Whale Sharks Rhincodon typus
These plankton feeders are the largest fish on Earth. Reaching lengths possibly in excess of 45 feet/14m, they weigh up to 15 tons. Whale Sharks are most often observed feeding near the surface in open water, but occasionally venture inshore. A juvenile whale shark was even observed cruising over the intertidal zone at high tide in front of the CEDO research station in Puerto Penasco.
Manta Rays and Mobulas
Filter feeders like the whale sharks, Manta rays Manta birostris frequent the offshore islands where they may enjoy a nice cleaning from angelfish, barberfish, and butterflyfish. With soaring motions and a wingspan of over 22feet/6.7m, these graceful creatures are difficult to mistake for any other.
Other species of pelagic rays, the Mobulas , Mobula munkiana and M. thurstoni are also found in San Carlos waters. These are smaller, with wingspans of only about 6 feet/1.8m. Unlike the mantas, mobulas prefer to travel along the coastline in large schools. Lucky divers may look up to see the shadows of hundreds of these rays overhead. They are most often observed by scuba divers and snorkelers at window rock, haystack, seamount, and most frequently, San Antonio Point.
Mobulas eat the small invertebrates that are attracted to scuba diver’s lights. This author was surprised to be slapped by a mobula’s wing as it arched past my face consuming the cloud of crustaceans that had formed around me during a night snorkel outside of the Guaymas harbor. This mobula was soon joined by dozens of others, all of which continuously jostled for position in front of my lights. For over an hour I saw little else but the bellies of mobulas, as I was gently pushed to and fro by these harmless creatures.
Hammerhead Sharks, Sphyrna lewini
The Sea of Cortez, particularly the El Bajo Seamount in La Paz, is known for great schools of these oddly shaped creatures. Docile bottom feeders, they are skittish and easily spooked by loud noises or even bubbles so scuba divers must be patient and calm in the water if they hope to approach hammerheads. The slightest ruckus, and they will disappear into the blue. Hammerheads may be found sporadically throughout the year at deeper depths around San Pedro Island, particularly the Southern and Western sides.
Over-fishing and poor resource management has decimated the hammerhead populations in the Sea of Cortez. Shark fishing for shark-fin soup has been a particularly harmful practice where often the shark is “finned”, then the rest of the living fish is dropped back into the sea only to suffocate, as it is unable to swim. Despite these practices, hammerheads have been seen with increasing regularity in San Carlos, although they are still uncommon.
Other Elasmobranchs
Few other large, mid-water sharks are seen
with any regularity in the Sea of Cortez, although there are occasional reports, mainly from fishermen. More often, scuba divers are likely to find horn sharks, Heterodontus francisci , shovelnose guitarfish Rhinobatos productus (a seeming blend of shark and ray), stingrays Urobatis maculatus, Urobatis concentricus , etc., and even two species of electric rays, the torpedo ray, Narcine entemedor and the bullseye electric ray, Diplobatus ommata .