Species Conservation of San Clemente Island, CA - Event Details

Species Conservation of San Clemente Island, CA

Wednesday, October 1, 2025, 9:00am – 10:00am

Location: Wentworth Hall 1 or on Zoom at https://hawaii.zoom.us/j/81666098430 (Meeting ID: 816 6609 8430, passcode: TCBES)

Conservation of Threatened & Endangered Plant & Animal Species on San Clemente Island, CA

A research seminar presentation from Dr. William Mautz

Professor Emeritus, Department of Biology and Tropical Conservation Biology and Environmental Science, University of Hawaiʻi at Hilo


San Clemente Island is the southernmost of the large California Islands. Lying 63 miles west of San Diego, it is 21 miles long, 4 miles wide, and 2000 feet high with a steep uplifted fault scarp on the east side and a set of 17 identified marine terraces on the west side. It was occupied by humans for thousands of years and used for sheep and cattle ranching from the mid 1800’s to 1934 when the U.S. Navy took over the island.

Goats and pigs were probably introduced during the ranching years, and those invasive animals devastated the island vegetation. The character of the flora and fauna is that of an oceanic island and comprises 39 endemic plants of a 272 species native flora. Native terrestrial vertebrates include an endemic deer mouse, an island fox, and 2 species of lizards. Non-native invasive animals currently present include house mice, rats, and feral cats.

Beginning in 1972 with the Endangered Species Act, the Navy began a conservation program focusing on eradication of the goats. Seven plant species were listed Endangered and one Threatened. Among animals, the island loggerhead shrike was listed endangered, and Bell’s sparrow and the island night lizard were listed Threatened. Goats and pigs were removed by 1991. The island ecosystem then began a natural recovery assisted by the U.S. Navy’s Natural Resources Program with plant nurseries, loggerhead shrike breeding and re-introduction, and predator controls on rats, mice, and cats.

In recent times, 4 species of plants, and the Bell’s sparrow and island night lizard have been de-listed. The conservation and ecosystem recovery efforts continue. I began work on San Clemente Island as a graduate student in 1973 studying the physiological ecology of the island night lizard (Xantusia riversiana). This lizard and the whole family, Xantusiidae, is characterized by being intensively secretive and confining activity to dense shelter in the form of rock crevices, dense thickets of vegetation, or caves. Island night lizards are only found on 3 California islands, San Nicolas, Santa Barbara, and San Clemente, and although they are called “night” lizards, they are active by day. They have an extreme life history pattern of low reproductive rate, slow growth, late maturity, low metabolic rate, and long life span (documented up to 25 years), which makes them vulnerable to habitat disturbance and high predation rates. Because of this, and that they were rarely seen abroad, and their habitats had been severely altered by invasive mammals, the lizards were listed as Threatened in 1977.

I then began population biology studies to determine their status on San Clemente Island. It turned out that they were extraordinarily abundant in their favorable habitats with population densities of up to 1500/ha in dense shrub and cactus cover habitat. In parallel with studies by others on the other islands, this led to their being de-listed from Threatened in 2014. I continue to do “Post De-listing Monitoring” of their populations. A new potential problem for these lizards is the accidental introduction of Argentine ants to this and other California islands. On the mainland these invasive ants attack and kill reptiles when they are inactive, and the ants disrupt arthropod and other invertebrate communities. Effort is underway to remove Argentine ants from San Clemente Island.

For more information, contact: canale@hawaii.edu (808) 932-7571

Tags: conservation Wentworth Hall TCBES William Mautz San Clemente Island plant conservation animal conservation Xantusia riversiana