We often hear that sharks are “nasty”, when comparing them with “gentle” dolphins. Animals are neither gentile, nor nasty.
There are only human beings who are the only ones to testify of the wickedness by qualifying it as a “sample defect" in the best case and who is capable of raising the cruelty a lifestyle for some others …
In order to let people know a little bit more about these incredible animals, TENDUA presents, in this dedicated file which will be completed as one goes along, some of these magnificent animals encountered during our journeys.
As such, TENDUA thank the photographers who were kind enough to give their images to illustrate our comment.
Firstly, don’t forget that sharks are indispensables to the balance of our oceans. But unfortunately they are extremely threatened either by the practice of ‘finning’, the accidental (or not) overfishing, the sea pollution, a late sexual maturity and a low rate of reproduction… We would like to participate to the “sharks’ rehabilitation” in the people’s mind and we sincerely hope that we won’t have to classify sharks as extinct species.
During the following overview, we will cover the points listed below, and to follow the last news about sharks, go on http://www.protection-requins.org. Enjoy your reading!
- 400 million years of evolution deserves some respect
- Elements of the sharks anatomy and physiology
- In 2009, around 500 shark species are in danger, some very close to extinction: threats and objectives of conservation
- An indispensable link in the food chain
- Sharks and Men: myth and reality
- Some advice to scuba divers
- Some Red Sea sharks … and others
to know more about pelagic sharks go to http://www.protection-requins.org/f...
to know more about reef sharks go to http://www.protection-requins.org/f...
to know more about less known sharks go to http://www.protection-requins.org/r...
400 millions years evolution deserve some respect
- The megalodon (Carcharodon megalodon)
- Carcharodon means “sharpened teeth” and megalodon “with big teeth” - was a shark that was living in the oceans 16 million years ago. It disappeared some 1,6 million years ago. It is considered as being the most redoubtable fish of anytime and maybe the biggest carnivore that has ever lived - DR
-* -430/-400 My, thorny sharks or the acanthodians with a cartilaginous skeleton and osseous jointives scales
- -400/-350 My, 3 classes of fish appeared :
- The armoured fish which died out in the Carboniferous period,
- The cartilaginous fish from which actual sharks have evolved,
- The osseous fish from which most of the modern fish species have evolved (a branch of which engendered the amphibians, from which will derive reptiles, mammals and birds).
- -350 My: the cartilaginous fish types divided in 2 sub-classes: :
- The Elasmobranchs which are strictly speaking sharks, among whom are the selachians which will engender a new group: that of the skates,
- The Holocephales or chimaeroid fishes which adapt themselves to abyssal zones (some rare species remain such as elephant fish).
- -50 My: the first modern tiger shark (genus Galeocerdo).
- The most terrible: the Carcharocles megalodon, 15 metres in length, with 15cm teeth, as massive as the whale shark but carnivorous.
- The giant shortfin mako shark (Isurus hastalis), the Great White’s ancestor.
- Many shark species adopted their modern shape 100 My ago and have hardly evolved since, what would be the sign of a completed adaptation to their environment.
Nota : Disappearance of dinosaurs: - 65 Million years (My)
The 530 species of sharks known to date (2015) are classified into the following eight orders based on certain physiological parameters.
Elements of anatomy
The typical squale has a lengthened body; the trunk is cylindro-conical - in torpedo - with an almost flat lap face, a roun snout, a lap mouth, armed with several rows of teeth. But among the 500 species, there are a big variety of sizes and aspects.
The head, jaw and teeth
The skeleton of the head consists of 2 parts:
- The neuroskull: a box of cartilage which protects the encephalon, including the seat of the olfaction which is highly developed, the seat of taste, balance and the endocrine system (pituitary gland), the seat of vision, memory and driving coordination
- The splanchnocranium: this concerns the jaw and the brachial gill slits.
The jaw of the majority of the modern sharks is hyostylic: that means it is independent from the skull, what allows a spectacular extension of jaws to attack big prey and a prehension (pressure of the jaw) of significant power. For example, a 3-metre shark possesses a jaw pressure of 3t/cm ².
