Since 1970, pollution, climate change and overfishing have killed off half of the world's marine life.
The World Wildlife Fund is calling it a crisis and warns it could have a devastating effect on our global food supply.
This study is said to be the biggest ever of marine ecology where conservationists looked at more than 1200 species of birds, mammals, reptiles and fish.
The findings are based on work from the Zoological society of London who, from 1970 – 2012, observed an overall drop in marine life of 49 percent.
Global fish stocks fell 50 percent while deep sea fish stocks were down to 72 percent.
Conservationists are saying much more needs to be done.
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