Animal Series #13; The Apex Predator Of The Sea

Picture Source - Pixabay

Hi everyone,

Let's talk about one of the scariest apex predators which have been commercialised in movies regarding the tendency of this particular creature to eat humans. Even though there is a word "white" which should describe the colour appearances of this creature, a great white shark is not white in actuality. This particular creature can be found in almost all major oceans, swimming around the coastal surface, hunting for prey. Unlike any other predators, the female great white shark is larger than a male, measuring up to 6.1 metres weighing about 1,900 kg. This creature is one of the longest-lived cartilaginous fish which can survive up to 75 years or more.

The only natural predators that would be able to take this creature down in a fight is an orca or commonly known as a killer whale. Otherwise, a great white shark is one of the largest predators which hunt for various marine mammals for food. This creature would be able to swim down to 1,200m ocean's depth with speed up to 60 km/h. Nevertheless, being the strongest doesn't guarantee species survivability as indicates by my previous articles about conservation biology. This animal is vulnerable to extinction, and it is protected by a few countries such as Australia to ensure the survivability of this species of predators.

There are a lot of novels, science fictions and tv-shows which depicted a great white shark as an animal which is actively searching for any humans for prey. Even though this creature is responsible for a significant number of shark attack compared to the other shark species, it doesn't prefer human for food.

Habitat and Adaptations

Even though the majority of great white sharks has been observed wandering around the coastal region, this animal can be found in the open ocean which can be as deep as 1,200 metres below the sea level. It is not entirely sure whether or not this animal can be classified with the other coastal species fishes, but it is known to travel as far as a place called the White Shark Cafe located in between Baja California Peninsula and Hawaii. I guess it is a place where various species of sharks gather around, socialising or something. They usually spent 100 days at that particular location before returning to Baja California Peninsula.

Some of the great white sharks which inhabit the coastal area in South Africa are known to travel as far as 20,000 km in nine months which provide an argument to include great white sharks in the list of coastal's predators. Some studies indicate that this sort of migrating behaviour has been for social purposes such as seasonal feeding or finding a mate for reproduction. It is relatively rare for them to found each other when they lingered far away from each other, so having a gathering area for all sort of social activities seem logical. Despite all of the conclusion made, the actual purpose of the gathering is unknown. They can be found in all of the major oceans, but most of the populations of great white sharks can be found in South Africa.

Like any other species of sharks, great white sharks are equipped with ampullae of Lorenzini which give them the ability to sense any electromagnetic waves emitted by moving prey. They were so sensitive to the changes in the voltage variation, which enable them to detect any immobile prey by sensing their heartbeat. The great white shark has a higher body temperature relative to the surrounding water which enables them to swim efficiently especially if they want to catch an agile prey. Their body temperature was kept warm by a mechanism called "rete mirabile".

The mechanism of reheating their surface body temperature is quite sophisticated. There is some sort of web-like structure situated lateral to the shark's body. This web-like structure was actually veins and arteries which play an essential role in heat regulation. The blood which is used to keep the surface body temperature warm is provided by the veins which carried warm blood produced by the working muscles. During migration, they rely mostly on their liver for energy, as the deep ocean is a poor-nutrient area. They will use any lipids which are stored in their liver accordingly. The rate of energy expenditure would depend on their speed and the depth of the sink.

Behaviour

Even though great white sharks have been shown to gather in a specific area which suggests some social interaction between them, their social structure is not fully understood. Compared to a male great white shark, the female is much larger and stronger. It would mean, anytime in an argument; a female great white shark would be able to dominate a male great white shark. However, the attack between great white sharks rarely occurred, and it only happens if there is a need to assert one dominance over the other. A study was conducted in 2008 to measure the power exerted by a great white shark's jaw during a bite, and it was found that a single bite could exert 19 newtons of force.

Spy-hopping is one of the most popular features of the great white shark. I think we had seen in some movies which depicted some sort of behaviour before a shark started to attack its prey; it will gaze upon the prey by raising their eyes above the sea level. This behaviour was also observed in a blacktip reef shark, but it was speculated to serve a different purpose. When a great white shark shows a spy-hopping behaviour, it tries to locate their prey to perform a precise attack by sight or by smell (compared to water, smell travels relatively fast through the air). For a blacktip reef shark, the spy-hopping behaviour might be adopted when they try to communicate with humans. The interaction between different groups of great white sharks has been somewhat peaceful. If they encountered another group which is lead by an alpha shark, they would combine and re-established their ranks in the social ladder by using various kind of communication technique.

