Sharks are familiar to practically everyone thanks to movies like “Jaws” and the sensational TV documentaries on them that fill up Shark Week every year. Despite this prominence, lots of the “facts” everyone knows about shark behavior are, in fact, misconceptions. If you find yourself fielding shark questions from non-diving friends and you feel the need to set the record straight, here are three apocryphal sharks “facts” you can debunk for them.
No shark in the world tries to kill humans or hunt them as prey. Human flesh isn’t even appetizing to sharks. In the overwhelming majority of shark-on-human attacks, the violence is ultimately caused by a case of mistaken identity. The shark simply mistakes a person for a natural prey animal, like a seal or turtle. A shark will bite a human because its mouth is one of its strongest sensory organs, but it will virtually never try to consume human flesh. However, with larger species of shark, even one “exploratory” bite might prove fatal.
Forward motion is important for sharks because of the way they get oxygen. They absorb it straight from the water through capillaries in their gills, so maintaining a constant flow is necessary for their survival. Not all shark species, though, rely on continuous swimming to meet their oxygen needs.
Several shark species, including angel sharks, nurse sharks, and wobbegongs, have mastered a skill called buccal breathing. These sharks suck water into their mouths and then push it out through their gills, allowing them to get oxygen while stationary. Sharks that are capable of buccal breathing spend lots of time lying motionless on the ocean floor.
Other sharks solve their breathing problem by swimming into areas that have strong currents. They let the motion of the water itself move it through their gills, remaining (mostly) stationary. This behavior is especially common in reef sharks in the Caribbean and great whites on the South African coast.
The world’s oceans are home to 400 different species of shark. At least two of them, though, can survive in brackish tidewaters and even freshwater rivers. One of these is the rare Byzant river shark or spear tooth shark, which can be found in coastal waters and rivers in New Guinea and northern Australia. The other freshwater-capable shark species is the bull shark, found all over the world. The bull shark, like all fish, is capable of osmoregulation, keeping the concentration of water in its body constant. What sets the bull shark apart is its ability to adapt its osmoregulation to account for the salinity of the water around it. This allows it to thrive in river mouths and even swim upstream into freshwater.
In reality, sharks are hardly the deadly hunters they are portrayed as in the media. Sharks are fascinating sea creatures with complex and curious biologies. Learn more about sharks and help educate your non-diving friends by dispelling the misconceptions discussed above. We hope that this post can help you to something more about shark behavior.