http://www.bbc.com/news/science-environment-37775622
The Living Planet assessment, by the Zoological Society of London (ZSL) and WWF, suggests that if the trend continues that decline could reach two-thirds among vertebrates by 2020.
The figures suggest that animals living in lakes, rivers and wetlands are suffering the biggest losses.
Human activity, including habitat loss, wildlife trade, pollution and climate change contributed to the declines.
Dr Mike Barrett. head of science and policy at WWF, said: "It's pretty clear under 'business as usual' we will see continued declines in these wildlife populations. But I think now we've reached a point where there isn't really any excuse to let this carry on.
