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Shark Info 1 / 99   (02-15-1999)

Author

  Intro:

Shark Accidents or Shark Attacks ? 2/2

Shark Info

  Main article:

Which shark species are really dangerous?

Dr. E. K. Ritter

  Article 1:

The GLOBAL SHARK ATTACK FILE (GSAF)

Marie Levine

  Fact Sheet:

Biology of the Megamouth Shark

Dr. J. F. Morrissey


Which shark species are really dangerous?

By Dr. Erich K. Ritter

Bull sharks

The bull shark (Carcharhinus leucas) belongs to the potentially dangerous sharks. This rather large species can grow to a length of 350 cm and weigh 230 kg.

© Shark Info / Doug Perrine

The first problem is already revealed in the question. Sharks are basically not dangerous. Only circumstances may lead to situations which are potentially dangerous for humans. Now many people may feel this is splitting hairs. But there is a big difference between animals which are considered dangerous and certain situations which may be potentially threatening.
Many situations pose no threat whatsoever to humans, even though a large shark may be swimming around. The dangerous shark is just as rare as the nonaggressive shark. Obviously there are species which - simply due to their size - should only be approached with great caution, for body size is a problem when it comes to dealing with sharks. Still, even though most sharks shown on television or in aquariums are mostly imposing in size, it must be emphasized that of the over 460 shark species only a small fraction of them grow so large as to cause serious injuries to people. Most are much too small to accomplish this. However, size alone only plays an indirect role. Much more important is the fact that many large species of sharks seek prey whose size is comparable to that of human beings.
In order to attack their prey, sharks inevitably need the respective "tools". Undoubtedly, shark teeth can cause serious wounds on humans. However, these teeth were developed amidst a natural environment unrelated to humans in order to guarantee survival in the natural environment. Yet human beings often tend to view nature and its inhabitants from a very narrow-minded, anthropocentric perspective which may completely overshadow the true circumstances. For the genuine danger is not the mere presence of sharks but rather the fact that the size of people who find themselves in the ocean clearly falls into the spectrum of prey sought by large-sized sharks. This fact, combined with the shark's inability to analyze the human "objects" enountered whose vibrations make sharks believe they are prey, are the most essential factors explaining the possible danger of sharks (also see Shark Info 2 / 98: "Shark attacks - a continually fascinating mystery"). The root, or imminent danger, is then controlled by the shark's inhibition threshold which prompts him to either approach an unfamiliar "object" or avoid it. The inherent danger is thus not the animal itself but rather the fact that by virtue of his size, man fits perfectly into the shark's range of prey, that humans spend time in areas where sharks live and hunt, and that sharks cannot analyze and eliminate us from their normal palette of prey.

Which shark species may be threatening under unfavorable circumstances?

If we go by the official list of dangerous sharks (e.g. from the International Shark Attack File ISAF, an institution which analyzes and collects reports on shark attacks) the white shark (Carcharodon carcharias) ranks first, followed by the tiger shark (Galeocerdo cuvier) and the bull shark (Carcharhinus leucas). Most ranks are established on the basis of questionable shark accident statistics which leave the reader with the impression that approximately 78% of all attacks were not provoked by humans and that the amount of "unprovoked" attacks by white sharks even amounts to 98.7%.
But does this really mean that a shark practically always bites without having been provoked beforehand? That is exactly what statistics such as those stemming from the ISAF would like us to believe. The fact is, however, that when analyzing the situation in greater detail, the victims usually put themselves into situations, or already found themselves in situations which sharks find challenging or provoking and which prompt their reaction.
Attack statistics must thus avoid reverting to useless and undiscussed numbers. Innocent readers who accidentally come across such Internet statistics may otherwise receive a completely wrong picture on the realistic danger surrounding sharks. Not only because the numbers are twisted to the disadvantage of sharks, but also because opportunities are wasted to find explanations for what really happened. In addition, not everyone is familiar enough with sharks to realize that these tables include species which only reach a maximum length of 50 cm (e.g. cookie-cutter sharks Isistius brasiliensis) who pose no real threat to humans. And yet: According to the ISAF even these dwarfs among the numerous shark families allegedly make unprovoked attacks!

Does real danger exist?

Of course it is legitimate to connect accidents with "danger", but many of the accidents listed must be questioned. Nonetheless, when such statistics are used as a benchmark for the potential menace of sharks, it is clearly proven that only about 25 out of 460 existing species of sharks have been involved in an accident more than once. In addition, 10 to 15 other species have only been involved in an accident once. Accordingly, potentially threatening situations can be reduced to 9% of all shark species. However, this small percentage does not allow us to draw any conclusion on their frequency. Larger animals, i.e. species, are found in substantially less numbers than their smaller relatives due to their energy consumption. Thus, the omnipresent hysteria connected with the few shark species who under certain conditions can actually cause damage and are classified as potentially "dangerous", is in no way justified.

