The ominous silhouette of a shark gliding through dark waters is an iconic image that strikes fear in many. This has led to a common belief that sharks are attracted to light at night. But is this really true?
In this comprehensive article, we’ll examine the science behind shark vision and behavior to find out if sharks are truly attracted to light.
If you’re short on time, here’s a quick answer: Research shows that most shark species are not attracted to light. Their vision is adapted for low light conditions. However, some sharks may be drawn to the presence of prey around artificial light sources.
How Shark Eyes Work
Tapetum Lucidum Enhances Vision in Low Light
One of the most amazing things about shark eyes is the presence of a tapetum lucidum. This reflective layer behind the retina allows sharks to see exceptionally well in low light conditions. It works like a mirror, bouncing light back through the retina and effectively giving it two chances to be detected by the photoreceptors.
This allows sharks to hunt confidently at night or in murky waters where prey animals would normally be difficult to spot.
Researchers have found that some sharks like the lemon shark (Negaprion brevirostris) can achieve light sensitivity levels 100 times greater than humans! This super-charged vision gives them a huge advantage when hunting under the cover of darkness.
Some species like the tiger shark (Galeocerdo cuvier) even seem to prefer hunting at night, likely thanks to their specialized eyes.
Most Sharks See Color and Detail
Contrary to the popular myth that sharks have poor vision, most species can actually see color and fine details quite well. Their eyes contain rod cells for low light vision as well as cone cells for seeing color and details.
Several studies have proven that sharks can distinguish colors and respond to visual cues and patterns.
For example, researchers in Australia conditioned Port Jackson sharks to associate black and white symbols with food rewards. The sharks were able to learn the meaning of the symbols and preferentially swim towards the one associated with food, proving they could discern the difference in color patterns.
However, while most sharks see in color, their cone cells tend to be concentrated in a horizontal band across the retina. This means their color vision is stronger sideways and weaker looking up and down. Still, it is sufficient to make out the colorful patterns on the reef fish they prey upon.
In clear ocean waters, sharks have been observed reacting to swimming humans from a distance of over 160 feet (50 meters) away, sometimes even aborting their approach. This shows their visual acuity and ability to identify potential threats is quite sharp.
Shark Hunting Behavior and Senses
Smell and Electoreception Aid Hunting
A shark’s sense of smell is central to its ability to find food. Their olfactory organs, located in the short ducts between the nostrils and mouth, are extremely sensitive and can detect traces of blood, gases, or bodily fluids in concentrations as low as one part per 25 million.
This allows sharks to detect injured fish or mammals from a great distance.
Sharks also utilize specialized electrical receptors called the ampullae of Lorenzini to locate prey. These jelly-filled pores on a shark’s snout sense the natural electrical signals given off by muscle movements of potential prey.
By comparison, this “sixth sense” allows sharks to effectively see with their nose. Together, smell and electoreception turn sharks into precise hunting machines.
Vision Plays Secondary Role in Finding Prey
While smell is the primary sense used in hunting, a shark’s vision does assist in capturing prey at close range. Their eyes are adapted to the ocean environment with special lenses, corneas, and a tapetum lucidum (reflective layer) allowing for enhanced vision in low light.
However, shark eyesight is still considered relatively poor compared to their other senses.
For example, studies show sharks have limited color vision and struggle to distinguish details or stationary objects. Their eyes are best suited for detecting moving prey after it’s already been localized through scent.
Surprisingly, sharks have a blind spot directly in front of their snout due to placement of their eyes on the sides of their head!
| Shark Sense | Prey Detection Role |
| Smell | Track prey scent trails from long distances |
| Electoreception | Pinpoint muscle movements once in proximity |
| Vision | Aid in final attack at close range |
Light as an Attractant to Prey Species
Artificial Light Attracts Small Fish and Plankton
It’s no secret that many marine creatures are drawn to light sources at night. Small fish, plankton, and other prey species tend to congregate around artificial lights from boats, platforms, and coastal towns.
This behavior, known as phototaxis, likely evolved as a way for plankton to orient themselves vertically in the water column and regulate their proximity to the ocean’s surface. For small fish, gathering near light sources may reduce the risk of predation in otherwise dark, open waters.
Research has shown that illuminated offshore oil platforms can attract dense aggregations of juvenile fish, squid, and krill during nighttime hours.
Coastlines illuminated by urban glow can also become hotspots for bait fish and zooplankton. A study published in 2019 found that artificially lit areas of coastal Spain supported significantly higher densities of plankton and small pelagic fish compared to adjacent dark zones. The availability of prey is also known to be higher near light sources.
These light-induced “halo effects” can spread outward for hundreds of feet, creating a buffet for opportunistic predators.
Sharks May Follow Prey Drawn to Light
Because sharks rely heavily on their vision and electroreceptors to locate prey, especially after dark, congregations of fish attracted to light often act as a dinner bell. Several studies have provided evidence that predatory sharks do indeed frequent illuminated sites to capitalize on prey availability.
Research conducted on coral reefs in the Red Sea found that reef sharks were much more abundant around an experimental underwater light compared to nearby control sites. The light’s halo attracted more bait fish, which in turn drew more sharks to feed.
