To casual observers, one shark’s fin slicing its way through the water looks much like any other. But researchers, aided with high-definition cameras, have discovered that much like fingerprints, no two shark fins look alike – and that’s helping conservationists keep track of these toothy predators.
The Importance of Fin Photos
The fin photo database used to identify and protect great white sharks has been in the making since 1987, when great white shark researchers at the University of California, Davis, Point Blue, Montana State University, Stanford University, and the Monterey Bay Aquarium began taking close-up shots of great white dorsal fins. The first research took place in waters off California’s Farallon Islands, and later, researchers aimed their cameras at sharks seen off Ano Nuevo Island and Tomales Point.
The database to date includes various images of 270 unique dorsal fins and is being used as the basis for estimating the population of adult and adolescent great white sharks off Central California’s coast. The database is used to help scientists understand a bit more about sharks’ lives – where they go, and whether they regularly return to the same hunting grounds. Fin photo IDs also help researchers to estimate the number of great whites at given locations while monitoring individual lifespans.
Some fins are sleek, barely notched; others are distinctly ragged and scarred. Like the whorls and loops on a human fingerprint, the shapes and various notches on each shark’s fin are unique, and they allow researchers to easily track sharks. Just like we humans tend to travel routinely from one place to the next – work, school, home, or the gym – sharks do too. They have a habit of congregating seasonally at various stops along a vast migration route that leads from the Central coast of California to the middle of the Pacific Ocean, down past southern California and Mexico.
But how do the scientists get the sharks to pose for clear fin photos? It’s easier than you might think. Using seal-shaped decoys, they lure the sharks to the surface and entice them to swim alongside research vessels where they can take photos, identify each shark’s gender, and take notes on each fish’s size as it pursues the decoy. In 2013, researchers managed to photograph 80 individual sharks. About 65 percent of those had been seen previously, and like human fingerprints, the shark’s fins remained fairly constant in overall shape though some display fresh scars and scrapes. This data suggests that the researchers are getting close to recognizing the majority of the adult great white sharks frequenting Central California’s waters.
Many of the same sharks are spotted each year and several have been seen for twenty years or longer. The current record-holder for highest number of sightings is a sixteen-foot male named Tom Johnson after the first naturalist who photographed him. He’s been seen every year for the last 26 years, usually in the Red Triangle, a feeding ground located between Monterey Bay, Bodega Head, and the Farallon Islands.
Salvador Jorgensen a research scientist for Monterey Bay Aquarium, says Tom Johnson is just one of many sharks to return to the Central California Coast right on schedule. “Each year,” says Jorgensen, “We congratulate him on another successful year.” If you want to track great white sharks yourself, you can use Monterey Bay Aquarium’s Shark Net app, which lets you keep tabs on sharks wearing electronic tags.