Rarity of the new hammerhead shark species indicates the frailty of shark diversity in the face of human predation, scientists said. University of South Carolina

A team of researchers from the University of South Carolina has discovered a new rare species of shark, named the Carolina Hammerhead, which had long eluded discovery as it is outwardly indistinguishable from the common scalloped hammerhead sharks.

Joe Quattro, an ichthyologist and biology professor in USC’s College of Arts and Sciences, did not set out to discover a previously unknown species but found one exclusively living in saltwater. According to scientists, the rarity of the Carolina hammerhead shark, or, Sphyrna gilberti, underscores the fragility of shark diversity in the face of relentless human predation.

“South Carolina is a well-known pupping ground for several species of sharks, including the hammerhead,” a statement from the USC read. “The female hammerhead will birth her young at the ocean-side fringes of the estuary; the pups remain there for a year or so, growing, before moving out to the ocean to complete their life cycle.”

Studying the hammerhead sharks with genetic data, Quattro and his team uncovered an anomaly, which was that the scalloped hammerheads, or Sphyrna lewini, which they were collecting had two different genetic signatures in both the mitochondrial and nuclear genomes.

After some research, the scientists found that Carter Gilbert, curator of the Florida Museum of Natural History from 1961 to 1998, had described an anomalous scalloped hammerhead in 1967 that had 10 fewer vertebrae than the Sphyrna lewini. Such a shark was captured near Charleston, S.C., and its sample was kept in the National Museum of Natural History.

Quattro’s team was able to examine the sample morphologically and suggested that it constituted a cryptic species -- one that is physically nearly identical to the more common species.

After publishing the preliminary genetic evidence for the new species in the journal Marine Biology in 2006, the researchers followed up by making thorough measurements to fully describe the new species, Sphyrna gilberti, named in Gilbert’s honor, in the journal Zootaxa recently. The difference in vertebrae, 10 fewer in the cryptic species, is the defining morphological difference.

“The biomass of scalloped hammerheads off the coast of the eastern U.S. is less than 10 percent of what it was historically,” Quattro said. “Here, we’re showing that the scalloped hammerheads are actually two things. Since the cryptic species is much rarer than the lewini, God only knows what its population levels have dropped to.”