Yet Ocean is a surprisingly optimistic film about the sea’s ability to recover faster than was previously thought possible from even devastating over-fishing.

In the Channel Islands, the Mediterranean and Hawaii’s Papahānaumokuākea, the introduction of marine protected areas has seen sea life return in abundance after years of depletion.

“Wherever we have given the ocean time and space, it has recovered faster and on a greater scale than we dared to imagine possible,” Attenborough says.

Another encouraging discovery is that ocean plankton “removes almost a third of our carbon emissions, [which] could be our greatest ally in avoiding climate catastrophe”.

The film, which will be released before the UN Ocean Conference in France next month, is a passionate plea for nations to create fully protected marine reserves in 30 per cent of their waters, ending the most damaging fishing methods while supporting local fishing communities.

As Attenborough says, “If we save the sea, we save our world”.

According to Butfield, the aim was to present an optimistic story.

“We wanted to tell a story of a hundred years of the ocean,” he says. “That obviously spans David’s lifetime, but it also spans that period of discovery of how the ocean works and the damage we’ve done to it.

“We [hoped] there’d be some really good recovery stories, but it wasn’t until we dug into the research that we found we could stand them up scientifically – the optimism was really valid.”

Butfield says that after an agreement to protect 30 per cent of the world’s land and sea by 2030 at the 2022 UN Biodiversity Conference in Montreal, it is time for “real commitments to proper marine protected areas” at the UN Ocean Conference.

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“It’s a win-win,” he says. “Everybody knows fish stocks are in trouble, the fishing industry is in trouble. There’s a chance you can actually improve everything.”

Australian underwater cinematographer Tom Park, who shot some of the footage for Ocean, says sections of the Great Barrier Reef have bounced back to life after bleaching last year.

“Reefs are far more resilient than we’ve been giving them credit for,” he says. “But we’re seeing [more] bleaching events happening in shorter and shorter time periods.

“If we actually buy them time, if we do what we can to allow them time to bounce back, they will recover.”

Park, who calls Attenborough an inspiration for generations of filmmakers, says Australia has a high percentage of marine protected areas by world standards, but they are enforced to varying degrees around the country.

“We have a long way to go in terms of protecting our protected areas,” he says.

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