Invisible sharks

08september2010
Source: nu.nl
Researchers found out that some shark species use bioluminescence for communication with other sharks as well as for camouflage. This was studied in the velvet belly lantern shark.
This shark species (Etmopterus spinax) is a kind of small spiny dogfish. The shark is also called velvet belly because its black belly sharply contrasts with the brown coloration of the rest of its body. The shark is bioluminescent, which means it has organs in the skin that send out light. These organs are called photophores.

A group of scientists from the University of Louvain (Belgium) caught some sharks and brought them over to dark tanks filled with cold water (the sharks’ natural environment). They measured the amount of light that was emitted by the photophores. This appeared to be dependent on the amount of light present above the tanks. This makes it possible for the sharks to adapt their ‘colour’ in open water, where there are few hiding possibilities, so they are better able to approach their prey unseen.

Besides camouflage, the photophores are also used as a means of communication among the sharks. For instance, they can highlight the genitals under the belly.

Not only the velvet belly lantern shark is bioluminescent. Some 50 other shark species - more than 10 percent of all shark species – are known to be bioluminescent.