We know from studies made by Harold Pratt at the marine laboratory in Narragansett that blue shark females—and many other female sharks—are capable of storing sperm for months after insemination, ready to fertilize eggs whenever they mature. Among several thousand sharks that I examined during the 12 years I directed shark research at Cape Haze, I often took smears from the reproductive tracts of female specimens. Once, after a female shark had been frozen for several months, a smear from her reproductive tract showed revived spermatozoa swimming around in the drop of seawater under my microscope.
ROUGHLY A THIRD of all sharks are egg layers; the rest are viviparous, that is, they give birth to live young. All female sharks have paired wombs, where the embryos may remain from a few months to two years.
The instant these embryo sharks are born, they are ready to begin feeding. The only time I was ever bitten by a shark was when I reached into the uterus of a live, 12-foot female tiger shark and pulled out a healthy baby hanging onto my fingers!
Some sharks start eating before they are even born. “Intrauterine cannibalism” was first discovered by Stewart Springer, then with the shark industries division of the Borden Company, who dissected a female sand tiger shark and found embryos with their stomachs full of eggs—they were eating their potential brothers and sisters.
Adult sand tiger sharks grow to ten feet and look more ferocious than most sharks, since their large daggerlike teeth hang out and they always keep their mouths open. David and Anne Doubilet and I met with three sand tiger sharks in a dark cave near Kitano Shima, a far-off corner of Japan’s Bonin Islands.
It was scary at first. The sharks came slowly but directly toward us, like grinning vampires inviting us into their castle. But their initial curiosity passed. We stayed nearly two hours. We watched and photographed them, careful to make no sudden movements, barely flippering around. The sharks seemed to accept us in a languorous,casual way. Neither my soft murmurings to them through my mouthpiece as I lay on the smooth white sand floor of their cave nor the flash from David’s strobe light seemed to ruffle them.