Sharks have inhabited the ocean for over 400 million years. Understanding the specialized terms associated with these animals allows for a deeper appreciation of their unique biology and behaviors. This vocabulary reveals how these creatures navigate, hunt, and reproduce in diverse marine environments.
Understanding Shark Anatomy and Senses
Shark skin is covered by tiny, V-shaped scales called dermal denticles, which are more akin to teeth than typical fish scales. These denticles provide a protective armor and enhance hydrodynamics, reducing drag and enabling sharks to swim efficiently and quietly. Their structure also makes it difficult for parasites and algae to attach.
Sharks possess specialized sensory pores, primarily concentrated on their heads, known as ampullae of Lorenzini. These electroreceptors detect the faint electrical fields produced by the muscle contractions of prey, even those hidden in sand. This unique sense also helps sharks detect Earth’s electromagnetic field, which may aid in navigation during migration.
The lateral line system, a series of fluid-filled canals running along the shark’s body and head, detects water movement and pressure changes. This system alerts sharks to nearby prey and predators by sensing vibrations caused by swimming motions, providing spatial awareness and aiding in obstacle avoidance. The caudal fin, or tail fin, is the primary source of propulsion for sharks, generating thrust. Its shape varies among species, with lunate (crescent-shaped) tails providing maximum thrust for fast swimmers like makos, while more asymmetrical tails are common in bottom-dwelling sharks.
The dorsal fin helps maintain stability and balance, preventing the shark from rolling. Some sharks have one dorsal fin, while others have two, and their size and position can offer clues about a shark’s swimming speed and habitat. Pectoral fins, located behind the gills, assist with steering and provide lift, counteracting the downward force generated by the caudal fin.
Shark Behavior and Their Role in Ecosystems
Some shark species employ ram ventilation, a breathing method requiring continuous swimming with open mouths to force water over gills for oxygen. While many sharks use this method, some species can switch to buccal pumping, actively drawing water over their gills while stationary.
Tonic immobility describes a temporary, trance-like state of paralysis induced by gently turning sharks upside down or stimulating snout sensory pores. This state causes muscles to relax and breathing to become deep and rhythmic, and it is sometimes used by researchers for handling sharks. While its exact purpose is still debated, theories suggest it may be a defense mechanism, a component of courtship, or a way to limit overwhelming sensory input.
Breaching is the behavior of a shark leaping entirely out of the water, often seen in species like great white sharks. While the exact reasons are not fully understood, it is believed sharks breach to ambush fast-moving prey like seals, to remove external parasites, or for communication. This energetically demanding act requires significant speed to propel the shark into the air, sometimes as high as 10 feet.
A feeding frenzy occurs when multiple sharks aggressively compete for the same prey, losing inhibition and biting at anything. This intense behavior is often triggered by “supernormal stimuli” such as distressed prey, the scent of injured fish, or the vibrations caused by other feeding sharks. While it can seem chaotic, some species maintain a form of hierarchy even during a frenzy.
Many large shark species are considered apex predators, at the highest trophic levels in their marine ecosystems. These sharks, such as great whites and tiger sharks, regulate populations of other species, which helps maintain the health and diversity of ocean life. However, not all sharks are apex predators; smaller species or juveniles may be prey for larger marine animals.
How Sharks Reproduce
Sharks exhibit diverse reproductive strategies, with three primary methods. Oviparous sharks lay eggs, fertilized internally and deposited into the ocean. These eggs, often encased in a leathery “mermaid’s purse,” contain a yolk sac nourishing the embryo. Some egg cases have tendrils that help them attach to structures on the seafloor, preventing them from being washed away.
Viviparous sharks give birth to live young, similar to mammals, with embryos developing inside the mother via a placental connection. The placenta transfers nourishment from the mother to the developing pups via an umbilical cord. Examples of viviparous sharks include bull sharks, hammerhead sharks, and blue sharks.
Ovoviviparous sharks also give birth to live young, but their eggs hatch inside the mother without a direct placental link. Instead, the pups are nourished by a yolk sac, and in some species, the first pup to hatch may consume unfertilized eggs or even other siblings within the womb. This intrauterine cannibalism ensures only the strongest pups survive, resulting in smaller litter sizes (typically 1-8 pups).
Male sharks possess specialized reproductive organs called claspers, elongated, cartilaginous structures on the inner edge of their pelvic fins. These paired organs are used for internal fertilization, with the male inserting one clasper into the female’s cloaca to transfer sperm. Claspers are a distinguishing feature of male sharks and are present from birth.