Overfishing could be
the cause
Will
we soon be forced to eat jellyfish? Since the beginning of the 2000s, these
gelatinous creatures have invaded many of the world's seas, like the Japan Sea,
the Black Sea, the Mediterranean Sea, etc. Is it a cyclic phenomenon, caused by
changes in marine currents or even global warming? Until now, the causes
remained unknown. A new study conducted by IRD researchers and its partners,
published in Bulletin of Marine Science, exposes overfishing as the
main factor.
Jellyfish have free rein
Jellyfish
predators, such as tuna and sea turtles, are disappearing due to overfishing.
However, jellyfish are primarily taking advantage of the overfishing of small
pelagic fish. Just like these cnidarians, sardines, herring, anchovies and more
feed off zooplankton. Thus, they represent their main competition for food.
In areas
where too many of these fish are caught, they free up an ecological niche.
Jellyfish now have free rein and can thrive. Furthermore, small fish eat the
eggs and larvae of jellyfish. Therefore, under normal conditions, they regulate
the population. In their absence, there is nothing to stop the proliferation of
these gelatinous creatures.
Comparison as proof
In
order to demonstrate the major role played by overfishing, researchers compared
two ecosystems belonging to the same ocean current, the Benguela, which flows
along the south of Africa. The first ecosystem is located off the coast of
Namibia. Here, fish stock management measures are not very restrictive. The
stocks are barely restored before fishing activities start up again. Jellyfish
are currently colonising these coastal waters.
The second ecosystem is located
1,000 km further south, off the coast of South Africa. Here, the opposite is
true: fishing has been tightly controlled for 60 years. The jellyfish
population has not increased.
Fisheries suffer the effects
A
vicious circle is developing in affected areas. Under the water, the links in
the food chain are much more flexible than on Earth: prey species can feed off
their predators. As such, jellyfish devour larval fish. Their proliferation prevents
the renewal of fishery resources. This invasive species in turn threatens
fisheries. In Namibia, some 10 million tonnes of sardines in the 1960s made way
for 12 million tonnes of jellyfish.
Jellyfish
are the pet peeve of tourists. The sting of their poisonous filaments --
although seldom deadly -- is very painful. Therefore, they put economic
activities in many regions across the world at risk. This is particularly true
in countries which depend on these resources, such as several developing
countries.
This
research work underlines the necessity of an ecosystemic approach towards the
exploitation of the sea. In other words, the implementation of management
measures which take into account all levels of the trophic network. According
to scientists, this is the only way to prevent jellyfish from landing on our
plates in the near future.
Did you know?
Jellyfish
are made up of 98% water. They have neither a brain, nor a heart or teeth… And
yet, they are fierce predators! They immobilise their prey with their poisonous
tentacles.
The
boom in jellyfish is observed across the entire planet. To date, however, there
is no hard data on the increase in their global population.
There
are hundreds of species of jellyfish which come in a great variety of colours,
shapes and sizes, ranging from a few millimetres to several metres in diameter.
The majority of them are carnivorous.
Story Source:
The
above story is reprinted from materials provided by Institut de Recherche pour le Développement (IRD).
Note: Materials may be edited for content and length. For further
information, please contact the source cited above.
Journal Reference:
1.
Jean-Paul Roux, Carl D
van der Lingen, Mark J Gibbons, Nadine E Moroff, Lynne J Shannon, Anthony DM
Smith, Philippe M Cury. Jellyfication of Marine Ecosystems as a Likely
Consequence of Overfishing Small Pelagic Fishes: Lessons from the Benguela. Bulletin
of Marine Science, 2013; 89 (1): 249 DOI: 10.5343/bms.2011.1145
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Institut de Recherche pour le Développement (IRD) (1969, December
31). Boom in jellyfish: Overfishing called into question. ScienceDaily.
Retrieved May 4, 2013, from http://www.sciencedaily.com/releases/2013/05/130503094700.htm