SHARK: THE LONGIMANUS

 Text: Steven SURINA

As part of the series of articles about sharks, we invite you to discover in this issue the longiman shark (Carcharhinus longimanus).

LONGIMANUS: DESCRIPTION

It is a shark very easy to recognize with its shape both spindle-shaped and massive. It has very large pectoral fins and a very high first dorsal fin. The ends of these three fins are rounded and pearly white in color. Some scientists think that this peculiarity would attract by contrast, clear spots, white in the blue, the predators of lower rank in order to facilitate the hunting. Its body is gray, bronze and beige above and white below. It is very often escorted by pilot fish (Naucrates ductor) and remoras (Remoras sp.). Not to be confused with the white tip reef sharks (Carcharhinus albimarginatus) or the coral shark (Triaenodon obesus).

LONGIMANUS: HABITAT

The oceanic shark is epipelagic. It is found in the open sea throughout the tropical belt. It only rarely approaches the coast, to frequent drop offs and passes. This species prefers water temperatures above 20 ° C and lives between 0 and 180 meters deep. Little is known about the dynamics and structure of their population. It would be solitary according to some biologists, but could move in groups according to others. The males and females would be non-gregarious part of the year to finally end up around the oceanic islands to reproduce, in the course of the fall. They regularly follow communities of marine mammals - dolphins, pilot whales - on the high seas.

LONGIMANUS: FOOD

Opportunistic, it feeds on all bony oceanic fish - tuna, barracudas, billfish - or cartilaginous - rays, other sharks - squid, dead whales, turtles, marine mammals and even garbage! Like the tiger shark (Galeocerdo Cuvier), it acts as a “dustbin of the seas”. A deep-sea marauder, the scarcity of his potential prey drives him to attack without warning when the opportunity presents itself. It forages mainly near the surface.

LONGIMANUS: MEETINGS WITH MAN

The oceanic shark is one of the species of sharks said to be potentially dangerous for humans, although because of its habitat, it is rarely confronted with humans apart from castaways and divers. Although few attacks are officially attributed to it, some scientists consider the longimane shark as the one that most often attacked humans; this does not necessarily mean deadly attacks or bites but especially intimidating charges; but since only hypothetical attacks on shipwrecks are involved, they are not included in the statistics. However, it displays an inquisitive behavior towards the divers and does not hesitate to get closer very closely. His internal section is less than 3 meters, so he is rarely shy during his encounters with man. It can be territorial even aggressive if it is under stimulation of food.

LONGIMANUS: REPUTATION

The oceanic shark is also called the "castaway shark". Powerful predator in its ecological niche, the longimane is one of the least fearful sharks in the presence of humans. Its predation pattern, the rare encounters between it and humans, its size and its diet, make it one of the liveliest and most inquisitive sharks in the 0-10 meter zone. He is credited with part of the casualties of the shipwrecked USS Indianapolis which sank off the Philippines in July 1945. He is considered the fourth most “dangerous” shark to humans after the Tiger Shark (galeocerdo cuvier), the Bulldog Shark (Carcharhinus leucas) and Great White Shark (Carcharodon carias). However, it is better to say that a situation is risky, even dangerous, rather than saying that a shark is dangerous! However, it is advisable to display the greatest respect for safety instructions in the presence of this shark so as not to aggravate the situations.

Observation No. 1

Oceanic whitetip do not react in the same way depending on the region, its age and the number of individuals. Indeed, his behavior will be different if the shark is alone or in number, if he is accustomed to the divers or not and if he evolves with humans on the surface, in scuba diving, close to the surface or at greater depths .

Observation No. 2

The encounters with the "longimanus" are multifactorial and take into account several important criteria such as:
- The behavior of the diver - positions and attitudes: calm, neutral, excited or panicked
- The diver's spatial situation - 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 at the surface
- The distance between the man and the animal.

Observation No. 3

The white offshore fin is a fish with which it is easy to interfere because, not shy in the presence of man, it is he who will approach the divers and decide on interactions. So far, eight different types of approaches have been observed. Every action leads to a reaction. The study of these approaches is based on this multifactorial theme.

PASSIVE APPROACHES / CURIOUS ATTITUDES

PASSAGE

The shark is in the observation phase on its area of ​​evolution. His swimming is calm, directed towards what aroused his interest. He passes quietly around the plunger (s) in his internal section to gather as much information as possible, sent by the signals of his subject of study, the man. Generally, its only spatial limit is the surface.
So: Avoid an extended stay on the surface that could send a different message to the shark and thus transform his behavior.

