Though often thought of as nature’s perfect swimming machines, not all sharks are optimally designed to glide straight through the water. According to a new study appearing in the journal Nature Communications, hammerhead sharks are actually better at swimming on their sides than upright, and therefore keep their bodies contorted in this unnatural position around 90 percent of the time.
As strange as it may sound, almost all sharks are negatively buoyant – meaning they sink rather than float. To stop themselves from getting a mouthful of seabed, they use their pectoral fins to generate vertical hydrodynamic force that counteracts gravity, much like the wings of an airplane. The dorsal fin, meanwhile, is used to steer and change direction, like the rudder of a boat.
Hammerheads in particular have extremely powerful dorsal fins, which give them an advantage when hunting prey by enabling them to twist and turn at great speed. However, it turns out that this enlarged dorsal fin is also perfect for generating lift, which is why the sharks spend most of their time swimming on their side in what the study authors call a “rolled” position.
The tagged sharks spent most of their time swimming in a "rolled" position, with the optimum angle for swimming being between 50 and 70 degrees. Nicholas L. Payne et al / Nature Communications
The researchers discovered this by tagging two hammerhead sharks – one in Australia’s Great Barrier Reef and one in Belize. Using cameras and accelerometer loggers, they calculated that the Australian shark spent 90 percent of its time swimming at a roll angle of between 50 and 75 degrees, while the other maintained a body position of 30 to 80 degrees.
To figure out why the sharks do this, the team then carried out a series of experiments in a wind tunnel using a scale model of a hammerhead. Their results showed that swimming at a roll angle of between 50 and 70 degrees reduces drag by around 10 percent, suggesting that this is the best swimming position for hammerheads as it requires the least amount of effort.
All in all, the researchers suggest that not only does sideways swimming make sense for sharks, but it could also provide a solution for mechanical engineers seeking new ways to reduce drag and increase lift – though it could make walking up and down the aisles of a plane a little tricky.