Teeth grow inside the gum, in successive rows and become functional when they coincide with the fish bone (edge) of the mouth. Eventually they wear out and fall off.
Their shape varies according to the type of predation. The bull shark possesses disentangled teeth adapted to the capture of slippery fish; the Port-Jackson shark has almost flat teeth, used to crush shells.
The shark’s eyes
On lateral-back position, eyes have two eyelids. Often a nictitating membrane, called a “third eyelid" can be seen.
At the end of the snout, two symmetric but independent nostrils, which play no role in breathing. These nostrils constitute organs of olfaction.
The shark’ skin is so rough it can be used as sandpaper. It consists of uncountable dermal denticles, which are small rough placoïd scales, homologous in structure to teeth. As a result, the skin is often dried and used as a leather product or sandpaper. It would seem that these denticles are aligned in several rows, channelling the water to produce a laminar flow and hence reducing resistance to movement in the water.
This skin structure allows the shark to be almost silent in the water, a certain advantage for a predator.
The gill slits
On each side and at the back of the head, are brachial gill slits, 5 pairs for most shark species, but 6 or 7 to hexanchiforms.
Gill openings are very fragile organs without a protective membrane; they are mobile and can be contracted or dilated. They can be damaged by pollution or blocked by parasites (there are frequent observations of fish specialised in cleaning gill openings).
- Grey reef sharks from below
- Two pairs of symmetric fins on the stomach correspond to the tetrapod’s members: the pectoral fins, often, enlarged in wings, represent arms; pelvic or abdominal fins represent legs. - © M. Dupuis
Shark fins are used for stabilising, steering, lift and propulsion. Each of the fins is used in a different manner.
There are one or two fins present along the dorsal midline called the first and second dorsal fins. These are anti-roll stabilising fins. These two fins may, or may not have spines at their origin. When spines are present they are defensive, and may also have skin glands associated with them that produce an irritating substance.
Pectoral fins originate behind the head and extend outwards. These fins are used for steering during swimming and help to provide the shark with lift.
Pelvic fins are found near the cloaca and are also stabilisers. In males they have a secondary function as they are modified into copulatory organs called claspers.
Anal fins may be absent, but if present they are located between the pelvic and caudal fins.
The tail region itself consists of the caudal peduncle and the caudal fin. The caudal peduncle may have notches known as precaudal pits found just ahead of the caudal fin.
The caudal fin has both an upper and lower lobe that can be of different sizes and the shape varies across species.
Two dorsal fins, of variable form and dimensions, according to the species, are situated on the sharks back:
The first dorsal fin can be raised in aileron or, on the contrary, lowered.
The second dorsal fin is smaller and fatter. Even here, hexanchiformes distinguish themselves by their unique dorsal fin.
The caudal fin of the tiger shark and of the blacktip shark
The tail includes 2 uneven, sometimes almost symmetric lobes (i.e. great white shark) and it determines the type of propulsion of the animal.
A hetereocercal tail: the upper lobe is longer and heavier than the lower lobe (blacktip shark, tiger shark).
This species moves by rocking its body from one side to the other, the upper lobe delivering the maximum of the necessary power to swim slowly or accelerate rapidly.
The types of prey of these sharks require them to be able to bend and to turn quickly.
The caudal fin of the shortfin mako and of the great white
The tail of the great white shark is different: it provides the propulsion for a more heavily built body.
This shark, which is closer to the common shark-mole and to the shortfin mako, travels more by the movement of its tail than by the balance of the body.
The important lower lobe assists with high speed and the side hulls, on the base of the tail, reduce the trail hydrodynamics. The shape of the porbeagle caudal fin, like the one in this picture is lunate or crescent shaped. This means that the upper and lower lobes of the tail fin are similar in size.
The caudal fin of the nurse shark
The nurse shark spends most of its time on the sea bottom (caves, crevices). It does not travel over great distances. As invertebrates establish the main part of its diet, it does not need a tail assuring a high speed, but it needs considerable flexibility.
