THE HALICORNE HAMMER SHARK

The scalloped hammerhead shark is a fish belonging to the family Sphyrnidae. Like the eight species of this family, it is easily recognizable by its very flattened head whose eyes are on the sides. The leading edge of the rostrum has a well marked median notch (1), flanked by two lateral notches (2) which give the set a sawtooth profile. His body ranges from pale gray to brown on the top, with off-white metallic highlights on the underside. The dorsal fin is triangular. Some populations are sedentary, others migratory. Young people form benches sometimes exceeding ten or even hundreds of individuals. Adults live either alone or in pairs.

Habitat:

The scalloped hammerhead shark is present in all temperate or warm tropical seas of the world. It is the most abundant shark in coastal areas, but it can also be pelagic. He usually lives between 15 and 60 meters deep, but he can go down to 250 meters to feed himself.

Food: It is a species that consumes all kinds of fish. It feeds on both cephalopods and crustaceans, rays and small sharks.

Dating with the man:

Rather fearful with divers, he usually maintains a safety zone. Its internal section is about ten meters and varies depending on the situation. A sudden movement from an awkward observer or a simple scream in his regulator can cause a general leak. This is why it is important to respect certain rules during the interaction phases.

Attitudes in the presence of divers:

There are no rules, underwater in the wilderness. However, there remain behavioral similarities where the same reactions are constantly observed. Again, it is not possible to normalize the attitude of an animal. It is by studying the situations and reactions of these sharks that we will develop the analysis of the interaction between them and the divers.

Observation N ° 1:

Hammerhead sharks do not react in the same way depending on the region, their age and the number of individuals. Indeed, the attitude will be different depending on whether the shark is alone or in schools, whether it is experienced or novice in the presence of divers, or whether it evolves in warm waters as in Sudan or cold as in the Galapagos.

Observation N ° 2:

Among the attitudes noticed in the hammerhead shark, we will find cause and effect relationships directly related to the context of the encounter:
- The diver's behavior: calm, excited, intrusive, fearful, etc.
- The spatial situation of the diver: in the blue, on the reef, in a pass or other
- The depth of the diver: above, at the same level or below the shark.
- The distance between the man and the animal.

NB: The development below will not take these criteria into account.

Observation N ° 3:

It remains difficult today to give a general appreciation of the behavior of this shark depending on the situations because, evolving at great depths and divers can stay with him for a few tens of minutes, most of the development below is the synthesis of daily observations during hundreds of dives in his presence only. Note, however, that the more hammerhead sharks are numerically superior, the greater the chances of interaction.

Solitary hammerhead sharks or fearful schools:

The behaviour :

The shark (s) remain (s) at a good distance, do not approach (do not) or disappear (disappear) in the blue.

Probable causes:

- Too inquisitive divers, who swim towards the animal or descend on him, for example.
- First encounter of an inexperienced shark with divers.
- The shark does not like to be disturbed. He therefore chooses to stay under the deep thermocline.

Shy Solitary Hammerhead Sharks:

The behaviour:

They stay at a good distance from the diver and continue their journey, to reach the bench for example, or else turn around the diver's area without breaking their inner circle: this is then a pre-observation phase.

The causes of this shyness:
- The shark does not like to be disturbed.
- The shark is not interested in the diver.
- The shark is uncomfortable in the presence of the diver.

Solitary Hammerhead Sharks and Observers Benches:

The behaviour :

When the school is curious, it is possible to interact directly with the sharks to the point of evolving at a short distance, right in the middle of the group. We may wonder if it is not then an assimilation into the community on the part of sharks ...

Possible causes:

- The shark collects information thanks to the signals sent by the diver.
- The shark can be a scout on patrol for the rest of the bench.
- The shark can be intrigued by an unrecognized sound.

Solitary hammerhead sharks and curious benches:

The behaviour:

It is the same as before with the observer benches.

The causes of this curiosity:

- Making contact between the intruder, the diver, and the resident, if the shark lives on this area.
- The shark is attracted by the noise (s).
- The shark can be inquisitive: to have a domineering attitude for example.
- The shark is trying to communicate or play.

NB: When hammerhead sharks are numerically superior, the chances of interaction are greater.

Observation N ° 4:

In addition to the factors previously described, there are also phenomena
natural influences on the meeting.

- Depth: Is the shark above and dominating the area, below and observing the area or at the same level as the diver, which he observes?
- The current: If the current is strong, the diver is more likely to encounter hammerhead sharks close to a substrate thanks to the venturi effect that the latter provides. On the other hand, if there is no current, they will rather evolve in the blue.
- Water temperature: Hammerhead sharks prefer waters between 18 ° C and 25 ° C. This is the reason why they generally evolve under the thermocline, that is to say under 20 meters of depth in tropical waters, and at any level of evolution, close to the surface and up to to 40 and more in the waters of the Pacific around islands such as Cocos, Malpelo or the Galapagos.
- Time of day: Depending on the regions of the world, it will be easier to observe this fish very early in the morning at sunrise or at the end of the day.
- Rally area: These very specific dive sites offer the opportunity to contemplate hammerhead sharks more easily. These are magnetic landmarks that help the animal in its migration. The sharks gather there according to the moon, rising or falling, currents, hot or cold and their period of reproduction.
- Territoriality: Some groups of sharks are sedentary between migrations, which favors meetings on some sites more than on others.

NB: Let's repeat it again, there are no definitive rules and it is enough for a shark to refute the situations seen above! That said, it still persists habits observed regularly in the presence of divers.

Observation N ° 5:

Despite the factors, causes and phenomena seen above, sometimes the animal so sought after is not at the rendezvous. This may be due to currents, immersion times, water temperature, moon changes, migration of food, various gatherings, or noise generated by diving activity.

Observation N ° 6:

The best places to swim with this shark are:
- The Galapagos, Darwin and Wolf Islands (Ecuador) - all year round
- The Cocos Islands (Costa Rica) - all year round
- Malpelo (Colombia) - all year round
- Layang Layang (Malaysia) - periodically
- Ponto do Ouro (Mozambique) - periodically
- Shaab Jumna, Sanganeb (Sudan) - all year round

Observation N ° 7:

What is the best course of action for this shark?

- To avoid panic, be prepared psychologically
- Not to surprise the animal by our size, adopt a vertical position to look more imposing and allow the animal to know our intentions.
- Do as little movement as possible, no sudden movements, no agitation.
- Make as few bubbles as possible, avoid shortness of breath and excitement.
- Do not use flash because they can scare the animal.
- Do not join the animal if the animal is deeper than we are, at the risk of probing it by breaking the internal area.
- If you are not comfortable, leave the area calmly.
- Finally, let the animal approach if it accepts your presence.

Recently listed in Appendix II of the CITES Convention, the scalloped hammerhead shark remains a species of threatened status according to IUCN. Its geographic distribution being tropical coastal areas, it is an easy prey for longliners that fish for its fins. Despite his recent official protection, he remains extremely fished and vulnerable.

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.

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