A new study co-led by scientists at Duke University and published as a peer-review paper in Ecology has shown that female sand tiger sharks have returned to the same shipwrecks off the North Carolina coast.
The suggestion of this 'site fidelity' by the sharks is that the shipwrecks are essential habitats for the fierce-looking but docile species, which experienced dramatic population drop toward the end of the last century and the International Union for Conservation of Nature (IUCN) listed it as globally vulnerable.
The lead author of the study and a visiting scholar at the Duke University Marine Laboratory in Beaufort, North Carolina, Avery B. Paxton said that the population of the sharks is estimated to have dropped by as much as or more than 75 percent in the 1980s and 1990s. It is hard to know if it has stabilized or is still declining in large part because researchers have mostly had to rely on anecdotal sightings.
She pointed out further that having photographic evidence that these wrecks form an essential habitat the sharks return to create time to time gives them a focal point for ongoing research and study so they can better understand how the species is fairing.
Formerly a postdoctoral researcher at the South-East Zoo Alliance for Reproduction and Conservation, Paxton said further that they are now trying to figure out why they return. It is possible for them to use the wrecks as rest stops along their migratory paths, but they could also be returning there for mating or possibly to give birth. There are several hypotheses the researchers are testing.
Paxton added that there is a reason for the place to be called the Graveyard of the Atlantic as it has hundreds of wrecks. And it is not possible for researchers to have eyes underwater at each of them. They were able to extend their reach by relying on scuba divers, and other citizen scientists who are out there have cameras with them.
Each sand shark has a unique pattern of brown spots on its skin that acts like a fingerprint which allows scientists to identify individual sharks and distinguish them from others of their species.
Through analysis and comparison of the spot patterns on sharks' photos dating back to 2007, Paxton and her colleagues identified six female sand tiger sharks that have returned to the same wrecks, or identical shipwrecks nearby, at periods ranging from one to 72 months apart.
