A shark’s hunt works like a relay rather than a single super-sense, with different senses leading at different distances. Smell and the feel of the current guide it from far away, water-movement sensing and sight take over nearby, and the last moments of an attack are steered by something people rarely think about: the faint electricity that living animals give off. The senses overlap enough that a shark can switch to another when one isn’t available.1SICB. Sensory switching in sharks the role of multimodal stimuli in prey tracking and capture
How a Shark Picks Up a Scent From a Distance
Smell has the longest reach of any shark sense, but scent drifts only downstream of the prey.2PubMed Central. Multisensory Integration and Behavioral Plasticity in Sharks from Different Ecological Niches A shark upcurrent of bleeding prey would smell nothing at all, and even a shark downstream has only detected something, not located it. Far from the source, the odor is broken into patches that give little sense of direction.3PubMed Central. Multisensory Integration and Behavioral Plasticity in Sharks from Different Ecological Niches So when a shark catches a scent it can’t yet locate, its sensible move is to swim against the current.4PubMed Central. Multisensory Integration and Behavioral Plasticity in Sharks from Different Ecological Niches Upcurrent is where the scent came from.
A shark judges which way is upstream by sensing how it drifts in the moving water.5PubMed Central. Multisensory Integration and Behavioral Plasticity in Sharks from Different Ecological Niches It can feel that drift through pressure-sensing organs along its body.6PubMed Central. Multisensory Integration and Behavioral Plasticity in Sharks from Different Ecological Niches Bottom-dwelling nurse sharks can feel the drift by touching the sea floor.7PubMed Central. Multisensory Integration and Behavioral Plasticity in Sharks from Different Ecological Niches Near the bottom, sharks can also see that they are drifting.8PubMed Central. Multisensory Integration and Behavioral Plasticity in Sharks from Different Ecological Niches
Once the shark is heading upcurrent, timing matters more than strength. Sharks turn toward the nostril that smells an odor first, even when the later whiff from the other nostril is stronger.9PubMed. The function of bilateral odor arrival time differences in olfactory orientation of sharks Each turn steers the shark back into a patch of scent, which keeps it on the trail.10PubMed. The function of bilateral odor arrival time differences in olfactory orientation of sharks More widely spaced nostrils could sense smaller angles at higher speed, which may help explain the hammerhead’s wide head.11PubMed. The function of bilateral odor arrival time differences in olfactory orientation of sharks
In the water, this looks like a zigzag path into the current. The shark turns each time it slips out of a patch, and the stage can last minutes. A shark that loses the scent keeps swimming upcurrent, since the next patch may lie ahead in that direction.
Feeling the Wake as the Shark Closes In
Along a shark’s sides run rows of tiny sensors that feel water movement.12American Zoologist. Structural and Functional Organization of the Lateral Line System of Sharks It works somewhat like touch at a distance, since the shark feels water pushing on its body.
The sensors pick up movement from other animals and from the shark’s own swimming.13American Zoologist. Structural and Functional Organization of the Lateral Line System of Sharks That means the shark has to separate its own motion from outside disturbances. When it does, it can turn toward something stirring the water nearby.14American Zoologist. Structural and Functional Organization of the Lateral Line System of Sharks
A struggling fish is an easy target: an injured or thrashing fish makes irregular water movement, and these sensors are tuned to such disturbances. A calm, still animal sends far fewer of these signals.
Close to prey, the wake carries both scent and swirls of moving water at once.15PubMed Central. Multisensory Integration and Behavioral Plasticity in Sharks from Different Ecological Niches Sharks follow trails of small scented swirls using smell and the water-movement sense together.16PubMed. Sharks need the lateral line to locate odor sources: rheotaxis and eddy chemotaxis They need both senses for efficient, precise tracking of a scented wake.17PubMed. Sharks need the lateral line to locate odor sources: rheotaxis and eddy chemotaxis Pinpointing exactly where the trail ends uses the same pair of senses.18PubMed. Sharks need the lateral line to locate odor sources: rheotaxis and eddy chemotaxis When the water-movement sense is unavailable, sight can help sharks still find food.19PubMed. Sharks need the lateral line to locate odor sources: rheotaxis and eddy chemotaxis
What Sharks See When They Hunt
Blacktip sharks and bonnetheads can use sight to aim a strike from any angle, upcurrent or down.20PubMed Central. Multisensory Integration and Behavioral Plasticity in Sharks from Different Ecological Niches Unlike scent, light from the prey reaches the eye whichever way the water is flowing, so once prey is in view the shark can come in from the side or downcurrent.