The lower lobe of its tail is almost confused with the upper lobe; so, its tail makes wide sculling movements, it swims in a similar fashion to an eel.
The caudal fin of the tresher shark
The 3 species of tresher sharks, which populate the tropical and moderate oceans, are powerful swimmers.
Active hunters of fish and squid, they use an original hunting technique: they gather their prey before knocking them out thanks to the very elongated caudal lobe.
The extension of the tail, almost as big as the rest of the body, does not affect the speed and efficiency of these hunters.
Elements of physiology
The sharks’ breathing mode depends on the lifestyle of the particular species:
Pelagic species swim continuously; if they stop, they will be asphyxiated ; benthic sharks spend their day on the sea bottom. Brachial breathing is convenient for the benthic and sedentary species. They inhale water and pass it through their gill slits without needing to swim or to be in a moving current. They dilate their pharynx and open their mouth. The principle used is to pump water by muscular contractions.
To move, the ‘open sea’ sharks need a major contribution of oxygen. If they stop swimming, it is suffocation. Water enters through the mouth and is filtered out through the gill slits. It is same principle as a “ramjet engine”: these sharks (Carcharhinadae and Lamnidae) use this flow of water which is filtered by gill slits, opening onto 5 to 7 gill slits, to extract the oxygen from it.
Certain sharks (such as bull sharks) can alternate their breathing either by swimming, or sucking up the water according to their current situation. Others can benefit by eating and by breathing at the same time (whale shark). Certain nurse sharks can intake water by their anterior gill openings and expel by their posterior gill openings, assuring a complete dissociation of the feeding and respiratory functions.
The efficiency of breathing also depends on the quantity of haemoglobin in the blood. This rate varies according to the species from 3g to 14g for 100ml of blood.
The copulatory organs
To mate, the pelvic fin is enlarged, on its internal edge, by a stiff, fluted stalk, which is called clasper and which constitutes the copulation organ. Provided with 2 claspers, the shark can use only one at a time. A siphonale gland sends the sperm from the cesspool to the clasper, which is not directly bound with testicles.
To decrease their physical density and facilitate active swimming, elasmobranchs developed (as they don’t have a swim bladder), an organ allowing a neutral buoyancy: the liver.
In certain species, the hepatic gland can reach 25 % of the total weight of the body (blue skin shark).
The liver is also an enormous reserve of energy. The major hydrocarbon in this oil is called squalene. The oil of the liver of both rays and sharks is rich in vitamin A.
Squalene, coming from shark’s liver oil, is used in particular in food supplements to, it seems, strengthen the immune system. These supplements are sold in certain “organic” stores and on the Internet. It is also used in beauty care, in moisturising creams as an agent that quickly penetrates the skin. Squalene is also used as an additive: one of the substances, administered together with a vaccine, which stimulate the immune system and increase the response to the vaccine.
Sharks have a very acute sense of hearing
Situated on both sides by the brain and connected to the side line, the internal ear is not only the auditory organ, it is also the organ for the balance, orientation and coordination.
The shark has much finer hearing than human beings and it is all the more advantageous as in the water the sound propagates 5 times faster than in air (1500m/s).
Covered with numerous ciliate cells identical to those of the lateral line, the internal ear sends to the brain very low frequencies waves passed on by the water at the speed of 1500m/s within the range of 10Hz to 1000Hz. (Frequency band for humans is 25Hz to 16000Hz). Sharks may track sounds over many miles, listening specifically for distress sounds from wounded prey.
For information, the active detection sonars of super-silent submarines are situated in the 2000Hz band.
Taste is achieved by a myriad of sensory buds: papillae similar to ours and spread not only on the tongue, but also on the lips, the palate, the pharynx, and on the wall of the oeasophagus.
These diverse receptors explain why sharks often reject a piece of ‘food’, once three quarter swallowed by mistake, after an ‘investigative bite’.
The sensitive taste buds clustered in the mouth analyse the potential meal to see if it’s palatable. Sharks will often reject prey that is outside their ordinary diet (such as human beings).
The main chemical receivers are the ones for the sense of smell. Sharks are often called the “nose of the sea”.
