Shark Family

Shark Family

Cartilaginous fish are generally designed by nature to be stealthy predators, usually hunting other fish but also preying on invertebrates, reptiles, birds and mammals when the chance arises. Most species live in marine habitats only, although a few have adapted to cope with brackish water and fresh-water. The fish of the chondrichthyes class all have skeletons made from cartilage, rather than bone cartilage is a flexible material containing collagen, which is also present in bone alongside brittle calcium compounds. Members of the shark family, therefore, have tough and bendable skeletons.

Giant Sharks

The largest shark species is the whale shark (Rhincodon typus), which can grow in excess of 12m (39 ft.) and lives in the open ocean. Despite its size, the whale shark is a benign fish as it has adapted to eat plankton by filtering it from seawater. Plankton can comprise all seawater of small organisms in adult or larval form. The term zooplankton describes plankton consisting of animal species, while phytoplankton is the term used for plankton consisting of microscopic marine plants. A similar, but smaller species is the basking shark (cetorhinus maximus). While the whale shark and basking shark filter feed at, or near the ocean surface during the day, a third species, the mega-mouth shark (Megachasma pelagios), filters the water at night. It is even equipped with luminous lures around its mouth to attract larger prey, which swim towards the light. Due to their overall form, it is possible to tell that these filter feeding species have descended from predatory ancestors, but evolved to fill ecological niches that were hitherto unexploited.

Typical Sharks

Typical sharks have changed very little from ancestors that lived tens of millions of years ago. This is because their design had already been perfected by the process of natural selection, so the passage of time has seen modern species change in only minor ways, according to specific lifestyles. Typical species include the great white shark (carcharodon carcharias), the tiger shark (Galeocerdo cuvier), the blue shark (Prionace glauca), the mako sharks (genus Isurus) and the reef sharks (genus Carcharhinus). All of these species are built with speed and efficiency for chasing down and dispatching prey. They have torpedo- shaped bodies with powerful tails for propulsion and blade- like fins for precise steering maneuvers.

The ability to move apace through water is known as hydrodynamics and works in a similar way to the aerodynamics of birds of prey flying through air. The idea is to create as little resistance as possible, so that energy is not wasted and momentum is maintained. Even the shark`s skin is adapted to reduce water resistance or drag. It has a rough texture that traps a layer of water, so that the shark is effectively lubricated as it moves forwards. The mouth of the typical shark is also well designed for its job. It is set beneath the nose of the fish. For large prey, the jaws extend to ensure that a good bite is achieved. Inside the mouth there are concentric rows of razor sharp teeth. They work in the manner of a tank- cutting saw, removing bite- sized chunks from the victim as the shark rotates its mouth by twisting from side to side. Sharks are able to detect their food in two ways:-

1. They have very sensitive chemical receptors (chemoreceptors) that can taste or smell the water, alerting them to the presence of blood from injured prey. Similarly, they can detect chemicals given off by other injured sharks and will quickly flee from danger if the situation arises.

2. Many sharks can detect the tiny electromagnetic pulses produced by the muscles in prey animals. They scan the seabed in a similar way to a metal detector and strike when they home in on the electrical signals. This makes it possible to detect animals hidden in the mud or sand. The experts at this type of hunting are the hammerhead sharks. They have widened heads to increase the surface area of the skin carrying the electro-receptors or ampullae. As they cannot always see the prey they have detected, they rely instead on touch and agility to locate and eat them.

Rays and Skates

The rays and skates are fundamentally similar to sharks, except that their bodies have typically become flattened to suit life spent largely on the seafloor. They are often camouflaged to match their chosen background as they are preyed upon by sharks and other marine animals. Some are armed with poisonous spines to deter would be attackers. There are also species called ghost, or elephant sharks. The first name alludes to their iridescent and faintly luminous skin. The second alludes to their nose, which bears some resemblance to a baby elephant. They are also known variously as chimaeras, ratfish and rabbit fish. In scientific terms, they share features with sharks, rays and skates, but they also have a number of dissimilarities.