Jellyfish population surge to blame for drop in fish stocks?

Sailing Jellyfish
David and Heather Churcher
Swells in jellyfish populations due to overfishing may be one of the causes behind the drop in fish stocks observed in the Mediterranean and Black Sea, according to a new United Nations report which argues for including jellyfish in fisheries management.

Overfishing removes top predators from the sea helping to create conditions where jellyfish 'blooms', or suddenly increased numbers, according to the report published by the UN Food and Agriculture Organisation’s (FAO) General Fisheries Commission for the Mediterranean.

The Review of Jellyfish Blooms in the Mediterranean and Black Sea advocates incorporating jellyfish research into fisheries management, 'Normally, only the impact of human fishing activities is taken into account in setting sustainable fishing limits, but jellyfish can also have a high impact.'

According to the report, an increased number of jellyfish in the waters creates a 'vicious cycle' where the jellyfish increasingly prey on fish eggs and larvae, and compete for the same food source as the fish stock already depleted by overfishing.

If the trend continues, jellyfish could supplant fish in the world’s oceans, according to some experts cited in the FAO report who speak of 'a global regime shift from a fish to a jellyfish ocean.'

In addition to overfishing, the report’s authors note the impact of global warming which enhances the species that thrive at tropical latitudes to span out, and the prevalent use of sea walls – built to prevent coastal erosion – which are ideal habitats for some jellyfish.

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