Key Takeaways

• Under ideal conditions, sharks are able to smell blood from 1/3 mile (0.5 km) to 1/4 a mile away.
• According to Yannis Papastamatiou, a scientist from the Florida National Museum of History who led the study into sharks' ability to make mental maps, their navigation must be exceptional due to the distances that they cover. He notes that tiger sharks' orientation far exceeds their sensory range. Furthermore, he is impressed by their ability to travel through the seemingly featureless deep ocean, pointing out that it is an indication that they can sense Earth's magnetic field.
• Shark skin is composed of small teeth-like structures referred to as dermal denticles (placoid scales) that point toward the shark's tail. These scales reduce the friction from the surrounding water when the shark swims.
• Sharks' vision is ten times better than human vision in low light. Their eyes are especially suited to see in murky ocean water and are able to see objects that are 20 to 30 meters distant.

Introduction

Smell

• Various sources have theorized that under ideal conditions, sharks are able to smell blood from 1/3 mile (0.5 km) to 1/4 a mile away.
• How far away a shark smells blood underwater depends on various factors, including the species of the shark, the direction of water, and the speed of water. Some species of sharks, such as great white sharks, have a greater sense of smell than others.
• Sharks have nares, which are openings that look like nostrils. However, sharks specifically use them for detecting scents. They are not connected to the throat and aren't responsible for any other functions. Still, thanks to their effectiveness, sharks are sometimes called "swimming noses."
• Currents carry smells in water through molecules, including from blood. When water enters one of the nares, sensory cells (Olfactory epithelium) extract the smell "and then send signals to the shark’s brain. In the shark’s brain, the olfactory lobes kick in and analyze the scents, which can be those of a potential mate or prey."
• To illustrate the importance of smell for the shark, around 66% of its brain consists of olfactory lobes.

 

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Mental Maps

• Sharks have been known to make and remember mental maps. Among different theories on how they do it, the research published in the Current Biology Journal speculates that some "sharks may use Earth's magnetic field to help them generate a mental map and compass."

• Scientists that examined tiger sharks found that they took direct "paths from one side to another." This demonstrated that they have a strong capacity to mentally store maps of important locations.
• According to Yannis Papastamatiou, a scientist from the Florida National Museum of History who led the study into sharks' ability to make mental maps, their navigation must be exceptional due to the distances that they cover. He notes that tiger sharks' orientation far exceeds their sensory range. Furthermore, he is impressed by their ability to travel through the seemingly featureless deep ocean, pointing out that it is an indication that they can sense Earth's magnetic field.
• It is also noted that this ability may be particular to certain species of sharks. For instance, blacktip reef sharks do not seem to have it and never travel such long distances.
• Additionally, sharks can also be taught to identify shapes and can retain this knowledge for up to a year.

Dermal Denticles

• Shark skin is composed of small teeth-like structures referred to as dermal denticles (placoid scales) that point toward the shark's tail. These scales reduce the friction from the surrounding water when the shark swims. Therefore, they allow sharks "to swim faster and more quietly."
• According to Florida Museum, rubbing the skin of a shark from head to tail would feel smooth while in the opposite direction, it would feel like sandpaper.

 

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• Great white shark's dermal denticles are so effective that they inspired Olympic swimsuit designers. They were able to vastly improve swimmers' speed by "creating a fabric that mimics the exact proportion of the shark’s denticles."

Vision and Hearing

• In addition to the sense of smell, sharks possess six other senses including sight, hearing, touch, taste, pressure detection, and detection of electric fields.
• Sharks' vision is ten times better than human vision in low light. Their eyes are especially suited to see in murky ocean water and are able to see objects that are 20 to 30 meters distant.
• Tapetum lucidum is a proactive layer behind the retina that reflects light and enables sharks to improve their vision in dim light. This makes sharks effective hunters in the dark.
• While sharks are known for their exceptional sense of smell, their sense of hearing is the most important, as it allows them to locate prey from a distance, given that sound travels farther and faster through water than through air.
• Sharks are also sensitive to low-frequency sound waves. They can "promptly detect the sound of injured prey and follow the sound until they spot the prey because underwater, sound travels faster than the outer atmosphere, sharks can detect sounds in a wide range as compared to humans."
• According to Sharks Info, sharks are capable of hearing sound waves up to 250 meters away.

