SharkoFiles: Bonnethead Shark

The Bonnethead sharks are the second smallest shark in the hammerhead family. They bore close resemblance to their much bigger relatives, the hammerhead sharks, but are distinguished by their considerably narrow head which is much more rounded in the front. These morphological features earn these sharks the nickname shovelhead sharks. Based on their morphological features, the Bonnethead sharks must remain in constant motion for their survival because if not, they would sink and drown.

The Bonnethead sharks are the only known shark species to be omnivorous, as they can consume both animal and plant materials. The Bonnethead is neither aggressive nor dangerous to humans, also they are not known to bite, which may be due to their shy nature. The bonnethead sharks are social animals and rarely found roaming alone as individuals, as they are typically observed in groups of 3-15. Despite being considered a good delicacies and consumed by humans, yet due to their large population size, the bonnethead sharks are listed as stable species by the IUCN red list. These species of sharks are among the species that have not been extensively studied, thus more information about the biology of the bonnetheads are still missing.

The lifespan of the bonnethead shark is approximately 12 years.

Taxonomy

The shark species belongs to the order Carcharhiniformes of the family Sphyrnidae. The scientific name of the bonnethead shark is Sphyrna tiburo

Morphology

Even though this species belongs to the hammerhead family and often mistaken for the hammerhead shark, the bonnethead are characteristically distinguishable by their morphological appearance. The head is observed to appear more rounded than any other members of the Sphyrnidae family. Furthermore, there are no indentations on the anterior edge of the shark’s head. The posterior edge of the first dorsal occurs before the anterior edge of the pelvic origins. The upper lobe of the caudal fin is noticeably larger than the lower lobe. The shark is not as large as some other members of the sphyrnidae family as they attain full size of just 4.9 feet. The female bonnetheads are usually larger than the males.

The sharks have an evenly grayish-brown coloration on the dorsal side, and a lighter color on the ventral side. In contrast to the hammerhead shark species, the bonnethead sharks have a larger and more developed pectoral fins proportionate to their body size, which is effective for escaping from predators. Being an omnivorous, the bonnethead sharks teeth are not serrated, revealing gradual differences in shape along their jaw length. There exist some physical differences between male and female bonnethead sharks, for instance, while the female has a rounded, broad head, the male has a unique bulge on its head top, which is a prominent feature of the hammerhead species.

Adaptation

The bonnetheads are known to secrete a special chemical or body fluid known as cerebrospinal fluid, which is a warning signal to potential predators and enemies. Also, this chemical secretion is used for communicating with other bonnetheads in a particular environment to inform them of their presence in the area. Unlike most species of sharks, the bonnethead sharks have well developed sensory and nervous system, coupled with excellent visual prowess that enable them to prey effectively under the radar of bigger predators.

Feeding

The bonnethead shark is the only shark species known to be omnivorous, thus their diet consists of animal and plant materials, such as seagrass, which is an essential part of their diet, small fish, crabs, squid, snails, shrimp, as well as other invertebrates.

Habitat

The bonnethead sharks can be found across the American coast, ranging from New England to the Gulf of Mexico and Brazil, as well as from southern California to Ecuador. These species of sharks are typically found in shallow waters in all the territories they live. They have a preference for environment with warmer waters above 70^oF of the estuaries, shallow bays over seagrass mud, sandy bottoms, and also the coral reef along the coastline. Since they share habitat with larger shark species, such as the lemon and tiger sharks, these two serve as potential predators of the bonnethead sharks.

Reproduction

Unfortunately, the reproductive activities of the bonnethead shark are one of the things yet to be extensively studied about these sharks. Nevertheless, it is known that the shark species reproduce sexually and they engage in a viviparous mode of reproduction similar to most shark species. The gestation period of bonnethead shark is one of the shortest of all shark species, lasting approximately between 4.5 to 5 months. The pups reach maturity when they attain a body size of 30 inches in length. A single litter produces about 8 to 12 pups at a time. The pups are born around late summer to early fall. At birth, baby bonnethead sharks measure around 12 to 13 inches in length. Moreover, the pup survival basically depends on size selective predation by other larger marine predators. The male bonnethead attain sexual maturity at 20 to 30 inches body size, while the female reaches maturity at 33 inches or less.

More Bonnethead Shark photos