Ecologists ask public to stay away as beluga is seen 25 miles east of London and 1,500 miles from its normal habitat

Experts are monitoring a beluga whale in the Thames estuary for a second day as fears grow for its safety.

The whale’s movements are being monitored by experts on a Port of London Authority patrol boat moored to a barge east of Gravesend.

Speaking to the Guardian from the boat, the authority’s spokesman Martin Garside, said: “I can see it now. It’s a beautiful animal – a ghostly looking thing. It is popping up every few minutes for a few seconds, more or less in exactly the same place as yesterday.”

The beluga was first spotted in the estuary on Tuesday, 25 miles east of London and 1,500 miles from its normal habitat in the Arctic. It is believed to have veered off course in search of food.

Garside said: “It is diving as if it is looking for food. We are reviewing options. The species could theoretically live off the stuff in the Thames estuary.”

Hundreds of onlookers have lined the banks of the Thames east of Gravesend hoping for a glimpse of the whale. But boat owners are being urged to keep away.

Garside said: “There was another boat in the area which we asked to leave. It was private citizen who wanted to take some photos. We have turned our engines off and we are tied up to one of the barges, so our footprint as far as the whale is concerned is minute.”

Sally Hamilton, director of the whale and dolphin charity Orca, said it was worrying that the beluga was still lingering in the area. She said: “The key is to ensure that the whale isn’t disturbed and carries on feeding. It needs to consume 2% of its body weight [each day] so as long as it carries on feeding we are hopeful it would make its own way out of the Thames.”

Rob Deaville, who is from London’s Institute of Zoology and responsible for investigating all whale strandings in the UK, said it was too early to try to rescue the beluga.

He said: “We really can’t intervene at this stage. There is not much you can do in an estuarine environment. There are some things we might begin to look at downstream involving herding, but that carries a risk of stranding too, so it is really not something we should be considering at this stage.”

Deaville, who is contracted by the government to conduct post-mortems on all stranded whales in the UK, said it was very uncommon for belugas to get stranded on the British coast.

He said: “The last beluga whale stranding we had in the UK was in 2014 with a very decomposed animal in Scotland. And prior to that the last one in the UK was in 1932, so strandings of belugas are really rare.”

Deaville pointed out that belugas are often found feeding in estuaries, but not this far south. He said: “As a species, they can cope quite happily in estuarine environments.

“But it is in a busy shipping lane and there lots of media helicopters overflying it at the moment. We are trying to discourage that and leave it to its own devices. The down draft from helicopters can also cause risks of stranding.”

He added: “We don’t know if it’s lost. I understand the speculation that it might be linked to changes in the Arctic area, but one animal does not make a trend. If we see many more animals out of habitat then that might be more cause for concern about a wider issue. But we can’t say that yet.”

Samantha Lipman, from British Divers Marine Life Rescue, a charity that specialises in saving marine animals in distress around the UK, also urged the media and the public to keep a safe distance.

Lipman, the charity’s Thames area coordinator on standby near the scene, said: “It is illegal to disturb or harass any whale, dolphin or porpoise in British waters. It is the same with helicopters that have been going overhead. Noise from above and the wind movement from propellers is going to affect them and could start herding the animal in a direction we don’t want it to go in.”

She expressed concern that the beluga could go further upriver towards central London. “The further up you go, the busier the river is,” she said. “A sighting will attract more traffic so we are really urging people to watch from shore if it is around.”

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“If it were to deteriorate and look as if it was in trouble, or it did actually strand, then we have got a team of medics and volunteers ready to intervene if necessary.”

The Environment Agency said it was not planning to close the Thames barrier to prevent the beluga from swimming further upriver.

Garside, also played down the prospect of closing the barrier. “That would be a huge decision to take and a desperate last resort. And it would only stop it moving from one part of Woolwich to another part of Woolwich. It would be in a right old pickle if it ends up there,” he said.