What happens when you take away the predators?

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It has long been suspected, but researchers have recently provided the strongest evidence that overfishing is indeed having a massive effect on the oceans' ecosystems.

Scientists from the Fisheries Centre at the University of British Columbia have found that larger predatory fish such as cod, tuna, and groupers have declined by over 65% over the past 100 years, whilst smaller forage fish such as sardine, anchovy and capelin have more than doubled over the same period. Shockingly, 54% of the predatory fish decline has been in the last 40 years.

The team used more than 200 global marine ecosystems and extracted more than 68,000 estimates of fish biomass from 1880 to 2007.

Lead scientist Professor Villy Christensen said of their findings: "Overfishing has absolutely had a 'when cats are away, the mice will play' effect on our oceans. By removing the large, predatory species from the ocean, small forage fish have been left to thrive."

Christensen also warned about welcoming the doubling of forage fish and pointed out that the lower trophic-level food web is more vulnerable to environmental fluctuations.

"Currently, forage fish are turned into fishmeal and fish oil and used as feeds for the aquaculture industry, which is in turn becoming increasingly reliant on this feed source," said Christensen. "If the fishing-down-the-food-web trend continues, our oceans may one day become a 'farm' to produce feeds for the aquaculture industry. Goodbye, wild ocean!"