Sharks are fish that have been around before the dawn of time . . . before the existence of the dinosaurs. Even though they are classified as fish, they have no bones but cartilage, which is not as hard as bones, though they do have, fins putting them in that class. They live in many bodies of water all over the world but are rarely found in rivers and lakes, as they prefer salt water.
There are many different species (about 368) of shark ranging in size from seven inches long like the spine pigmy shark to 50 feet long, which is the whale shark, the larges fish in the world. However, the majority of sharks range in size from 5 – 7 feet long.
Sharks belong to a group of fishes called the Elasmobranchii that also includes the stingrays, skates and ratfish. These are all fish that have no bones, only cartilage.
Sharks mate similarly to other fish species. The male inserts one of his claspers, which is a finger-like appendage on the male’s underside, into the female’s genital opening, which is her cloaca. The sperm then travels through the female to any eggs that can be fertilized. Unlike the other fish, the eggs grow and fertilize within the female, not in the water. A select few sharks do lay eggs at the bottom of the ocean known as the devil’s wheelbarrow or mermaid’s purse. Most do bear live young and go through a pregnancy of up to 22 months, bearing between one and 135 young, which are called pups.
There are three types of egg development.
• Viviparity is when the eggs hatch inside the female and are nourished by a placenta as with most live bearing type births. Some of the sharks that bear this type of live young (pups) are the Bull sharks, White tip reef shark, Lemon shark, Blue shark, Mako, Porbeagle, Salmon shark, the Silvertip shark, and Hammerheads. Whale sharks are also viviparous, bearing hundreds of pups.
• Oviparity is the sharks that lay their eggs at the bottom of the ocean, which will hatch, later if not eaten by predators. A tough leathery membrane covers all the eggs. Some of the eggs have tendrils that attach to the bottom of the ocean and the yolk within, much like a chicken, feeds all these eggs. Some of these sharks are the zebra shark, the cat sharks, swell shark, the necklace carpet shark, some epaulette sharks, and the horn shark.
• Ovoviviparity is a process where the eggs fertilize within the female with no placenta nourishment . . . they are still nourished from the yolk within the egg but still grow within the female. If there is not enough nourishment within the yolks of these eggs, they eat other embryos and each other within the female, leaving very few pups to survive until birth. Great white sharks, saw sharks, Mako, crocodile sharks, Cookie cutter sharks, Pelagic thresher, Greenland shark, Gummy shark, Soup fin shark, Pacific Angel shark, Pygmy sharks, Nurse shark, Tiger shark, and Sand tiger sharks reproduce this way.
We do sometimes hear about shark attacks but for the most part, sharks do not deliberately attack people. It is unfortunate when it does happen but usually there are only 100 known shark attacks against people each year. We have a better chance of being struck by lighting or stung by a bee. Most times when attacked, it is mistaken identity . . . they see an object as potential food such as a seal or other mammal or fish in the water.
Most sharks live in the open waters of the oceans all over the world; some prefer the warmer waters such as the Pacific Ocean while others may prefer the colder Atlantic waters. Some species are deep-sea divers and may even hide on the bottom of the ocean while others may stay closer to the surface. Rarely are there any sharks found in fresh waters and rivers though some sharks may venture many miles up into the fresh water of rivers like the Mississippi in the USA and the Amazon in Brazil such as the bull shark. It does sometime venture into fresh water.
I can’t say that I would not fear this predator because they are not my favorite creatures to meet close up. I do know that they are not hunting for me specifically and I choose to give them the respect that they deserve and learn about them from afar for the interesting legendary fish that they are.