One of the only times that most members of the general public ever come into contact with sharks, is when they see a report of a shark attack on the news. Of course a shark attack is horrifying and terrible for the victims and their family, but these reports are often unnecessarily alarmist, leading many people to believe that sharks are incredibly dangerous and ferocious, or that attacks are common. In reality, shark attacks are incredibly rare and even if you regularly use the ocean, the probability of ever having a traumatic encounter with a shark is almost negligible. Many seem to believe that shark attacks are on the rise in recent years... BUT, recent research suggests that, in fact the opposite is true; that shark attacks are actually declining globally!
The Stats
Every year between 80 and 100 shark bite incidents are recorded globally. This does not mean that 100 people were killed by a shark! In fact, an average of around 6 people are killed by sharks every year globally (ISAF, 2020).
People can be bitten by a shark in many different contexts... sometimes these bites are "unprovoked", such as a shark biting a surfer and their board, gnawing on a boat propellor or biting down on a SCUBA diver's fins with no provocation. On the other hand, sometimes shark attacks are "provoked"; sometimes this is due to someone accidentally stepping on a shark in the shallows or this may be caused by people intentionally crowding or harassing sharks when snorkelling or diving, resulting in defensive behaviours (ISAF, 2020).
According to the International Shark Attack File (ISAF) the highest number of unprovoked shark bites which have been reported, have occurred in the USA (1483 bites), Australia (652 bites), South Africa (255 bites) and Brazil (107 bites) (ISAF, 2020).
On the Rise?
As global economics improve and more and more people, in many different countries are enjoying a higher quality of life, recreational ocean use is becoming more common. Subsequently, there was fear that shark attacks might rise as well. So, a recent study sought to understand how the trends of shark bites have changed over time. They achieved this, not by looking at the absolute number of shark bites, but by considering how many shark bites occurred in the past as a function of the population size. This allowed them to account for population growth and the associated rise in ocean use. They called this the 'bite rate' (Ritter et al, 2019).
They analysed the top 10 countries which had the highest numbers of shark bites annually between 2000 - 2016 (including The USA, Australia and South Africa (ISAF, 2020). They found that the bite rate in these 10 countries has been consistently declining since 2016 and quite rapidly, in fact! To check this was correct, they used their statistical model to predict how many shark bites would occur in 2018; the model expected 88.3 incidents and the actual count that year was 82... so the model seems to be quite accurate (Ritter et al, 2019).
"Against common assumptions, the world’s shark bite rates are decreasing!"
- Ritter et al, 2019
The researchers suggested that the actual numbers of shark attacks each year, may indeed be rising, but this is because global populations are higher and more people are entering the ocean.
Going Down
They suggested that shark bite rates are declining globally because the density of sharks in the oceans is declining... It is estimated that at least 70 million sharks are killed annually, but some studies suggest this may be as high as 300+ million every year! All sharks are significantly overfished and the species most commonly involved in incidents with humans (the tiger shark (Galeocerdo cuvier), white shark (Carcharodon carcharias), bull sharks (Carcharhinus leucas), blacktips, (Carcharhinus limbatus), spinners (Carcharhinus brevipinna), and silky sharks (Carcharhinus falciformis)) are consistently caught in fisheries. So it likely that their population declines have contributed to the declining trend in shark attacks (Ritter et al, 2019).
Whatsmore, the scientists hypothesised that degradation of their habitats, likely played a key role. Many of these species are coastal and do not swim into deeper, offshore waters. Therefore, they are affected by human activity, such as coastal urbanisation, dredging and "eutrophication" (when chemical runoff from agriculture causes increased growth of plants life in an aquatic environment, which can shift the balance fo an ecosystem). They suggested that coastal sharks have probably shifted their distribution and are now not found so commonly in areas where humans enter the water, reducing the number of incidents (Ritter et al, 2019).
The researchers concluded their work by mentioning that it is important that the general public understands that human beings we are far more dangerous to sharks than they are to us! Whilst it is great news that people are not being hurt my sharks as often, maybe this has come at a terrible cost... Should we value human life more than marine life? And is that acceptable from an ethical standpoint?
References
ISAF (2020). International Shark Attack File, Florida Museum of Natural History. Access online.
Ritter E, Amin R, Cahn K & Lee J (2019). Against common assumptions, the world’s shark bite rates are decreasing. Journal of Marine Biology, Article ID 7184634. Access online.
By Sophie A. Maycock for SharkSpeak
