How Does a Shark Swim? The Science of Their Movement

Sharks swim by sending waves of muscle-driven bending down the length of their body, finishing with a powerful sweep of the tail fin that pushes water backward and propels the animal forward. This looks superficially like how many fish move, but sharks have evolved a set of engineering solutions that are genuinely distinct: a skeleton made of cartilage that flexes and rebounds like a spring, skin covered in tooth-like scales that manipulate water flow, an asymmetrical tail that generates complex vortex patterns, and in some species, warm-blooded muscles that rival a mammal’s. Each of these features shapes how a shark converts muscle contractions into forward motion, and the details are stranger and more varied than most people expect.

Body Undulation and the Sweet Spot for Efficiency

The basic movement pattern is undulatory swimming: muscles on alternating sides of the body contract in sequence, producing a traveling wave that runs from somewhere near the head all the way back to the tail. The wave’s amplitude increases toward the rear, so the tail sweeps through the widest arc and does the most work pushing water backward. The rate at which the tail beats back and forth is a major knob that sharks adjust to control speed. In the lesser spotted catshark, a common bottom-dwelling species, high-speed video analysis in a flow tank showed that tail beat frequency and wave speed both increase as the shark is pushed to swim faster, while the body angle flattens out into a more streamlined posture.

There is a measurable efficiency window in this arrangement. Engineers use a number called the Strouhal number to describe how efficiently an oscillating body generates thrust. In the catshark, that number falls within the optimal range for propulsive efficiency at moderate cruising speeds of about one to two body lengths per second, suggesting the animal gets the most thrust for its effort at a comfortable cruise rather than at top speed or very slow swimming.

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A Skeleton Built to Bounce Back

Unlike bony fish, sharks have a skeleton made entirely of cartilage. This is often framed as a primitive trait, but it turns out to be a surprisingly effective material for swimming. The vertebral column flexes during each tail stroke, and as it bends, the individual vertebral segments compress. In a free-swimming spiny dogfish, the mineralized cartilage within each vertebra can compress to between about 3% and 8% of its original length.

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That compression stores elastic energy, which is then released at the end of the tail stroke to help power the next one. The vertebral column can store and release roughly 10% of the shark’s locomotor energy this way, functioning as a dynamic spring rather than just a passive structural support.

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The spring effect is not confined to the joints between vertebrae. Mechanical testing of isolated spinal segments showed that strain during bending occurs within the vertebral bodies themselves, not just at the intervertebral joints. The spiny dogfish vertebral column also contains an open internal canal covered by a thin membrane, which may help the column function like a pressurized tube, stiffening the spine in a way that is tunable depending on how the animal is swimming.

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The upshot is that a shark’s spine is not just holding the body together. It is an active participant in propulsion, recycling some of the energy that would otherwise be lost to internal friction during each tail beat.

The Asymmetrical Tail and What It Actually Does

Most sharks have a heterocercal tail, meaning the upper lobe is noticeably longer than the lower lobe. For a long time, the standard explanation was that this shape kicked the rear end of the shark upward, pitching the nose downward and requiring the pectoral fins to generate compensating lift. That story turns out to be incomplete.

A careful mechanical analysis of how the heterocercal tail actually moves during swimming showed that it is capable of directing thrust through a wide range of angles in the vertical plane. Under normal cruising conditions, the tail delivers its thrust roughly through the shark’s center of mass, rather than consistently angling it upward or downward.

⁵ The shark can adjust this angle, but the default is closer to a straight backward push than the traditional textbook diagram suggests.

The wake the tail leaves behind is also more complex than previously thought. When researchers used three-dimensional volumetric flow imaging to capture the full vortex field behind a swimming shark’s tail, they found a dual-linked vortex ring structure produced with each half-stroke. Earlier two-dimensional studies had pieced together a different wake shape from cross-sectional slices, but the full 3D picture revealed a more intricate pattern of spinning water that the shark generates to extract thrust.

