Of all the shark species known to man, more than half only produce two pups at a time. One of them, the tiger shark, only breeds once every two years, so that over its estimated lifespan of 30 years; it cannot produce more than 30 young.
目前人類已知的鯊魚中，有二分之一以上每胎只生產兩隻幼鯊，其中虎鯊甚至每兩年才生產一次，以三十年壽命估算，等於一生繁殖不超過三十個子孫。