Research Strategy

Key Takeaways

• Carcharodon carcharias, or the great white shark, is the most aggressive shark species towards humans, with a total of 354 confirmed attacks.
• Galeocerdo cuvier, or tiger shark, has the second highest number of confirmed attacks on humans at 138 in total.
• Carcharhinus leucas, or bull shark, has been implicated in a total of 121 attacks on humans, which is the third highest amount among shark species. It has 50 rows of teeth (compared to the average of 15 for most sharks), which adds to 350 teeth.
• Blacktip sharks possess an impressive sense of smell, as they are capable of detecting a single portion of a fish's flesh in up to 10 billion parts of seawater.

Introduction

Most Aggressive Shark Species

1. Carcharodon Carcharias (Great White Shark)

• According to the Florida Museum of Natural History's International Shark Attack Files, Carcharodon carcharias, or the great white shark, is the most aggressive shark species towards humans, with a total of 354 confirmed attacks. Around 297 of these attacks were non-fatal, while the remaining 57 were fatal.

 

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• The great white shark is among the largest shark species in the world, reaching a maximum size of at least 20 feet in length and weighing up to 3,000 kgs (6,614 lbs). It has a torpedo-shaped body, with large pectoral dorsal fins and a pointed snout, as well as large serrated teeth and grey or bronze skin.
• As stated by the Australian Museum, Carcharodon carcharias have been spotted around the world in coastal and temperate waters. They typically swim along small coastal archipelagos that are usually inhabited by a variety of life forms, including sea lions, walruses, and seals. Also, they are able to move on intercontinental, regional, and localized scales.
• While the great white sharks are widely considered to be apex predators at the top of the food chain, killer whales frequently target them for their livers, which are fat and rich.
• Also, the great white sharks are endothermic, which means that their body temperature is higher compared to the water they swim

2. Galeocerdo Cuvier (Tiger Shark)

• Galeocerdo cuvier, or tiger shark, has the second highest number of confirmed attacks on humans at 138 in total. About 102 of these attacks were non-fatal and the other 36 attacks were fatal.

 

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• Tiger sharks can grow up to 18 feet in length, while weighing between 385 and 635 kgs (849 to 1,400 lbs). Members of this species can be identified by their skin color, which is grey with dark reticulations that modify to vertical bars or spots as they grow. They also have sickle-shaped teeth along both their lower jaws and upper jaws.
• This species is not considered to be an oceanic species and are found in subtropical and tropical waters around the world. They reside in pelagic and coastal waters and appear to prefer turbid and murky waters located adjacent to or on insular and continental shelves. Furthermore, the Galeocerdo cuvier can be found within lagoons, river estuaries, and coral atolls.
• An interesting fact about tiger sharks is that they are willing to consume just about anything and are considered to be the least discriminative of shark species when it comes to food consumption. Their typical diet consists of sea turtles, other sharks, sea birds, rays, carrion, various crustaceans, squid, dolphins, etc., but they have also been found to consume refuse and garbage dumped by humans.
• Also, female tiger sharks give birth to up to 80 pups at once, though the typical amount of pups is 30.

3. Carcharhinus Leucas (Bull Shark)

• The bull shark has been implicated in a total of 121 attacks on humans, which is the third highest amount among shark species. While 95 of these attacks were non-fatal, around 26 of them resulted in the loss of human life.

