One in four species of shark, ray and skate is threatened with extinction

The number of fish, turtles and other wildlife in the world’s oceans has halved in decades, conservationists warn.

Overfishing, pollution and changing climate are blamed for the ‘potentially catastrophic’ decline in marine life.

From the temperate UK waters to tropical coral reefs, the planet’s seas are emptying fast, the World Wildlife Fund and the Zoological Society of London say.

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Species in crisis: The new report found a 49 per cent drop in numbers among the 6,000 populations studied around the world, including leatherback turtles (pictured)

Species in crisis range from leatherback turtles, ‘monsters of the deep’ that can be seen off the coast of Britain, to the colourful corals of the Great Barrier Reef.

The Living Blue Planet report tracks the fate of more than 1,200 species of marine mammals, birds, fish and reptiles since 1970. It found a 49 per cent drop in numbers among the 6,000 populations studied around the world.

Some declines were even more dramatic, with populations of the Scombridae family of fish, which includes tuna and mackerel, falling by 74 per cent.

Sea cucumbers – animals shaped like the vegetable that are prized as a luxury food but play a vital role in improving water quality – have all but disappeared from the Red Sea. And Australia’s Great Barrier Reef has lost more than half of its coral in the last 30 years.

Worldwide, one in four species of shark, ray and skate is threatened with extinction. The porbeagle shark, a favourite with UK anglers, has undergone a ‘precipitous decline’, as has the leatherback turtle. Other species in peril in British waters include puffins, sand eels and sole.

But there is some good news, with more than half of the herring, haddock and other fishing in the North Sea now being done at a level that allows stocks to recover.

The WWF said that there is no time to be lost if the tide is to be turned worldwide.

Marco Lambertini, director general of WWF International said: ‘In the space of a single generation, human activity has severely damaged the ocean by catching fish faster than they can reproduce while also destroying their nurseries.

‘Profound changes are needed to ensure abundant ocean life for future generations.

‘We are in a race to catch fish that could end with people starved of a vital food source and an essential economic engine. ‘Overfishing, destruction of marine habitats and climate change have dire consequences for the entire human population, with the poorest communities that rely on the sea getting hit fastest and hardest.

‘The collapse of ocean ecosystems could trigger serious economic decline – and undermine our fight to eradicate poverty and malnutrition.’

Dr Louise Heaps, head of marine policy at the WWF, called on governments to set up more Marine Protected Areas – essentially national parks of the seas – as well as do more to tackle climate change.

She added: ‘Every one of us can take meaningful action, starting today, by ensuring that all the seafood we eat is responsibly sourced and Marine Stewardship Council accredited.

‘As well as being a source of extraordinary natural beauty and wonder, healthy seas are the bedrock of a functioning global economy.

‘By over-exploiting fisheries, degrading coastal habitats and not addressing global warming, we are sowing the seeds of ecological and economic catastrophe.