Shark agonistic display
Approximately 23 shark species are capable of producing such displays when threatened by intraspecific or interspecific competitors, as an evolutionary strategy to avoid unnecessary combat.
[6][2][1] A shark which is in distress will behave in a manner that is easily recognizable, due to the sheer oddity of the sequence of movements and torsional elements characteristic of agonistic displays - juxtaposed to normal behaviour, which appears visibly more relaxed and natural.
To successfully hunt and kill prey, sharks regularly encounter competing conspecific and heterospecific individuals, each willing to fight them to earn dominion over the meal, which in itself is a rare, valuable resource.
In the past, combat was the sole means to determine which competing organism attained dominion over valuable resources, including access to prey, territory and reproductive partners.
[1] Sustained injuries impede each individual's ability to perform necessary biological functions, including foraging, courtship and mating behaviour.
[14][4][2][1] The stereotyped postures and movements displayed by the shark are subsequently interpreted by competing organisms as honest, predictive signals of their level of commitment.
[1] In this sense, displays are evolutionarily beneficial as they cost very little in the grand-scheme, but maintain the potential benefit of not sustaining life-threatening injuries during combat, which would negatively impact the organism's fitness.
The overlapping kinetic and postural elements of the pseudodisplay and the typical agonistic display include twitching, shaking, body rolling, flexure or depression of pectoral and caudal fins, jaw gaping, and accelerated, jerky movements.
A significant number of displays are mistaken for the actions produced during attempts to lessen the irritation caused by sharksuckers (Echeneis naucrates) along the length of their body.
In recognition that the majority of behavioural elements exhibited during a genuine agonistic encounter overlap with those performed as part of the pseudodisplay, it is easy to understand how and why accurately differentiation between the two is a challenge.
[1] The very slight distinction between true agonistic behaviour and the irritation-borne pseudodisplay has historically, and will continue to confound scientists dedicated to this area of research, since the two are nearly indistinguishable from each other, at first glance.