A similar study in the Pacific Ocean showed that baits placed near underwater lights had double the predation rates by reef sharks than baited cameras in the dark.
There are also reports of increased shark interactions with fishing boats under bright deck lights. The dangling legs of fish being cleaned on illuminated decks likely resemble small prey attracting sharks in for closer investigation. However, while sharks may initially be curious of lit areas, they often do not linger for long in the bright lights themselves.
Overall, sharks seem most strongly keyed into the prey-gathering effects of artificial light rather than being visually attracted themselves.
Shark Deterrents Using Light
Strobe Lights and Glow Sticks Repel Sharks
An innovative way to deter sharks is by using light. Studies have shown that sharks tend to avoid bright, flashing lights. Devices like strobe lights and glow sticks can effectively drive sharks away when used correctly.
Researchers tested strobe lights on Caribbean reef sharks and found the flashing lights caused an avoidance response. The sharks fled the area, swimming away rapidly when the strobes were turned on. This demonstrates light’s potential as an eco-friendly shark deterrent.
Surfers, divers, and swimmers can use waterproof strobe lights to scare sharks away. The lights should emit high-intensity flashes at random intervals. This unpredictable pattern is key – sharks seem most wary of sporadic flickering illumination.
Strobe lights on surfboards, dive cages, or attached to life jackets provide portable protection.
Chemical glow sticks also make sharks beat a hasty retreat. But they only repel sharks when cracked to activate the luminescence. The glow sticks must be mounted in clear view of approaching sharks. Research confirms glowing green and blue light sticks ward off curious sharks looking for a snack.
Green Lasers Disrupt Shark Vision
Handheld green lasers have recently emerged as another means to thwart sharks. Studies led by Australian researchers revealed the beams irritate a shark’s vision. Shining 532nm green lasers near sharks distorted their vision enough to deter bites.
The research tested lasers on grey nurse sharks, bull sharks, bronze whalers, and great whites. All species rapidly darted away when lasers aimed near their heads. The intense green light overwhelms a shark’s sensitive retinal cells causing them to evade the irritating beams.
But aiming lasers directly at a shark’s eye is dangerous and illegal. The proper technique is scanning the laser beam in arcs near approaching sharks. Just 30 seconds of exposure prompts sharks to depart hunting grounds.
- Compact size easily fits in pocket
- Long range – beams maintain intensity for 65 feet
- Non-toxic for marine life
- Portable battery-power
The scientists concluded non-lethal laser repellency has exciting possibilities for mitigating shark attacks. But more testing is still needed to confirm long-term impacts before formally approving lasers as deterrents.
The Verdict: Most Sharks Avoid Direct Light
After reviewing the available research, the verdict is clear – most shark species tend to avoid direct light. Here’s a detailed look at shark behavior when it comes to light:
Sharks Have Sensitive Eyes That Function Better in Low Light
Sharks have very sensitive eyes that are adapted for low light conditions. Their retinas contain light-sensitive cells called rods, which allow them to see well in dim lighting. However, bright light can overload their visual system and temporarily blind them.
This makes sharks naturally inclined to avoid direct sunlight or artificial light sources.
Some Sharks Are Nocturnal or Prefer Murky Waters
Many shark species like bull sharks, tiger sharks, and great white sharks do most of their hunting at night or dawn/dusk. This allows them to take advantage of their excellent night vision while avoiding the bright overhead sun.
Other sharks prefer turbid or murky waters which block out sunlight, like lemon sharks which inhabit mangrove swamps and estuaries.
Direct Light Can Reveal Their Presence to Prey
Sharks rely on stealth and the element of surprise when hunting. Swimming into bright light would compromise their camouflage and cast an obvious shadow, alerting potential prey of their presence. Sharks maximize their chances of a successful hunt by remaining in shaded or low-lit areas out of sight.
Some Shark Feeding Patterns Correlate with Moon Phases
Studies on some shark species like bull sharks and lemon sharks have shown their feeding activity correlates with moon phases. When there is a new moon with no moonlight, feeding increases since it’s darker. When there’s a full moon producing more light, feeding decreases.
This further indicates light influences shark behavior.
Artificial Lighting Can Alter Shark Behavior
There’s evidence that artificial light sources like underwater lights on docks or illuminated boats can alter shark movements and activity levels. It’s hypothesized this could be disrupting their natural rhythms.
Conservationists recommend reducing artificial shark attractants to minimize ecological impacts.
While a few shark species are active during daytime or in shallow waters, most species clearly prefer the cover of darkness and avoid direct light where possible. Their visual systems and predatory strategies have evolved around low light conditions.
So the verdict is in – sharks generally see the light, and they swam the other way.
Conclusion
In conclusion, the belief that sharks are attracted to light appears to be mostly unfounded. While a few speculative shark attacks have involved light sources, most research indicates sharks rely far more on smell and electroreception when hunting.
Light likely disrupts their vision that is adapted for dark waters. However, sharks may indirectly follow light that attracts their prey. Overall, sharks are formidable hunters that should be treated with caution, but there is little evidence that light serves as a magnet drawing them near.
