FOCUS: THE SILKY SHARK

Description

The silky shark is the slimmest shark. Its dark gray / bronze back sometimes has silky reflections, hence its name. The ventral surface is white, with a whitish lateral stripe extending over the head. It is often confused with the requiem shark (Carcharhinus plumbeus). What characterizes it is the relatively low height of its first dorsal fin and the extremely elongated rear edge of the second. The first dorsal fin originates behind the free posterior tips of the pectoral fins. It is also distinguished by its long rounded muzzle and the sickle shape of its pectoral fins. It can live up to 25 years. Not to be confused with the Gray Reef Shark (Carcharhinus amblyrhincos), the Rimmed Shark (Carcharhinus limbatus) or the Copper Shark (Carcharhinus brachyurus).

Habitat

It is one of the most abundant sharks in pelagic areas, especially tropical, mainly at temperatures from 23 ° C to 24 ° C. Very mobile and migratory, it is most often found near continental shelves between the surface and 500 meters deep. It is occasionally found near the coast if the depth is sufficient. He often meets divers near oceanic islands.

Food

The silky shark feeds mainly on bony fish and cephalopods. Preys are relatively rare in the areas where it lives. He turns out to be a fast, curious and obstinate hunter. Adult and large specimens are often solitary, but the youngest hunt in groups. They would follow the schools of tuna. Their hunting technique would be to swim at high speed in the schools of tuna, mouth open, to optimize their chance of catching prey.

Lifestyle

According to observations made in different regions of the world, there are specific places of birth for juveniles. Indeed, the young silky sharks live and hunt in schools of several dozen individuals, where there are several generations! Nurseries are most often islands or ocean reefs, not far from the high seas, but sufficiently sheltered from predators, thus providing secure areas for juveniles. In adulthood, they rather live alone on the high seas and gather to reproduce or follow the migrations of their food.

Dating with the man

Because of their habitat, like the longimanus, silky sharks are rarely confronted with humans outside of shipwrecks and divers. It is a curious shark that approaches divers without attacking them. The juveniles are lively and inquisitive while the adults display a calm and controlled attitude. However, the testimonies are contradictory: some divers have experienced misadventures with this species. It seems to be dangerous under food stimulation. It also happens to charge frontally without warning. At the same time, Caribbean diving instructors handle them regularly to remove hooks stuck in their mouths. It is therefore nevertheless advised, especially for inexperienced divers, not to get too close.

Reputation

Although no attack has been attributed to them, it is a shark considered to be potentially dangerous for humans, mainly because of its size and abundance.
The silky shark has the reputation of being a shark that is not shy towards humans, curious but less inquisitive and less dangerous than the oceanic whitetip shark (Carcharhinus longimanus), although its environment is much the same. Its behaviors, interactions and approaches to humans are less complex than those of the “longimanus”. Guided by his hunting instinct, these interactions will remain basic. Very receptive to wave changes and variations in low frequencies, it is particularly sensitive to noise thanks to extremely fine hearing. He will define the essential of his approaches according to what he will perceive.

Observation N ° 1

The silky shark does not react in the same way depending on the region, age and number of individuals. In fact, its behavior will be different if the shark is alone or in number, if it is used to divers or not, and if it evolves with humans on the surface, in scuba diving, near the surface or at deeper depths. important.

Observation N ° 2

Meetings with the “silky” are multifactorial and take into account several non-negligible criteria such as:
- The diver's behavior (diver's positions, calm, neutral, excited or panicked attitude).
- The spatial situation of the diver (in the blue, on the reef, under the boat or in the open sea).
- The depth of the diver (above, at the same level, below the shark or on the surface).
- The distance between the man and the animal.
- Food stimulation or not.

Observation N ° 3

The silky shark is a fish with which it is easy to interfere because, not shy in the face of humans, it is he who will approach divers and decide on interactions. So far, six different types of approach have been observed. Every action leads to a reaction. It is on this multifactorial theme that the study of these approaches is based.

Passive approaches / Fearful attitudes :
- Distant observation approach: The shark shows itself in the diver's visual field, but maintains a safe distance. This behavior is most often observed in adult specimens which are only rarely interested in humans. Juveniles, such as children discovering the world, are more inclined to curiosity. On this type of approach, either the silky will turn slowly around the area where the divers are moving to deepen the situation later, or it will quietly disappear into the blue.

Causes and Motivations :
- Approach interest (noise)
- Inspection of its training area
- fear

Passive approaches / Curious attitudes :
Rapid observation approach : The shark swims laterally next to or below the diver to gather information using its different senses. By showing itself parallel or below, it exhibits its size and power to the diver operating in the same area as him. Its approach is rather rapid because the preliminaries are quite rare with this species. This phase generally lasts between 30 seconds and 2 minutes, between the surface and 40 m deep. Depending on his interest for you, he can then leave or deepen his approach. Maintain an upright position and do not shake or end up on the surface.

Territorial patrol : The shark inspects its zone of evolution - not territorial because they are active swimmers who very rarely delimit (feeding for example) private zones - with trajectories directed towards the diver. His swim is fast, lively with acceleration. His movements are lively around the diver, but not aggressive. He once again shows his territorial superiority through his body language. Most often, this behavior is observed near a food source, such as under boats for example, assimilated to food sources or, for another example, near a school of tuna. In order not to alter the attitude of the shark in the face of our intrusion, it is preferable to leave the area calmly. Maintain an upright position and visual contact with the animal without backing down from its approach, as one of its natural prey would.

