Shark activity noted around Cape Cod on July 12, 2023/Sharktivity app

Planning to visit Cape Cod National Seashore this summer to splash in the surf? There are plenty of great white sharks in the water, so you should download the free Sharktivity app onto your smartphone.

I have the app on my phone, and in recent days it's been pinging with some frequency to show where sharks have been sighted off the cape. On the accompanying image above, each "fin" in a blue block reflects where a shark has been sighted. Click on the block and the date and time of day of sighting are revealed. Fins in an orange block are unconfirmed sightings. Yellow blocks reflect a tagged shark that has been named.

You can zoom in and zoom out, too.

Sharktivity lets you see shark activity around Cape Cod for the past two days, the past week, the past month, and the past year. It also can be used to monitor shark presence around Fire Island National Seashore, Assateague Island National Seashore, and further south and north along the East Coast.

Great white sharks are lured to the cape's waters by prey: thousands of gray seals that summer there. Once plunging in population due to bounties placed on them from the late 1800s until about the 1960s, the seals have bounced highly back in number thanks in large part to the Marine Mammal Protection Act of 1972.

Gray seals can weigh up to 800 pounds and chow down on more than 30 pounds of fish a day.