Researchers confirmed that humans who swim and paddle surfboards bear a strong resemblance to seals and sea lions in the eyes of young white sharks, supporting the mistaken identity theory behind some bites. Most sharks are color blind, meaning that colors on surfboards and wetsuits make little difference when it comes to a shark's view of humans in the water, researchers said.
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This has led to increased numbers of great whites in the area too during the warm summer months as they look to feast on the seals that pull themselves out to bask on the beaches. Sadly, last autumn, Massachusetts suffered its first fatal shark attack in 82 years and growing numbers of shark sightings have led to a string of beach closures.
But there is no real evidence that sharks are actively hunting humans, according to the scientists who study them. Great whites in the North Atlantic, for example, show seasonal movement patterns, migrating thousands of miles to warmer waters further south during the winter months.
Some mature adults will venture out into the open ocean for months at a time , covering tens of thousands of miles and diving to depths of 1,m as they seek prey. But despite being potentially such an easy meal, sharks are really not that interested in hunting humans.
I think if people knew how frequently they were in water with sharks, they would probably be surprised. However, Naylor believes that the official statistics on shark attacks are probably an underestimate. Most reports come from highly developed countries with large populations and highly active news media.
Attacks on remote islands or in less developed communities probably go unreported. Looking at the statistics for the number of shark attacks last year can reveal some fascinating trends. Just four of these were fatal according to the International Shark Attack File, although another database of shark attacks records seven deaths. So far in , there have been four fatal shark attacks. Tiger sharks are one of the three main species responsible for attacks on humans but much of the time they ignore people in the ocean Credit: Getty Images.
The reason for the fall — which bucks the overall trend of growing numbers of attacks — has been attributed to a sharp decline in the number of black-tipped sharks. These sharks account for many of the bites around the south-eastern US, migrating down the coast of Florida due to rising sea temperatures that have led their prey to become more dispersed.
The findings highlight one of the key challenges in understanding why sharks bite humans. There are dozens of different species responsible for bites , each with their own unique behaviour, hunting strategies, prey and preferred habitat — although in many cases the species can be misidentified or not identified at all.
The majority of unprovoked attacks on humans where a species is identified involve three large culprits: the great white, tiger and bull sharks. Great white sharks are considered to be the most dangerous species in the oceans today, but we still know very little about their life cycle and behaviour Credit: Getty Images. Bull sharks, for example, tend to hunt in shallow, murky water that will require them to rely less on vision and more upon their sense of smell and electroreception, which allows them to detect minute electrical fields produced by their prey.
There is also some evidence that shark teeth may also function as mechanosensory structures — similar to touch — to help the animals learn more about what they are biting. Chapman believes there may be a complex set of reasons for why unprovoked attacks on humans appear to have risen in recent decades.
In , for example, there was a sudden spate of shark bites off the coast of Recife, Brazil — an area that had no unprovoked attacks for the entire previous decade. Chapman believes that heavy commercial port construction in the area damaged large areas of reef and mangrove, potentially displacing species like bull sharks , which moved to new areas like Recife in search of prey.
Bull sharks are aggressive animals that typically hunt in water with reduced visability Credit: Getty Images. Since , there have been 11 fatal attacks on Reunion , mainly on surfers. Those who survive often lose limbs. Researchers have found that around two-thirds of the Reunion attacks have occurred in turbid water and swells of more than two metres — the favoured environment for bull sharks, which are thought to be responsible for most of the attacks.
Great whites typically attack from below, delivering a massive catastrophic bite. In some cases they will withdraw while their prey bleeds to death before returning to eat. He should know — last year, as he was leaning over the pulpit on the bow of a research vessel while trying to tag a shark, a large great white breached directly underneath him with its jaws agape. Most of the time we put a camera in the water and the sharks are completely complacent. We must have done it thousands of times.
But on a handful of occasions they attack straight away, breaking the pole and the camera. It is like they are in a heightened predatory state where their senses lock onto any kind of stimuli. Efforts to tag great white sharks is starting to provide insights into the behaviour and life cycles of these enormous predators Credit: Getty Images.
But for every attack on a person, there are just as many stories of people who have managed to get up close to these giant predators without any harm.
Take Ocean Ramsey for example, who swam alongside an enormous feet-long great white off the coast of Hawaii and made headlines around the world. Skomal and his colleagues are now using new high-resolution tags that can give the researchers minute by minute and second by second data on what the sharks are doing.
He hopes it might help to answer questions about the behaviour of these animals as well as about where and how they breed. It could, ultimately, also help to tell us something about the reasons underlying attacks on humans, he says. Some researchers are turning to forensic methods to try and unravel some of the reasons behind attacks. They are developing techniques to use DNA and bite-mark patterns to identify species, while others are examining video footage of attacks and comparing these to injuries to get a better understanding of what happened.
Data from shark spotters in South Africa have shown that great whites are more active near the surface, and so more likely to be seen, when water temperatures are above 14C , during a new moon and in the afternoon. Other research, however, has suggested that great whites are more successful hunters at night when there is a full moon. Sharks are opportunistic feeders, but most sharks primarily feed on smaller fish and invertebrates.
Some of the larger shark species prey on seals, sea lions, and other marine mammals. Sharks have been known to attack humans when they are confused or curious.
If a shark sees a human splashing in the water, it may try to investigate, leading to an accidental attack.
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