Bonnethead Sharks are the Smallest Member of the Hammerhead family

My dog Tucker is easily captivated by dolphins, and normally, he will only go in the water if he hears dolphins nearby.  But the other morning, we needed to hold him back, because he was utterly fascinated by the undulating pattern of a bonnethead shark, feeding along the edge of the shore, just inside a tidepool.

Bonnethead sharks are common in summer in South Carolina.  In late summer, females move inshore to give  live birth to anywhere between 4 and 14 pups, each about a foot long.  During this maternal phase of their lives, the females actually STOP EATING in order to be sure they don’t accidentally consume their offspring.

Mouths on the Underside

Bonnethead Sharks, Sphyrna tiburo, have their mouths on the bottom of their heads, facing the sand.  Their large, shovel shaped head is slightly different for males and females. Rows of teeth are designed for crushing bottom-dwelling prey~ this is why the dog (and humans) are in no danger from this shark. The shark swims along the bottom, swinging its head back and forth and sensing electrical vibrations in the sand that might lead to a squid, crab, shrimp, or small fish. The location of the mouth (and comparative size) means that the dog is in no danger, and swimmers are unlikely to be targets.

Counter Shading

Like many other fish and ocean residents, sharks show counter shading~ the underside is bright to blend in with the light when seen from below, and darker to blend in with the water when seen from above. We usually see just the fins, but you can see how the top is gray.

Dolphin or Shark?

When you see fins near shore just at the edge of the waves, how do you know if it’s a dolphin or a shark?  Both splash and move through the water in search of prey.

  • One way is to look at the swimming pattern.  GENERALLY (there are plenty of exceptions) sharks undulate from side to side and dolphins move through the water in vertical leaps up and down. If the fins move up and down, it’s probably a dolphin.
  • Also check out the tail fin: sharks have an upright tail for steering(photo above) and dolphins tails are flat for diving. If you see a second vertical fin, it’s probably a shark.
  • The dorsal fin (top)of a shark is more sharp and pointed than a dolphin’s, which has a slight curve.
  • The breathing. Dolphins are mammals and regularly surface for air, making a pffff sound through their blowholes.  Sharks are fish with gills, and they don’t surface for air.

Ongoing Research

There are several research initiatives in South Carolina that tag, measure, and track sharks.  SCDNR has a federal grant with Georgia Southern University to measure the outcomes of sharks that get caught by anglers. By outfitting 140 bonnethead sharks with satellite and acoustic tags across both fisheries, the research team will be able to monitor the status of post-release sharks.

And one of our 2013 Dewees Island Blog posts featured College of Charleston students making the news by discovering the oldest known bonnethead: at 17 years! (The shark had been tagged as an adult, and recaptured twice.)

Where to see Sharks

An early morning walk along the beaches in late summer might yield a great view of feeding sharks: our turtle team regularly reports sightings of bonnethead sharks. On our island, they can also be seen near the ferry dock, cruising the oyster beds for the crabs that can be found in the shallow water there. Fishing piers can provide a good vantage point, and even inshore docks in late summer can provide a sighting.