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Tooth-like scales on shark skin reduce drag as they manoeuvre through the ocean, and they are at their most effective when the sharks accelerate.

Josephine Galipon at Keio University in Japan and her colleagues created synthetic shark skin from 3-D printed moulds based on scanning electron microscope images of skin samples from Pacific spiny dogfish (Squalus suckleyi). They then covered an aeroplane wing-shaped model with the skin and studied the fluid dynamics 鈥� specifically, the vortices, or water swirls, left in the model鈥檚 wake 鈥� as they moved it through water.

In some experiments, they moved the model at a constant 鈥渃ruising鈥� speed, while in others they accelerated it at the shark鈥檚 natural range of acceleration.

They found that the wake was thinnest, meaning that drag was reduced the most, when the object was accelerating.

鈥淪hark skin helps avoid 鈥榝low separation鈥�, meaning it prevents these water vortices from crashing into each other in the wake of the swimming body, specifically during acceleration,鈥� says Galipon. 鈥淭hat makes the shark鈥檚 take-off and turns extremely effective.鈥�

This would help improve a shark鈥檚 speed and manoeuvrability, important when chasing down prey or evading larger predators.

The findings might lay to rest a decades-old debate about how exactly the scales, called denticles, reduce drag.

鈥淢any researchers have tried to resolve this mystery, but they may not have considered that a shark is always oscillating and turning through acceleration,鈥� says Galipon, whose team worked in collaboration with scientists at Queen鈥檚 University in Kingston, Ontario, Canada.

The study could also change how people view, manufacture and use synthetic sharkskin in aquatic sports equipment, and especially better understand its benefits.

鈥淚t鈥檚 possible that, for the moment, they are not used with the right purpose in mind,鈥� says Galipon. 鈥淭he benefit may be minimal at constant, cruising speeds.鈥