The idea that sharks have bad eyesight doesn’t hold for many species. Many see well in dim, murky water, trading color and sharp detail for sensitivity to low light.
The Greenland shark’s eye has only the type of light-sensing cell that works in low light.21PubMed Central. The visual system of the longest-living vertebrate, the Greenland shark These cells are densely packed and elongated, like those of other deep-sea or night-hunting sharks.22PubMed Central. The visual system of the longest-living vertebrate, the Greenland shark Great hammerheads keep finding prey at night at rates similar to daytime, despite swimming slower and seeing less far.23Animal Behaviour. Searching day and night: diel hierarchical search patterns in a large marine predator that never stops swimming
Eyes are also vulnerable at the moment of contact. Some sharks shield their eyes during the strike, and whale sharks can pull their eyes into the socket in under a second.
The Final Meter Is Guided by Electricity
Sharks have electrosensory cells that detect the weak electric signals made by other animals.24UF Health. UF scientists trace origin of shark’s electric sense – UF Health This sense is sensitive enough to pick up the electricity from a single muscle twitch, even from a flounder buried under sand.25UF Health. UF scientists trace origin of shark’s electric sense – UF Health
The cells are concentrated around the head and snout, where they can be pointed toward a target. The signal fades quickly with distance, which is why the electric sense only matters at very close range.
Within about a meter of prey, that sense becomes the most useful way to locate it and aim the jaws. The hunt shifts from minutes of tracking to a strike lasting a second or less.26PubMed Central. Multisensory Integration and Behavioral Plasticity in Sharks from Different Ecological Niches In that strike, the water-movement and electric senses give the precise target position.27PubMed Central. Multisensory Integration and Behavioral Plasticity in Sharks from Different Ecological Niches Capture depends most on the electric sense to time jaw movements lasting 10 to 100 thousandths of a second.28PubMed Central. Multisensory Integration and Behavioral Plasticity in Sharks from Different Ecological Niches
The electric signal can even beat the smell of food. In field trials, sharks following food scent turned away at the last moment to bite a live electrode.29Scientific American. How Does a Shark Hunt? From Senses to Strike They strongly preferred the live electrode over both a switched-off one and the food odor.30Scientific American. How Does a Shark Hunt? From Senses to Strike
That finding helps explain why sharks sometimes bite metal or cages. Metal in seawater can give off weak electric fields, and a shark in its final approach may aim at that signal, though this is likely only one reason among several.
How a Shark’s Jaws Deliver the Bite
Unlike ours, a shark’s upper jaw is not fixed to its skull and can push forward. In lemon sharks, this forward push accounts for about a quarter of the jaw’s closing distance.31PubMed. Feeding mechanism and functional morphology of the jaws of the lemon shark Negaprion brevirostris (Chondrichthyes, Carcharhinidae) Wobbegong sharks can push their jaws forward by a third of their skull length.32PubMed. Kinematic analysis of jaw protrusion in orectolobiform sharks: A new mechanism for jaw protrusion in elasmobranchs
The forward thrust happens as the mouth widens to suck prey in.33PubMed. Kinematic analysis of jaw protrusion in orectolobiform sharks: A new mechanism for jaw protrusion in elasmobranchs The space inside grows quickly and water rushes in, carrying nearby prey with it, while the sliding jaw brings the teeth a little closer in the final moment. Striking near the sea floor can double how far the suction reaches.34PubMed. Hydrodynamics of prey capture in sharks: effects of substrate Suction only works over short range, so the shark must already be very close, which is the job of the electric sense.
Bite and teeth then match the diet. Sand tiger jaws are built to snap shut fast, while great white jaws are built for maximum force.35PubMed. Mechanics of biting in great white and sandtiger sharks Sand tigers eat slippery fish that must be grabbed quickly. Great whites take large prey like seals that need force to cut, and their serrated teeth, compared with the needle-like teeth of sand tigers, reflect this.