As the shark moves, water flows through two forward facing nostrils, positioned along the sides of the snout. The water enters the nasal passage and moves past folds of skin covered with sensory cells. The twin nasal cavities act something like your two ears: Smell coming from the left of the shark will arrive at the left cavity just before it arrives at the right cavity. In this way, a shark can figure out where a smell is coming from and head in that direction.
Their olfactory center occupies two thirds of their brain.
They can detect a tiny quantity of olfactive particles diluted in a large quantity of water. A great white shark, for example, would be able to detect a single drop of blood in an Olympic-size pool. Most sharks can detect blood and animal odors from many miles away. It is very useful in the quest of food or sexual partner.
Note: In sharks, taste and sense of smell are not connected, contrary to what occurs in human beings.
- Structure of the eye of a shark
- Sharks have a common to all vertebrates eye’s structure with some particularities - © Internet Source
- Lateral line
- It seems that lateral lines are playing a role in the gathering of certain species at the mating period - © Canadian Research center
- Ampullae and lateral line
- Water flows through the lateral line systems. Vibrations in the water stimulate sensory cells (neuromasts) in the main tube, preventing the shark to the proximity of predators or prey - © Internet Source
Night-vision has no secrets for sharks.
Sharks posses the basic eye structure that is found in all vertebrates, but with some modification. The tapetum lucidum is a layer of reflecting, guanophores cells, behind the retina, acting as mirrors by reflecting back onto the sensory cells 90 % of the light, which touches them.
This effectively boosts the visual signal, especially in low light levels giving sharks high visual acuity.
- The Lamnidae (white shark) would be sensitive to hot colors (red, orange, yellow).
- The C. longimanus adapts its view between the bottom and the surface in 1 second when a man needs 30 seconds to adapt his eyesight from darkness to full light.
In addition to these familiar senses, sharks also possess some senses we don’t fully understand.
The electro-sensory system: the ampullae of Lorenzini and the lateral line
The lateral line, together with the ampullae of Lorenzini comprises the electro sensory component of the sharks sensory system (detections from 1.05 to 0.05 microvolts/centimetre).
The head of the shark (nose and rostrum) is stuffed with ampullae of Lorenzini, which consist of small clusters of electrically sensitive receptor cells positioned under the skin in the shark’s head. They detect low electric currents and their direction, produced by every living being.
Every living organism, even stationary, emits an electric field (cardiac beats, contraction of muscles). A fish hidden in a crevice will automatically be located. They thus serve:
- to find prey (detection down to 5 billionth of volt/cm ²: the highest electrical sensitivity of any the animal kingdom!) ;
- to orientate by means of the variations of earths magnetic field (the role of a compass),
- to detect the salinity of the water, the gradients of temperatures and vibration waves.
The lateral line allows the shark to orient towards particular movement or sound. It is a nervous canal, filled with mucus, connecting small pores at the bottom of which extreme precision sensors are located. These structures are called neuromasts. Similar to the ampullae of Lorenzini, the neuromasts open to the outside through pores and detect the movement of prey.
Basically it is a set of tubes just under the shark’s skin. The two main tubes run on both sides of the body, from the shark’s head all the way to its tail. Water flows into these main tubes through pores on the skin’s surface. The insides of the main tubes are lined with hair-like protrusions, which are connected to neuromasts.
These cells are sensitive to the low frequency waves of pressure (imperceptible to the human ear): when a vibration propagates in the water, it hits the shark’s lateral line (a role similar to sonar). Everything that moves produces vibrations, which propagate through the water. The frequency of the vibrations depends on the size and on the health of the transmitter.
They also register the variations of pressure of the water and of the temperature, which indicates depth and allows the shark to orient itself in 3 dimensions.
Scientists still don’t yet understand everything about these ampullary organs, but they do know the sensors let sharks “see” the weak electrical fields generated by living organisms. The range of electrosense seems to be fairly limited — a few feet in front of the shark’s nose — but this is enough to seek out fish and other prey hiding on the ocean floor.
