Shedd Aquarium Researchers Document Extreme Recovery Capabilities of Shark Species

Shedd Aquarium researchers and colleagues published a research study this month in the scientific journal Marine & Freshwater Research that documented the unique recovery capabilities sharks possess using the case study of a wild lemon shark, Negaprion brevirostris, in Florida. In the study, scientists documented a lemon shark’s ability to expel a large metal fish stringer out of its body cavity over the course of 435 days. Such a behavior elucidates the resilience of sharks and, with more research documentation, could be used to inform best fishing practices.

“This shark was able to survive for over a year with perforation of its stomach lining, coelom, and muscle wall,” said Dr. Steve Kessel, director of marine research at Shedd Aquarium. “Seeing the shark in a healthy state after this extreme event showcases the recovery capabilities of these animals, likely a behavior that’s enabled sharks to survive for more than 400 million years.”

From Dec. 6, 2014 to Dec. 14, 2016, Kessel et al. recorded 12 sightings of a single lemon shark off the coast of Juno Beach, Florida at a recreational diving site. At first sighting, the shark possessed a foreign object protruding out from its right side near its pectoral fin. Initially, researchers were unclear what the object was, but identified that it was of a metallic composition. 

About a month later, they identified the object as a “fish stringer,” a piece of equipment spear fishermen use to retain captured fish while continuing to hunt. Researchers came to assume that the shark consumed the stringer while eating fish that were attached, and it was gradually working to expel the object. At the time of the last sighting, the only evidence left of the expulsion was residual scar tissue on the shark’s body wall.

“Many shark species are able to expel indigestible objects through stomach eversions, a voluntary process that rejects indigestible matter from their stomachs,” said Kessel. “To my knowledge, this is the first documented account of a transcoelomic expulsion of a foreign object by an elasmobranch fish. The lemon shark’s successful expulsion of the fish stringer highlights the elevated level of trauma that sharks’ bodies are capable of sustaining, and draws questions about the impact of foreign objects on sharks’ post-ingestion health and survival.”

Carcharhinid sharks are well-documented to survive and exhibit considerable tissue regeneration following extensive external trauma; however, the scientists observed that they are also resilient to considerable internal damage. According to Kessel et al., this is to be expected because the prey items of many shark species include porcupine fish, spiny crustaceans and stingrays, all which have the potential to cause internal damage after consumption.

“Our observations suggest that cutting leaders on gut-hooked sharks may be better practice than trying to forcibly remove the hooks, as we’re learning that sharks may be able to expel these objects on their own,” said Kessel. “Being that this research note is a case study of one, further research into sharks’ capabilities to expel foreign objects could help support this suggestion and help shark survival post-fishing encounters.”

Sharks are an iconic marine species that have survived for more than 400 million years. Celebrated each year during Discovery Channel’s Shark Week, Shedd Aquarium’s Daniel P. Haerther Center for Conservation and Research seeks to continue to celebrate and protect elasmobranch fish through research that advances our understanding, informs policy and enhances livelihoods.

The most direct way you can help conserve species is to prevent marine debris from winding up in our waterways that might negatively impact ocean and fish health. The pollution in our ocean, rivers, and lakes threatens nearly every species of aquatic life, including sharks. For more information about how you can join Shedd Aquarium in protecting species, visit www.ourhands.org/.