LATERAL APPROACH

The shark swims sideways alongside the diver in order to gather information using its sight, lateral lines, and Lorenzini bulbs. By showing himself parallel to the diver, he shows off his size and power in the face of this stranger who has penetrated his territory. It swims to the limit, even inside its internal section, drawing phases of “8” approaches.
So: Maintain a vertical position, do not move, never end up on the surface.

TERRITORIAL PATROU

The shark inspects his territory with trajectories directed towards the diver. His swimming is moderate but sometimes lively, with acceleration shots. His movements, lively around the diver, are not aggressive. It shows once again only its territorial superiority through its body language. Most often, this behavior is observed under diving boats that can be likened to a potential source of food. Its spatial limits are the surface, the area of ​​the boat and the area of ​​evolution of the diver, which explains the anxiety of the shark in his movements.
So: In order not to provoke any change of attitude of the shark in response to our "intrusion", it is best to leave the area calmly, keeping a vertical position and eye contact with the animal, without ever recoiling in front of its approaches like one of his natural prey.

CAUSES & MOTIVATIONS

- Curiosity
- Inspection of the territory
- Indifference
- fear

DOMINANT INQUISITING APPROACHES / ATTITUDES

The approaches described below are always the result of failure to respect the imperative safety instructions required by interaction with this species. Let's say it once again: there are no dangerous sharks, there are only dangerous situations.

FRONT LOAD

This intimidation charge, essentially based on territorial behavior, presents us with a nervous shark. The animal faces the diver and moves in the last meters of his approach. Despite the vividness of the interaction, the shark is not aggressive and does not strive. Two scenarios are then possible: either the shark is from the outset in inquisitive approach phase because of the signals sent by the diver, or he reacts to a change of attitude on the part of the diver to his approach, related to the signals of stress sent by the diver who made the shark into dominant status.
So: It is better to leave the area without wasting too much time, before the shark becomes too inquisitive. It is also necessary, always, to maintain a vertical position, a visual contact and to react as little as possible to its approaches.

BLIND ANGLE APPROACH

Any self-respecting underwater photographer knows, never look a fish in the eye until it is within flash range. Marine animals are sensitive to the eyes. For example, nature has endowed the lemon butterflyfish (Chaetodon semilarvatus) with a blue spot under the eye; this makes it appear larger than it is, to intimidate its potential predators. The bigger the eye, the bigger the fish! As you will have understood, fish do not like to feel looked at, even less observed, because this is the attitude of a predator interested in a prey ... At the top of food chains, sharks rarely feel observed. When this happens, they become timid or even fearful and try by all means to get around this embarrassment, either by disappearing or by going out of your visual field - cf. Article The Mag N ° 57. When a longimanus leaves your field of vision, it is intrigued by your lack of reaction to its approach. Usually, when approaching a diver, the shark receives in response electrical signals sent by the diver's brain and muscles - stress, increased heart rate, etc. Outside your visual field, you react differently and therefore no longer send the same messages, which has the effect of encouraging the shark to get even closer, sometimes even to contact, in search of additional information. Based primarily on curiosity, this blind spot approach, if it is repeated too much, can turn into an inquisitive round in search of food! Remember, as an opportunistic surface scavenger marauder, if you don't react to this shark's approaches, then it can see you as a potential food source!
So: Never lose eye contact with the shark and always stand vertically.

CROSSED APPROACHES

This phase of approach has several aspects. The shark swimming above the divers is already in a dominant position - cf. Article The Mag N ° 57, on zones and spaces of evolutions. He does not consider the diver to be a potential threat. In addition, it adopts a fast, jerky swimming, with lowering of the pectoral fins and well-defined approach points. His inquisitorial behavior is based on territoriality. The oceanic shark then seeks to intimidate the diver to drive him out of his territory. In order to achieve this, the shark will fly over the area of ​​evolution of the intruder at high speed before descending on him. He will perform these approaches at a steady pace by crossing his angles from top to bottom and from bottom to top until the diver leaves the area. Experiencing, this phase of interaction can lead the shark to an inquisitive round if you do not leave the area quickly.
Therefore: As little agitation as possible is recommended, in an upright position and permanent eye contact, while leaving the area.

