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Shark Info 4 / 99   (12-15-1999)

Author

  Intro:

Shark Accidents

Shark Info

  Main article:

Anatomy of Shark Accidents

Dr. E. K. Ritter

  Article 1:

U.S. Government Shark Research Project

Shark Info

  Article 2:

The shark fin market in San Francisco

Harald Gay

  Fact Sheet:

Tiger Sharks

Dr. E. K. Ritter


Anatomy of Shark Accidents

By Dr. Erich K. Ritter

Great White Shark

A white shark (Carcharodon carcharias) snaps. Why humans can also be bitten is not yet known.

© Shark Foundation

No one can deny that accidents with sharks do happen - it is an incontestable fact. And when such an accident does occur, reports flash like wildfire through the world press, giving the event so much attention that it becomes "extra-ordinary". If they happened every day, like car accidents, they would probably not be worth mentioning except on the side.
Nevertheless, despite the fuss surrounding a few shark accidents, public opinion on the danger of sharks has significantly changed over the past few years. More and more the idea is gaining momentum that the chances of being bitten by a shark are actually minute and most likely quite exaggerated. Considering other sources of danger in day-to-day living, shark attacks are certainly overrated and do not deserve the attention given to them, as a comparison with daily accidents can demonstrate: For example, every year in the US and Canada alone, around 40 people are involved in deadly accidents with pigs - this is four times (!) more than the worldwide number of shark attacks. And in Florida, the same number of people are killed every year by lightning.

Provoked versus unprovoked accidents

And yet accidents do occur. But are they exceptions confirming the rules, the result of unfortunate circumstances, or are they caused by other reasons? To find the answer we must first reconstruct the sequence of events of an accident and second investigate the shark's motivation.
Again and again, employees of the ISAF (International Shark Attack File) in Gainesville appear to take the completely wrong approach by differentiating between "provoked" and "unprovoked" attacks. The meaning of these terms may be evident, but unfortunately they were never clearly defined. In other words, ISAF advisers quite often assess an accident as "provoked" or "unprovoked" at their own discretion, depending if the victim caused the accident or not. This subjective evaluation challenges the real validity of such reports, because if one were to believe them, many of the attacks would - based on the pattern - turn into so-called hit-and-run accidents: the shark bites and swims away. The ISAF usually explains most such accidents as being caused by shiny objects like jewelry or flashing chrome on the victim and/or by his or her nervous movements in the water. In other words, the shark was attracted by certain stimuli, bit the victim and swam off after noticing his mistake. Now this kind of definition actually contradicts itself in the sense that the flashing of jewelry or chrome and the agitated behavior of a swimmer actually does provoke the shark. Most swimmers are not aware of this so that one should preferably speak of provoking or triggering factors.
Up to the end of 1998, the ISAF registered about 231 apparently unprovoked bites worldwide by white sharks (Carcharadon carcharias) in contrast to four provoked bites, a number which must be questioned considering the fuzzy evaluation methods. The same holds true for the other two notoriously feared shark species, the tiger shark (Galeocerdo cuvier) and the bull shark (Carcharhinus leucas). If one tends to believe ISAF statistics, then only about 3.7% of all accidents were provoked by humans. In my opinion, however, it is generally wrong to differentiate between provocation and nonprovocation since first it is quite impossible to underpin this scientifically and second it only reflects the personal feelings of the individual making the judgment. A shark never attacks without a reason, which means that at some level the attack was provoked or triggered by some event.

Scientific analyses of shark accidents

The scientifically correct approach when investigating shark attacks is not a question of whether they are "provoked" or "unprovoked", but rather means analyzing the cause and purpose behind an attack. The most important question to be answered by any investigation is: Does the shark attack a human deliberately or "on the side".
The two last "shark attacks" reported in the Bahamas which I reviewed for the GSAF (Global Shark Attack File, Princeton) turned out to be such "coincidental bites". Harpooned fish and not humans were the real target of the attack. In both cases the sharks attempted to get close to the harpooned, still wriggling fish. In the confusion resulting from the divers attempting to throw the fish into the boat while at the same time trying to keep away the sharks, an accident occurred. In interviews both victims testified that the sharks were only interested in the fish, which means that such events do not qualify as attacks but as accidents.
Does this mean that no accidents will occur when sharks are not provoked? In the majority of cases the answer is yes, and yet accidents still occur for which science has not yet found any explanation. At the moment we cannot say conclusively which factors have a provoking effect on sharks. It may involve certain sounds which attract the sharks and induce them to bite, or scent molecules (see Shark Info 3/99), particular motions in the water, currents or atmospheric events. Of course we know that factors like wriggling fish trigger a respective reaction with sharks, but we do not know what finally motivates a shark to bite a human - a life-form unknown to the shark - instead of the fish. Generally, predators have a naturally high inhibition to approach unknown objects, another aspect which makes shark accidents more complex since in the last analysis shark bites are not accidental.

