What Are The Odds? Assessing The Changing Odds Of Surviving An Unprovoked Shark Bite.

Monster. Man-eater. Mindless killer.

These are the words that come to mind for many when you so much as utter the word ‘shark.’ One of the most feared entities on our planet, the perceived and actual real threat of shark bites differ. Yet, what if scientists could understand the motives of these bites? What if they found out how to survive these rare encounters with one of the ocean’s mightiest predators?

Easier said than done.

But Dr. James P. Tucker of the National Marine Science Centre at Southern Cross University is trying! Tucker and an Australian team have come together to assess the changing odds of surviving an unprovoked shark bite using 200 years of Australian records. “Understanding the predictors of unprovoked bites, as well as survivability (year and water activity), may be useful for developing strategies that reduce the number of serious or fatal human-shark interactions without impacting sharks and other marine wildlife,” say the authors of this new study.

Shark bites are extremely rare; in fact, you are more likely to get bit by someone in New York before you get bit by a shark. Yet while the likelihood of being bitten or killed by a shark is small, the effects on the people involved and associated communities are significant, often resulting in negative attitudes or perceptions towards these predators. It’s a complex relationship between us and sharks, which can in turn have influence on their local protections and overall management. Try as we might, this isn’t a problem that will be going away any time soon – as our population continues to grow and more people than ever before are being recorded hitting out shorelines, the occurrence of global unprovoked shark bites has seen an increase for over 30 years. After the USA, Australia has been identified as a ‘hotspot’ by the International Shark Attack File kept by the Florida Museum. Australia has its own Australian Shark-Incident Database (ASID), formerly known as the Australian Shark Attack File (ASAF), and has records that date back to 1791. A joint partnership with Taronga Conservation Society Australia, Flinders University, and the New South Wales Department of Primary Industries, it’s a comprehensive repository with 100 descriptor fields including information such as geographical location of the incident, weather conditions, victim recovery status, shark species, and time of incident. However, Tucker points out it’s missing something: “The probability of surviving a shark bite is an important factor when assessing the potential risk of shark-human interactions. While most investigations have quantified temporal trends in shark bites, they do not provide specific detail on the potential drivers of human survivability.”

Focusing on the three species considered most dangerous to humans in Australia – the bull (Carcharhinus leucas), tiger (Galeocerdo cuvier), and white (Carcharodon carcharias) sharks – the scientists examined the influence of environmental and human factors on survivability of shark bites. “For each species, a generalized linear model (GLM) was used to estimate the probability of surviving an bite as a function of the following predictor variables: year, habitat (as defined by Australian Shark Incident Database), season, meshed/protected area (area protected by exclusion barrier, including netted ocean pool), distance from river, latitude, activity (activity person was performing at the time of bite, such as surfing, swimming, diving, etc.), injury location (on human body), person’s age and shark size,” the authors explained. In total, there were 157 bull (60 fatal), 120 tiger (56 fatal), and 270 white shark (67 fata) bites included in the analysis. The percentage survivability of unprovoked bull, tiger and white shark bites were 62, 53 and 75% respectively.

Year was a significant predictor for surviving bull shark bites, with the survivability rate increasing over time between 1807 and 2018. Could this be because of modern-day advances in emergency response, medical knowledge and training, and an increased number of people nearby on the beach to assist a person who has been bitten? Yes; in fact, previous research attributes deaths from shark bites to a lack of on-scene resuscitation, haemorrhagic shock or drowning. “The time between suffering an injury and stopping a haemorrhage has been recognised as crucial in affecting survival outcome,” say the authors. “This is supported by bull shark survivability. Bites that occur inland, or closer to the shore, may result in faster response times and thus increase survivability.” Bull sharks can get into the lower salinity environments – such as rivers and estuaries – that tiger and white sharks can’t, meaning their bite rates are the highest in these areas. Meanwhile, tiger sharks are common in tropical and sub-tropical waters throughout the world, making them a known resident of Australia’s warmer waters. Here, they dominate the open ocean islands that are scattered across the continent’s northern parts, so it’s no surprise that they have the most recorded bites here. In contrast, white sharks are commonly found in colder waters in the mid- to high-latitudes, where they patrol beaches, bays, and the open ocean. While the waters are a bit cooler down in Sydney, the coastal metropolis is famous for a number of beaches thanks to a rising popularity of snorkeling, scuba diving, surfing, or just plain lounging about; it’s around here where most great white bites occur.

A surefire way to make sure you don’t get bit by a shark? Take it from this marine biologist: don’t get in the water. Up until the 1960’s, almost all white shark bites were on swimmers and mostly fatal, whereas since the 1960’s most of the bites attributed to white sharks have been on surfers. “This is likely due to a number of factors, including that swimmers are generally protected by surf life savers between the flags, the increasing number of surfers, the improvements in wetsuit technology that allow surfers to surf all year round, and the propensity to surf isolated breaks and/or alone,” says the team. Not unsurprisingly, a watercraft for protection or as a flotation device increased survivability from a shark bite to 92% from 30% for tiger sharks and 88% from 45% for white sharks.

It will also probably come to no surprise that since legs are the limbs most commonly under the water’s surface and doing most of the moving during water activities, they are the most commonly injured limb. And there may be a behavioral strategy involved, too: “Legs and thighs are also often bitten because of the bite mode and behaviour of the shark, which often appear to have struck from the side or underneath, indicating some innate behavioral strategy.” Worrisome, since one of the major arteries in the human body is located in this area. With its primary function of supplying blood to the lower section of the body, if the femoral artery is hit it may result in morbidity, death, hemodynamic instability, limb loss, and permanent physical disability just to name a few.

So can we co-exist with these animals when the odds seem to be against us at times? Yes, if shark mitigation focuses primarily on reducing the number of negative human-shark interactions, say the authors. “The trends of survivability with the type of water activity should also be considered in future mitigation plans. Information packages provided to stakeholders should include the predictors of survivability which may influence the type of activities water users undertake, and of the importance of rapid and effective trauma management. More beach goers, particularly surfers, are becoming familiar with the correct use of tourniquets and minimising blood loss, and authorities should consider the distribution or placement of trauma kits in key locations.” While this work is just focused in Australia, the team is confident the new study indicates that it is time to reassess shark mitigation programs used here. Perhaps, potentially elsewhere as well.