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Skin That Manages the Water

A shark’s skin is covered in dermal denticles: tiny, tooth-like structures with grooved surfaces. The ridges on each denticle, called riblets, interact with the thin layer of water flowing right along the body. In general, the riblets reduce drag by disrupting the small swirling motions in the boundary layer that would otherwise pull against the shark’s forward movement.

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The drag-reduction story, though, is more complicated than the popular version where shark skin is simply “nature’s anti-drag surface.” Whether denticles reduce or increase drag depends heavily on speed. Experiments with 3D-printed replicas of shark skin showed drag reduction of up to about 9% at low flow speeds, but once speed crossed a critical threshold, the same surface began increasing drag, reaching roughly 15% more drag than a smooth surface at the highest speeds tested.

⁸ Similar results appeared in tests of different denticle arrangements, with drag reduction below about 25 centimeters per second but drag increases above it.

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Some computational models predict an even harsher picture. A high-resolution simulation of flow over denticle geometry found that denticles increased drag by 58% compared to a smooth flat plate.

¹⁰ So why have them at all? Part of the answer may be that denticles do more than just reduce steady-state drag. On the shortfin mako shark, the flexible denticles can passively bristle in response to reversing flow, which helps control flow separation during rapid maneuvers.

¹¹ In other words, the denticles’ main advantage might be less about saving energy during a straight cruise and more about preventing stalling and maintaining control when the shark turns, accelerates, or decelerates.

Staying Afloat Without a Swim Bladder

Bony fish typically maintain their depth with an internal gas-filled swim bladder that adjusts buoyancy automatically. Sharks lack this organ. Instead, they rely on a combination of a large, oil-rich liver, the relatively low density of their cartilaginous skeleton, and dynamic lift from their pectoral fins.

How well this works varies by species and lifestyle. Many open-ocean sharks are slightly negatively buoyant and must keep swimming to avoid sinking, somewhat like an airplane that stalls if it slows down too much. Shortfin mako sharks, for instance, swim faster during descents than ascents at the same tail beat frequency, confirming they are negatively buoyant and get a gravitational boost on the way down.

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Deep-sea species face a different calculus. The Greenland shark, a slow-moving deep-water predator, appears to hover near neutral buoyancy on average. Individual Greenland sharks vary on both sides, with some slightly negative and some slightly positive, but the population as a whole does not show a consistent bias. In the most extreme cases measured, a negatively buoyant individual expended up to about 225% of the effort in the counter-buoyancy direction compared to the buoyancy-aided direction. The finding supports the idea that very slow deep-sea sharks face strong evolutionary pressure toward neutral buoyancy, since they cannot generate enough lift from forward swimming to stay at depth if they are heavy.

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Warm-Blooded Muscles in a Cold-Blooded Fish

Most sharks are ectothermic: their muscles work at whatever temperature the surrounding water happens to be. But a handful of species in the lamnid shark family, including the great white, the shortfin mako, and the salmon shark, have evolved the ability to keep their core body temperature well above ambient water temperature. This is called regional endothermy, and it has a direct and dramatic effect on swimming performance.

The salmon shark has pushed this adaptation to an extreme. Its red locomotor muscles, the ones that power steady cruising, function only within a narrow and elevated temperature range of about 20 to 30°C. At cool water temperatures, these muscles are essentially useless. Even when warmed 10 degrees above ambient, they still produce only about a quarter to half the power they generate at their preferred operating temperature of 26°C.

¹⁴ The salmon shark’s muscles have, in effect, become so adapted to warmth that they have lost the ability to function in cold conditions, making the shark entirely dependent on its internal heating system.

This warm-muscle strategy pays off in speed. Across species, sharks and tunas with regionally endothermic red muscles cruise at about 1.9 times the speed of similarly sized cold-bodied fish at the same water temperature. The speed advantage comes primarily from a higher tail beat frequency rather than a longer stride. Interestingly, within the endothermic club, lamnid sharks and tunas take different approaches: tunas beat their tails faster, while lamnid sharks take longer strides per beat.

