RARE ALLUVIAL SANDS OF EL MONTE VALLEY, CALIFORNIA (SAN DIEGO COUNTY) SUPPORT HIGH HERPETOFAUNAL SPECIES RICHNESS AND DIVERSITY, DESPITE SEVERE HABITAT DISTURBANCE

Abstract/Summary

We characterized the species richness, diversity and distribution of amphibians and reptiles inhabiting El Monte Valley, a heavily disturbed, alluvium-filled basin within the lower San Diego River in Lakeside, California. This rare habitat type in coastal southern California is designated as a critical sand resource by the State of California (California Geological Survey) and is currently under consideration for a large-scale sand mining operation with subsequent habitat restoration. We conducted field surveys in the valley from June 2015-May 2016 and placed emphasis on detecting the coastal form of the California glossy snake (Arizona elegans occidentalis) given its status as a species of special concern by the California Department of Fish and Wildlife, its preference for sandy/gravelly habitats, and its documented historical presence in the valley. Survey techniques included drift fence lines with funnel traps, cover board arrays, walking transects, and road driving. We recorded 1,208 total captures in five sampling sections extending across the valley floor, revealing high species richness and diversity but with marked unevenness in species’ abundances. Two species are covered in the San Diego Multiple Species Conservation Program and 10 are listed as species of special concern in California. Snakes were the most species rich taxonomic group (13 species representing 11 genera), followed by lizards (11 species representing nine genera). Next to the southern Pacific rattlesnake (Crotalus oreganus helleri), A. e. occidentalis was the second most frequently detected snake species (n = 23 captures). Amphibian species richness was limited to two species of toad and one frog. Despite the relatively limited 12-month sampling period, a longstanding drought, and severe habitat disturbance, our study demonstrates that El Monte Valley harbors a rich herpetofauna that includes a number of sensitive species, including the largest known concentration of A. e. occidentalis in coastal San Diego County.

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