Airplane or airship? Different shark bodies for different environments
If you take a look at the different types of sharks, you'll see that some are sleek and streamlined like fixed-wing airplanes, while others are more bulbous and blimp-like. A new study has determined that this difference in body type is determined by what part of the ocean the creatures inhabit.
The study was led by Dr. Adrian Gleiss from Murdoch University Centre for Fish and Fisheries Research, working with Dr. Jean Potvin of Saint Louis University and Dr. Jeremy Goldbogen at Stanford University-Hopkins Marine Station. They assessed the body composition of 32 shark species, looking at how it affected their buoyancy control.
It was found that sharks living in deep, cold waters tend to have very large fatty livers, sometimes making up over a quarter of their body. This adds to their buoyancy, allowing them to move through the water using little energy, but also going relatively slowly because of the added bulk. Fortunately, the deep-water animals that they eat (and that eat them) are also pretty slow.
Sharks living in warmer and shallower waters, on the other hand, have comparatively smaller livers. This makes them negatively buoyant, meaning that they must move quickly in order for their wing-like pectoral fins to generate lift. While such a design might seem seem less energy-efficient than that of the blimp-like sharks, it actually makes sense for living in an ecosystem where everything else also moves faster.
"The zeppelins of the shark world must live in cold places where slow swimming is the rule for both predator and prey," says Potvin. "As with the sharks inhabiting shallow waters, trying to fly zeppelins at the speeds and accelerations common to fixed wing aircraft of same the weight class would require significantly more energy, unless that is, it is reshaped into a more javelin-like body. It would follow that slimmer, and thus more hydrodynamic sharks will require less energy for swimming at the high speeds necessary to catch agile prey, especially in environments where fast swimming is common."
A paper on the research was recently published in the journal Proceedings of the Royal Society.
Source: Saint Louis University