The Observer view: bottom trawlers must be outlawed everywhere

Every day, thousands of bottom trawlers scour the seabed off the coasts of the UK, Africa and Asia and across the Mediterranean. They drag heavy beams and weighted nets across kelp forests that were home to countless species and corals that can take centuries to grow. The damage they do to fish stocks and ocean ecosystems is indiscriminate. Their waste in discarded “bycatch” is unconscionable.

Bottom trawling is like bulldozing virgin rainforest, and every year the global fleet scrapes bare an area the size of the Amazon basin. A lot of people know this because the comparison features in Ocean, the new film by David Attenborough. It’s a heartbreaking piece of work for its imagery of life and death, and the sense it leaves of human senselessness.

Herring is almost gone from British waters, where bottom trawlers operate even in 90% of so-called marine protected areas. At this rate mackerel will be next, and then the common dab. A million of these flatfish a year are thrown overboard, dead.

This is the reality of modern fishing, a far cry from the cottage industry romanticised by politicians more concerned with stirring up anger than reviving fish stocks. But Ocean shows how marine wastelands can recover if properly protected. Plantlife regrows. Minnows, great predators and everything in between return and – oceans being oceans – expanding populations spill out of protected areas into fishing grounds where they can be sustainably harvested for food.

The film’s release coincides with the run-up to the UN Ocean Conference, which opens tomorrow in Nice. It’s the third conference of its kind. The conference website says its goal is “accelerating action and mobilising all actors to conserve and sustainably use the ocean”. With the greatest of respect to the French host, all urgency has been lost in translation.

A coalition of scientists is pleading for a firm commitment to protect at least a third of the planet’s oceans. That would be 10 times more than the 3% protected now, but most marine protections are not sensibly enforced. In some areas, bottom trawling is actually legal – like a tiger reserve in which every species bar the tiger can be hunted and all the trees cut down. If that continues, so will the destruction of the ocean environment, including in Antarctica, where whole food chains are close to collapse because of industrial krill fishing, which processes what used to be the staple food of whales for chicken feed.

The onward march of bottom trawling accelerates climate change. It destroys flora and mollusc beds that serve as carbon sinks. If a third of the world’s oceans were properly protected, this carbon sequestration could begin again. Fish stocks could recover, and marine megafauna could return to Britain’s coastal waters as they have to California’s. A 10th of the state’s marine protected areas were declared “no take” zones in 2012. Nowadays, grey whales, blue whales, dolphins and porpoises in their hundreds can be seen a short boat ride from Los Angeles.

“No one alive today has known the abundance of a truly wild ocean,” Attenborough says. But today’s children could. It just needs their parents’ generation to take ocean stewardship seriously. In Nice, Steve Reed, the environment secretary, will announce a ban on bottom trawling in more than half England’s marine protected areas. But Britain has yet to ratify the high seas treaty, and broader progress at giant UN conferences is often sabotaged by national interests. No nation has an interest in fishing its waters to extinction. Self-interest alone dictates conservation to keep the blue planet a living planet. Sea monsters were once mythical creatures. It turns out, they’re us.