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Tracking White Sharks by their Fin-gerprints

Senior Research Scientist Salvador Jorgensen, PhD, has a job other people might envy, but probably from a comfortable distance. Sal tags and tracks adult white sharks, which can put him within feet of these large ocean predators.

You could also say he's on a first-name basis with several white sharks he's been following for many years. Sal and research colleague and shark biologist Scot Anderson identify these sharks by the distinctive shape of their dorsal fins.

Each fin is like a fingerprint, having a unique series of notches and ridges that allow Sal and Scot to distinguish one shark from another. They may name the sharks based on the features of their dorsal fin, such as "Sickle Fin."

Shark dorsal fins remain distinctive over decades, so if Sal gets a good image of a shark's fin, he can identify that shark five, 10, 15, even 20 years later.

We spoke to Sal exclusively for Shorelines online to find out more about his fascinating job in general, and the white shark fin ID catalog in particular.

Why did you want to study white sharks?
I think most kids probably go through a "shark obsession" phase at some point; I guess I just never grew out of it. What I learned, however, was that a lot of the information available about sharks was incorrect—sharks have been demonized in movies like Jaws and the typical shows you might see during Shark Week. The most feared, and hyped, is the white shark. I became fascinated with studying white sharks and learning they are not the mindless indiscriminate killers they are made out to be—in fact they are incredible ocean navigators, very picky eaters, and creatures of habit with very predictable patterns of behavior.

Shark researcher Scot Anderson watches a large adult white shark feeding at the Farallon Islands
Shark researcher Scot Anderson watches a large adult white shark feeding at the Farallon Islands.

Each year, you and Scot tag sharks off the Farallon Islands, Año Nuevo Island and Point Reyes. What is it about those places that attracts white sharks?
Those are sites known as rookeries where elephant seals haul out of the water in large groups. When they're not hundreds or thousands of miles offshore, elephant seal groups take turns hauling out during different seasons. There is a pupping season around Christmas where only mothers and their pups haul out, a mating season around Valentine's Day with only mature males and females, and in the fall around Halloween juveniles haul out. These juveniles are what the sharks target. The young elephant seals are still naïve and not too large, so they are relatively easier to capture. White sharks are focused around these sites, sometimes hanging around for months between September and December.

What's a typical tagging day like?
It is a balance between hours and hours of boredom and exhaustion interspersed with moments of intense adrenaline and excitement. One day you might stare at the seal decoy floating behind the boat for six straight hours in rough weather and nothing happens. Another day you might set the decoy in the water and seconds later a 16-foot white shark launches out of the water with the decoy in its mouth. You might go three weeks without a shark swimming close enough to place a tag, and then tag six sharks in a day!

Notches and tears make the shape of each shark fin unique
Notches and tears make the shape of each shark fin unique.

How can you identify sharks by the notches on their dorsal fins?
White sharks are born without any nicks or tears along the trailing edge of their dorsal fin. But as they grow the fin begins to collect small tears and tatters that give each fin a distinctive shape. We think that the first notches are a result of "bug bites." There are small parasites called copepods that attach to sharks' bodies and in particular on the trailing edge of the dorsal fin, which is very thin when sharks are small. Little scabs and cuts develop, and as the shark grows and the fin gets thicker, these sores leave small gaps along the fin's edge. Additionally, bites or injuries that sharks receive on their dorsal fin may add more notches. When viewed in profile, the notch pattern often becomes very recognizable, and we often give a name to a shark based on particularly memorable characteristics, like "Middle Notch" or "Sickle Fin."

Why catalog fin IDs?
Cataloging fin IDs has allowed us to track the same individual sharks over decades. Some of the longer records extend 25 years between when we first obtained a photograph and their most recent record. Also, as the number of identified sharks has increased, the photo IDs have allowed us to estimate how many adult white sharks reside off central California. And most importantly, this is a way of tracking the population to ensure their numbers do not decline.

Tell us more about sharks you have tracked by their dorsal fins for over 25 years.
There are two well-known sharks in this category, Tom Johnson and Elvis. Tom Johnson was named after the photographer who first captured a fin image of this shark in 1987, and photographed him over a dozen different years through 2012. Elvis has a fin with a rounded top that resembles the pompadour hairstyle of his famous namesake. We have seen Elvis a half a dozen times over that period, most recently in 2015.

Salvador Jorgensen and Scot Anderson tag a great white shark near the Farallon Islands
Salvador Jorgensen and Scot Anderson tag a great white shark near the Farallon Islands.

What do you hope to know about white sharks in five years, in 10 years?
One of the big goals is to understand whether the population of white sharks is increasing, decreasing or staying constant. We are cautiously optimistic that the numbers may be slowly increasing, but we need to confirm that with long-term fin ID data. Tracking the number of reproductive-aged white sharks over time is the only sure way to answer this question.

Want to know more?

Learn where and why we study white sharks to better understand and protect this ecologically important and threatened species.

Learn more