Effects of pool characteristics on California tiger salamander larval density at Dutchman Creek Conservation Bank, Merced County

The California tiger salamander (Ambystoma californiense; hereafter, CTS) is classified as a federally threatened species (U.S. Fish and Wildlife Service 2004). Consequently, much research has been done to provide information for its management and conservation. However, previous research has primarily focused on the use of upland, terrestrial environments by CTS (Trenham and Shaffer 2005), the demography of populations (Trenham et al. 2001), and the effects of hybridization between CTS and the introduced, barred tiger salamander (Ambystoma tigrinum mavortium; Johnson et al. 2013). Information on the characteristics of wetlands (e.g., hydrologic regime) that support reproduction and metamorphosis by CTS is limited. Understanding the relationship between the hydrologic regime of pools and use of the pool by CTS for reproduction is critical, because scenarios of climate change predict warmer temperatures and less precipitation across the species’ range. If these scenarios are realized, the hydrologic regimes of pools are expected to be affected. The timing of inundation and the period over which wetlands contain standing water could change, which could have negative consequences for CTS.

Westervelt Ecological Services has contracted data collection on CTS at the Dutchman Creek Conservation Bank (DCCB). We originally proposed to use occupancy models (MacKenzie et al. 2006) to analyze those data, to guide the design of our sampling at the refuge complex and regional scales and develop preliminary inferences regarding the wetland characteristics that were associated with use of wetlands by CTS. While the data were not appropriate for use with occupancy models, we have applied an alternative approach to generate insights towards effects of pond characteristics on CTS larval density at DCCB, and to guide our future sampling efforts to the extent possible.

Our goal with this report was to analyze existing data collected at the DCCB to: 1) evaluate relationships between CTS larval density and pool characteristics assessed at this site (pool depth, area, type, and water temperature); and 2) develop insights and sampling considerations useful for data collection efforts underway over larger spatial extents.