Manta Mexico Research Bulletin :: The Manta Network

(Bulletin Reprint)

Our third year of Photo-ID based research on the giant manta rays in the Sea of Cortez was a shocker. No mantas to photo and none to ID. None. In 2001, 22 mantas were cataloged using Photo-ID from the research site near Cerralvo Island. The following year 33 mantas in the same location, three of these had been sited the previous year, giving us a minimum population of 52 animals in two years.

In addition to the 3 individuals that returned from one year to the next, numerous mantas in each season exhibited site fidelity of 3 to 4 months with daily resights of these mantas by the research team. Local fisherman say mantas have been swimming here for as long as anyone can remember. Clearly this small seamount, had some significance for this population of mantas. But then they disappeared ? Where had they gone? What may have happened to them?

With the help of Dr. Felipe Galvan of the Centro Interdisciplinario de Ciencias del Mar ,CICIMAR, we have spent the winter looking at several possibilities. Last year, 2003, the Sea of Cortez was hit by two hurricanes, Ignacio and Marty, over the span of two weeks in September. The hurricanes may have explained the absence of mantas in September and certainly decreased our ability to conduct surveys. However before and after the hurricanes the sea temperatures and conditions were similar to past years as recorded by the research team and CICIMAR.

Another strong possibility would be the absence of food. Mantas consume planktonic animals, especially Euphasids. Krill is the best known example of this type of animal. The Sea of Cortez is home to four species of the genus Mobula, a close relative of the manta that eats the same prey. All four species were present in the Sea this past year and according to fisheries data, CICIMAR and observations by the research team the mobulas were in normal abundance. Prey must also be in normal abundance.

Fishing, accidental or deliberate, could account for some loss of population. Again we relied on Dr. Galvan whose graduate students monitor the fishing camps in the area for shark and ray catch. There was no increase in manta catch according to this data. However another possibility exists which is outside of our ability to monitor at this time. It has been reported that long-line fisherman may be catching the mantas to use as bait chunks on the thousands of hooks each boat deploys nightly in the Sea of Cortez.

Some have suggested the increasing presence of divers at the research sight would chase away the mantas. We agree that aggressive divers who try to touch or ride the mantas may chase them from a location for an unknown period of time. However we never sighted mantas before the tourist season began last year and usually have several months of data before the sport divers arrive. Logically, if the divers were scaring away the mantas we would have seen some and then they would leave when the high season came for sport diving. Additionally the divers act as back-up for the research team informing us when they have seen mantas and many times have usable photos of the mantas they saw. Not one single sport diver from the six dive shops in the area reported seeing a manta last year.

While we struggle to solve the mystery of last year we prepare for the 2004 season which begins in June. In past years this is the month when mantas have been first sighted. We welcome your participation in the project and thank you for your interest. Good News!

IEMANYA OCEANICA, a non-profit 501(c)3 based in California that conducts shark and ray research in the Sea of Cortez has partnered with Manta Mexico. This allows our research project to receive cash donations from the U.S. which will be tax-deductible for the donors. Donations in any amount should be sent to: IEMANYA OCEANICA C/O LALEH MITCHELL 5190 E. BROMELY DR. OAK PARK, CA 91377. Please attach a note explaining that donation is for Manta Mexico and the money will be passed on to the project and you will receive your tax deduction information from Ms. Laleh Mitchell of IEMANYA. For more information about IEMANYA OCEANICA and their work please visit www.IEMANYA.org on the internet. For questions or comments on this bulletin please write to mantamexico@hotmail.com