Causes and Motivations :
- Curiosity (noise)
- Inspection of its training area
- Mistrust
- Territoriality?

Inquisitive approaches / Dominant attitudes :
The approaches described below are completely unpredictable and again lacking in foreplay. Unlike other inquisitive sharks, this one, because of the exigency of its environment, must act and behave quickly, without warning. Apart from undergoing the situation and behaving as best you can, it is because of these approaches that the silky shark is also qualified as an animal potentially dangerous for humans.

- Frontal charge: This charge of intimidation, essentially based on territorial behavior, presents us here with a nervous shark. The animal faces the diver and emerges from the blue at high speed. Unlike the oceanic shark (Carcharhinus longimanus) which does not go after the diver, the silky can be very persistent. Three scenarios are then possible: either the shark is from the start in the inquisitive approach phase because of the signals sent by the diver, or it reacts to a change of attitude on the part of the diver on his approach, linked to the signals of stress that it sends, then passing the shark into dominant status. Finally, the shark can consider the diver as a rival during feeding. Since the shark is dominant from the start, it is best to leave the area without wasting too much time before it becomes too inquisitive. Maintain an upright position, make eye contact and react as little as possible to his approaches, keeping the hands at your sides.

- Persistent round: This approach is the most trying to live with a silky shark and the most difficult to manage. Occurring most regularly under dietary stimulation, the shark seeks to chase you away using force and intimidation through contact. He tightens his approach circles, turns 180 ° in your direction with a short maneuver, contorts to reach you better, in short, it's a real fight to keep his cool and react with relevance. The shark is not trying to bite you, otherwise it will swim out of your visual field, it is just trying to get you to leave its area, you are at its place, at its meal, and you are not invited!

If this approach occurs without food stimulation, you are therefore the source of the animal's annoyance by not being in the right place at the right time and it will try to make you leave the area.
Its nictitating membranes rise to protect its eyes, not to open its mouth. The best way to repel it is to maintain a strong pressure directed towards the outside at the level of its gills, vital point of breathing. Warning! If you hit his body with your palms or your hands, the response to an attack being defense, a counter-attack may well follow! Maintain an upright position, stay grouped, get as restless as possible, listen to the safety instructions specified during the briefing, signal your presence on the surface with a parachute until the inflatable arrives or get closer to the reef. The arrival of the zodiac or the proximity of the reef wall usually makes it leave.

Causes and motivations :
- Food stimulation.
- Territoriality with the diver (s).
- Stress (sends prey signals to the shark).
- Electromagnetism (camera, muscle activity, brain activity).
- Noises.

Observation N ° 4

Despite the different approaches and observations mentioned above, these explanations are the result of empirical research based essentially on daily observation. In conclusion, this information can be refuted, supplemented, detailed or even modified. However, what is described above is an axis of study relating to behavioral habits still observed by divers for more than ten years on thousands of dives in the Red Sea (Egypt / Sudan).

Observation N ° 5

The best places in the world to swim with this shark are:
- The Sudanese Red Sea (oceanic islands and offshore reefs south of Suakin) - all year round
- The Bahamas (Cat island) - (April / May)
- Cuba (The Queen's Gardens) - all year round
- Malpelo - all year round
- French Polynesia (Rangiroa) - all year round

Observation N ° 6

Some recommendations for interacting safely with the silky shark?
- To avoid panic, be psychologically prepared.
- Adopt an upright position to appear more imposing and allow the animal to know our intentions.
- Make as few movements as possible, no sudden movements, no agitation so as not to excite the shark.
- Make as few bubbles as possible (avoid shortness of breath and excitement).
- Do not use flash (this stimulates the animal, irritates it).
- Never find yourself isolated.
- Do not end up on the surface (snorkeling strongly discouraged).
- Do not lose eye contact.
- Avoid drifting in the open sea far from reefs.
- If food stimulation, be sure to supervise and remember the briefing instructions.
- If the shark becomes too insistent, too inquisitive, leave the area.
- If not comfortable, leave the area calmly.
Clearly, diving with this shark implies strict compliance with certain safety rules. If you keep calm while respecting the instructions, you will have the exceptional chance to enjoy a moment of intimacy with this majestic shark, unfortunately disappearing from our oceans.

Threat to the species

Due to their abundance, these sharks represent the main resource for artisanal shark fishing in many countries. In 2007, IUCN recognized that populations of silky sharks are declining worldwide: the species has been classified as "threatened". It is the most fished shark species, as well as the blue skin shark (Prionace glauca).

Steven Surina

Steven Surina is a diving instructor in the Red Sea. In this capacity, for a decade, he has accompanied cruises along the Egyptian, Sudanese and Eritrean coasts. He worked in partnership with the Italian publishing house “Magenes Editoriale” on the project of a collection of dive sites all over the Egyptian Red Sea as an author and illustrator. He wrote a dissertation on the behavior of oceanic sharks in 2008 and distributed interactive booklets on the protection and preservation of sharks to Egyptian schools.

This is how he created, in 2010, Shark Education which offers shark diving trips whose objective is to help them get to know and understand them better.