Gary Lynch, age 11, of "Niagara Falls, Ontario, Canada, for her questions
Now do sharks multiply?
A few of the sharks lay leathery, peculiar shaped eggs, known to beach combers as mermaid purses. But the great majority give birth to live, well developed youngsters. This seems odd because bearing live young is said to be more advanced than egg laying. Yet almost all the more advanced bony fishes lay eggs and most of the more primative gristly sharks give birth to live babies.
Our warm and tropical seas are patrolled by some 250 large, medium and small shark species. The giant is the well behaved whale shark, often 45 feet long. The real tigers of the sea are in the ten to 35 foot range. These menacing monsters bear live young. The giant and some of the small sharky cousins lay eggs.
In every species there are male and female sharks and the eggs are fertilized inside the female's body. The development of the embryo differs from species to species. Some females lay broods of eggs, one by one. Each egg is plentifully supplied with nourishing yolk and sealed inside a tough, horny case.
In most of the live bearing sharks, the eggs remain inside the mother's body until they hatch, then emerge as frisky youngsters. However, the embryos of the smooth dogfish are attached to the mother's bloodstream and nourished inside her body. The dogfish are small shark running, from two to five feet. The frisky youngsters are born after about ten months and each measures 14 inches.
Other small sharks include the catshark and the swell shark, cyho swallows air and swells up like a balloon. The egg cases of most catsharks are rectangular cushions, often with a spike at each corner and sometimes with trailing tendrils. One species lays fancy capsules shaped like spinning tops with curly tails. The little spotted dogfish also lays eggs.
The female black tip shark is only three feet long. She rives birth to a pair of 18 inch Vyins. A female titer shark nay be 18 feet long. She also gives birth to 15 inch infants, though there are from ten to 80 youngsters in a litter. A 14 foot thresher shag bears a pair of live twins, each measuring three feet or more.
The female sand shark is about ten feet long and she bears one live infant at a time. The embryo is nourished inside her body on egg yolks and the newborn youngster is very well developed.
The mild mannered ifale shark is the lamest fish in the sea. He enjoys a docile life in tropical seas and the female lay eggs. Each horny capsule measures a foot long and three inches wide. It is thought that the giant shark lays her eggs in broods of 16 or so. And like all sharks, she lays there one by one.