Diet

Picture Source - Pxhere

I don't think I need to tell you guys what kind of food that this particular creature prefers to eat. It's well-understood by the majority of people in the world that a shark is a carnivorous creature. They ate various kind of marine mammals which include whales, dolphins and porpoises. When this particular predator was juvenile, they only hunt small fishes as their jaws are underdeveloped which could not provide a sufficient amount of biting force to grab its prey. When they have reached a length of 3 metres, their biting actions were reinforced by mineralised cartilages found within their jaw. It allows them to hunt for larger prey such as cetaceans and pinnipeds, but they were yet to eat marine mammals.

They began to hunt marine mammals when they reached a length of at least 4 metres. The development of their jaws was directly proportional to their length. From the result of various studies, it was found that this particular predator likes to hunt marine mammals which have high-content of fat. They are opportunistic creatures which specialised in a different kind of prey. Some great white sharks love to hunt dolphins; some like to eat whales; the type of victims would be determined by the shark's preferences. They were known to hunt prey which is larger than themselves. Even though in terms of strength they could be outmatched, great white sharks are extremely intelligent. They would bite any parts of their prey which would disable their movement, and wait for them to bleed to death.

The success rate of a shark attack is usually determined by the time of the day. They prefer to hunt 2 hours before the onset of sunrise, which meant most of the prey couldn't see clearly. During that particular hour, their success rate was 55%, and it drops to 40% when the sun has risen high.

Picture By Brocken Inaglory - Wikimedia

One of the most favourite food sources for a great white shark is a whale carcass. The fat content which can be found in a whale can keep a shark well-satiated for a month or so. This apex predator was attracted to the carcass by the odour spread through the wind detected while they were spy-hopping for any potential prey. The will consume any part other than the blubber of the whale as this particular fat-rich area would be eaten last. Whale carcasses are the primary food source for a large and old great white shark which lack the speed and manoeuvrability to hunt for any prey.

Reproduction and Natural Threats

A male great white shark would take 26 years to achieve sexual maturity while a female great white shark would take about 33 years. Originally, they were thought to live up to 30 years, but some research involving various kind of great white shark specimens has proved that this particular creature can live for more than 70 years. They have a low rate of reproduction compared to the other predator which make them vulnerable to extinction from various human's activities such as overfishing and any environmental changes imposed by humans.

Picture Source - Opencage

Little is known about this particular creature's sexual habit, but it was speculated that the specific gathering area or around the whale carcass are the places where a male shark courted the female for reproduction. The gestation period for this creature is 11 months, and they were ovoviviparous. Most of the delivery were observed during the spring and summer.

Even though it seems this particular creature was too strong to be taken by any other predators, there is only one kind of predator which could kill and eat a great white shark. An orca could hold this apex predator immobilised for 15 minutes, suffocate them and finally eat its liver. A dead great white shark would emit a particular scent which can be recognised by its peers. After detecting the scent, the other great white sharks would flee the area; it's acted as a warning signal to stay away. The cause of death of a particular great white shark can be determined by its liver. If its liver is missing from the body, then it's most probably killed by an orca.

There are a few stories which have been told regarding how a human was saved from a shark attack by an orca. A local population of great white sharks in California which consist of a hundred mature apex predators disappeared in 2000 possibly due to death of one or a few others by the hand of orcas. This would cause the other to flee, searching for another safe coastal area to establish a new population.

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I have always admired this apex predator. They were so interesting in so many regards, but this creature has been threatened with extinction due to human's activities and the fact that they have a low reproduction rate. We will be discussing some of the conservation aspects of this creature sometimes. Thank you for your attention, and have a nice day.

References and further reading materials

• Henry Nicholls. BBC Earth. The truth about great white sharks. Retrieved March 31, 2018, from http://www.bbc.com/earth/story/20151005-the-truth-about-great-white-sharks
• Brent Swancer. Mysterious Universe. The Mystery of the White Shark Café. Retrieved March 31, 2018, from http://mysteriousuniverse.org/2015/07/the-mystery-of-the-white-shark-cafe/
• Facts and Details. Great white shark. Retrieved March 31, 2018, from http://factsanddetails.com/world/cat53/sub337/item1275.html
• Wikipedia. Great white shark. Retrieved March 31, 2018, from https://en.wikipedia.org/wiki/Great_white_shark