Showing posts tagged as "white sharks"
How do you FIN-gerprint a Great White Shark?
To the untrained eye, one shark fin cutting through the water probably looks like any other. Yet each great white shark dorsal fin gives our researchers and their colleagues important clues that will help to identify and protect them.
Like the swirls on a human fingerprint, the shape and notches of each white shark’s dorsal fin are unique, enabling scientists to catalog and track sharks across the oceans.
Building a Fin Photo Database
Since 1987, great white shark researchers at the aquarium, Stanford University, Point Blue, Montana State University and the University of California, Davis, have been photographing dorsal fins – first in waters off the Farallon Islands, and later at Año Nuevo Island and Tomales Point. They’ve created a photo database identifying 270 individuals over the past quarter century, providing the basis for the first-ever population estimate of adult and adolescent white sharks off the Central California coast.
This database helps scientists better understand where white sharks go and whether they return to the same waters on a regular basis. Fin IDs also help them estimate the number white sharks at these locations, and monitor the survival of individual animals.
Scientists have found that just as humans routinely travel between important locations — home, school, work — so too do great white sharks. White sharks congregate seasonally at spots along a migration route that takes them from the Central California coast, to the middle of the Pacific, and past southern California and Mexico.
Scientists use seal-shaped decoys to entice white sharks to the surface where it’s easy to photograph their fins. They also gather information such as size and sex when the sharks swim alongside their research boats. By comparing fin photos of the same sharks over the years, researchers concluded that – just as with our fingerprints, which remain the same over a lifetime – the overall shape of a shark fin remains fairly constant (with the exception of scrapes and scars).
In 2013, of the 80 individual adult white sharks photographed by researchers from the Aquarium and other institutions, nearly 65 percent had been seen in previous years. This suggests that the team is getting close to recognizing most of the adult great white sharks that frequent Central California waters.
Several have been coming back to the same waters for more than 20 years. One, a 16-foot male known as “Tom Johnson,” has been sighted for the last 26 years - the longest tracking period for any white shark on earth.