How to attract lots of sharks and count them

The jagged edge of a shark’s dorsal fin is unique — like a human fingerprint — and was a key characteristic in allowing researchers to count one population.

In this video, watch great white sharks surface for a fake marine mammal, and notice the jagged edge of each shark’s dorsal fin (the fin on top). Researchers from Stanford and UC Davis examined the fins — as individual as fingerprints — to distinguish different sharks and produce, over a period of several years, the most rigorous estimate of any white shark population in the world.

First learning where sharks like to congregate, based on satellite tag studies, the team positioned themselves in small boats in sharky waters off the central coast of California. Then they tossed seal-shaped decoys on fishing line into the water, with small pieces of bait attached just for fun. When sharks surfaced, the researchers photographed their dorsal fins.

After sorting out individuals, the researchers used a statistical model to calculate an important baseline count for future studies — much needed, as shark populations worldwide have declined.

Via Sanctuary Integrated Monitoring Network
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