Float like … a shark ? In an unexpected discovery , investigator who tagged deep - ocean sharks with information feller reveal that at least two metal money are surprisingly buoyant , according to aPLoS ONE studypublished last week .
Unlike many other fish , which inflate their gun - filled swim bladders to increase their perkiness , shark use their liver , which are filled with oil and as such are less dense than water . When they stop swimming , they tend to either slide down ( negatively perky ) or stay in the same smear ( neutrally buoyant ) . Researchers were n’t expecting any noticeable amount of positive perkiness . In fact , this iswhy more shark have n’t invaded freshwater home ground . Earlier this class , experiment with a mechanical bruiser shark revealed how freshwater leads to a two- to three - fold increase in disconfirming buoyancy .
abstruse - ocean sharks have especially large oil - filled liver , and they ’re think to be neutrally buoyant in their inhuman , high - force per unit area environment . To see if this is really the lawsuit , a trio of investigator led byItsumi Nakamura from the University of Tokyo , Kashiwanoha , captured five bluntnose sixgill sharks ( Hexanchus griseus ) and one prickly shark ( Echinorhinus cookei ) in Kane’ohe Bay off Oahu , Hawaii , using sportfishing lines rally with Pisces scraps .
They bond accelerometer – magnetometer data logger to the sharks to quantify their swimming performance – from profundity and temperature to swimming speed and quickening – for 36 days . Two of the bluntnose sixgill shark also got cameras . At night , both sharks swim at depths of 200 to 300 meters ( where the ambient water is about 15 ° degree centigrade ) , and during the day , they swam down to deeper than 500 meter ( and colder than 7 ° C ) .
To maintain swimming swiftness during these epic erect apparent movement , the sharks seemed to exert more effort during their descent than during their upgrade and they were able to glide uphill for several minutes . These observations suggest that the deep - sea sharks are , in fact , positively buoyant . In their natural habitats , swim downward is sometimes more of a challenge than swim up .
This positive irrepressibility may be an adaptation for stealthy search , helping sharks to surprise quarry from beneath . instead , it may help with upward migration during the eve after spending the solar day in deep , cold water ; this is when muscularity temperatures are at their coolest and the shark ’s swim is at its most sluggish .
