Overfishing of small species causes jellyfish curse

Mar 19, 2013
A barrel jellyfish (Rhizostoma pulmo) is displayed in a transparent bucket in Villefranche-sur-Mer, France on July 6, 2012. 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.

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 This has been replaced by 12 million tonnes of jellyfish," Philippe Cury at France's Institute for Development Research (IRD) told AFP on Tuesday.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 , 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 that keep the jellyfish population under control; and the , 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 " in the marine mix, said Cury.

Explore further: Dwindling wind may tip predator-prey balance

add to favorites email to friend print save as pdf

Related Stories

Jellyfish replacing fish in over-exploited areas

Sep 16, 2011

(PhysOrg.com) -- Over-fished commercial stocks of plankton-eating fish have been replaced in several locations by jellyfish species. This appears to be something of a paradox because fish move quickly and ...

Small fish exploits forbidding environment

Jul 15, 2010

Jellyfish moved into the oceans off the coast of southwest Africa when the sardine population crashed. Now another small fish is living in the oxygen-depleted zone part-time and turning the once ecologically ...

Jellyfish joyride a threat to the oceans

Jun 08, 2009

Early action could be crucial to addressing the problem of major increases in jellyfish numbers, which appears to be the result of human activities.

Harvesting of small fish species should be cut: study

Jul 22, 2011

(PhysOrg.com) -- New research on the fishing of small fish species near the bottom of their food chains suggests harvesting at levels previously thought to be sustainable could have devastating effects on ...

Recommended for you

Dwindling wind may tip predator-prey balance

19 hours ago

Bent and tossed by the wind, a field of soybean plants presents a challenge for an Asian lady beetle on the hunt for aphids. But what if the air—and the soybeans—were still?

Asian stars enlisted to fight African rhino poaching

Sep 19, 2014

Increasingly desperate South African conversationists are turning to a multi-national team of "rhino ambassadors" to try to end the scourge of poaching—and Vietnamese pop diva Hong Nhung has been recruited ...

Tropical fish a threat to Mediterranean Sea ecosystems

Sep 18, 2014

The tropical rabbitfish which have devastated algal forests in the eastern Mediterranean Sea pose a major threat to the entire Mediterranean basin if their distribution continues to expand as the climate ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Sinister1811
1 / 5 (5) Mar 20, 2013
This is especially demonstrated in Japan, with the Nomura's Jellyfish being the most populous organism in their oceans. It's enough to put the fisheries out of business.