Whilst many animals have evolved highly specialised camouflage, or have equipped themselves with defensive teeth, spines or poisons, manta rays rely on their large size and smart behaviour to avoid predation.
Manta rays are considered to be the most recently evolved and highly derived form of all the elasmobranchs. Their flattened body shape is superbly adapted for life in motion; they are extremely energy efficient swimmers and with one powerful beat of their wing-like pectoral fins they are capable of short bursts of speed easily in excess of 15 mph (24 kph)…
The manta ray’s speed, coupled with their flattened shape, helps to protect against predators which find it hard to bite hold of the mantas in an area of the body which contains vital organs. Unlike some of their relatives the including stingrays, manta rays do not possess a functional defensive spine at the base of their tails.
However, the evolutionary remnants of this ancestral spine can still be seen in some specimens as a small lump, known as a vestigial spine, where the spine used to be in their ancestors; much as humans still retain the coccyx bone, which is the remnants of our ancestral tail.
Manta rays have good eyesight and like most prey animals their field of vision is very wide; their wide set eyes giving them a better chance to spot a potential threat which may be approaching. However, manta rays do have a blind spot directly behind themselves, so they will sometimes flip their body upside-down and turn around to appraise an unknown object, such as a diver, if they sense it’s close presence but cannot clearly see it.
This technique gives the manta a much better view, but it also presents the largest surface area of the manta possible to the unknown object. So, should the unknown object turn out to be a threat, such as a large predatory shark, the manta presents itself as a difficult and imposing target to bite hold of. Most of the time however, the manta’s response to a potential threat is fright and flight, with one powerful beat of their pectoral fins they accelerate away from trouble.
If the manta’s eyes fail to spot a predator sneaking up from behind, then their tail can serve as a last second warning system, potentially giving them an extra split second to react as the predator will touch the end of the tail first. Manta rays are careful not to expose themselves to such sneak attacks any more often than is necessary and one of the best ways to ensure this is to hug the seafloor. By staying close to the seabed whenever possible the manta rays ensure that predators cannot easily approach and attack their more vulnerable belly without the manta first sensing the predators presence.
Predators & Wound Healing
Because of their large size only the largest of marine predators, such as Tiger (Galeocerdo cuvier), Greater Hammerhead (Sphyrna mokarran) and Bull (Carcharhinus leucas) sharks, or the False Killer Whale (Pseudora crassidens) and Orca (Orchinus orca) would attempt to attack an adult manta ray. Predation rates appear to vary considerably in different locations around the world.
In the Maldives for example, manta rays have few natural threats to worry about, with just a handful of new predatory attack bites and scars recorded in the study population each year, less than 10% of this population exhibits any evidence of natural predatory attacks. Mortality rates within the population appear to be very low and virtually all of the mantas which have been observed with fresh wounds are sighted again months, or years, later having completely healed from their injuries. Flesh wounds which remove portions of the posterior section of the pectoral fins can also recover remarkably quickly, with large sections of missing flesh able to regenerate with scar tissue to fill back in the missing portion of wing over the years.
However, severe bites which cut deep into the manta’s body, removing whole sections or ends of the pectoral fins, will never allow regeneration of cartilaginous tissue in these areas, leaving the mantas with major disfigurements. In other parts of the world, such as Mozambique, the resident population of reef mantas rays suffer from much higher levels of shark attacks, with over 70% of the studied population exhibiting some form of injuries and scaring from predatory attacks.
In both of these locations an injured manta ray will spend significantly more time visiting a cleaning station to have its wound/s cleaned. In Mozambique small butterflyfishes (Sunburst Butterflyfish – Chaetodon kleinii) act as the wound specialists, removing dead and infected flesh, helping the injured area to heal faster, while in the Maldives the blue-streak cleaner wrasse performs this task.