The "most dangerous" sharks

We shall now briefly define the three most important species related to accident statistics, explaining what makes these animals so exceptional. Even though all other species should be included, these three are listed in their behalf. To the accidents: The "unprovoked" attack is only a label which is tagged on these animals. A finer analysis would show that human beings make the most mistakes in these encounters.

Great White Shark (Carcharodon carcharias)

The "danger" connected to this species is undoubtedly associated with its size and the curiosity with which it approaches its alleged prey. Great whites, as well as other species of sharks, have no way of precisely analyzing an unknown potential prey. In rare cases, they will test the object with their jaws, inspecting it with their taste buds. Their curiosity must, however, not be equated with actually biting. The "unprovoked attacks" cited in over 98% of the accident reports are thus not only wrong, but also represent an erroneous description of a biological function.
Rumors often say that white sharks mistook surfers for seals and thus attacked them - a very appropriate theory if one considers sharks to be stupid. However, these and other theories only found acceptance because no one doubted or disproved them (also see Shark Info 2 / 98: "Shark attacks - a continually fascinating mystery"). Latest research shows, however, that many supposed "facts" are nothing more than the initial impressions of scientists. Since scientists from earlier generations were neither able nor willing to substantiate their theories, and since current research funding is usually applied in other areas, such theories continue to be considered standards by which all incidents are measured.
A new generation of scientists is now putting their efforts into more detailed investigations and verification of these old theories. Statements to the effect that white sharks mistook surfers with seals, or that they attacked and then retreated to protect themselves from the claws or bite of the victim, will soon only be cited as anecdotes. The real "danger" surrounding these animals is more the fact that their behavior is stigmatized with too many unanswered questions. Although swimming or diving with white sharks certainly must go hand in hand with great caution, the timing is appropriate to refute their long-term reputation as being "notorious beasts", a description which may have filled movie houses but which in no way reflects their true nature.

Tiger Shark (Galeocerdo cuvier)

The tiger shark is undoubtedly the least described but most questioned species of large sharks. Although found more frequently than the equally large white shark, it was never made the focus of behavioral research. Tiger sharks probably have the most perfect teeth structure of all sharks which, combined with their size, enables them to successfully kill almost every category of prey. Contrary to old theories which regard omnivorous animals as primitive, current research is based on the assumption that this type of diet represents a high type of "specialization". When the food supply is low, these animals are capable of changing from one prey to another. Tiger sharks live in warm waters and are thus predestined to come into frequent contact with humans. Their broad spectrum of prey makes possible confrontations more likely, also because humans unconsciously emerge as competitors. Both tiger sharks and white sharks are curious animals, a characteristic which, however, must not be mistaken for being aggressive because it simply reflects the nature of these animals.

Bull Shark (Carcharhinus leucas)

Many people believe that these are the "most dangerous" of all sharks: They are fast, strong and are endowed with teeth which need not fear comparison with those of its tiger or white shark counterparts The real problem with this shark species is more the fact that they like to spend time in shallow waters close to the shore and often also in river estuaries. Rivers carry fresh water and much live food which often dies when coming into contact with salt water. The broad palette of food attracts a wealth of organisms - including sharks. However, only few species of sharks can survive in brackish water and this requires physiological adaptations which can stress the shark's body. The mixture of fresh and salt water is mostly enriched with a high concentration of organic and anorganic substances, resulting in limited visibility. The bull sharks which roam these regions must not only cope with physiological adaptation but also with an overdose of electrical fields which stem from all these substances. Limited visibility can lead to confrontations with humans and to accidents because their biting inhibition is considerably reduced due to the unusual environmental conditions.

All shark species which at some point in time were involved in accidents should theoretically be described in their biological composition. Up until now this has been lacking, so that somewhere and at some time when one single shark has bitten someone - most likely because it was provocated - generations later the entire species is labelled "dangerous", irregardless of whether or not this one particular animal was really "guilty" or not. There are no limitations in people's minds when it comes to generally denunciating sharks because of shark accidents! Still, hope remains that later generations will finally begin to realize and understand how to properly assess any danger or risks in connection with this animal.

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*Dr. Erich Ritter is a shark biologist and senior scientist at the Green Marine Institute and Assistant Professor at Hofstra University, New York.

May be published only by indicating the source: Shark Info / Dr. Erich K. Ritter



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