Sharks with strong bites for their size tend to have more pointed front teeth.36PubMed. Is extreme bite performance associated with extreme morphologies in sharks? Species that eat hard prey have strong bites and narrow, pointed teeth at the front.37PubMed. Is extreme bite performance associated with extreme morphologies in sharks? Teeth of some sharks, such as tiger sharks, cut better than those of others, such as the sixgill shark.38PubMed Central. Modelling tooth–prey interactions in sharks: the importance of dynamic testing
Sharks With Unusual Hunting Tricks
Not every shark hunts the same way, though specialists still use smell and other senses to find prey. What differs is the final capture method.
Thresher sharks have a long, scythe-like tail they throw overhead to stun prey.39PubMed Central. Vertebral morphology in the tail-whipping common thresher shark, Alopias vulpinus To strike, the shark tucks its front fins so its rear end lifts sharply.40PubMed Central. Thresher Sharks Use Tail-Slaps as a Hunting Strategy The tail-whip bends the backbone up and down, unlike the side-to-side motion of swimming.41PubMed Central. Vertebral morphology in the tail-whipping common thresher shark, Alopias vulpinus The whip stuns or injures fish at the surface of a school, and the shark can then pick off the affected ones.
Cookiecutter sharks must rotate their bodies to cut the round, oval bite wounds they leave.42Zoomorphology. Simulating cookiecutter shark bites with a 3D-printed jaw-dental model White sharks often swim near other white sharks while hunting.43PubMed Central. Social dynamics and individual hunting tactics of white sharks revealed by biologging Being near others may let them pick up clues to large prey or leftovers.44PubMed Central. Social dynamics and individual hunting tactics of white sharks revealed by biologging That doesn’t make them pack hunters. They don’t coordinate attacks like wolves, many associations seem random, and the likely benefit is passive information sharing.
Whale sharks filter instead of chase. They feed by swimming slowly with mouths open, about 1.1 meters a second.45PubMed. Feeding anatomy, filter-feeding rate, and diet of whale sharks Rhincodon typus during surface ram filter feeding off the Yucatan Peninsula, Mexico A whale shark about 6 meters long can filter around 614 cubic meters of water an hour.46PubMed. Feeding anatomy, filter-feeding rate, and diet of whale sharks Rhincodon typus during surface ram filter feeding off the Yucatan Peninsula, Mexico That shark can take in nearly 3 kilograms of plankton an hour.47PubMed. Feeding anatomy, filter-feeding rate, and diet of whale sharks Rhincodon typus during surface ram filter feeding off the Yucatan Peninsula, Mexico Their filters catch plankton smaller than the mesh while avoiding clogging.48PubMed. Feeding anatomy, filter-feeding rate, and diet of whale sharks Rhincodon typus during surface ram filter feeding off the Yucatan Peninsula, Mexico Whale sharks gather where plankton swarms after reef spawning.49Fisheries Research. Ram filter-feeding and nocturnal feeding of whale sharks (Rhincodon typus) at Ningaloo Reef, Western Australia They are searching for patches of plankton rather than single animals.
What Puts a Shark Off Its Hunt
When orca calls or an artificial sound were played, sharks approached bait less often.50PubMed Central. The effect of underwater sounds on shark behaviour Interactions with the bait dropped from 434 to about 50 with either sound.51PubMed Central. The effect of underwater sounds on shark behaviour Orca calls cut how long sharks stayed near the source from about 16 to 11 seconds.52PubMed Central. The effect of underwater sounds on shark behaviour The artificial sound did not shorten their time nearby.53PubMed Central. The effect of underwater sounds on shark behaviour Sound can discourage feeding approaches, but no sound is a guaranteed shark repellent. Orcas prey on sharks, so sharks may treat their calls as a threat, but an unfamiliar artificial sound also caused avoidance.
The tests measured how sharks reacted to bait, which is not the same as how they would react to a person in the water. Sharks can also get used to a sound over time, so a result on first exposure may not last.