THE CASE FOR DRAWING DOWN FISHLESS PONDS: PREDATION ON CALIFORNIA RED-LEGGED FROG EGGS BY OVERWINTERING NEWT LARVAE

Michael F Westphal; US Bureau of Land Management; mwestpha@blm.gov; Eva Gruber, Karen Kiemnec-Tyburczy, Max Westphal, Christopher Lortie

In February 2017, we observed unusually large salamander larvae eating the eggs of California red-legged frogs (Rana draytonii) in an artificial stock pond on the coastal slope of the Santa Cruz Mountains at Cotoni Coast Dairies National Monument. Using mitochondrial DNA, we determined the presence of larvae of two species of salamander, the California newt (Taricha torosa) and the rough-skinned newt (Taricha granulosa), and determined the large larvae to be individuals of T. granulosa that had likely overwintered. Further sampling throughout the following 12 months determined that T. torosa larvae appeared at approximately the same time as eggs of R. draytonii were deposited and did not attain large size soon enough to pose a risk to frog eggs. Newly hatched T. granulosa larvae appeared for the first time in May. Overwintering newt larvae appear to pose a unique threat to successful R. draytonii reproduction that can potentially be managed by drying down ponds in late fall. However, overwintering in T. granulosa expresses natural variation in the reproductive cycle of that species that may warrant conservation itself, posing a potential tradeoff in conservation priorities between two native species.

Ecology and Conservation of Amphibians and Reptiles II