A glow-in-the-dark shark scares off predators with "lightsaber-like" spines on its back, a study suggests. The research was carried out on the velvet belly lanternshark, a small species found in the deep waters of the Atlantic Ocean and Mediterranean Sea.
The scientists believe that while the light-up spines can be seen by larger, potentially dangerous fish, they are harder for the shark’s prey to spot. The study is published in the Nature journal Scientific Reports. This species of lanternshark (Etmopterus spinax) lives in the mesopelagic zone of the ocean, which has a range between 200m and 1,000m in depth.
It is a diminutive shark; the largest can measure up to about 60cm in length, but most are about 45cm long. Until recently, little had been known about this species, apart from the fact that like many deep sea creatures it has the ability to glow – a trait called bioluminescence. Previous research found that the shark has light-producing cells called photophores in its belly, and it uses this light to camouflage itself.
"Imagine you are below the shark, the shark is swimming and you have the light from the Sun coming down," explained Dr Julien Claes, a shark biologist from the Catholic University of Louvain in Belgium, and the lead author of the study.
"If you are just below the shark what you are going to see is a shadow. So imagine if the shark can actually produce a light, which is identical to the light produced by the Sun. Then the shadow of the shark is going to disappear."