Every year, from May through September, whale sharks congregate in a small area off the Yucatan Peninsula of Mexico where the Mexican Caribbean meets the Gulf of Mexico. They are attracted to this area due to upwelling of cool, nutrient-rich water (the Yucatan Current) that encourages relatively high densities of zooplankton near the surface. These largest of all living fishes are planktivores. They use both ram-feeding and vacuum-feeding strategies to capture tiny organisms (about 2 mm and up [Anonymous 2010]) and small schooling fishes. The upwelling of the Yucatan Current off the peninsula is productive enough that whale sharks, locally known as tiburones ballena, (Rhincodon typus in scientific lingo) are thought to travel from all corners of the Gulf of Mexico and the Caribbean during summer to this tiny feeding ground to feast on the abundant food there.
For those of us interested in the hydrographics behind the upwelling, this paragraph is for us! The Yucatan Current north of Cape Catoche, Holbox Island, experiences bottom friction at depths of 220 to 250 meters along the Yucatan Shelf, probably due to the underwater presence of one or more seamounts. The current glances of the seamounts and then rises at a rate of 2 to 10 meters per second towards the surface. In the summer months, the upwelling creates a two-layered water column, with the upwelled water moving westward across the shelf and creating a cyclonic gyre north of Cape Catoche (Merino 1997). This process is strongest during summer, resulting in the upwelled water occasionally breaking the surface and providing nutrients for plankton to thrive.
This year, ANAMAR senior biologist Jason Seitz traveled to the Yucatan to experience for himself these beautiful and harmless sharks. He and his wife, Jenny, arrived by ferry in Holbox Island in Quintana Roo in July and took three excursions out to the whale shark feeding ground north of Cape Catoche to swim with the gentle giants. As luck would have it, they were not only able to swim with several large whale sharks, but also were fortunate enough to swim with another amazing beast—the giant manta!
See the photographs above of the whale shark and manta (Mobula cf. birostris) encounter that Jason and Jenny experienced off Holbox Island and view the video below. Enjoy!
All the photographs and the video are by the author, Jason Seitz.
Merino, M. 1997. Upwelling on the Yucatan Shelf: hydrographic evidence. Journal of Marine Systems 13:101–121.
Anonymous. 2010. Whale Shark, Rhincodon typus, Mexico. Deep Motion, Redwood City, CA.