The meaning of pectoral fin position part III

The meaning of pectoral fin position part III

Hunched back: threat- or feeling threatened display – a guestpost by Pascal Gospodinov

First we will discuss how a hunched back is created, talking about general appearance and than in a second part we will try to enlighten what the meaning of this hunch display might be.

The general appearance of the hunch display is lowered pectoral fins, upward pointing snout and the resulting hump and as result an arrhythmic swim motion.

Here both pectoral fins are lowered. Why? The reason is simple the shark is preparing himself to turn in every direction, because he probably don’t know exactly which direction is gonna be the safest. The result of lowering both pectoral fins is an upward pointing snout. We discussed in part I that the pectoral fins are also used to counteract the downforce. as we don’t have this counteraction when both pectoral fins are lowered, the shark try to get more water under his belly, to compensate the missing fins. The result of the upward ponting snout is the hunchback and the result of the hunchback is the arrhythmic swim motion. All the hunch display is just the result of both pectoral fins being lowered, not more not less. Again both lowered pectoral fins will enable the shark to turn left or right.

As discussed in part I lowered pectoral fins increases the lateral surface and enables the shark to turn. In the hunch display the pectoral fins are mostly lowered to the maximum, to give the shark the possibility to turn with the narrowest bow possible.

Sharks will show the hunch display when pressure of any kind is put on them; for example if divers hassle them, or in very closed environment or both… but all kind of scenarios are possible. So back to our question what can be the meaning of the display? The general assumption is that the hunch display is a threat display.

Why should an animal prepare himself to escape, because thats what the shark do in lowering his pectoral fins if he wants to threat, show dominance, aggression or even attack? It makes no sense. An animal that prepares himself to flee feels threatened. The shark feels stressed and is looking for an escape. At that point its up to the diver that is confronted to that kind of behavior to react correctly and to relax the situation whilst giving the shark more space to maneuver and not hassle even if it wasn’t deliberate… When sharks show hunch display its because they feel threatened and its not a sign of aggression, dominance or any kind of agonistic display.

Picture 1. On the right side: hunch display. On the left: cruising posture

It exists another scenario in which the pectoral fins are lowered and the shark will show a hunched back. A scenario triggered by Remoras a.k.a sharksuckers that sucks in themselves to sensory areas of the shark. The shark will try to force the Remoras to move by shacking his body or bending his skin in the area in which the sharksuckers put suction pressure. This bending and shacking can look very similar to the hunch display explained before…

As asked at the beginning: „is the hunch display a threat- or a threatened display?“, what would you say?

A behavior is caused by a need. Why would a shark create a behavior against a person, because they never show that in regard of other sharks. We were not part of their evolution so how can a behavior against humans be created in less than 100 years (the time in which humans are swimming in the oceans frequently), its simpley impossible.