White sharks
The white shark, scientifically known as Carcharodon carcharias and commonly referred to as the great white shark, is one of the most recognized shark species, often associated with human interactions that can sometimes be fatal. Despite their notoriety, much about their biology remains poorly understood due to limited opportunities for study, as these sharks are seldom seen by humans and do not thrive in captivity. White sharks have a distinctive cartilage-based skeleton, featuring five pairs of gill slits and a streamlined, powerful body adapted for fast swimming. They possess unique anatomical features, such as a jaw structure that allows for an efficient biting mechanism and specialized circulatory adaptations that enable them to maintain a higher body temperature than the surrounding water.
Reproductively, white sharks are believed to be ovoviviparous, with young developing in the mother's uterus, although details about gestation and birth sizes remain largely unknown. Their diet varies with age; juvenile white sharks primarily consume fish, while adults favor marine mammals like seals and sea lions, using stealthy hunting tactics from below. While white sharks have been linked to a small number of unprovoked attacks on humans, these instances are not reflective of their typical feeding behavior, as humans are not part of their natural diet. Conservation efforts are increasingly important, as white sharks face significant threats from human activities, leading to protective legislation in various regions.
White sharks
White Shark Facts
Classification:
Kingdom: Animalia
Subkingdom: Bilateria
Phylum: Chordata
Subphylum: Vertebrata
Superclass: Gnathostomata
Class: Chondrichthyes
Subclass: Elasmobranchii (sharks, skates, and rays)
Order: Lamniformes
Family: Lamnidae (mackerel sharks, also porbeagle salmon and mako sharks)
Genus and species:Carcharodon carcharias
Geographical location: Worldwide, generally in temperate and subtropical seas, occasionally in tropical seas
Habitat: Continental shelf and occasionally inshore
Gestational period: Unknown
Life span: Unknown
Special anatomy: Large (up to six meters long) and moderately stout-bodied, with a blunt, conical snout and an almost symmetrical caudal fin; pronounced lateral ridge or keel where the tail is attached to the body; large teeth, broadly triangular and serrated; gray-blue or gray-brown (often bronze) on the upper body surfaces, with a white belly; a black spot often present at the axil (armpit) on the bottom surface of the pectoral fin
The white shark (Carcharodon carcharias), also known as the great white shark, white pointer, or white death, is one of the best-known sharks principally due to the interest surrounding the occasionally fatal interactions between humans and this species. Nevertheless, surprisingly little is known about their biology. White sharks are large, active fish that are only infrequently encountered by humans and which have not survived long in the few attempts that have been made to keep them in captivity. Attempts to study the biology of white sharks are therefore limited to brief observations of their biology and what can be inferred from the anatomy of captured dead sharks.
White Shark Anatomy and Physiology
Like all sharks, the white shark possesses a skeleton composed of cartilage, a tough elastic connective tissue found in all vertebrates. The cartilage in the skeleton of white sharks is strengthened by deposits of calcium carbonate, but there is no true bone as in most other fishes. Like most sharks, the white shark has five pairs of gill slits located just in front of the broad pectoral fin and a heterocercal tail, in which the spinal column extends into the upper lobe. The tail, or caudal fin, of the white shark, as in all members of the family Lamnidae, is almost symmetrical and possesses a pronounced lateral keel at the point where the tail is attached to the body trunk. Such a lateral keel may improve the efficiency of the tail in swimming and turning and is a common element of many large, fast-swimming fishes. The upper jaw of white sharks is suspended from the skull by ligaments rather than fused directly to the skull, as in most terrestrial vertebrates. This amphistylic suspension of the jaws allows them to be pushed forward and out, increasing the efficiency of the biting mechanism in a mouth that is located below and behind the broadly conical snout. White sharks, like all sharks, lack a gas-filled swim bladder to provide buoyancy in the water and rely on the lifting action of their fins and body shape to prevent them from sinking. The streamlined, spindle-shaped body, broad fins, and powerful, symmetrical tail of the white shark suit it well to a fast and powerful swimming style, and white sharks, like others in the family Lamnidae, are among the most active sharks.
