LONDON, Sept. 25 (Xinhua) -- The people of Tilbury in Essex in southeast England received a shock on Tuesday afternoon as a beluga whale was spotted making its way up the River Thames, the first time that the mammal was spotted in the famous British river in 105 years.
The large marine mammal was seen off Coalhouse Fort near Gravesend and Kent's Shorne marshes, where ecologist Dave Andrews tweeted his sighting.
Meanwhile, footage was also shared by Andrews.
"For anyone twitching the beluga, it's been feeding around the barges for the last hour and hasn't moved more than 200 metres in either direction. Still present," he wrote.
There have been between 20 and 30 beluga sightings in Britain over the past 30 years, the last recorded arrival in British waters occurring in Northumberland in 2015 when the whale was able to simply turn back and return to the sea.
There has not been a beluga sighting in the Thames since 1913.
Precisely what attracted the latest beluga is unknown but there are a number of theories.
"It could have followed a food source, it could have become disorientated or it could have been motivated by a disturbance," said Lucy Babey, head of science and conservation at cetacean charity Orca.
The whale, "out of its normal habitat" away from the coasts of the Arctic and Greenland, ordinarily swims in groups but might have become separated from its pod as a result of illness or injury or been driven off course by a "disturbance" at sea, Babey speculated.
This disturbance could be anything from a weather front to it being startled by a noise from a ship, she said.
On the question of whether Britain's unseasonably warm summer might have played a part in leading it off course, Babey suggested this could be the case if the whale's food supply had cause to behave differently as a result of the balmier conditions.
