Are Sharks Easy to Spot in the Dark?

Scientists have discovered that many shark species, living secretively in the dark depths of the ocean, actually glow to become more visible to each other, and presumably to make it easier to find a mate. The latest documentation of biofluorescence in marine life came in a 2016 study of two species, the chain catshark and the swell shark. Both are small fish -- about three feet (.9 m) long -- that hide in crevices at depths of 1,600 to 2,000 feet (488 to 610 m).

In the case of the swell shark, this biofluorescence is bright green and is produced by fluorescent proteins inside its skin. Humans can’t see it, but other sharks can, thanks to a higher density of light-sensitive cells in their retinas.

Finding biofluorescence in the sea:

• Biofluorescence in fish is a relatively new discovery by scientists, who now believe that it occurs in more than 200 species of sharks and bony fish, as well as marine turtles, eels, and jellyfish.
• To see the fluorescent markings, shark researchers used cameras with yellow filters to block out the natural blue light, the same way a shark’s eye does.
• Biofluorescence has been used by medical researchers to track how cells work, leading to medical advances in the study of AIDS, cancer and Alzheimer's disease.

Frequently Asked Questions

Can sharks see well in the dark?

Yes, sharks have excellent night vision. Their eyes are adapted to low-light conditions with a reflective layer called the tapetum lucidum, which enhances light sensitivity. This allows them to effectively spot prey even in murky or dark waters, giving them a significant advantage as nocturnal hunters.

How do sharks navigate in the dark?

Sharks rely on a combination of keen senses to navigate in the dark. Apart from their enhanced vision, they use electroreception through their ampullae of Lorenzini to detect the electrical fields emitted by other organisms. This sensory system is so precise that sharks can detect prey buried in sand or hidden in coral.

Are certain species of sharks more active at night?

Many shark species exhibit nocturnal behavior, becoming more active at night. For instance, the great white shark is known to hunt in low light conditions, taking advantage of their superior night vision and the cover of darkness to ambush prey. This pattern varies among species and can be influenced by prey availability and environmental factors.

What adaptations help sharks hunt in the dark?

Sharks have several adaptations for hunting in the dark, including large, complex eyes for improved light sensitivity, and the aforementioned tapetum lucidum. Additionally, their lateral line system detects vibrations and movements in the water, allowing them to hone in on struggling or swimming prey without relying solely on vision.

Is it more dangerous to swim with sharks at night?

Swimming with sharks at night can be more dangerous due to their increased activity and hunting behavior during these hours. The reduced visibility for humans also adds to the risk, as it becomes harder to spot and monitor shark movements. It's generally advised to avoid entering waters frequented by sharks after dark.

How do researchers study sharks in the dark?

Researchers study sharks in the dark using various technologies, such as tagging with satellite or acoustic transmitters to track movements. They also employ underwater cameras with night vision capabilities and sometimes use submersibles or remotely operated vehicles (ROVs) to observe sharks in their natural habitat without disturbing them.