I think it's a basking shark....don't they eat plankton and that type of thing?
Anyway, I should know better that to try to tell a Greek that they are wrong!! But I'll give it one more go - Makis there ARE sharks in Greek waters and some of them are ones that don't eat tiny plankton (can't remember the exact species but I believe that there's a stuffed blue shark in Rhodes aquarium that was caught off the island). There is a research project on Great Whites which live in the Med and although they seem to be mainly situated around Sicily, they are migratory and almost certainly make their way into the Aegean very occasionally.
It won't stop the majority of people coming to Greece - I've been coming for over 20 years now and I still go in the water despite having seen 2 large "dogfish".
Shall we agree to disagree?? I say "shark", you say "dogfish" - doesn't really matter in the great scheme of things!
Kala Christouyenna!