One of the people we take on fishing charters lives in Truro, and told me last year when he was lobster diving in Provincetown on the Bay side he saw a white shark cruising by him and he won't dive there anymore.- Tom
I grew up on the Cape and we swam off (what used to be) North Beach in Chatham, Nauset, Truro and Welfleet all summer, every summer. We never saw a seal. Ever. Hence, we never saw a shark.
Admittedly- this was in the previous century;)
My friends that still live there pretty much avoid swimming in those places now. They swim off the bay beaches.