How to deal with marine life underwater should be taught in the OW course- though personally, i teach more about how to avoid damaing the underwater environment and be respectful of where you are diving, and about the local flora and fauna underwater, than what to do when you see a shark specifically.
That said, where you do your certification dives is the dependant factor when covering this section. when i worked in the bahamas where sharks were frequently seen, i covered the topic in more depth than, say, when i am teaching in the water off vancouver where (at least at our local teaching sites) sharks are rarely, if ever, seen. I think it also depends on the questions asked by students during the course; if a student were to specifically ask, then no matter the environment, i would answer the question in depth. but i think the OW course i more about learning how to dive safely- if a student wants to know more about sharks maybe he/she should enroll in a fish id or other speciality course.
I dont think its necessary to say that in every course an instructor must handle how to react when seeing a shark underwater specifically (though remember the padi manual teaches us to stay close to the bottom until dangerous animals swim away from the area, or to swim slowly away from the area along the bottom and ascend when its safe to do so). If we HAVE to cover sharks, why not lionfish, scorpion fish, etc? it would be a long lecture... and further we would need to cover many species- seeing a nurse shark is much different than a great white, so do we need to teach shark ID as well??
also, how a person should, or does, react when seeing a shark underwater varies upon the person, the shark, the environment etc. I personally love diving with sharks- i go to sites where they are more likely to be seen and like to see them up close. on one hand a new student might feel uneasy about the situation, or they might want to see a shark quite badly (i have had students with both preferances). when you go to a location where there are frequent shark sightings, how to react around the species seen there is generally covered in the dive briefing. also, some shops offer speciality courses about the subject of sharks (where i worked in the bahamas for example, we taught a distingtive shark awareness cert. we covered many topics ranging from anatomy, identification and even media msconceptions)