=> Very usefull for orientation, hunting and during the mating period.
Special care to photographers and cameramen: the electric field scattered by equipment attracts sharks that come into contact.
About 500 species are endangered : the threats
- Mokarran death on a reef flat
- Great hammerhead shark (Sphyrna mokarran) whose fins were cut, found dead on the shore in Rangiroa, French Polynesia - © Tendua
- Jar of shark fins
- All over the world, poachers practice finning and a “mafia of fins” now exists, dealing second only in value to the worlds drug trade... - © Y. Lefèvre
Shark ‘finning’ consists of fishing for sharks by cutting off their fins. The rest of the dying body is thrown back into the sea. Without fins to swim and thus conversion to oxygen, and considering the bleeding resulting from this fishing, the shark will inevitably die. This practice results in considerable waste as only 3 to 5 % of the mass of the shark is utilised. The body of the shark, with its high amount of urea, contaminates the other fish and a separate onboard storage would be necessary and of low profit.
The fishing in itself is not very costly and a pound of fins can be sold for up to US$200. Only the fins are exploited, leading to real massacres at sea and putting these ecosystems in danger.
Finning is certainly the most important cause in the decline of the worlds population of sharks. It convinced the United States in 2000 to legislate to forbid this practice in American waters.
Europe confirmed the same legislation in 2003. However, even if France did not ask for it, dispensations are granted to the fishermen, in particular by Spain, for about 200 boats which are allowed to fish for sharks’ fins.
The long liner fishing
This is a real trap for any marine surface or moderate depth fish. Long liners are gigantic fishing lines, sometimes measuring several hundreds of kilometers in length. These lines are set with baited fishhooks every 3m approximately. They are then unwound following the boats which leave them be lying in the sea before reeling them in. Very few fish species interest the fishermen and the great majority of the fish are rejected and thrown back into the sea, mostly already dead (fish, sharks, tortoises, cetaceans, pinnipeds, birds). They are all the victims of the accidental fishing.
Fishing with long liners is forbidden in numerous countries but poachers continue to practice it. Inquire about the origin of the fish that you eat, because buying fish resulting from long liners guarantees them their business, without taking into account the life of the ecosystems.
- Schematic of drift nets
- Drift nets normally range in length from 25m to 4Km. Nets of up to 50 km have been set in recent times - © Internet Source
- This kind of nets is used in the South Pacific ocean and Indian ocean by long liners fishing for tunas and other pelagic and demersal species as sardines, sea bass, mackerels, herrings - © P. Kobeh
- A dolphin and a marine bird are the victims of a ghost net
- A dolphin and a marine bird are the victims of a ghost net - © Internet Source
The drift nets
The pelagic drift nets are wide and long straight nets (in a single tablecloth-like shape) left temporarily drifting at sea by the fishermen.
They are used in the South Pacific by the Asian fishermen to fish for the tuna and in other places to fish for pelagic and demersal species such as sardine, seabass, mackerel, herring. But this technique captures all sorts of non-target species among which are dolphins, whales and tortoises: more than 300 000 cetaceans are victims of these nets every year.
The Wellington convention of 1989 forbade the use of drift nets of more than 2.5 km in the Pacific. Japan then stopped fishing with drift nets in 1992.
Nets generate direct environmental impacts (overfishing) or indirect (fish taken accidentally). Even fragile or modest nets can capture and trap big species of cetaceans, or sharks. Since the 1980’s researches are investigating the means to reduce their impact. We may wonder about the fact that nothing good appears to have been found after 30 years of research...
Drift nets lost offshore (following storms or after collision with big cetacean, cargo boats, submarines, etc.), also called “ghost nets”, can become macro-wastes. A long time after their loss, they can continue to trap fish or other animals. They are solidly made and with little degradable synthetic material (nylon) and as with any on-surface floating object it attracts fish. Some of these “ghosts nets” hang onto reefs or on wrecks which then become traps for numerous marine animals. Others, are more or less torn up by the sea or the screws of ships are eventually washed up in the tide. Small pieces of nets, covered with eggs laid by fish or other marine bodies can be ingested by sea birds (albatros, ...).
