NOVA: Can sharks survive finning (when the dorsal fin is cut off for shark-fin
soup and the animal released)?
Gruber: In nature, occasionally fins get bitten off with no detriment to the
shark, and finned sharks have been caught in a starved state during
shark-fishing tournaments. But generally finning kills sharks.
Sand tiger shark
NOVA: Do shark embryos really eat one another?
Gruber: One group, the sand tigers, has evolved a true survival-of-the-fittest
strategy in the womb. Six to eight embryos are produced in each of the mother's
two oviducts. The strongest, fastest-growing sibling kills and consumes the
others, so that sand tigers typically have two babies, one per oviduct. This is
really a great system, as only the best are born. They're big, up to two-fifths
the length of the mother. It's a good head start. Otherwise, the different
groups of sharks have evolved all the usual developmental strategies—egg
laying, egg laying with eggs retained, even up to a real maternal-fetal
connection via an authentic placenta.
A hammerhead parade.
NOVA: Can shark cartilage cure some cancers?
Gruber: Yes and no. All cartilage—shark cartilage, cow cartilage, whatever—possesses an anti-angiogenesis (AG) factor that, if injected into a solid
tumor, will cause the growth to dry up, shrink, and die. Merely eating shark
cartilage will give you some extra calcium, but it will be useless against
cancers, as no complex molecules pass through the gut wall. Even if the AG
factor got through, how and why would it seek out the tumor like a magic
bullet? I say if you want calcium take supplements! This hocus pocus is bad for cancer
victims, as they get false hope and discard their effective but uncomfortable
treatments for snake oil, and they die. And it is bad for sharks, as they have
to give up their skeletons for nonsense.
NOVA: Do sharks get cancer?
Gruber: The Registry of Tumors in Lower Animals housed at the Smithsonian
Institution has recorded tumors, and I have seen things that appear to be
neoplasms. But sharks are very resistant to cancers. Carl Lauer at the Mote
Marine Laboratory in Florida has shown that the usual carcinogens do not induce
cancer. I have several theories as to why they're so resistant. First, the AG
factor in their cartilage is very strong in the living shark, though they still
have the same problem of getting it to a potential tumor site. Next, sharks
have a primitive but very potent immune system—the key to cancer resistance.
Finally, shark DNA is very conservative and resistant to mutations.
A silky flashes through a bait ball.
NOVA: Are sharks primitive?
Gruber: New evidence suggests that the cartilaginous fishes to which sharks
belong may be the oldest of the jawed vertebrates. So they are ancient. Indeed,
some sharks survived as a group for 200 million years. (They are all gone now;
no trace of them exists outside of some teeth and scales.) But modern sharks,
skates, and rays arose only 30 million years ago. The biological definition of
primitive is "only slightly evolved from early antecedent forms." Modern sharks
are greatly evolved from the stem cartilaginous fishes and contain some of the
most derived, sophisticated animals on the planet. So they are anything but