An ailing killer whale adrift in France's River Seine will be euthanised after a plan to guide it back to sea failed and scientists concluded it was in agonising pain and terminally ill, the local prefecture says.
The four-metre-long orca, identified as a male, was first spotted at the mouth of the Seine on May 16 between the port of Le Havre and the town of Honfleur in Normandy, before it swam dozens of kilometres upstream to reach west of the city of Rouen.
Following a meeting with local and international scientists, including marine mammal specialists, the local prefecture tried on Saturday to guide the whale back to the sea with a drone while emitting orca sounds.
But the whale responded "erratically" and "incoherently" to the sound stimuli, the prefecture of the Seine maritime area said in a statement.
Sound recording of the whale captured what they said was akin to distress calls by the animal.
"The attempt to bring back the whale to sea having failed, and to prevent adding to its stress levels, a decision was made to stop the intervention in the evening," it said.
Scientists reviewed pictures and data from the intervention and concluded that the animal was suffering from mucormycosis, or black fungus, a disease seen in whales in North America but that had not been observed in Europe yet.
After infecting the skin of weakened animals, the disease can spread to the heart, lungs and brain, which explained the whale's disorientated behaviour, the prefecture said.
It added that the disease seemed very advanced in this case and was probably causing the whale major suffering.
"In these conditions, the expert group concluded unanimously that the only possible solution was to euthanise the animal to end his suffering and, also, to carry out advanced analysis of the disease it is carrying," the prefecture added.
Experts from the French office for biodiversity (OFB) as well as the Sea Shepherd NGO were among the specialists involved in the failed rescue operation.
Usually, orcas are more at home off the coasts of Scotland, Iceland and Norway, as well as further south in the Atlantic Ocean in the Bay of Biscay.
It was speculated that this orca initially strayed into the English Channel because it had fallen ill and could feed more easily in the calmer waters there but then wound up trapped in the French river.
with reporting from DPA