Sir David Attenborough has issued a heartfelt statement ahead of his 99th birthday on May 8. In advance of the release of his new film Ocean, which will hit cinemas the same day he blows out his candles, the natural history legend says: "We are almost out of time." The remark came as he highlighted the catastrophic decline in life in the world's oceans as his new documentary gives an understanding of how they have changed in the course of his long lifetime. Remembering his first scuba dive on the Great Barrier Reef nearly 70 years ago in 1957 he said: "I was so taken aback by the spectacle before me I forgot – momentarily – to breathe."

Today he says the ocean is: "In such poor health, I would find it hard not to lose hope, were in not for the most remarkable discovery of all, the ocean can recover faster than we had ever imagined. It can bounce back to life."

He hopes this latest feature length film could play a decisive role in saving biodiversity and protecting the planet from climate change.

The documentary features astonishing underwater footage including a graphic images of the damage bottom trawling can do to the seabed.

This is a common, and legal, industrial fising practice which sees trawlers drag a behind them scours the seafloor, forcing the creatures it disturbs into the net behind.

More than three-quarters of what they catch can be discarded as they are often seeking a single species. "It's hard to imagine a more wasteful way to catch fish," David observes.

"When I first saw the sea as a young boy, it was thought of as a vast wilderness to be tamed and mastered for the benefit of humanity.

"Now, as I approach the end of my life, we know the opposite is true," he admits in the trailer for the film.

"After living for nearly a hundred years on this planet, I now understand that the most important place on Earth is not on land, but at sea.”

"If we save the sea, we save our world. After a lifetime of filming our planet, I’m sure nothing is more important."

Ocean with David Attenborough is releasing as a Global Cinema Event from May 8. It will also be made available on National Geographic, Disney Plus, and Hulu later this year.