WWF says humanity's mismanagement of the ocean has led to the loss of almost half the world's marine mammals, birds, reptiles and fish in a single generation.
An emergency edition of WWF's Living Blue Planet Report reveals a 49 per cent decline in marine vertebrate populations between 1970 and 2012.
For some fish this figure was almost 75 per cent.
Tracking 5829 populations of 1234 species, the report gave a much broader overview of ocean health than previous studies.
It highlighted the impact on commercial fish stocks and the role the private sector must play in slowing rates of overfishing.
It shows, for example, that scrombidae, the family which includes tuna, mackerel and bonito, suffered a 74 per cent decline between 1970 and 2010.
The chief executive of WWF in Australia, Dermot O'Gorman, says 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.