Ecological interactions whose effects have conservation significance are often difficult to test in the wild. A potential negative predatory interaction between larval roughskinned newts, Taricha granulosa, and California red-legged frogs, Rana draytonii, was recently observed in a coastal pond in Santa Cruz County, California. In order to explore the effect of larval newts on R. draytonii, we constructed 9 small ponds where factorial experiments can be conducted in a setting where confounding factors can be controlled. The ponds are approximately 6 meters in diameter and one meter deep and are arranged in a triangular array to create three sets of three ponds, each of which is approximately 6 meters apart from center to center. Ponds will be ringed with 18 inch aluminum flashing to control ingress into the ponds and the array will be fenced to exclude cattle and pigs. Preliminary experiments will include rearing R. draytonii from salvaged egg masses to assess background reproductive success in the absence of predators. Subsequent experiments will include factorial treatments where newt larva will be combined with R. draytonii eggs, and eggs-only ponds and larva-only ponds will constitute the controls. The results will guide ongoing management of natural populations where R. draytonii and T. granulosa are sympatric.

Predation events that result in the mass mortality of amphibians are sporadically reported in the literature; most often involving predation of the terrestrial adult stage of biphasic amphibians by avian or mammalian predators. Recently, reports from multiple locations in California describe egg predation (oophagy) by adult newts (Taricha spp.) on the egg masses of California red-legged frogs (Rana draytonii), significantly depleting the number of developing ova or eliminating the egg mass altogether. Specifically, I will describe oophageal predation events that occurred concurrently at two ponds, by two species of newts (T. torosa and T. granulosa), on the Mitsui Ranch in Sonoma County, California in Spring 2021. Predation was not limited to the egg masses of R. draytonii, but occurred on three additional native amphibian species in one of the ponds and three species total in another. Predation enets occurred over a 6-week period, from February through April, during the most severe drought recorded on the Mitsui Ranch in 47 years of ownership. The Mitsui Ranch has hosted continuous research and monitoring teams since 2011, but this is the first observed incident involving significant oophagy by Taricha spp. I’ll discuss environmental, behavioral, and evolutionary factors that might lead to these mass predation events, and whether they could have long-term demographic effects on amphibian populations. Finally, I’ll discuss whether and when such events compel mitigating management actions.

The endangered Santa Cruz long-toed salamander (SCLTS; Ambystoma macrodactylum croceum) inhabits a restricted range and is in decline due to multiple stressors including climate change, habitat loss, and competition with nonnative species. From 2007 to 2017, we implemented a Habitat Conservation Plan (HCP) at Tucker Pond in Santa Cruz County. The HCP required control of nonnative American bullfrogs (Lithobates catesbeianus), specifically culling and annual pond draining. Bullfrogs were successfully eliminated by 2015. However, three pitfall trapping studies conducted under the HCP documented lower numbers of breeding SCLTS adults (~200-400) as compared with a baseline estimate (~1,000 in 2001-02). Over the same period, relative abundance of native rough-skinned newts (RSN; Taricha granulosa) increased exponentially, with nearly 7,000 adult captures in 2016-17. Observations of predation by RSN on SCLTS eggs were documented. We are concerned that high numbers of predatory RSN in the pond could result in extirpation of an already depressed SCLTS population. Annual pond draining, timed to favor SCLTS transformation, is ongoing. In addition, a study testing the effectiveness of a mesh fence, designed to permit free movement of SCLTS while restricting entry by larger RSN, was initiated in 2017 and continues to the present.

In the winter of 2017 we transferred 20 egg masses of the California red-legged frog, Rana draytonii, a species listed as ‘threatened’ under the Federal Endangered Species Act, into a small pond in coastal Santa Cruz County, California. We unexpectedly discovered large larval salamanders devouring the eggs. Sampling that spring and summer showed no R. draytonii tadpoles in the pond. Mitochondrial DNA indicated that the salamander larvae were rough skinned newts, Taricha granulosa. Continued sampling throughout 2018 and 2019 found both larval T. granulosa and the California newt, T. torosa, to be present in the pond, but larval T. granulosa alone was present throughout the winter months. Predation by overwintering T. granulosa larvae constitutes a previously unreported ecological pressure on R. draytonii and thus may have a significant effect on recovering this sensitive species.

Very few studies have been conducted on the Sierra newt (Taricha sierrae), a species that is distributed throughout the western slope of the Sierra Nevada. During late winter and early spring, the Sierra newt congregates in intermittent streams to breed. During the 1998-1999 breeding seasons, T. sierrae instream movement and distribution were studied in a segment of the south fork of Little Dry Creek, located on the McKenzie Preserve in eastern Fresno County. In this study, T. sierrae individuals exhibited high site fidelity within stream subareas, but there were several individuals that moved extensive distances, particularly after storm events. In 2004-2010 and within this same population and stream segment, a total of 634 newts were marked with PIT tags. Starting in 2004, this stream segment was surveyed weekly or biweekly for 18 breeding seasons, through 2021/2022. Numbers of breeding individuals detected in the study stream segment have varied significantly from year to year depending on timing of precipitation and stream conditions. Individuals marked with PIT tags continue to be detected, particularly during years with good breeding conditions, indicating that this is a long-lived species which may skip breeding in less optimum years.