We are up to our gills in shark myths. Aoife Muckian takes a dive into the legends surrounding these fascinating creatures, and puts some of the more fantastical ones to (sea)bed.
Throughout the world of popular culture, sharks have been depicted as an aquatic beast on the hunt for blood. This reputation has been aided and abetted by the Jaws films, which George Burgess, a shark biologist in the University of Florida notes that the films “perpetuated the myths about sharks as man-eaters and bloodthirsty killers … even though the odds of an individual entering the sea and being attacked by a shark are almost infinitesimal.”
One prevalent notion inspired by such films is that sharks can smell a drop of blood from a mile away. While it is true that sharks have a more sensitive olfactory system than humans, the sensitivity does not extend so far as to allow sharks to detect a drop of blood from a mile away. The highly sensitive olfactory system provides assistance to sharks in reproduction, as it allows them to locate a mate by detecting pheromones even in low concentrations.
The highly senstive sense of smell is enabled by sharks having separate openings for breathing and smelling; gills to the side of their heads allow them to breathe, whereas they use the nostrils at the front of their snouts to bring scents into a nasal chamber. This chamber is lined with tissue, which picks the scent and carries the information to the brain, which interprets them as scent.
Research on five species of sharks published in the Journal of Experimental Biology in 2010 has shown that at most, sharks can detect a drop of a dissolved chemical in a volume of water about the size of a back garden swimming pool, but not as large as an Olympic-sized swimming pool. Furthermore, the obvious bears pointing out: a drop of blood first has to diffuse across the pool to be detectable by our hypothetical shark. A singular drop of blood cannot be smelled from even a metre away unless it spreads.
“As impressive as its sense of smell is, it does not extend as far as to allow sharks to detect a drop of blood from a mile away.”
The myth that sharks can smell blood a mile away is often used to further perpetuate the myth that sharks will deliberately hunt, attack, and kill humans. According to the National Oceanic and Atmospheric Administartion (NOAA), humans are not part of a shark’s diet, with sharks having evolved millions of years before humans, and so their diets evolved to consist mainly of smaller fish and marine invertebrates. Scientists have suggested that the reason for shark attacks on humans (between five and 10 fatalities reported each year) is due to more humans being in sharks’ feeding grounds: the ocean, rather than being due to sharks actively seeking out tasty humans to munch on.
Sharks attacked 88 people in 2017 according to the International Shark Attack file, they kill fewer than 10 humans every year, humans kill between 20 and 30 million sharks on a yearly basis. Whatever the reasons for the myths about sharks’ ferocity, humans are far more of a threat to sharks, than they are to us.