Marine life is disappearing faster than conservationists have feared, according to a report published by the World Wide Fund for Nature (WWF).
A study of data of global data on 1,234 species - ranging from sea birds to sharks - shows populations declined by 49% on average between 1970 and 2012.
The figure is 10% higher than conservationists' previous best estimate.
WWF claims the Living Blue Planet report, which is based on work carried out by the Zoological Society of London, shows a catastrophic loss of marine life which amounts to a crisis.
"By over-exploiting fisheries, degrading coastal habitats and not addressing global warming, we are sowing the seeds of ecological and economic catastrophe," said Dr Louise Heaps, chief advisor on marine policy at WWF-UK.
The report claims over-fishing and climate change are mainly to blame for halving global fish stocks, with the deep sea fish population down 72%.
It says rising water temperatures and increasing acidity have left three quarters of coral reefs under threat.
There are also fears that a quarter of the world's sharks, rays and skates could become extinct.