Sharks are not kosher, because in order for a fish to be classed as kosher it must have both fins and scales (see Leviticus 11:9). Sharks do not have normal fish scales. Rather, their skin is covered by tiny, super sharp, flat V-shaped dermal denticles, which are more like teeth than the scales of kosher fish.
For more, see All About Kosher Fish.
but sharks have scales and the scales do detach
Thanks for pointing that out. We have modified the article a bit to make this point clearer.
Thank you it cleared it up