How a scientist accidentally discovered a shark that regenerated its mutilated fin: 'The revelation was astonishing'

I made an accidental and astonishing discovery while studying the movements of sharks off the coast of Jupiter, Florida. I set out to record the migration routes of silky sharks, named for their smooth skin. Instead, in a story filled with twists and turns, I ended up documenting the rare phenomenon of a shark regenerating a dorsal fin.

Tagging, then trauma

It all started in the summer of 2022, when my team and I tagged silky sharks (Carcharhinus falciformis) as part of my Ph.D. research. Silky sharks are commonly found in the open ocean and grow to be 10 feet long. Scientists know these sharks congregate in South Florida each summer, but where they go the rest of the year remains a mystery — one I hoped to solve.

Local boat captain John Moore took us to a site where sharks are known to gather. We carefully caught and gently attached GPS trackers to the dorsal, or top, fin of 10 silky sharks.

The tags, which are attached like large earrings, do not interfere with swimming and are designed to fall off after a few years. When the tag's antenna breaks the surface of the water, its GPS location is picked up by overhead satellites, hopefully revealing details of the shark's secret life.

I headed home to track their Travels from my laptop.

The story took an unexpected turn a few weeks later, when I received disturbing photos from an avid diver and underwater photographer, Josh Schellenberg, who knew of my work.

The photos showed a male silky shark with a large, gaping wound in its dorsal fin, as if someone had taken a satellite-tag-shaped cookie cutter and punched it right through. Josh wondered if this individual was one of the sharks from my study.