Dr Abalone

 

We should be afraid of sharks
half as much as sharks should be afraid of us.

 — Peter Benchley (Author of Jaws)

[Listen and read]

The classic tune to Jaws strike fear even in the most causal beach goer. As a marine biologist and surfer I spent a fair amount of time in the water and way too much time thinking about sharks. After I first saw Jaws at age 18 you couldn’t pay me to get in the ocean for a couple of weeks. There is something terrifying about the idea of a giant powerful creature suddenly decided to eat you and there is nothing you can do about it. The truth however is this: after literally thousands of surf and dive sessions all over the globe I am actually more concerned about the rarity of sharks then being attacked. I have probably only seen sharks a few dozens times, and then only very briefly at that. If you want to see sharks these days just go where people aren’t and they are all over the place, as they should be. You see Jaws had two major effects, neither of them good: it scared the hell out of people who spend time in the ocean and it created a man-hungry stereotype of sharks that simply isn’t true (with some important exceptions) that has had major negative consequences for shark populations. So here are five things you should know about sharks and shark attacks.

1. The Population Bomb: shark attacks increase with the human population boom.

Yes, shark attacks are increasing but don’t worry: your chances of an attack are probably not changing. The primary reason attacks are increasing is that there are more and more people surfing, swimming, diving and just hanging out in the ocean, so there is a higher absolute number of attacks. In place after place the trend of increasing attacks coincidences with increasing human population size and in turn the number of people entering the ocean (see below). In the USA, for example, about 264 million people visited beaches in 2000 and the odds of drowning were 1 in 3.3 million while the odds of being attacked by a shark were 1 in 11.5 million (and 1 in 264 million for a fatal attack) (International Shark Attack File). For comparison the odds of dying in a car accident are about 1 in 500. Thus despite the global increase in shark attacks your chance of being attacked is astonishingly low. Still, there are few others things you need to know.

 

2. The Endless Summer: surfers are the most common victims.

Surfers are the most likely people to be attacked by sharks. There are among a group of victims called “surface recreationalists” by the International Shark Attack File that also includes water skiing, windsurfing, boogie boarding, rafting, or floating on inflatables that make up the largest single group of people attacked. Next in line are swimmers and bathers, then divers (mostly Scuba but also hookah and  free-diving). The last group are those entering or exiting the water, such as when climbing a ladder into a boat or jumping off a platform. Of the 242 known attacks in California, for example, 28% were surfers,10% swimmers, 9% Scuba divers, 8% free divers with most of the rest were fishers, kayakers and skin divers. No one knows why surfers are the largest group of victims. But the sharks that cause most of the attacks (see below) are large, powerful predators that commonly prey on surface-based prey such as marine mammals, sea turtles and birds. Also, surfers tend to spend longer amounts of time in the water than most other groups, making them more vulnerable, and the shape of their surface profile unfortunately resembles many of their marine mammal prey.

 

3. Cape Fear: Great white sharks are the most likely to attack.

Of the 500+ species of sharks at least 34 species have been observed to attack humans. Of those just three — the Great White, Tiger and Bull sharks — are responsible for 63% of all attacks and 83% of all fatal attacks (click here to see all species). Great white sharks alone account for half of all fatal attacks. Why? These are large, powerful predators that often target large prey items such as fish (including other sharks), dolphins and to some extent whales, sea lions, seals, turtles and sea birds. However, all of these are opportunistic to varying degrees and may eat a wide range of items. Tiger and Bull sharks, for example, may consume just about anything and are also called “garbage eaters.” Great whites, although they can be extremely aggressive, are ambush predators, often taking their marine mammal prey by surprise from below; which is why most people never see the shark until they are attacked. Tiger and Bull sharks are known to frequent shallow waters; Tigers may dwell in river mouths and Bull sharks often swim up rivers and can survive in freshwater for extended periods of time.

4. Jinxed by “Jaws”: most sharks are harmless.

Despite the vision of a man-eating predator crashing through ship hulls and buildings as depicted in Hollywood in Jaws (and more recently Sharknado) the vast majority of sharks are harmless to humans. The reality is that this misplaced stereotype has resulted in massive senseless killings of sharks across the globe. This situation, combined with the harvesting of sharks for food and by-catch in nets (unintentional catches) has resulted in the death of 100 million sharks a year and a 90 percent reduction in many species over the last 50-100 years. Sharks now represent the largest group of threatened marine species on the World Conservation Union’s Red List and only three species have any form of protection (basking, whale and white) (Oceana report, 2008). For example, shark finning, the use of shark fins to make soup, kills an estimated 26-73 million sharks annually.

5. Life in the Balance: sharks are essential for healthy marine ecosystems.

Sharks have been a natural predator in marine communities for 100s of million of years and play an essential role in maintaining healthy ecosystems. As the top predators in these systems they limit the abundance of their prey, which in turn has cascading effects in the food chain. By limiting the population of other species sharks increase the species diversity of the ecosystem. As a result, when sharks are removed or reduced in natural ecosystems through human activities, marine communities can change drastically and cause imbalances among species. For example, along the east coast declines in blacktip sharks from fishing resulted in increases in the shark’s prey, cownose rays, and subsequent decline in bay scallops from ray predation.

In summary, although shark attacks have been increasing over time, especially the last few decades, this is almost entirely due to growth in human populations and subsequently more people in the water. Humans are the true top predators in the oceans and sharks have much more to fear from us then the very small risk we face of being attacked in the ocean. Sharks play a very important role in natural ecosystems and we need to reduce their take in fisheries and stop the practice of shark finning. Ultimately sharks need global conservation measures in place to protect them from our activities and maintain health ecosystems.

References:

• International Shark Attack File
• Global Shark Attack File
• Griffin, E., Miller, K.L., Freitas, B. and Hirshfield, M. July 2008. Predators as Prey: Why Healthy Oceans Need Sharks. Oceana Report. 20. pp
• Friedlander, A.M. and DeMartini, E.E. (2002). Contrasts on density, size, and biomass of reef fishes between the northwestern and the main Hawaiian islands: the effects of fishing down apex predators. Marine Ecology Progress Series 230: 253-264
• Heithaus, M.R, Frid, A., Wirsing, A.J and Worm, B. 2008. Predicting ecological consequences of marine top predator declines. Trends in Ecology and Evolution 23(4):202–210.