White sharks possess special modifications of the circulatory system in the body wall and central nervous system that are known as rete mirabile. These modifications permit the shark to return the heat generated by metabolism to the body core rather than losing it to the surrounding water, as in most fish. The rete mirabile allows white sharks to maintain a core body temperature that is higher than the surrounding water; this may provide an advantage to the shark by raising its metabolic rate and permitting greater activity in the cooler waters which they typically inhabit.
White Shark Reproduction and Feeding Habits
Little is known about the reproductive biology of white sharks. Like all sharks and rays, fertilization is internal, and the males possess special modifications of the pelvic fins called claspers, which are inserted into the female oviduct. White sharks are believed to be ovoviviparous, with juvenile sharks developing in eggs within the uterus of the mother until they are ready to be born live. During early embryonic development, the developing white sharks are nourished by the yolk sac of the egg. When this is consumed, the developing shark consumes unfertilized eggs produced by the mother, a reproductive strategy known as intrauterine oöphagy. There have been relatively few captures of pregnant females or free-swimming juveniles, and the duration of gestation and the size of the juveniles at birth are unknown. The best estimate of white shark size at birth is between 1.2 and 1.4 meters.
White sharks are known to reach a length of six meters (twenty-one feet) and may possibly grow larger. Their life span is unknown. As the white shark grows, the nature of its diet changes; juvenile white sharks appear to feed principally upon fish, whereas marine mammals play an important role in the diet of mature sharks. The high energy yield of the blubber in seals and sea lions may make them attractive prey for these very large predators. White sharks hunt seals and sea lions by swimming deep below them and searching for their silhouettes against the bright surface. Once prey is spotted, the shark attacks with a very swift lunge from below and inflicts an incapacitating or mortal wound with its bite.
White sharks have been responsible for fatal attacks on humans, but humans are not a normal part of their diet. It is more likely that the shark mistakes a human for a marine mammal or may merely be curious. It is also more likely that shark attacks gain attention due to their sensationalized coverage in the media. Still, in 2022, there were eighty-one unprovoked shark attacks globally. White sharks themselves are in considerably more danger from humans, and several nations and states have passed laws protecting these sharks from the effects of human depredations.
Principal Terms
Amphistyly: the mechanism by which the jaws of sharks are suspended from, but not directly fused to, the skull
Cartilage: a tough and flexible tissue that constitutes the skeleton of all sharks and rays
Caudal Fin: the tail fin of fishes, which supplies the forward thrust in locomotion
Clasper: a modification of the pelvic fins in male sharks and rays that acts as the male sexual organ in the internal fertilization of the female
Elasmobranch: the classificatory subbranch of sharks and rays
Heterocercal: a type of caudal fin in which the spinal column extends into the upper lobe, producing an asymmetrical and distinctly shark-like tail
Oviphagy: a mode of reproduction in which embryo sharks develop in the maternal uterus and feed on unfertilized eggs produced by the mother
Bibliography
Ellis, R., J. E. McCosker, and A. Giddings. Great White Shark. California: Stanford UP, 1997. Print.
Domeier, Michael L. Global Perspectives on the Biology and Life History of the White Shark. Boca Raton: CRC P, 2012. Print.
Helfman, Gene S., and George H. Burgess. Sharks: The Animal Answer Guide. Baltimore: Johns Hopkins UP, 2014. eBook Academic Collection (EBSCOhost). Web. 6 Jan. 2016.
Klimley, A. P. The Biology of Sharks and Rays. Chicago; London: U of Chicago P, 2013. Print.
Klimley, A. P., and D. G. Ainley, eds. Great White Sharks: The Biology of “Carcharodon carcharias.” San Diego: Academic, 2008. Print.
Kluger, Jeffrey, and Elijah Wolfson. “Are Shark Attacks Increasing? Here Are What the Data Say.” TIME, 7 July 2023, time.com/6292696/shark-attack-data-2023. Accessed 11 July 2023.