A research project addresses shark accidents

Sharks do not attack blindly, but are motivated by external circumstances. A part of our work addresses this aspect as we similate the most common accident scenarios. For example, during an investigation of bull sharks (Carcharhinus leucas) and lemon sharks (Negaprion brevirostris) we observed how they approach their food when an unknown life form, such as man, is nearby but not in direct contact with the food. A rather surprising result of tests with species of large sharks and their approach to a food source was that their individual behavior is different and atypical. Bull sharks, in particular, demonstrate some interesting behavior. They are practically never alone when something attracts their attention. Another animal is often found in the immediate vicinity or at some distance away, only recognizable by its outline. We are not yet sure how to interpret this behavior which could involve a certain ranking order in the feeding process, a teacher-pupil relationship, or may be something entirely different. Bull sharks are social feeders who like to feed in groups. Their strategy when seeking prey thus differentiates them from lemon sharks. The question whether this behavior reflects protective instincts, help instincts, demonstrative behavior or just plain social company cannot yet be definitely answered.

We never observed any such behavior with lemon sharks. Even when several animals appeared one after the other, nothing indicates any form of coordination or for that matter cooperation.

The observance of these two species alone makes it obvious that there is no such thing as THE shark attack. Different species have different strategies. But happens when their food is located directly on the human? Another typical scenario is a dead or dying fish, still bleeding and attached to the belt of a diver or snorkler. Results of this test have presented us with more questions than we have so far been able to answer. Most astonishing is the amount of time a shark often takes before even approaching a fish under these circumstances. What is the reason for this? And yet why is it one of the most frequent reasons for accidents? During such a test, it first took a long time before a shark approached the possible food source, and in addition it never resulted in a bite in passing. Here the answer appears to be that the test person expected the shark, which obviously poses the question what does the shark notice in such a situation. Does the shark somehow recognize that the unknown object is aware of his presence? By finding out the reason for this behavior, it should be possible to also substantially reduce this type of accident.

The cause of an accident

Every couple of years literature revives the idea that sharks have territories which they defend, a rumor which has its source back in the beginnings of diving. Up until today there is no proof that sharks are territorial, even only for limited time periods, and that attacks may be connected with defending their territory. By comparison, there are several well-known reasons why they may attack, ranging from group hierarchy to mating. Is it conceivable that humans are considered as possible competitors during mating? Or does a shark view the size of a human as a dominant object in the reef, making him ready to defend his position in the hierarchy? The real causes for a bite are still unknown but chances are that some of the aforementioned problems may foster a shark attack when no food is found in the immediate vicinity. Very often during my review of shark attacks I noticed that victims who were bitten several times suffered no loss of tissue and that no food was in the immediate vicinity, indicating that any respective motivation on the part of the sharks to feed was indeed very questionable. Perhaps we must completely modify our way of thinking and look at a shark's approach maneuver and resulting act of biting from a totally different perspective.

Still, human parts have been found in shark's stomachs

On rare occasions human remains have been found in sharks' stomachs. Here we must consider that most such sharks probably did not attack the victim to feed on them, but rather found them already dead either as the result of an accident, from drowning or some other cause, and then fed on their remains, which is one of their main tasks in the marine ecosystem.

But what about the shipwrecked who were bitten by sharks and then died?

There are reports, for example from World War II, on how humans died because they were bitten to death by sharks. Probably the most famous example is the "USS Indianapolis" which was torpedoed on July 30, 1945, and sank within 12 minutes with approximately 900 crew members on board, left to their destiny in the open waters. Four days later 316 crew members were saved but the others died. No matter which history books or reports one reads, sharks always figure prominently in the death of these crew members. Although eyewitness accounts and other proof exists that sharks were around and that it quite obviously came to contacts and bites, today's knowledge of the biology and behavior of sharks indicate that they were not the main reason for the tragic losses in this accident.

* Dr. Erich K. Ritter is a shark biologist and Senior Scientist at the Green Marine Institute and Adjunct Assistant Professor at Hofstra University in New York.

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



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