There are many, many myths about sharks that make scientists roll their eyes, but undeniably, the most irritating and pervasive myth is that sharks eat people. Nearly every shark monster movie includes someone cutting themselves and it attracting sharks and so, so many sensationalist media headlines talk about 'man-eating sharks'. It is NOT TRUE that human blood attracts sharks because sharks simply DO NOT like to eat people. Don't believe me? Let me show you the science...
Not All Sharks are Dangerous
Scientists have currently discovered about 540 different types of sharks, but this number rises every year as we find new species. The vast majority of these animals are relatively small and completely harmless to human beings. In fact, most sharks have quite tiny teeth for eating shellfish, crabs and small fish. If you have ever been swimming in the ocean, it is very likely that you have, in fact, swum with one type of small shark or other, but they have just minded their own business and kept out of your way as you splashed around.
According to the Florida Museum International Shark Attack File (ISAF), only about a dozen shark species have been involved in attacks on humans. The top three most dangerous species of sharks are:
The great white shark (Carcharodon carcharias)
The tiger shark (Galeocerdo cuvier)
The bull shark (Carcharias leucas).
Shark Attacks are Incredibly Rare
These species are often referred to as "The Big Three" because they are responsible for the highest numbers of "unprovoked attacks" on humans every year. As these sharks are large compared to humans and armed with big teeth, they can be quite dangerous. Since records began in 1580, white sharks have been responsible for 333 unprovoked attacks upon humans, 52 of which were sadly fatal (ISAF, 2021).
You might have noticed that these numbers are very low when you consider that records began 440 years ago! Not to downplay how tragic and traumatic it is for a person to be injured by a shark, but it is incredibly rare to be the victim of a shark attack. To learn more you can read You are More Likely to be Killed by a Coconut (ISAF, 2021).
What's more, as their populations have been so decimated by overfishing, the rates of sharks bites are now actually also going down every year. So the risk is getting even smaller. See Myth Busted: Shark Bite Rates are NOT Rising (They Are Falling!) to learn more (ISAF, 2021).
Shark Attacks Are Often Not Fatal
It is also important to notice that many shark attacks are not fatal, even when they involve the heavily armed Big Three. Pooling all three totals together, only 17.3% of all Big Three shark attacks which have ever been reported were fatal. In fact, some of the shark bites reported each year involve what can only be described as a nip. Sometimes people accidentally step on a small, bottom-dwelling shark for instance, or they are bitten when they catch a shark whilst fishing. This can lead to injury, but certainly does not mean someone has been eaten. Fatalities are also declining in recent decades thanks to our excellent emergency services. (ISAF, 2021).
Sharks Do Not See Humans as Prey
What is even rarer still is that the unfortunate victim of a shark attack is actually consumed by the shark in question. It is almost unheard of for a human being to actually be eaten by a shark! It is also important to note that, when a person is killed by a shark, not being able to find a body does not necessarily mean that the victim was consumed by the shark. Sadly, sometimes it is not possible to return a body to the family, as the victim is lost in the currents after they have passed away.
When we look at shark attacks which have been witnessed by onlookers or described by the victim themselves, the vast majority of shark attacks on people are actually a single bite, sometimes two bites. At this point, it is very common for a shark to discard the victim and swim away (ISAF, 2021).
There are only a handful of incidents where there is evidence that sharks have consumed a human being. These often occur during maritime disasters. After the sinking of their a ship far out at sea, sailors left in the water have witnessed their comrades being taken by oceanic whitetips (Carcharhinus longimanus). The tragedies of the USS Indianapolis in 1930 (which was made especially famous by the movie Jaws), and The Nova Scotia and The Laconia, both in 1945 for instance. These events mean that oceanic whitetips are the greatest man-eating shark there is (Crawford, 2008).
But in reality, it is very unlikely that these sharks would attack a human under 'normal' circumstances. In these cases, due to poor communication and organisation, these men were left stranded at sea for many days, at which point many had already passed from drowning, dehydration or hypothermia. If they had been rescued in a timely manner, predation by oceanic whitetips would have been very unlikely (Crawford, 2008).
