By Bridget Altman
Leopard sharks (Triakis semifasciata) are a California ocean icon. If you have ever been in the waters off of the California coast between the months of May and September, chances are you have come in contact with these friendly faces. Each summer, they flock in numbers to the warm waters of La Jolla Shores.
Researchers from the Scripps Institution of Oceanography (SIO) discovered that the majority of the sharks showing up at this beach were pregnant females, using the warm waters of La Jolla Shores like an incubator. After reaching this conclusion, the scientists had more questions they needed to answer. One big question being: how do these pregnant sharks navigate their way to the same beach year after year?
You may already know that sharks have an awesome sense of smell. Here’s the frightening fact that you probably learned on the playground: “a shark can smell a single drop of blood from miles away!” Though that is not necessarily true, sharks really do have an acute sense of smell that helps them find food in a vast, blue ocean. Hunting was thought to be the main purpose of their magnified sense of smell, until Dr. Andrew Nosal and his colleagues at SIO proposed that leopard sharks might use smell to find their way back to shore.
By tagging and tracking 26 leopard sharks, Dr. Nosal was able to determine that in fact these sharks really do rely on smell to find their way to shore. He took these sharks for a boat ride, nine kilometers offshore. While en route, he blocked out the sunlight, inserted a magnet into the tank to confuse the sharks’ electrical sensor, and spun the boat around in all sorts of directions. The goal of this confusion is essentially the same as a game of “dizzy bat”: get the sharks disoriented and see which ones make it to shore fast and easy.
Some of these sharks had their sense of smell blocked by a cotton swab containing petroleum jelly; the others remained the control samples with their nostrils clear. The results of the study found that the sharks whose nostrils were blocked took a more roundabout route back to the shore. The sharks that had clear nostrils figured out the direction of shore faster. However, all sharks ultimately made it home. This means that there is likely another factor helping the sharks navigate, requiring further research.
As in almost every scientific study about sharks, one question may have been answered but dozens more remain. The scientists, like the sharks in the study, now have to navigate their way through a maze of unknowns to solve the puzzle that is shark science today. To most people, the shark remains most easily identified and known by its dorsal fins peaking above the surface of the water. The bulk of the shark and perhaps the answers that lie ahead remain beneath, yet to be explored.
To learn more:
- Read the full study: Olfaction Contributes to Pelagic Navigation in a Coastal Shark
Bridget Altman is a graduate student at Scripps Institution of Oceanography studying Marine Biodiversity and Conservation. She hopes to help the world understand the importance of ocean stewardship. She has a passion for all ocean creatures, specifically apex predators. She ultimately wants to become a PR agent for sharks.
Copyright © 2016 by Marine Science Today, a publication of Marine Science Today LLC.