Every two years the World Wildlife Fund (WWF) publishes its Living Planet Report, tracking wildlife populations, resource usage, pollution levels, and overall “ecological footprint.” Part of this study includes the Living Planet Index (LPI).

The LPI tracks population trends in 10,380 populations of 3,083 distinct species of fish, mammals, reptiles, amphibian, and birds, focusing on vertebrate populations that have been comprehensively monitored for many years.

Populations of both Marine and Terrestrial vertebrates were shown to have declined by 39 percent each between 1970 and 2010, while average size of freshwater populations fell by 76 percent.

That brings an overall average population decline of 51.3 percent for vertebrates.

This new average is significantly larger than the 28 percent presented in the last Living Planet Report two years ago. The WWF said that was largely because the previous report relied mostly on data from Europe and North America.

There are many different reasons for these dwindling numbers, and the LPI tracks those too. According to the WWF, habitat degradation, exploitation, and climate change are the three most prevalent threats to overall species population; with marine populations particularly threatened by overfishing and illegal fishing.

In addition to the LPI, the Living Planet Report also tracks what they call “ecological footprint”: essentially the amount of land it takes to produce the resources we presently consume on a long-term basis while keeping the land healthy and productive.

Currently the report claims our strain is 50 percent more than the earth can take.

“It is essential that we seize the opportunity – while we still can – to develop sustainably and create a future where people can live and prosper in harmony with nature,” said WWF International Director General Marco Lambertini.

The Living Planet Report can be found in its entirety here.