that with global warming, which affects the oceans even more than land environments, this generates substantial changes in marine environments, with changes in currents, changes in temperature, with a acidification, an increase in the level of carbon dioxide in the water.
All this means that the marine environment is quite "turned upside down".
It also impacts the movements of species, and in particular those that serve as food [plankton and fish that serve as prey for predators such as cetaceans].
All of these movements mean that some species will adapt less than others.
Among cetaceans, there are opportunists, such as the bottlenose dolphin, which has a sedentary group studied for twenty-five years at the Cotentin Cetacean Study Group.
He is lucky enough to be able to adapt: if he can't find any mackerel, he will eat cuttlefish and if he can't find any cuttlefish, he will eat something else and so on.
He has a very wide range of food, he adapts.
On the other hand, there are other species that eat targeted products and if the prey move, this will in fact encourage a population to move.
For the beluga,
From a more global point of view, it is true that the displacement of the resource has an impact on cetaceans.
I also think that overfishing, industrial fishing, drastically reduces certain stocks of certain species of fish, this also generates imbalances which are significant and this has an impact on all species, and, ultimately, on mammals who are top predators, just like us humans.
We are also concerned by the reduction of the resource.
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