Cape Cod National Seashore Chief Ranger Leslie Reynolds warned at a news conference that the powerful predators are coming close enough to shore to be a concern for swimmers.
Officials in Orleans also have documented at least two shark attacks on seals in recent days, the Cape Cod Times reports.
Most tend to favor the Atlantic Ocean-facing beaches where seals tend to congregate, but researchers have found them off nearly every part of the Cape.
More pilots have volunteered to radio in shark sightings as they fly over the peninsula, said Heather Doyle, co-founder of Cape Cod Ocean Community, a local group that advocates for white shark surveillance and detection measures.
The Atlantic White Shark Conservancy, a Chatham-based research group, is also offering its Sharktivity smartphone app, which allows users to report and track shark sightings.