Scientists have discovered that some sharks can become invisible to both prey and predators using an optical trick.
Lead author Julien Claes, a researcher in the Laboratory of Marine Biology, Earth and Life Institute at the Catholic University of Louvain, said that about 50 different shark species, or more than 10 percent of all known sharks, are luminous.
This means they can produce and emit light from their bodies, reports Discovery News.
The researchers chose to focus on one particular luminous shark, nicknamed ”the phantom hunter of the fjords”: the velvet belly lantern shark.
Claes said that this shark’s shimmer originates from light emitting organs called photophores from underneath its body, “effectively creating a glow from that region.”
“Since many predators have upward-looking eyes, it is a common method of camouflage in the mesopelagic zone (from 656 to 3,281 feet below the surface), although it is the first time it is demonstrated in sharks,” he added.
For the study, Claes and his team collected male and female velvet belly lantern sharks in Bergen, Norway. The sharks were then brought to Espeland Marine Station, where they were maintained in cold, dark water tanks, replicating conditions of their natural habitat.
The scientists next measured the luminescence intensity of each shark. Measurements were again taken after an overhead light simulation, some days later, in order to test the sharks” response to light.
Immediately after being caught, most of the sharks produced a spontaneous and long-lasting luminescence, occasionally lasting over an hour. The spectrum of this light closely matched that of the shark”s usual deepwater fjord home.
The sharks were able to adjust slightly their emitted light in response to external light changes. This ability suggests that they use both their eyes and a small gland in the brain to monitor information on light shining down from above.
Like most sharks, the mouth of this species is on its underside, so the camouflage system allows the shark to grab prey, such as krill and pearlfish, with invisible ease.
Similar to how lipstick makes a woman’s lips stand out more, the shark”s light may also turn on members of the opposite sex.
“Communication is also a function of the luminescence, since some parts of the animal appear brighter at close range, such as the pelvic part containing the sexual organs,” Claes said.
The study has been described in the current issue of the Journal of Experimental Marine Biology and Ecology.