Sharks are nearly impervious to infections, cancers and circulatory diseases and have shown the ability to heal and recover from severe injuries while healing rapidly. The down side of this mode is long life and slow rate of maturation and reproductive turn-over. Quality over quantity. Compared to other fishes like salmonids or tuna that may lay millions of eggs, sharks typically have litters of a dozen or so, but have some species can have as many as 136 pups or as few as 2. Most species of sharks give birth to live young whose eggs were hatched internally.
Some species drop egg cases of various design.
A few species practice various forms of intra-uteral cannibalism, some consuming developing embryos, some consuming siblings as well. These sharks are born ready to go, no quarter asked nor given. Gestation can take as long as 14 months, but many species of sharks simply aren't well understood by science. Movements, migrations and breeding habits of most sharks are blank spots. Many of the best know species of sharks are not well studied and every new season turns up new revelations and insights, even new species.