Is that a shark fin in the water? Here’s how to tell

SYDNEY — When Nessa Donovan posted a picture of a fin in the waters off Dominion Beach on the Cape Breton Police Scanner Facebook group on Sept. 2, her post garnered a lot of attention.

Donovan posts that the picture was taken at 8:50 a.m. She says she saw two sharks swimming in the waters around the beach, though she initially thought she was seeing a seal.

But were they really sharks? This topic gets debated fervently in the comments.

One woman thinks it could be a sunfish, while another seems sure that they're porpoises. One man agrees firmly with Donovan that it must be a shark.

Fins have been seen in the ocean quite a bit lately,

espcially around Cape Breton.

After a shark attack near Margaree Island on Aug. 13 and a shark sighting off the coast of Ingonish beach on Aug. 24, Cape Bretoners have had the fish on their minds in the latter half of this summer.

But regardless of where or when you spot a fin, how do you know what animal you're really looking at? The Cape Breton Post spoke to Fred Whoriskey, executive director of Dalhousie University's Ocean Tracking Network, to learn more.

SHARKS

“There's a characteristic shape of a shark fin, which differs somewhat from the characteristic shape of a dolphin or a porpoise fin,” said Whoriskey.

He said shark fins tend to come down much straighter on the trailing edge, the side facing the tail.

And speaking of the tail, their orientation is vertically oriented, meaning there will frequently be a second, smaller fin protruding behind the main one.

“When the shark comes up to the surface, when it hits there, it tends to continue on for a bit,” said Whoriskey. “So straight and narrow, doesn't go up and down in the water column.

“They tend to cruise.”

• Dorsal fin: Distinctive triangle that protrudes upwards much straighter than others

• Casual tail fin: Vertically oriented — A second, smaller fin will frequently protrude from the water

• Gills on sides of the body

• Behaviour: Solitary predators, not often found in groups

• Seen mot often around Cape Breton: Porbeagle sharks, blue sharks, white sharks, occasionally a basking shark

Typically, sharks are solitary predators. They aren't often found in twos or more, said Whoriskey. So if you're seeing two or more fins out in the water, it isn't likely a shark that you're seeing.

PORPOISES

“Dolphin and porpoise fins tend to be much more curved, especially on what's called the ‘trailing edge' of the fin, so the side towards the tail,” said Whoriskey. “As opposed to the side towards the head.”

Whoriskey said that dolphin and porpoise fins also tend to have a hook to them.

• Dorsal fin: Small, curved (less than a dolphin's, but more than a shark's), with a hook or arch, especially on the trailing edge

• Blowhole on top of the head

• Tail fin: Flat, oriented parallel to the water – no second smaller fin protruding up out of water

• Body: Shorter and stockier than dolphins

• Behaviour: Social, will usually be found in pods

• Comes up to take a breath (fin shows), dives back down (fin disappears), repeats these rolling motions then dives back down and disappears for long periods

DOLPHIN

Dolphin and porpoise tails are oriented parallel to the water, so you will never see them sticking out of the water behind their dorsal fin (unlike with sharks).

“The porpoises and dolphins tend to be social,” said Whoriskey. “You find them in a pod.”

Dolphins also tend to dive up and down frequently in their ocean behaviour, unlike sharks.

“It takes a breath, fins out of water briefly and then it's back down underwater,” said Whoriskey. “And then it comes up again in these sort of rolling motions: up, down, up, down. And then it dives and disappears for long periods and comes up again.”

• Dorsal fin: Very curved with a hook or arch, especially on the trailing edge (the side toward the tail)

• Tail fin: Flat, oriented parallel to the water – no second smaller fin protruding up out of water

• Blowhole on top of the head

• Body: Longer and leaner than porpoises

• Behaviour: Social, will usually be found in pods

• Comes up to take a breath (fin shows), dives back down (fin disappears), repeats these rolling motions then dives back down and disappears for long periods

OCEAN SUNFISH (MOLA MOLA)

Aquaculture consultant Robin Stuart, who holds a masters of science in marine biology, was diving around an aquaculture operation in the Blandford area of Nova Scotia when a fin shocked him from behind.

“I was down looking at the bottom of the net and I came back and there was a giant dorsal fin behind me,” said Stuart. “I thought it was a shark and I got out. It was a sunfish, which has a big floppy fin on the back of it.”

Ocean sunfish are a large, flat fish that can weigh up to a thousand pounds and eat mostly jellyfish, said Stuart.

“The sunfish will come up to the surface,” said Whoriskey. “They tend to be there at particular times of year, we pick them up in the spring and the autumn.”

Whoriskey said the fin that sticks out is abnormally high and sharply triangular.

“Generally speaking, they're lying sideways in the water when they're up on the surface, so you don't see the fins protruding. They're trying to sunbathe,” he said.

• Fin: Thin, abnormally high, sharply triangle

• Behaviour: Doesn't cruise slowly (like a shark) – moves in a directed fashion

• Often lying sideways along the surface of the water, so you won't see the fin

WHALES

Whoriskey said you can often see and hear a whale's blowhole from far away.

“The blow that comes out of a whale and the blow pattern that you'll see, you'll get a little cloud of respiration that will come up – especially when its cooler temperatures and it condenses — is a dead giveaway that this is not a shark or some other animal like that.”

Whoriskey said most whales, even smaller ones, are quite a bit bigger than most sharks.

“(Orca whales) have got a very tall dorsal fin that goes up about … one-and-a-half to two metres high out of the water,” said Stuart. “They're quite distinct, it's the highest fin of all the ones you'd normally see in the water.”

Stuart said with most whales, you'll see part of the body out of the water along with the fin.

• Fin: You'll often see part of the body along with the fin

• Blowhole on top of the head

• Behaviour: Don't spend a long time on the surface: they come, they go

• Tend to congregate in pods, rarely seen alone