Bonnethead Shark

Threat Level: low

The Bonnethead Shark is also known as bonnet hammerhead,
bonnet shark, bonnethead shark, bonnetnose shark, and shovelhead.

BONNETHEAD SHARK

Scientific Name.... Sphyrna Tiburo
Family Name...... Sphyrnidae

General Information: The bonnethead shark is a small hammerhead, and can be distinguished by its smooth, rounded, shovel-shaped head.
Bonnetheads are the smallest species of the Sphyrnidae. The eyes are located at the ends of the evenly rounded lobes of the flattened head, rather than a hammer shaped. Also the head lacks a notch at the midline. The pectoral fins are short and straight along the rear margin.

Size: The bonnetheads reach an average size of 3-5 feet. The maximum recorded weight of a bonnethead is about 24 pounds.

Teeth: This shark has a remarkable dentition, with small sharp teeth in the front of the jaw for grasping either its mate or a soft-bodied prey, and broad molar-like teeth at the back of the jaw for crushing hard-shelled invertebrates. Like all sharks they have additional rows of teeth that are used as the older teeth become lost or worn.

Color: Its body is plain gray to gray-brown and occasionally to a green tint above and shading to a light color underneath.

Feeding Habits: Bonnethead sharks feed daylight hours and feeds primarily on invertebrates, crabs, shrimp, mantis shrimp, snails cephalopods, as well as small bony fishes. Upon locating a prey the bonnethead swims slowly within range, followed by a quick acceleration to attack the prey. The prey is then crushed in the molariform teeth. This differs from the capture event typically of other sharks, where the jaws are initially closed and biting ceases at jaw closure. This allows the bonnethead to take advantage of prey that is not available to other species of sharks. After the prey is crushed, it is moved by suction to the oesophagus.

Senses: The bonnethead has a well-developed sensory and nervous systems that allow them to be efficient predators. Vision and hearing capabilities are exceptional as well as the sensitivity of the lateral line to small vibrations, alerting them to nearby potential prey.

Social Behaviour: The behaviour of the bonnetheads has been well studied. Some sharks exhibit specific types of behaviour toward other sharks, including patrolling, head-shaking, jaw-snapping, hitting, and hunching. It is believed that the function of this behaviour is to establish and maintain dominance and other agonistic relationships. Another example an individual bonnethead may swim over top of another and "hit" the shark below it with the edge of its head. The shark that was "hit" accelerates off and often bears a slight contusion in the area where it was struck. A study conducted on a captive colony of bonnetheads demonstrated that this species forms linear dominance hierarchies, with the size and sex of an individual determining its position in the "pecking order". As the group swarm about their enclosure, subordinate individuals would "give way" to dominate specimens ( that is, they would change their course to avoid colliding with the dominant shark ).

Habitat | Migration | Distribution: Bonnetheads are found in North Carolina to Brazil in the Western Atlantic and from southern California to Ecuador in the Eastern Pacific. This shark occurs in many different habitats within the temperate and tropical waters of its range. It is abundant surf zone, bays and estuaries, on coral and rocky reefs, and over sandy or muddy bottoms. It also inhabits waters of the continental shelf to depths of about 260 feet.

Reproduction: Bonnetheads are viviparous (giving birth to live young) with a gestation period of four to five months, which is the shortest gestation period of all other sharks. Females reach sexual maturity when about 2 1/2 feet long. They retreat to shallow bays and estuaries to give birth, in late summer or early fall. Litter sizes average of 8 to 16 pups and each approximately 14 inches in length. During this time , the females lose their desire for food, which prevents them from feeding on their pups. Males move to a different location, also an adaptation to avoid feeding upon their own young.

Swimming: This species must swim continuously so that its gills receive oxygen from the water, otherwise it will sink. Bonnetheads swim continuously travelling long distances following changes in water temperature.

Bonnethead Shark Attacks: Considered harmless to humans, this species is shy. There has only been one recorded unprovoked attack.