*[Enwl-eng] Surge In Jellyfish Driven By Overfishing of SmallSpecies

[ENWLine]

*Overfishing of small species causes jellyfish curse*

by Staff Writers
Paris (AFP) March 19, 2013

Marine biologists say they have proof that excessive trawling of small
fish species leads to proliferation of jellyfish, a worsening phenomenon
whose causes have been unclear.

The scientists monitored ecosystems in two ocean zones a thousand
kilometres (600 miles) apart, traversed by the same current.

One zone was off Namibia, where fishing has been unregulated, and the
other was off South Africa, where catches of so-called forage fish --
sardines, anchovies and herrings -- are controlled according to
available stocks.

"In the 1960s, the waters off Namibia used to yield 10 million tonnes of
sardines annually. This has been replaced by 12 million tonnes of
jellyfish," Philippe Cury at France's Institute for Development Research
(IRD) told AFP on Tuesday.

"There was very poor management of sardines and anchovies, which were
overexploited and have now almost disappeared," said Cury, a co-author
of a study that appears in the journal the Bulletin of Marine Science.

"In South Africa, there was very careful management of forage fish
stocks, and there has been no jellyfish outbreak."

Experts have fiercely debated the explosive growth in jellyfish
populations in many ocean regions.

Suspected culprits have been damage to the seabed ecosystem by bottom
trawling; the removal of predator fish that keep the jellyfish
population under control; and the greenhouse effect, which is warming
the sea.

But Cury said the new research points to the impact of removing a small
but important strand in the food web.

With little fish removed from the sea, jellyfish have no competitors for
plankton, their source of food. As a result, they proliferate uncontrolled.

"This is why it is essential to keep a certain abundance of forage fish"
in the marine mix, said Cury.



http://www.terradaily.com/reports/Overfishing_of_small_species_causes_jellyfish_curse_999.html

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