Bonnethead Shark

The Bonnethead Shark is one of the hammerhead shark species. Other common names are bonnet shark, bonnetnose shark, and shovelhead shark. Its distinct shovel-shaped head easily recognizes it and is commonly found at different location in the warm waters of the American coasts.

It is the only shark species known for its omnivorous diet, which includes both marine animals and seagrass, making it the only known shark to consume plant matter. Despite their somewhat intimidating appearance, bonnethead sharks are generally harmless to humans and play a crucial role in maintaining the balance of their ecosystems.

Keep reading to explore the fascinating world of the Bonnethead Shark.

Appearance 

The bonnet shark can be recognized by its broad, bonnet-shaped head. The body is grey-brown on top and lighter on the underside, a characteristic common to large marine creatures known as countershading. Sometimes, darker spots are present on the sides of their bodies.

Their bodies are slender and streamlined, designed for swift and agile movement through water. Their maximum length reaches 3 ft. Although larger specimens, up to 4.9 feet, have also been recorded.

Their eyes are at the far sides of their head, providing a nearly 360-degree field of vision.

They possess sharp, small teeth with the upper ones being narrow and cusped, while the lower teeth are broader and flatter.

Their dorsal fin is large and triangular, aiding stability while swimming. Two smaller pectoral fins on either side of their body help them maneuver through water. Their bodies taper towards the tail, ending in a crescent-shaped anal fin that propels them forward.

Bonnethead Sharks also have specialized electroreceptor organs known as ampullae of Lorenzini, located on their snout, which they use to detect electric fields produced by potential prey. Combined with their wide-set eyes, this feature gives them an impressive hunting advantage.

 

Habitat

The geographic distribution of bonnethead sharks is observed on the sides of the American coast, in the Atlantic and Pacific oceans. In the eastern Pacific, they are found from southern California to waters off of Ecuador. During the summer bonnetheads are commonly seen in inshore waters off the Carolinas and Georgia while during the spring, summer, and autumn they are found in the western Atlantic waters from Rhode Island (occasionally) south to the Gulf of Mexico and Brazil, and throughout the Caribbean including Cuba and the Bahamas. The shark spends most of its life in shallow bays and estuaries.

They prefer warmer waters of the world’s oceans, around 70 degrees F or 20 degrees C.

These sharks travel in small groups of between five to fifteen members. The sharks tend to do migrations with changes in ocean temperature, and, like all shark species, the bonnethead has to keep moving, or it will sink. It is one of the most negatively buoyant of all marine species.

They are also found on the continental shelf to depths of about 80 m (260 ft) but more commonly at 10-25 m (31-82 ft).

Diet 

Amazingly, the bonnethead shark is the only species of omnivorous shark. It feeds on blue crabs and other crustaceans, as well as small fishes, bivalves, and shrimp. 

They use the electroreception organs on their hammer head to find animals hiding under the sediment.

While hunting, it moves its head along the seafloor in an arch-like pattern, seeking out the smallest disturbances. When the sharks catch a crab, they use their teeth to grind it, and then suction allows the shark to swallow. The sharks have small, sharp teeth in the front of their mouths and flatter molars in the back. It’s the latter that they use for crushing their prey, such as the shells of crabs.

They also eat plants and ingest a large amount of seagrass, more than half of their total diet. It’s unclear exactly why the sharks eat seagrass, but scientists have speculated that the grass protects the shark’s stomach against the sharp edges of the blue crab shells. 

Reproduction

These sharks reproduce viviparously. This means that the embryo becomes fully developed inside the mother’s body. This contrasts with some other shark species that use oviparity (the female lays developing eggs that hatch externally). 

Females are around 32 inches or 81 cm when they reach sexual maturity. In contrast, males are around twenty-four inches or sixty-one centimeters.

After mating, a female will store the sperm for months at a time until the environmental conditions for its young’s survival are just about right. They have a gestation period that is one of the shortest among shark species, lasting between 4.5 to 5 months. Broods contain 6-14 pups. When the embryos emerge from the egg, they absorb the yolk for nourishment.

In one amazing recorded instance, a female bonnethead shark reproduced via parthenogenesis at a zoo in Nebraska, which means that the specimen used asexual reproduction without fertilization by a male member of the species. 

Threats 

At the moment, the conservation status of the bonnethead shark is “endangered” by IUCN. It has been heavily targeted by commercial fisheries throughout its life.

In the Atlantic Ocean, along the coast of the Bahamas and Mexico, it is still a very common shark species. But, there have been significant declines in the Pacific along the coast of South America.

6 More Facts About Bonnethead Sharks 

1. Bonnethead Sharks are the smallest species in the hammerhead family.

2. They are the only known species of shark that is omnivorous, consuming both meat and plant matter.
3. Their distinctive head shape enhances their sensory capabilities, allowing them to effectively locate prey hidden in the sandy ocean floor.
4. Bonnethead sharks are capable of asexual reproduction.
5. These sharks are generally harmless to humans due to their small size and non-aggressive nature.
6. A cerebrospinal fluid is used in chemical communication among individuals, informing others when an individual is near.

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