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Herpetofaunal Survey of the Coronado Islands
March 2000

Survey Photo Gallery

Reptiles and amphibians living on the rugged Coronado Islands (Los Coronados) were the subject of a survey conducted in late March of this year by a research team of Museum scientists, Mexican biologists, and other experts. Led by the Museum's herpetologist, Dr. Brad Hollingsworth along with Dr. Jon Rebman, Curator of Botany, eight herpetologists, one botanist, and four general biologists participated in the survey

Consisting of four separate islands, Los Coronados lie eight miles off the coast of Tijuana, Mexico, and are easily visible from many parts of San Diego. In spite of the islands' close proximity, the logistics of getting to them and making it onshore are troublesome. They sit on a submarine shelf and are geologically tilted fault blocks. All four have treacherous coastlines; each essentially small fortresses lined with jagged rocks and steep cliffs. With the sea floor descending to great depths just beyond the Coronado Escarpment to the west, the waters around the islands are susceptible to unpredictable conditions.

The expedition team had planned to survey all four islands. However, increasing winds made the seas so rough they had to cut the trip short after exploring only the northern portion of Isla Sur, the southern island. Captain Nick Cates and the crew of the sportfishing boat, the New Lo-an, generously donated their services to get the research team on and off the island. Once anchored off the north coast a smaller boat was used to shuttle the research biologists into the surf zone, where they made a leap of faith from the bow of the boat onto the slippery landing site.

Searching a total of two hours, the researchers found seven of the ten species of amphibians and reptiles on the island. Due to recent rains, the ground beneath rocks and logs was still damp, leading to the discovery of an abundance of slender salamanders, skinks, and alligator lizards. A rattlesnake, three night snakes, and a number of legless lizards were also found. Only one side-blotched lizard was seen and no conspicuous whiptail lizards or gopher snakes were observed. Cooler temperatures and the short period spent searching are the likely explanations for not seeing them. A lighthouse keeper living on Isla Sur reports seeing a dozen or so rattlesnakes this year. He also reports that they are much more abundant during the late spring when the temperature is warmer.

The long history of human inhabitation on Los Coronados has lead to the introduction of burros, goats, rats, and feral cats, known to cause severe problems to insular floras and faunas. It is unknown whether the presence of exotics has been a detriment to any of the amphibians or reptiles. Captain Cates, who regularly fishes off the shores of the islands, reports that he has seen up to 17 burros walking the ridges. Only three burros were seen during the survey.

With four to eight foot swells crashing along the landing zone, the researchers had to wait over three hours for the tides to change and the landing area to become safe enough to depart Isla Sur. With the help of the lighthouse keeper, experienced with handling a panga along the treacherous shores, the researchers were shuttled back to the New Lo-an. Despite the short time on the island, the researchers had great success.

At present, it appears the introduction of burros and goats are not affecting the amphibian and reptile populations. The status of the flora and remaining fauna remains to be investigated. The herpetology team plans on returning to Los Coronados Islands next year with the hope of exploring the other three islands as well.

bhollingsworth@sdnhm.org