Biology professor: Animals in Hilton Head photo are sharks

A Facebook fan of The Island Packet shared a photo she recently took from near Port Royal Plantation. But exactly what the photo depicts has led to debate among many of our readers.

“They are sharks feeding on bait fish in shallow water,” according to Dr. Gavin Naylor, professor of biology at the College of Charleston. “Probably black tips (Carcharhinus limbatus), if I had to guess. The key giveaway that these are sharks and not rays, is that most of the dorsal fins (upright) are paired with a corresponding caudal fin (lower angle close to the water behind each dorsal fin) and that the spacing between each first dorsal and its corresponding caudal fin is fairly uniform and consistent (when parallax is taken into account).”

So why the color difference?

“The color difference between the fins of different animals is probably due to the angle the sun hits each fin. When the light hits at a low angle of incidence, it is reflected back (with the result that the fin appears lighter); when the angle of incidence is closer to 90 degrees the fins appear darker.”

On Tuesday, we heard from an expert of a differing opinion.

Joseph M. Quattro, professor of marine science at the University of South Carolina, took a look at the photo to give us the lowdown on these lowcountry critters photographed.

His answer? It’s up for debate.

“If I had to guess, some sort of ray – the giveaway to me is the two colors on the ‘fins’ out of the water – if it was a dorsal fin on a shark for example, they would be uniformly colored on both sides, not one dark, other light,” Quattro said.

Quattro said that it could be also be a skate, given the color shading on the fins.

“Fish exhibit a pattern called countershading where the dorsal surface is dark -- blends into bottom from above-- and light on the ventral surface-- blends with the bright sky from below,” he said. “So what it looks like to me is from a ray or skate, some bottom, some top.”

Quattro said that another thing leading him to lead toward stingrays is the way they are gathered.

“Note how the fins projecting out of the water of your picture are closely paired? Rays do school,” he said.

If he had to guess, Quattro would say the dozens of possible stingrays were feeding on something.

“Rays dig around in the soft sediment looking for mollusks, etc., maybe that’s what they are feeding on?” he said.

Quattro said that he can’t be entirely sure because the photo was taken far away, so “take it with a grain of salt.”

Were these sharks or stingrays or skates? Comment below to let us know what you think.

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This story was originally published June 7, 2016 at 10:32 AM with the headline "Biology professor: Animals in Hilton Head photo are sharks."