Sutter Basin Conservation Bank


2012 Giant Garter Snake Monitoring Report

Westervelt Ecological Services recently received the results from the second year of post-construction monitoring of giant garter snake (Thamnophis gigas) (GGS) presence and distribution at the Sutter Basin Conservation Bank (SBCB).  Monitoring has been conducted every other year, since the habitat was established in 2008, to evaluate habitat performance in regards to target species.  In order to increase the statistical rigor and informative value of data generated from current and future GGS monitoring at SBCB, the sampling approach implemented in 2010 (and repeated in 2012) was modified significantly from the pre-construction sampling approach with regards to the timing and duration of surveys and the spatial distribution of aquatic traps.  These changes will facilitate analyses of GGS survival, fecundity, population size, population age structure, population stability, and spatial distribution relative to habitat type and microhabitat characteristics, all of which are invaluable tools for informing the adaptive management process.  These modifications, while providing more flexibility and analytical rigor, are still expected to fully satisfy the elementary monitoring requirements of ascertaining GGS presence and distribution at SBCB.  This sampling approach was approved by the U.S. Fish and Wildlife Service and Westervelt Ecological Services prior to initiating surveys in 2010.

In accordance with this approach, GGS sampling was conducted during four discrete and equal survey periods between May 1 and September 30, 2012.  Additional survey efforts included periodically measuring water chemistry, cataloguing prey items collected in traps, and measuring GGS fecundity through radiography.  In total, 31 individual GGS (7 males and 24 females) were captured in 32 capture events at SBCB in 2012 (1 female was captured twice).  Of the 32 GGS capture events, 13 occurred in created habitat within SBCB and 19 occurred in the irrigation/drainage canals along the north, east, and west perimeters.  Two of the GGS captured in 2012 were recaptures from previous years, including a male marked in 2007 and a female marked in 2010.  Both of these snakes were recaptured in created habitat within SBCB in 2012 after previously being captured in irrigation/drainage canals along the perimeter of the property.  Of the 23 female GGS transported to the Sacramento Zoo to determine pregnancy status, four were confirmed to be at relatively early stages of pregnancy at the time of their radiographs (all in mid-June).