The first known example of fin regeneration in silky sharks (Carcharhinus falciformis) has been documented after scientists from the University of Miami observed an adult male shark off Jupiter, Florida that had regrown a large part of a serious wound to its dorsal fin over the course of almost one year.
Sharks and other elasmobranchs such as manta rays are known to regenerate well from serious injuries, but there is very little research in the field. Most species of shark are difficult to monitor on a long-term basis, and being able to document any healing requires that an injured shark is sighted and subsequently re-sighted after a period of time allowing the wound to heal.
The discovery was made by Chelsea Black, a PhD Candidate in Marine Ecosystems and Society at the University of Miami. Black and her team were tagging silky sharks – which gather each year of the coast of Florida – in order to track their subsequent movements, but one of the tagged sharks was photographed a couple of weeks later with a piece of its dorsal fin missing.
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The size and location of the wound indicated that the tag had been forcibly removed; hooks that were embedded in the shark’s mouth indicated it had been repeatedly caught following the tagging. Silky sharks are protected by law in Florida, so why the tag was removed remains unknown.
Dorsal fins are an important functional part of a shark’s body while swimming, helping to provide stability and direction in the water, and sharks with damaged fins are often unable to compete for prey, or are subject to debilitating infection. Black herself said that she thought she would never see the shark again.
Just under a year later, another photographer was diving off the coast of Jupiter photographing the sharks as they returned for their seasonal gathering, sending his images to Black for study. Among them, she noticed a shark with a strangely shaped fin – with a still-attached ID tag showing it was the same shark that had been injured the previous year.
‘I wasn’t expecting to make a groundbreaking discovery,’ Black writes in an article for The Conversation. ‘Simple curiosity led me to start analyzing the photos. But the revelation was astonishing: Not only had the wound completely healed, but the 2023 dorsal fin was 10.7 per cent larger in size than it was after the injury in 2022.
‘New fin tissue had regenerated.’
There is other evidence that sharks have an extraordinary capability for healing. In 2006, a whale shark reportedly regrew the entirety of its dorsal fin following a boat strike, and in 2021 a whale shark was documented as not only healing from an expansive abrasive wound but regrowing its spots in exactly the same position as they were before the injury.
Reef manta rays have also been found to almost wholly regenerate portions of their discs that are bitten off by sharks.
Black’s discovery, however, is the first time the healing process has been documented in silky sharks. Her final published study concluded that the shark’s dorsal fin was restored to 87 per cent of its original size over a period of 332 days between observations.
‘One person’s attempt to undermine shark science and harm a shark ultimately proved futile,’ writes Black. ‘Instead, the shark’s toughness prevailed and led to an amazing discovery about this species.
‘While I’ll never know for certain where [the shark] spends the rest of the year, I hope he continues to return to Jupiter each summer so we can further assess his progress. Based on the healing rate calculated in my study, we just might see his dorsal fin grow back to 100 per cent its original size.’
‘Resilience in the Depths: First Example of Fin Regeneration in a Silky Shark (Carcharhinus falciformis) following Traumatic Injury’ by Chelsea Black, is published in the Journal of Marine Sciences
