Photo: Stock

In the last fifty years, the world's marine populations have declined by half, according to a new study from the World Wildlife Fund and the Zoological Society of London.

Since 1970, 49 per cent of marine mammals, birds, fish and reptiles have disappeared.

Photo: Stock

The study says this is a result of both climate change and overfishing. Food sources like tuna and mackerel have dropped by a whopping 74 per cent.

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"Human activity has severely damaged the ocean by catching fish faster than they can reproduce while also destroying their nurseries," Marco Lambertini, head of WWF International, told the BBC.

Climate change has also played a huge part. The study says that more carbon dioxide being absorbed into the oceans, making them more acidic and ultimately damaging marine eco systems.