Researchers from the University of Hawaii – Manoa in collaboration with researchers from the University of Tokyo have discovered sharks which are able to float up in the case of two species: prickly and sixgill sharks. More details about this discovery can be found in the journal Science Daily.
It is conventionally known that are negatively and sometimes neutrally buoyant, however these two species of sharks have a hard time swimming downward than up. In addition just using their tails they can glide uphill.
Sharks’ cartilaginous skeletons have a lower density than bones. In addition the shark’s large and oil-filled liver also plays a role in generating buoyancy. But in spite of these features most sharks are not buoyant, which means that they would sink if they stopped swimming. Scientists have previously considered the possibility of neutral buoyancy in the case of some sharks that could save energy in austere environments, but they did not expect to discover species of positive buoyancy
In order to test the sharks’ buoyancy is positive the researchers used an accelerometer which recorded the swimming performance of the sharks. The accelerometer recorded information about heading, body orientation, tail beat frequency and speed. One of the authors of the study, assistant researcher Carl Meyer from the UHM’s Hawaii Institute of Marine Biology said that in order to make sure that the buoyancy was indeed positive they performed two tests.
It seems that the sharks live in deeper water during the day time than night time. During day time the cold water cools their muscles and that is why they become slow swimmers. The buoyancy could be a physiological trait which allows the sharks to explore the cold, deep habitats. In order to obtain a better insight into the behavior of the sharks the researchers also used a camera. It was the first camera mounted on a deep-sea shark.
Meyer said that they wanted do discover why these sharks can float up. He wondered whether this trait offers them stealth when hunting or if it helps them to migrate to shallow areas during night time. He remarked:
“When I first downloaded the camera, I thought it had failed because all I saw were thousands of completely black frames. Suddenly a string of images appeared with a brightly-lit, alien-looking reef and strange deep-sea invertebrates. I was elated and realized that the black frames resulted from the shark swimming around too high in the water column for the camera strobe to illuminate the seabed.”
Image Source: Wildlife Online