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Jellyfish Warnings

Jellyfish Warning
The Jellyfish Problem Print E-mail
Jellyfish are a normal part of the life in our surrounding oceans and individuals can sometimes be seen swimming in coastal waters or washed up on the beach. But, every now and then jellyfish may be seen in vast numbers - they bloom - a bit like Namaqualand daisies on our west coast. Blooms are a natural phenomenon in undisturbed areas.

Elsewhere in the world, jellyfish blooms are being observed more often and they are persisting for longer periods of time than usual. A number of human activities are being blamed for the increased number of jellyfish but, regardless of who is at fault, these blooms impact the way we use our oceans and coasts: jellyfish can have a negative impact on tourism and health; they interfere with fishing operations and they are likely to have an important effect on the numbers of fish available to catch.

Adapted from: Brodeur et al. (1999) Evidence for a substantial increase in gelatinous zooplankton in the Bering Sea, with possible links to climate change. Fisheries Oceanography 8: 296-306
A graph showing a  significant rise in jellyfish in the Bering Sea

Are jellyfish a problem around southern Africa? The short answer is yes - at least on the west coast and off Namibia. During 2005 ESKOM’s Koeberg nuclear power station outside Cape Town had to be closed for a couple of days because jellyfish got sucked into the seawater intake pipes. The interruption of power supply caused obvious financial hardship to ESKOM and represented an extra burden to local users of electricity.

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A picture shown in the Cape Argus when jellyfish caused Koeberg to shut down

Off Namibia, there are many more jellyfish than finfish. Finding sardines and anchovies there has become difficult and quotas have not been filled for many years. Jellyfish can clog fishing nets and cause them to burst, which means not only a loss of catch but also costly repairs. Jellyfish can also spoil otherwise clean catches of fish, which reduces their commercial worth.

ęDr. Andrew Brierley
Jellyfish caught on the net as a trawl is being pulled up on the research vessel: Nansen off the coast of Namibia