 

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• It can reach lengths of up to 340 centimeters (more than 11 feet), although the maximum recorded length was around 13 feet. They can grow to up to 698 lbs in weight and have short blunt snouts, no fin markings, triangular serrated teeth in their upper jaws, and a stout body. The creatures are grey in color and their second dorsal fin is significantly smaller than the first dorsal fin (one-third the height).
• This species prefers freshwater and coastal waters and are usually found in shallow waters in lakes, bays, rivers, and estuaries. Bull sharks have been spotted in the western Atlantic, eastern Atlantic, eastern Pacific, and Indo-West Pacific.
• One interesting fact about the bull shark is that the species was blamed for several shark attacks that occurred in the year 1916. This incident was the inspiration behind the novel Jaws by Peter Benchley, which was depicted on screen in the 1975 Steven Spielberg film of the same name.
• Furthermore, it has 50 rows of teeth (compared to the average of 15 for most sharks), which adds to 350 teeth.

4. Carcharhinus Limbatus (Blacktip Shark)

• As listed by the Florida Museum of Natural History's International Shark Attack Files, blacktip sharks are responsible for a total of 41 confirmed attacks on humans. All of these attacks have been non-fatal.

 

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• Blacktip sharks have a rather moderate size, with a maximum length of at least 6 feet and a maximum weight of about 40 lbs. Normally, they have a bronze or dark brown skin color on the upper part of their body, with black tips on their lower caudal lobe, pelvic fins, pectoral fins, first and second dorsal fins, and long, pointed snouts.
• Such sharks can be found near subtropical and tropical islands, and coastal waters around the Atlantic, Pacific, and Indian oceans. They like both offshore and inshore waters and have been observed near mangroves, river mouths, and bays.
• Blacktip sharks possess an impressive sense of smell, as they are capable of detecting a single portion of a fish's flesh in up to 10 billion parts of seawater.

5. Carcharias Taurus (Sand Tiger Shark)

• Carcharias taurus, or sand tiger sharks, were responsible for a total of approximately 36 confirmed attacks on humans, although none of these attacks have been fatal.

 

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• This species has an average size of between 4 to 9 feet in length, although the maximum length is reported as 10.5 feet. They have a maximum weight of around 350 lbs, and their skin color varies from light greenish to light brown (many of them have brown or dark red spots over their body). Additionally, members of the species have 41-46 teeth in their lower jaws and 44-48 in their upper jaws.
• Usually, sand tiger sharks prefer warm waters in the western Atlantic, eastern Atlantic, and parts of the Pacific. Sharks of this species can be located inshore at depths of 6-626 feet. They have been spotted in deep regions of the outer continental shelves, rocky reefs, surf zones, coral reefs, and shallow bays.
• Sand tiger sharks' embryos engage in adelphophagy or intrauterine cannibalism. This means that the furthest developed embryo inside the uterus consumes the less developed embryos.

Additional Findings

• In terms of attacks on humans that have resulted in a loss of life, the most deadly shark species include the great white shark (57 deaths), tiger shark (36 deaths), bull shark (26 deaths), blue sharks (4 deaths), and oceanic whitetip sharks (3 deaths).
• Members of the shark family Carcharhinidae are sometimes mentioned under the umbrella term "requiem spp." or "requiem sharks." The Carcharhinidae family includes 50 species, such as sandbar, spinner, blue, lemon, and blacktip sharks, among many others. According to the Florida Museum of Natural History's International Shark Attack Files, bites from these sharks are difficult to break down into species, as they share similar tooth shapes, appearances, and body sizes. However, they have been blamed for at least 69 attacks on humans (1 fatality).

Research Strategy:

Key Takeaways

• Orca is the apex predator of the ocean since it does not have a natural predator. With a maximum speed of 34 mph, or 56 km/h, they are "one of the fastest marine mammals."
• Great white sharks have 300 serrated teeth and strong jaws. Importantly, they can move at speeds of up to 21 miles per hour to reach their prey.
• Leopard seals prey on birds, fish, other seals, and cephalopods. They can be attacked by polar bears, great white sharks, and orcas.

