Sharks That Glow

Deep in the dark ocean, some sharks make their own light.

Sunlight doesn’t reach very far into the sea. Below a certain depth, the ocean is genuinely dark — and that darkness is home to a surprising number of sharks that glow.

Lanternsharks, a whole group within the shark family, are the star performers. Their skin is dotted with tiny light organs called photophores, especially along the belly and the sides. The light they give off is usually a soft blue-green.

Why bother glowing?

Two main reasons. The first is camouflage. Seen from below, any animal is a dark silhouette against whatever faint light filters down from the surface — a dead giveaway. But if a shark’s belly glows with just the right soft light, it blends into the background and disappears. Scientists call this counter-illumination.

The second reason is luring. Some glowing sharks use their light to attract prey, or to draw in curious animals that come too close.

The cookiecutter shark glows too, and it’s a sneaky one. It has a lit-up band around its body that can attract much larger animals, and then it takes a neat round bite before swimming off. Small shark, big nerve.

A glow only a shark can see

In 2019, scientists announced something surprising: swell sharks glow as well, and the light they give off is probably meant for other sharks to see, since it matches how their eyes are built. A private signal, written in light, for eyes tuned to receive it.

One last distinction worth keeping straight. Bioluminescence means an animal makes its own light, like a lanternshark does. Biofluorescence means an animal absorbs light and re-emits it in a different colour — a glow you only see if you shine the right light on it first. Some sharks do one, some do the other, and a few may do both. It’s a big, dark, dazzling ocean out there.

Did you know? Most of the animals that glow in the sea glow blue. Blue light travels furthest through water, so it’s the colour that carries.