Resurgence of seals on Cape Cod beaches means more sharks

MONOMOY ISLAND, Mass. -- A pilot flying over Monomoy Island recently captured a stunning image: miles and miles of grey and harbor seals basking in the spring sun.

It's not unusual to see seals there this time of year. What's unusual is seeing that many from that perspective.

Marine biologist Owen Nichols has studied them for fifteen years. He explained why the seal population has increased over the past few decades.

"Well, they were essentially exterminated, extirpated, from our waters right up until the 1960's. So you are seeing a recolonization, essentially a resurgence of seals."

They're not hunted because they are federally protected. Before 1972, when the Marine Mammal Protection Act went into effect, sightings of even a single seal were rare.

But CBS News spotted hundreds on the uninhabited nature reserve where the aerial video was shot. Biologists say the resurgence of seals is likely one of the reasons there's also been a rise in the number of sharks in these waters, looking for food.

Researchers counted 68 great whites off Cape Cod in 2014. That number doubled to 140 last year. But the hordes of seals are not only attracting sharks -- local fishermen like Doug Feeney say they're eating too many fish.

"To us as fishermen, that's way too much. It's very taxing on us, it's very stressing."

Seals are voracious eaters. An 800-pound male could consume up to six percent of his body weight each day. That's 50 pounds of fish, including valuable species like cod and flounder.

Feeney and Nichols are part of an alliance of scientists and fishermen who are trying to find a middle ground to perhaps control the seal population. They want to celebrate a conservation victory, while protecting many of these people's livelihood.