With so many species, sharks have evolved to an extent that will literally eat anything that moves. Their eating habits vary widely and depend on their habitat, and the variety of food and prey that is available therein. Sharks also adapt quickly when they find themselves in different habitats and situations. Being carnivorous, sharks can be broadly classified on their feeding habits as speedy hunters, slow moving hunters and filter feeders. The three types occupy a different but distinct niche at the top of food chain. Sharks are lithe and built for speed with a strong muscular and streamlined shape which makes them great hunters.
The speedy killing machines
The tiger shark, the great white shark, the blue shark, the mako and the hammerhead are large, fast moving and ferocious predators, and are at the apex of the food pyramid of the oceans and the seas. These predators have strong jaws and prey on almost any marine life that is available to them under water. Large sharks are known to have more than six rows of sometimes more than 400 teeth. Sharks can sense vibrations of the movement of their prey through the water. Their keen sense of smell, excellent eyesight in the water, and their sleek and supple body make them ideal predators in the sea, and enable them to hunt even in poor light of the depths, or in the dark.
These species hunt prey rich in fat content like sea lions, dolphins and other large fish. Their powerful jaws are used to tear flesh away from the prey. Although sharks generally don’t attack humans (we don’t have enough fat for shark’s taste), sharks have been known to sever human limbs in a single bite.
When they feed, sharks lose some of their teeth which are quickly replaced by new teeth. Sharks gorge themselves when food is available, but can go hungry for weeks at a time, during which they survive from the fatty oil reserves that are stored in their liver and body. However sharks that are hungry for a long time are known to go into frenzy when they smell blood. In these situations they will attack and devour anything that they smell. They are even known to cannibalize on other sharks.
The slow moving species prowl the bottom of the sea in search of prey. They are smaller in size and less aggressive. The angel shark and the zebra horn shark belong to this category. They eat less nutritious prey like crabs, lobsters, squids and clams. Although they too are built for speed, they will rarely pursue fast swimming prey, but use stealth and ambush for hunting. They have much smaller and fewer teeth than their larger cousins. These sharks will also resort to scavenging; eating the carcasses they find on the ocean floor, left-overs from the larger ferocious predators. Extensive fishing and depletion of their food source have driven these scavengers to eat refuge like coal, oil, discarded clothes and polythene bags. Although they are quite resilient, too much ingestion of such items can result in casualties.
The filter feeders
Basking sharks, mega mouths and whale sharks are filter feeders. They feed by sucking copious amounts of water, containing millions of plankton and small fish through their wide open mouths, and filter the prey through gills, that have rakers (fine filaments) which let the water out but retain the small fish and the plankton that the shark has taken in with the water. Mega mouths, whose mouth is disproportionately large as compared to its body, as the name suggests, have a luminescent tissue lining the inside of its mouth that attracts intended prey even in the murky depths of the deep sea. These species of sharks though large have very small teeth as they rarely have to seek large prey.
Do sharks drink water?
Sharks unlike other skeletal marine fish, do not drink water. The body tissue of a shark has a higher concentration of salt than the sea water. As a result the sea water enters the shark’s body by the process of osmosis. This is a process whereby the water from the solution with lower concentration, the sea water, flows into the area of higher concentration, the tissue and the blood of the shark, through the semipermeable membrane of the gills.
Sharks are endangered because of food shortage
With their habitats threatened and their food supplies depleted, most species of sharks are either endangered or are facing extinction. When man fishes he pays least attention to the fish that he casts away. Unfortunately sharks and other fish depend on this discarded catch for their food. This activity along with global warming depletes the food supply of sharks in their home grounds forcing them to migrate. Migration in search of food has an adverse effect on the breeding habits of sharks. As sharks do not breed too often their populations are depleting.
Efforts to prevent destruction of the hunting grounds of sharks will go a long way in protecting and conserving sharks. After all every living organism including man needs food and will go to any length to get it. So it is not surprising that sharks sometimes attack humans.