When filmmaker Sophie Lanfear arrived at the small island off Russia’s Arctic coastline in the autumn of 2017, the signs that something had gone terribly amiss were immediately apparent: dozens of walrus corpses littered the rocky shore.
But it was not until a few days into filming that she saw what was happening for herself.
Anyone familiar with new Sir David Attenborough series, Our Planet, will by now know the answer. As a result of melting sea ice, the walruses have started gathering in such high numbers on the island that the only space left is at the top of a precipitous cliff-face.
The animals haul themselves up, at which point they become so disorientated and confused about how to reach the sea below, that they hurl themselves off the edge.
Lanfear – who directed the episode – and her team captured the walruses bouncing hundreds of feet down the jagged rock face, before landing bloodied and broken below.
“I think about it all the time,” says the 36-year-old, who lives in Bristol. “I felt so helpless. Just seeing an animal that doesn’t know what is happening is so incredibly heartbreaking. The hardest things was watching them still in pain. It made me really self-reflective. I thought, we need to get this message out there.”
After the initial stir, the inevitable backlash. This week, a Canadian zoologist branded the clip “contrived nonsense”. Susan Crockford, of the University of Victoria in British Columbia, accused the filmakers of “tragedy porn” – arguing that the animals were almost certainly driven over the cliff by polar bears.
Lanfear’s response is a masterpiece in contained fury. After all, she and her team spent seven weeks on that rocky outcrop.
‘They were not being driven off the cliffs by polar bears. We know this because we had two team members watching the cliffs from afar, who could see the polar bears and were in radio communications with us to warn us about any approaching,’ she said in a statement, released this week.
‘Fundamentally, the reason walrus used this haul-out location is because of a lack of sea ice in the region, meaning they are coming ashore more frequently than they did in the past.’
Made by Attenborough’s long-term collaborator Alastair Fothergill (the co-founder of Silverback Films) in conjunction with the World Wildlife Fund, Our Planet prides itself on its scientific rigour, with every fact in the programme cross-checked by a team of scientists.
Dr Mark Wright is the WWF’s director of science and says it was his role to ensure credibility. “The walrus sequence stops you in your tracks; it is harrowing and hugely emotional,” he says. “It didn’t need to happen and that is the point. That does come down to us.”
Already the walrus scene is the stand-out from the series. If you search “Our Planet” on Twitter you will find a stream of messages posted by devastated viewers.
It has made a point of showing viewers what other nature programmes have not – that the decline of wildlife, as Dr Wright says, is down to people. This has prompted a debate whether such visceral images of the reality of climate change serve to alienate, rather than galvanise, the wider public.
According to Lanfear - who previously worked at the BBC’s Natural History Unit before joining Silverback films in 2014 - Our Planet is tapping into a demand previously revealed by the huge public reaction to plastic pollution, following Blue Planet II.
“People want to know the conservation message, they don’t just want pretty pictures and that is brilliant,” she says.
It is some 65 years since David Attenborough first appeared on the nation’s screens and, as the 92-year-old has entered the twilight of his career, the message of his programmes has sharpened.
On April 18 he will present an hour-long BBC One special: ‘Climate Change: The Facts’.
He has admitted that he was previously reluctant to speak out on climate change, as he felt scientists were better equipped to do so. But in a speech at the Our Planet premiere (attended by the Duke of Cambridge, the Duke of Sussex and the Prince of Wales), he said that the urgency of the situation has changed his mind.
“He spoke about how we’re the first generation to realise what we are doing and the last to do anything about it,” says Lanfear of the man she calls ‘Big Dave’. “We have to take ownership of this problem and wake up to the huge challenges.”
According to Lanfear, no walrus had been seen at that Arctic island for a century, until they suddently started arriving there in 2006. Previously they would stay on ice floes, closer to their feeding ground, but the rapid melting ice forced them to seek pastures new.
During filming, there were 108,000 Pacific walruses (around half the species global population) crammed on to the small landmass, meaning every inch was covered. At one point, the hut where the team of seven filmakers and scientists was staying was surrounded - and they could only film from the roof.
“I was the only woman and none of us had washed for seven weeks,” Lanfear says of their basic living conditions. “It really stank.”
Polar bears are a menace. In another location in 2015, Lanfear returned to her cabin to find it had been ravaged by a bear who ate the entire food supply, save for a jar of Marmite.
But while content to feast on the walrus corpses beneath the cliffs, Lanfear, who has a zoology degree from Bristol University, is adamant the bears played no part in them leaping to their deaths. She explains that the team watched the animals teetering back and forth unsteadily for hours, before taking the plunge. In total, during filming, an estimated 650 walruses died this way – plus another 400 or so at another site.
She believes it is down to herd mentality. “They are gregarious and hanging round in social groups. When the others below decide to go back to water, the ones on the top of the cliffs can sense they are leaving and that makes them anxious.”
Lanfear was joined on the shoot by her partner, Jamie McPherson, the principal cameraman. Both of them are visibly moved on camera. At one point Lanfear stands in front of a dying walrus, with a tear running down her cheek.
“We talk about it a lot. I guess the walrus is always there in my head, which sounds kind of crazy,” she admits. “But it’s a good to have it there, reminding you of how you can do better for the environment.”