Introduction

Predators in the Ocean

Orcas

• Orca (killer whale) is the apex predator of the ocean since it does not have a natural predator. It preys on other fish and seals as well as smaller and larger whales. Orcas also prey on sharks including the great white sharks. While there are no official subtypes of orcas, scientists distinguish ecotypes based on where the orcas live and what they eat.
• The name "killer whales" was given by ancient sailors after they witnessed orcas hunting and killing large whales.
• They sometimes beach themselves to prey seals. Usually "they jump out of the water, land on the ice or shore, latch onto their prey, and drag it back into the water."
• Additionally, they use echolocation to locate their prey, i.e., they create sound waves that spread through water and echo off prey (or other objects).
• Orcas are massive predators and can grow up to 26 feet long. They can weigh up to 8,800 lbs. Their bodies make them more effective hunters with the cylindrical shape and tapers that are hydrodynamic. With a maximum speed of 34 mph, or 56 km/h, they are "one of the fastest marine mammals." Their black-and-white coloring is also helpful as it obscures them in the water.

 

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Great White Shark

• Female great white sharks can weigh up to 2,400 lbs and are larger than male great white sharks. Great white sharks can grow up to 21 feet.
• The predators not only have 300 serrated teeth but also have strong jaws. They have "a bite force of 4,000 psi, that is 10 times the bite force of a lion. Once they identify their prey, great white sharks can move at speeds of up to 21 miles per hour to it.
• Great white sharks are adept hunters that prey on sea lions, fish, and smaller sharks.
• They tend to hunt alone early in the morning to benefit from low visibility. Furthermore, they camouflage themselves with countershading and use "spy-hopping" (peaking above the water surface to look for prey), biting the victim and leaving it to come back later when it is weaker, and grabbing and shaking the prey before killing it.
• Several strategies they use for catching and dealing with prey include "breaching" (jumping up to ten feet up to catch/kill the prey),
• Orcas, however, work together to take down great white sharks whenever they come across them. Usually, they circle the great white shark and flip it, immobilizing it and preventing it from moving or defending itself. The phenomenon called "tonic immobility" makes it impossible for a shark to move when it is on its back.

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• California, South Africa, and Australia are three locations where killer whales prevailed over great white sharks. Furthermore, a study at feeding sites on Southeast Farallon Island (SEFI) in San Francisco found that the appearance of orcas made great whites move, regardless of how disruptive it was to their feeding habits. They did not come back to the feeding spot for months afterward.

Leopard Seals

• The leopard seal is the second largest seal species in the Antarctic. On average, it grows to nine feet and weighs 1,320 lb.
• It is one of the most feared carnivores in its environment, which is buoyed by its physical attributes. It has a long and muscular body with massive jaws.
• Their jaws are arranged in a particular way, i.e., "they have large canines designed to latch onto prey, but their back molars lock together in such a fashion that they can strain krill from water, somewhat in the same manner that baleen whales sieve krill."
• Leopard seals prey on birds, fish, other seals, and cephalopods.
• According to Oceanwide Expeditions, leopard seals have very few natural predators. The only known predator is a killer whale. Leopard seals can survive in their dangerous environment for a long time, with the assertion that if they can evade the killer whale, they can survive for over 26 years.

 

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• It is worth noting that leopard seals do not only hunt to eat but also for fun. They have been known to endlessly chase young penguins and other species of seals just for entertainment.

Polar Bears

•  Found around the Arctic Circle, the polar bear is a predator in the marine environment despite being a land animal.
• It is the largest bear species. On average, polar bears weigh over 1, 000 lb and grow to up to 9.8 feet.
• Polar bears primarily prey on seals. They use a method called "still hunting," which involves long stalking, calmly waiting until the seal surfaces, and when it does, biting the head or upper body before flipping it to the ground.
• However, they can be attacked and preyed on by walrus es, who can kill polar bears in the water. Still, they will experience difficulty when fighting polar bears on land because the latter are more aggressive, powerful, and smart and only attack small and weak walruses on land.

Research Strategy