For information, the South African department, involved (theoretically) in the protection of sharks, was planning to install, for the Football Word Cup 2010, “protection nets” – with huge hooks every 3 or 5 metres along the Durban coast for 5km length to avoid any “shark attacks”. The net is installed at 2m depth and is 6m deep; fish baits are hooked and attract the sharks that die on these hooks. But, these sharks would probably never venture there if there were no prey on the hooks…
Out of interest, and no shark attacks have been recorded for years, what could then be the justification for this strategy?
These South African nets have killed more than 35,000 animals (sharks, dolphins, whale sharks, turtles and so on) between 1970 and 2000, without taking into account all those who were not born from these dead parents.
The main fisheries of sharks
- Coastal fishing
- Trawlers with gillnets fishing on the bottom take rays and small coastal sharks like the spotted dogfish (Scyliorhinus sp.), the smooth hound (Mustelus sp.), the spiny dogfish (Squalus acanthias) and the school shark (Galeorhinus galeus) - © Internet Source
- Deep water fishing
- Deep water fishing catches deep pelagic sharks such as the birdbeak dogfish (Deania calcea), the kitefin shark (Dalatias licha) or Portuguese dogfish (Centroscymnus coelolepis) using long lines, trawls and gillnets fishing on the bottom - © Internet Source
- Deep-sea fishing
- Deep-sea fishing catches big pelagic sharks, mainly the blue shark (Prionace glauca), the porbeagle shark (Lamna nasus) and the mako shark (Isurus oxyrinchus), especially with long lines on the surface - © Internet Source
Ask where and how the fish you are going to buy was caught, either in the fish shop or in the restaurant. It may help if people are more conscious and feel more concerned about this question.
The disappearance of prey
Because of overfishing and of the degradation of the oceans, the disappearance of prey is also a threat on the future of sharks.
An indispensable link of the trophic chain
The shark is situated at the top of the food chain; its predator’s role is essential for the balance of the oceans. He is the the oldest super-predator on Earth today...
- On weakened animals (a cleaner’s role)
- On healthy prey (role of balancing populations)
- Vulture feeding of dead animals (the gravedigger’s role)
but also Prey:
- Of the killer whale, the cetacean of the temperate seas
- Of stronger and bigger sharks
- Occasionally for a big octopus or a sea crocodile
- Of fish such as the red lutjan (on young of sharks) and huge grouper (on adults)
- Of men ...
How to help preservation?
- By forbidding shark fishing and finning: sign the petition via the link on SHARK ALLIANCE and TENDUA and boycott restaurants serving sharks’ fin soups, as well as stores or sites selling products with shark oil;
- By spreading the ban on long line fishing and drift nets to avoid accidental fishing which destroy the ecosystems;
- By asking where and how was fished the fish you are buying/eating in a restaurant ;
- By forbidding nylon and plastics nets for the preference of fishing nets made from biodegradable material;
- By creating corridors of protection by asking governments concerned to find a consensus as fast as possible;
- And something that each of us can do: to let people know what is going on and raise awareness about it.
SHARKS AND MEN : MYTHS AND REALITY
Between 1990 and 2005: 869 cases of attacks of shark were recorded in the world, among which, 94 were fatal, that is approximately one person in ten.
Fifteen years later, we notice that the average number of shark attacks in the world is of the order of 35 a year, and that the number of persons who directly died from attacks is less than four a year.
As a comparison, the number of sharks killed annually in the world was estimated in the 1990s as at least 100 million individuals and maintaining this number amounts officially to 150 million sharks exterminated a year.
Besides overfishing, a late sexual maturity and a particularly long duration of the gestation, as well as a poor production of embryos make sharks particularly vulnerable.
CONSEQUENCES: THIRTY SPECIES ARE CONSIDERED AS ENDANGERED, AMONG WHICH 13 ARE CONSIDERED IN CRITICAL DANGER OF EXTINCTION, 8 ENDENGERED SPECIES AND 9 CLASSIFIED AS VULNERABLE, ACCORDING TO THE 2008 IUCN LIST.