Sharks Are Not Attracted to Human Blood
So this brings us neatly onto the myth that sharks can be attracted by human blood in the water. If sharks truly become so frenzied by the smell of human blood... why do they abandon human prey when we are injured and ready for the taking? In fact, There is simply no evidence that sharks are attracted by the smell of human blood (and yes, this does include menstrual blood! Total myth! *Cue eye-roll*).
In fact, studies to determine which baits are best for attracting great white sharks have shown that these sharks are very picky about what they eat and cannot be lured to a boat by any old meat! For example, white sharks do not approach sheep or cow carcasses in the water and are disinterested in any chums which are not predominantly made up of fish blood. Human beings are simply not a valuable meal for white sharks, as we have too little muscle and fat compared to their natural prey (Klimley, 1994; Becerril‑García et al, 2020). If you would like to learn more about what great white sharks do and do not eat, you can check out Picky Eaters.
Mistaken Identity?
So if sharks do not like to eat humans, why do sharks bite people? We used to think that sharks were mistaking human beings for their prey. You have probably heard how surfers on their boards look very similar to a tasty turtle or a seal. However, we now know that many sharks are visual predators and actually have very good eye-sight, so it is unlikely that this is completely accurate. We now think that some sharks bite people because they are curious... (Strong, 1996; Martin et al, 2005).
Sharks have the vast majority of their sensory organs densely packed in and around their face (this is known as "central cephalisation"). As well as their eyes, nose, tastebuds and ears (yes, sharks have ears!), sharks also have sensory organs known as "ampullae of Lorenzini" scattered across their snout. These jelly-filled channels are capable of detecting electromagnetic impulses, such as those caused by muscle contractions of their prey.
As they don't have hands, sharks therefore often use their mouths to investigate objects in the water. This is known as "mouthing" and is not necessarily an aggressive behaviour. For example, sharks will often mouth metallic objects, like boat propellors, as they carry an electrical charge caused by friction with the water. It is not a 'crazed attack' or even an aggressive behaviour, this is simply their way of determining what this weird thing in their environment is (Strong, 1996; Martin et al, 2005).
So scientists now think many shark attacks are actually caused by a shark simply investigating a human being and our associated objects (surf boards, life preservers etc.) in the water. Once they have determined that we are unpalatable, they simply leave. Sadly though, as some sharks have such massive, sharp teeth, even this one bite can cause loss of limb or even death (Klimley et al, 1996).
Nothing to Fear
The pervasive (irrational) fear of sharks is not only unfair and unfounded, but is also seriously detrimental to their conservation. Many species of sharks are now threatened with extinction, but if the general public are frightened of (or even hate!) sharks, it is very challenging to champion for their conservation. Sharks are magnificent ancient creatures, that are vital to the the functioning of the marine ecosystem. Yet, if they are to be successfully conserved, myths like 'sharks are man-eaters' and 'sharks frenzy over human blood in the water' must become a thing of the past. Spread the word!
To learn more, you can check out my other articles on Shark Attack.
References
Becerril‑García EE, Hoyos‑Padilla EM, Micarelli P, Galván‑Magaña F & Sperone E (2020). Behavioural responses of white sharks to specific baits during cage diving ecotourism. Scientific Reports, 10:1. Access online.
Crawford D (2008). Shark. Reaktion Books.
International Shark Attack File (2021). Access online.
Klimley AP (1994). The predatory behaviour of the white shark. JSTOR, 82:2, 122-133
Klimley AP, Pyle P & Anderson SD (1996). The behaviour of white sharks and their pinniped prey during predatory attacks. In: Klimley, A.P. & Ainley, D.G.(Eds.). Great White Sharks The Biology of Carcharodon carcharias. Academic Press, San Diego, p. 175-191.
Martin RA, Hammerschlag N, Collier RS & Fallows C (2005). Predatory behaviour of white sharks (Carcharodon carcharias) at Seal Island, South Africa. JMBA-Journal of the Marine Biological Association of the United Kingdom, 85(5), 1121-1136. Access online.
Strong WR (1996). Shape discrimination and visual predatory tactics in white sharks. In: Klimley, A.P. & Ainley, D.G. (Eds.). Great White Sharks The Biology of Carcharodon carcharias. Academic Press, San Diego, p. 229-240.
By Sophie A. Maycock for SharkSpeak