FACE TO FACE

This behavior aims to intimidate the diver. If the diver reacts little to the approach of the shark and his signals are not very expressive, the shark, who needs to understand perfectly the situation, will evaluate the diver until contact. The anxiety generated by such interaction will have the effect of exciting and stressing both the shark. If the diver, cut off from his most extreme physical limits, still does not react, the shark will have to make a tight U-turn at 180 ° at the last moment to escape. In the opposite case, if the shark is in a dominant position, knows all the equations of the situation and takes the emotional advantage over the diver, the longimanus will not change course and jostle the diver to push him back. . Both inquisitive and territorial, this approach usually occurs after several tens of minutes between you and the animal because the latter took the time to gauge you and you took the time to get used to him.
So: Keep a maximum distance between you and the shark, upright and never back off.

INQUISITIVE ROUND

Of all the approaches, this is surely the most trying and the most difficult to manage. It appears when the shark understands that you are not a threat to it, or even a pretender to its territory. When the oceanic shark enters this inquisitive phase, it knows that the diver no longer has any physical advantage in its space of evolution. You are in the blue, far from the reef, with no annex above you, in the current, on one of its hunting areas. At the beginning it describes long concentric circles of observation followed by frontal loads and crossed approaches and it will seek as much as possible to get out of your visual field. Without any more fear concerning you, you will become the central point of his approaches and he will systematically come back to contact by all possible means, persisting and becoming insistent. Despite appearances, his swimming is not aggressive, even though he accelerates and is seized with spasms when he comes into contact. His nictitating membranes only rise to protect his eyes and not to open his mouth. The best way to repel it is to maintain a strong pressure directed towards the outside at the level of its gills, the vital point of its breathing. Hitting his body with your fins or your hands would be interpreted as an attack, and the response to an attack is defense, even defense by attack!
Therefore: Maintain a vertical position, remain grouped, move as little as possible, comply with the safety instructions defined in the briefing, signal its presence on the surface with a parachute until the arrival of the tire.
NB: The arrival of the zodiac usually leaves the shark.

CAUSES & MOTIVATIONS

- Curiosity
- Territoriality between sharks: Sharks are regularly fed. Over time, they associate places and food. When they see a boat (s) of the same size (s), they swim towards the spot and expect to be fed. The absence of a "reward" does not necessarily lead to an episode hostile to the divers, but it is always possible. During the spawning period, the females delimit secure territories for the very young so that they do not get eaten by other predators. It also develops stress between sharks.
- Territoriality with the diver (s)
- Stress - which sends signals identical to those of their prey to sharks
- Electromagnetism - camera, muscle activity, brain activity
- Noise (s)
- Food stimulation

Observation No. 4

This article is the culmination of empirical research essentially based on multiplied daily observations. Summary of the study of behavioral habits observed by divers for more than ten years during thousands of dives, it is not intended to be exhaustive and certainly not definitive. As a result, this information can be supplemented, reinterpreted or even refuted constantly, through new observations and encounters.

Observation No. 5

The best places in the world to swim with this shark are:
- The Egyptian Red Sea - oceanic islands and offshore reefs - In autumn
- The Bahamas - Cat island - In April, May
- Hawaii - off Kona - All year round

Observation No. 6

Some recommendations for safe interaction with oceanic whitetip:

- 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; it stimulates the animal and irritates it.
- Never find yourself isolated.
- Do not end up on the surface; snorkeling is strongly discouraged.
- Do not lose eye contact.
- Avoid drifting in the open sea far from reefs.
- If the shark becomes too insistent, too inquisitive, leave the area.
- If not comfortable, leave the area calmly.

In short, diving with this shark implies the strict respect of precise imperative safety rules. Remember that if you keep your calm while respecting the instructions, you will have the exceptional chance to enjoy a moment of exceptional intimacy with this majestic shark, unfortunately disappearing from our oceans.

THREATS TO THE SPECIES

Main victim of longline fishing, the offshore white fin is extremely popular… for its fins! According to experts, the population of oceanic sharks is in decline in different parts of the world by 70 to 99%! As a result of these statistics, the longiman's status on the IUCN Red List has changed from “near threatened” to “vulnerable”. In March 2013, the longimanus was added to Appendix II of CITES and therefore fishing and trade in this shark requires authorization and these activities are strictly regulated. Officially…

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 had interactive booklets on the protection and preservation of sharks distributed 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.

View the profile of Steven SURINA