Advises to scuba-divers
MAKE SURE OF THE EXPERTISE OF YOUR GUIDE, his knowledge of the site, for the season, and the sealife you may encounter during your dive.
PREPARE YOUR DIVE
The safety of a diver decreases with decreasing visibility, increasing depth, the presence of more or less strong currents, load of the diver (cameras, etc) and the number of sharks in the dive zone. Remember that the ocean and the sea, which surround you are more dangerous than the sharks. Prepare and plan your dives with all the divers well before undertaking the dive.
During the launch, if you locate sharks and decide to dive, enter the water slowly, paying attention not to make too much noise. Noisy launches, creating disturbances in the water can incite the sharks and make them dangerous.
Behave as a “polite” guest having “good manners”: during your dive you are the host of the sharks, masters of places and predators. Let any shark approach and allow it “to get acquainted” as it pleases it.
Do not touch the sharks, do not be aggressive: the shark is a wild animal, which only obeys its instinct and will try to defend itself if it feels threatened. (In all probability, if you behave in an aggressive way, the shark will leave and will not try to attack you, but it is better not to try to experiment with this).
AVOID LOSING YOUR GLANCE FROM THE SHARK
It is very important that you do not lose sight of the sharks that surround you. Remain very watchful after the (visible) departure of the sharks.
BE CAREFUL WITH YOUR MOVEMENTS
Remain immovable, rather near the bottom. Try to become one with the relief and the topography, which surround you. Abrupt or fast movements can frighten sharks, make them nervous and even provoke defensive attacks.
AVOID BEING ISOLATED FROM THE GROUP
The sharks often seem to perceive groupings of divers as a completely terrible super-body. Remain grouped, close to your body diver and remain watchful of the movements of the sharks, which surround you.
DO NOT FEED THE SHARKS
The fact of feeding the sharks changes their behaviour radically: it can confusen environment of competition between them, making them very aggressive and thus very dangerous for the divers.
CAREFULLY OBSERVE THE SHARKS’ BEHAVIOR
You have to leave the water at once if the sharks become nervous or agitated. A nervous shark is characterized by muddled, jerky and nervous movements, dorsal fins pointing downward, abrupt changes of direction, increased muscular tensions, nervous movements of the tail … If you do not want or you cannot leave the water, slowly increase the distance between the sharks and you, this could make them less agitated, and allow you to leave as quietly as possible.
BE ATTENTIVE TO THE BEHAVIOR OF FISHES AND FAUNA AROUND YOU
If fishes and submarine fauna that are around you become nervous and their movements erratic, it can mean that a predator is hunting. Trust your diver’s instincts, if you “are not quiet” carefully leave the water as soon as possible.
IF YOU HAVE TO SURFACE IN THE PRESENCE OF SHARKS
Move without haste.
Never take your eyes off the sharks. If necessary, use a snorkel, camera, knife... to keep the shark away.
Go directly your point of exit.
Avoid swimming long distances on the surface, it could tire you and leave you vulnerable to an attack from a shark from either behind or below you.
When you reach your exit point (boat, dock, beach...) leave the water quickly, but smoothly, otherwise you could arouse the curiosity and predator instincts of sharks.
Take the time to inform yourself about the possible implementation of practices such as chumming*  or feeding, which are often practised to attract the sharks - in spite of local regulations, safety must remain the absolute priority.
Do not behave like a prey, nor as an aggressor.
The wearing of a wetsuit is an effective protection allowing you to isolate your skin in case of contact. Avoid wearing the yellow colour, which seems to attract certain species of sharks able to perceive bright colours (as the great white shark).
For underwater photographers
WARNING on using of your camera flas: the light of the flash can provoke an aggressive reaction from sharks (risking bites).
Take advantage of these moments with a shark because it may not be readily repeated, considering the threats to survival of this predator, and you will never the encounter. Besides, it will give you an opportunity to recount your experience at your next family gathering, with your friends or at your workplace.
we wish you good dives,
magnificient encounters and
beautiful images …
and above all