A team of Spanish researchers has studied the diet of three
species of sharks living in the deep waters in the area of El
Cachucho, the first Protected Marine Area in Spain, which is
located in the Cantabrian Sea off the coast of Asturias. These
animals feed on the resources available in their environment,
according to changes taking place in the ocean depths.
"All the sections of the food chain are inter-related in these
deep-sea ecosystems, and a small change in any one of the links in
this chain can cause great changes in the rest", Izaskun Preciado,
lead author of the study and a researcher at the Oceanographic
Centre in Santander, which is run by the Spanish Institute of
Oceanography (IEO), tells SINC.
In order to gain a detailed understanding of the species that
inhabit El Cachucho (Spain's first Protected Marine Area located
off the coast of Llanes in Asturias), the scientists studied three
species of shark that live at depths of between 400 and 1,000
metres, the blackmouth catshark (Galeus melastomus), the
velvet belly lantern shark (Etmopterus spinax), and the
birdbeak dogshark (Deania calcea).
The researcher says the results of the study, which has been
published in the Journal of Fish Biology, showed that "the
sharks' diet is opportunist, because they feed off whatever
resources are available, in this case small euphausiid crustaceans,
benthopelagic prawns and fish".
Two different habitats
The samples gathered between October 2003 and April 2004 made it
possible to define two different habitats – the top of the
bank, at a depth of 454 to 642 metres and covered with a fine layer
of sediments with a low percentage of organic material, and the
interior of the inner basin, which separates the bank from the
continental shelf, at a depth of between 810 and 1,048 metres.
The study shows that the top of the bank (400-500 metres) is
inhabited by two of the three shark species studied (the blackmouth
catshark and the velvet belly lantern shark). "However, the velvet
belly lantern shark is substituted in the deeper parts of the basin
by the birdbeak dogshark", explains Preciado.
In the deepest waters, the scientists sampled down to a depth of
1,100 metres and found that the blackmouth catshark and the
birdbeak dogshark coexist there without any trophic competition
between them, "since each one has specialised to eat a particular
kind of food", says the oceanographer.
Predicting changes in the trophic chain
The team stresses the importance of these studies in monitoring
species in the El Cachucho area. "It is likely that the
establishment of the Protected Marine Area will cause changes in
the abundance of certain species of fish, above all commercial
ones. For this reason, understanding the trophic network of these
ecosystems will help us to predict future changes in the abundance
of species", explains Preciado.
The researcher warns: "A significant increase in a predator
species could lead to a drastic decline in its prey, and so
understanding the dynamics of the trophic networks will help us to
predict changes in each of the sections of the ecosystem".
The presence of larger blackmouth catsharks in shallow waters,
for example, is a good indicator of higher levels of zooplankton
production in these areas.
El Cachucho is an undersea mountain located in the Cantabrian
Sea, off the coast of Asturias. At around 4,500 metres in height
(measured from its base on the deep-water plain of the Bay of
Biscay), it has great faunal and biological wealth. It is the first
exclusively marine reserve in Spain. To date, only parks such as
Doñana, Cabrera and the Atlantic Islands of Galicia had
extended their protection to include part of the maritime
environment.
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