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The muscle architecture in these species is also distinctive. In both tunas and lamnid sharks, the red muscle is shifted forward along the body and connected to the tail by long tendons. This arrangement concentrates the mass of working muscle near the center of the animal rather than distributing it along the whole body, which limits the amplitude of side-to-side bending to the tail region and produces a stiffer, more efficient swimming style.

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How Mako Sharks Manage Their Energy

The shortfin mako is one of the fastest sharks in the ocean, and its energy management on long swims is revealing. Despite being negatively buoyant, tagged makos rarely used powerless gliding during descents. Glides accounted for only about 0.07% to 1.3% of their total swimming tracks, far less than theoretical models predicted for energy-saving sink-and-glide strategies.

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Gliding did show up in a different context. After periods of intense activity, particularly after capture when internal white muscle temperatures climbed toward 21°C against an ambient water temperature of about 18°C, makos were more likely to glide. This suggests gliding functions less as a routine commuting strategy and more as an emergency cooldown mechanism, preventing the shark from overheating its muscles during or after bursts of exertion.

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Shape Variations Across Species

The general undulatory plan gets modified in surprising ways depending on a shark’s lifestyle. The hammerhead’s flattened, wide head (the cephalofoil) is probably the most visually striking example. Hydrodynamic testing showed that the cephalofoil gives hammerheads greater maneuverability, which likely helps during rapid prey-capture strikes. But it comes at a steep cost: the wide head produces more drag than a typical shark head at all angles, and the energetic penalty works out to roughly a tenfold increase in the cost of moving that head through water compared to a conventional shark head shape. The cephalofoil does not generate meaningful lift when held level with the flow, so it is not serving as a wing.

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The thresher shark takes a different route, investing its body plan in an extraordinarily long upper tail lobe that it uses as a weapon. To strike, a thresher dips its snout and flexes its body sharply, tucking the pectoral fins to stall its forward motion while the tail whips overhead in a catapult-like arc. The tip of the tail travels all the way from behind the body to above the snout, stunning or killing schooling fish in the process.

¹⁹ The tail grows proportionally longer as the shark ages: the ratio of caudal fin length to total fork length increases from about 0.59 in juveniles to about 0.94 in adults, meaning adults have an even more exaggerated tail relative to body size than young animals do.

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The Lateral Line and Swimming Precision

A shark’s swimming is not just about power and efficiency. It also depends on real-time sensory feedback from the lateral line, a system of pressure-sensitive organs running along the body and head. As a shark swims, it generates its own flow field, and the lateral line detects distortions in that field caused by nearby objects. This allows the shark to sense obstacles and avoid collisions without relying on vision.

The lateral line also contributes to the precision of the final moments of a hunting strike. In blacktip sharks, disabling the lateral line caused the animals to fail to brake properly before striking prey, and they approached with their mouths at wider angles to the target, reducing capture success. The lateral line appears to function as a fine-tuning system that adjusts the shark’s final approach speed and alignment in the fraction of a second before contact.

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What Shark Skin Has Taught Engineers

The denticle drag story has fueled decades of biomimetic research, where engineers try to copy natural surfaces for human technology. Swimsuits, aircraft coatings, and underwater vehicle hulls have all been designed with shark-skin-inspired textures. But the research results suggest engineers need to be careful about what exactly they are copying. The drag-reducing effect of denticle-like surfaces is real but narrowly confined to low speeds and specific flow conditions. At higher speeds, the same surfaces create more drag than a smooth surface would. 3D-printed shark skin membranes showed a transition from drag reduction to drag increase at a specific critical flow speed, with drag-increasing effects growing as speed continued to climb.

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The spacing and arrangement of denticles also matters. Different patterns of denticles on a surface produced different drag profiles, with some arrangements performing better than others depending on flow speed.

⁹ This means there is no single “shark skin texture” that universally reduces drag. The real shark has hundreds of millions of years of evolutionary tuning behind the specific size, shape, spacing, and flexibility of its denticles for the flow conditions it typically encounters. Copying the shape without matching the operating conditions misses the point, and the growing recognition that denticles may primarily help with flow separation during maneuvers rather than steady-state drag reduction is pushing biomimetic research in new directions.