Beachgoers in Cape Cod, Massachusetts got a bit more than they bargained for this week when a great white shark swam in to feed close to shore. The incident sparked mixed reactions from onlookers: some were in awe of the shark's hunting prowess, while others were left feeling sorry for its seal meal. 

It's never easy to watch an animal be killed, but this predation event holds important clues that could explain why great white sharks keep stranding in the area.

[Warning: Some viewers may find this video disturbing.]

Several seal species can be found in the waters off Cape Cod, but only two remain throughout the year: harbour and grey seals. The latter can be spotted resting ashore in large groups, and thanks to a recent population boom, there are more of them now than ever.

Grey seals were once hunted to near-extinction in New England, so the rebound is good news – but it's possible that their haul-outs are now putting sharks in a precarious predicament. "You can see the shark struggling a bit to get back into deeper water," notes the Atlantic White Shark Conservancy (AWS). "This is what we believe may be happening when white sharks strand on Cape Cod." 

Lunging into the shallows is risky business, but so is gorging on seals. Past observations suggest that sharks can become lethargic after a large meal, making swimming against swells even harder. In this particular case, the seal appears to have gotten away – though its injuries were likely fatal. However, AWS director Cynthia Wigren offered another explanation when speaking with The Boston Globe. 

"We've seen on multiple occasions a white shark bite once and wait for the seal to bleed out," she said. "It's unclear if this occurred or if the seal was simply able to get away."

Some commenters have suggested that sharks in local waters "should be gone by fall", and instead, the booming seal population is keeping them in the Massachusetts area. In fact, this sighting is perfectly normal. Back in September, a 15-foot white shark known as "Scyther" cruised past the state, and in recent years, AWS biologists have documented great whites here well into December. 

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