Is that Jaws or Flipper? Spotting the difference between sharks or dolphins by their fins

Shark sightings are nothing new for Wilmington-area beaches and most of the time they're harmless.

However, just this week a Tennessee teen visiting Wrightsville Beach was bitten by what officials believe was a small shark.

The attack comes amid a series of possible shark sightings last month that prompted Oak Island Water Rescue officials to post warnings about the potential predator on their Facebook page.

Swimmers beware: Officials warn of large shark sightings off Oak Island

The post fanned a wave of speculation, with some sure the sightings were of a shark, while others were skeptical, claiming the creature was a dolphin, manta ray, or even a whale.

So how do you know for sure if you're dealing with a playful dolphin or an apex predator? Here's how to tell if you've spotted a shark.

Dorsal fin shape

Sharks are most often confused for dolphins but usually can be told apart by their distinctive dorsal fins, according to Michelle Passerotti, Fish Biologist with the National Oceanic and Atmospheric Administration's Apex Predators Program.

"Shark fins typically tend to be more triangular in shape," Passerotti said. "The leading edge of the dorsal fin might have a little curve to it depending on the species, but generally the back edge of the dorsal fin that point towards the tail is pretty squared off or flat."

Passerotti said across species most dolphin dorsal fins will be rounded, with sharks having a noticeably straight edge off the tail-end of their dorsal fins. While some shark species do have rounder fins, like the hammerhead, they are still distinct enough to tell the difference from the beach.

"If you just saw that the top of a hammerhead dorsal fin coming out of the water you might think, oh, that's got a curve to it, that might be a dolphin," Passerotti said. "But it's also pointier at the end; dolphins tend to be rounded, along with being more curved and hook-like in their shape."

Tail fin orientation

If a dorsal fin breaching the water's surface is accompanied by a smaller tail fin a few feet behind, that's another sure sign of a shark sighting, according Dr. Fred Scharf, a professor at UNCW's Department of Biology and Marine Biology.

"In the case of sharks, sometimes the tail or caudal fin will also break the surface of the water because they have a vertical caudal fin or tail," Scharf said. "The dolphin tail, however, is horizontal, like a whale's."

Scharf said the trailing tail fin won't always be visible for the smaller sharks most common to the beaches in this area - like black tips and spinners - but would be more noticeable on bigger predators like bull or tiger sharks.

Still, the triangular-shaped dorsal fins would provide enough contrast and warning.

"Their fins are going to be bigger, but they just they still have the same shape and pretty distinct from a dolphin," Scharf said.

Behavior

People can also watch the animal's behavior for clues to its species. Dolphins are known to swim in small pods whereas sharks are typically solitary hunters.

"Usually, when you see dolphin you'll see more than one," Scharf said. "The sharks that are feeding in the surf zone will tend to be solitary most of the time. There may be multiple sharks in the area, but they're not tending to swim together."

How they move can also be a giveaway, with dolphins having to constantly break the surface to breathe.

"Sharks tend to swim in a constant motion in one direction, you know, they're not bobbing like dolphins that go up and down in kind of a wave motion," Passerotti said.

"Sharks in that close are usually looking for food, kind of darting back and forth chasing after something but they're generally not going to have an up and down motion in the water."

Other sea creatures

Some have suggested the recent dorsal fin sightings could have come from a manta ray or even a whale, but according to experts that's unlikely.

Manta ray sightings usually involve two fins parallel to each other jutting out of the water, and they would generally be smaller than shark or dolphin fins.

As far whales, Scharf said while plausible, a whale sighting so close to the beach would be hard to mistake for anything else.

"If you've ever seen one, you would know," he said.

Typically whales would be spotted further from the beach and rather than just noticing a fin, it's likely a their whole body could be seen breaching the water's surface.

"If it's a whale they're going to be spraying out of their blowhole and they also will tend to be really big," Passerotti said.

Have you been bitten by a shark?

Although some of the recent attacks haven't been confirmed as coming from sharks since they weren't seen, Passerotti said it is possible to identify a shark bite by the injuries they leave.

"Shark teeth have a very distinct shape and that's very species specific," she said. "So a lot of times you're going to get an imprint that is going to have a distinctive look about it."

Earlier this year:Shark bites 7-year-old girl swimming at Ocean Isle Beach

Experts can use the tooth pattern, size of the teeth, the overall size of the bite and other measurements to determine if you've been bitten by a shark and can even narrow down the species.

"If you watch it long enough, you can kind of get an idea of what it might be," Passerotti said. "And if you're not sure it's best to just leave it be and not try to swim over and figure out what it is."

Reporter John Orona can be reached at 910-343-2327 or jorona@gannett.com.