Jellyfish invasion: Britain to fight them on the beaches

Posted by Michael McCarthy

      Tuesday, 14 April 2009
Author: By Michael McCarthy, Environment Editor
Jellyfish, which are one of the least studied forms of marine life, are
having an increasingly harmful effect on tourism, aquaculture and fisheries
as their numbers rapidly expand. Episodes of mass stinging of swimmers in
the Mediterranean and large-scale damage to fisheries from the Black Sea to
the South Atlantic have prompted the joint study from the universities of
Swansea and Cork.
They are hoping to test the theory that overfishing maybe partly responsible
for the rise in jellyfish numbers. Jellyfish and juvenile fish feed on the
same plankton resources and if one is reduced the other expands.
Last November a jellyfish invasion wiped out Northern Ireland's only salmon
farm, killing more than 100,000 fish. Millions of small jellyfish, known as
mauve stingers, flooded into the cages about a mile into the Irish Sea, off
Glenarm Bay and Cushendun.
The jellyfish covered an area of up to 10 square miles, with a depth of 35
feet, and although rescuers tried to reach the cages, the density of fish
made it impossible. The fish farm's managing director, John Russell, said
that he had never seen anything like it in 30 years in the business. "The
sea was red with these jellyfish and there was nothing we could do about it,
absolutely nothing," he said. Earlier in the summer, beachgoers in Cornwall
and Dorset were warned to look out for the highly poisonous Portuguese
man-of-war jellyfish.
Professor Graeme Hays, the head of Environmental and Molecular Biosciences
at Swansea University, is leading the project. He is an expert on sea
turtles, which hunt jellyfish as their principal prey. "There is actually
very little known about jellyfish despite the fact that jellyfish blooms may
be increasing because of overfishing and climate change, which could have
huge socio-economic impacts," he said.
Overfishing in particular allowed jellyfish to get a hold in an ecosystem
and take it over, he said. This had been seen off the coast of Namibia and
in the Black Sea, where fisheries had collapsed as jellyfish became more
numerous than the fish themselves.
"This is a serious threat," Professor Hays said. "In 20 years' time we may
be looking at jellyfish and chips, rather than fish and chips." The threat
to swimmers was also growing. The stings of some species of jellyfish found
in British waters, such as those of the lion's mane jellyfish, were capable
of causing death. The project would allow a broad-scale assessment of the
role of jellyfish in the Irish Sea ecosystem, he added.
Professor Hays and his Irish counterpart, Professor Tom Doyle, will attach
data loggers - small devices which record information such as water
temperature and depth - to the biggest species that is found in British
waters, the barrel jellyfish, which can measure three feet across.
Once the animals die, it is hoped that the data loggers will be washed
ashore and found by members of the public. Tests have shown that the idea is
workable in practice.
The scientists hope that they may be able to work out management strategies
for fish farms to avoid jellyfish problems, but they will look as well at
the possibility of harvesting some jellyfish species as food. This is
increasingly happening in Asia. They will also be assembling all the
information necessary to treat incidents of stinging from different species.