Cookie Cutter Shark

The Cookie-cutter Shark is named after the cookie-shaped wounds that it leaves on the bodies of larger animals. It has a cigar-shaped body, a short conical snout and 2 low, spineless dorsal fins. It is dark brown dorsally, lighter below, and has a distinct dark collar, is covered in a dense network of tiny photophores, which in life produce an even greenish glow. 

This species has small, erect teeth in the upper jaw and large triangular teeth in the lower jaw. It has a row of 19 huge teeth (proportionally the largest of any shark species) in the lower jaw. The cookie cutter attaches itself to its prey with its suctorial lips, and then spins to cut out a cookie-shaped plug of flesh from the larger animal.

In addition to plugs of flesh from larger animals, this shark is also know to eat squid. There are even reports of this species leaving crater-marks on the sonar domes of submarines.

Its anteriorly placed eyes may enable binocular vision. This shark grows to 50 cm in length. It feeds by biting pieces of muscle from the bodies of larger marine creatures. This species is recorded from specimens caught in the Gulf of Mexico, off Okinawa, Japan, from the eastern Atlantic and from Australia. They vertically migrate, being found in deep water, probably below 1000 meter during the day, and migrating into surface waters at night.

Horn Shark

The horn shark (also known as the Californian horn shark) gets its name because it has a short, blunt head with high ridges above the eyes. They range in size from approximately 97 cm to 120 cm (around 3 feet long from the tip of the tail to the nose). They are a brownish color covered in black spots and their underbellies have a yellowish tint.

Horn sharks live in rocky reefs and kelp forests although while juvenile, many often stay in open sandy waters. They can be found from central California to the Sea of Cortex and possibly South America in depths that range from 2 to 150 meters.

Adults tend to return to the same resting spot every day. Horn sharks hide in crevices or caves during the day and venture out at night. They nocturnally hunt for urchins, crabs, worms, anemones, and bony fish. 

These sharks are oviparous. That means that they lay egg cases. The horn shark has a distinctive auger shaped egg case with 2 threadlike filaments extending from one end. The egg will typically hatch in 7 to 9 months. They are kelp colored however sometimes they detach from the branch they were wrapped around and many float up and wash onto beach shores.

Horn sharks are not graceful swimmers and sometimes use their strong pectoral fins to crawl along rocks. The teeth lining the front of the horn shark's jaws are sharp and used for grasping prey; while the teeth in the back are flat (molar-like) which is useful for crushing shellfish. The common name 'horn" refers to the spines in front of each dorsal fin (they have 2) that are their main defense against bigger fish (and sharks) that try to swallow them.

Nurse Shark

The Nurse Shark is a beautiful member of the shark family. It has a stout body, obvious barbels, and strong jaws. Behind each eye, it has a spiracle (a special organ that takes in water for breathing when the shark is at rest on the ocean bottom). Nurse sharks are nocturnal hunters and spend most of the day in large, inactive groups of up to 40 individuals. They are often found in the reefs and the ocean bottom during the day in tropical and subtropical waters. By night, the sharks are largely solitary and spend most of the night hunting crustaceans, molluscs, tunicates, and other fish (particularly stingrays).

Nurse sharks can grow up to 13 feet (4.3 meters). Nurse sharks are ovoviviparous (meaning the eggs develop and hatch within the body of the female where the hatchlings develop further until live birth occurs). The gestation period is six months, with a typical littler of 21 to 28 pups. The young nurse sharks are born fully developed at about 30 cm long. They possess a spotted coloration which fades with age.

The nurse shark is not widely commercially fished, but because of its sluggish behavior, it is an easy target for local fisheries. Its skin is exceptionally tough and is prized for its leather. Its flesh is consumed fresh and salted, and its liver is utilized for oil. It has been reported in some unprovoked attacks on humans, but it is not generally perceived as a threat.

Bull Shark

The bull shark is arguably one of the most dangerous species of sharks, but also one of the most facinating. Known by many different common names, this animal has been linked to attacks around the world including some that have occurred deep inland in freshwater rivers and lakes.

They are common worldwide in warm and shallow waters along coasts and in rivers. The bull shark is well known for its unpredicatable and aggressive behavior. Unlike most other marine sharks, bull sharks tolerate not only salt water, but fresh water. They have been spoted hundreds of miles up the Amazon River, Ganges River, and Mississippi River!

The diet of bull sharks include fish, other sharks, rays, dolphins, turtles, birds, molluscs, echinoderms, crustaceans, and even terrestrial mammals. Bull sharks have been known to use the "bump and bite" techniques when attacking their prey. Bull sharks are solitary hunters as they cruise through shallow waters. They can suddenly burst into speed and are extremely territorial.

Bull sharks usually breed in the murky water of river mouths during the summers. Their gestation period is about a year long and one female may give birth to up to 13 live young that are about 28 inches long!

Humans pose the biggest threat to bull sharks followed by larger sharks (great white, tiger, etc) and saltwater crocodiles (may eat them if they enter their freshwater territories). All in all, this is a pretty fascinating animal, especially with its ability to survive in salt and fresh water.