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Realized detection and capture probabilities for giant gartersnakes (Thamnophis gigas) using modified floating aquatic funnel traps

Open-File Report 2015-1200
Prepared in cooperation with the California Department of Water Resources
By: , , , and 
https://doi.org/10.3133/ofr20151200

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Executive Summary

Rigorous analysis and management of animal populations requires that observers account for limitations inherent to the detection of those populations and the individuals within them. Researchers are usually unable to see every individual of a population or to even detect some entire populations. Ignoring this imperfect detectability can bias estimates of population characteristics, such as probability of occurrence, abundance, survival, recruitment, and population growth rate. Furthermore, the precision with which these population characteristics are estimated is dependent on detection probabilities (the probability that at least one individual of a species is detected during a survey, given that the species occurs where the survey is conducted) and capture probabilities (the probability that a given individual is observed or captured during a single survey); greater detection and capture probabilities result in less uncertainty about the values of population characteristics and a greater ability to evaluate the effects of variables or experimental treatments on the population characteristic(s) of interest.

Detection and capture probabilities for giant gartersnakes (Thamnophis gigas) are very low, and successfully evaluating the effects of variables or experimental treatments on giant gartersnake populations will require greater detection and capture probabilities than those that had been achieved with standard trap designs. Previous research identified important trap modifications that can increase the probability of snakes entering traps and help prevent the escape of captured snakes. The purpose of this study was to quantify detection and capture probabilities obtained using the most successful modification to commercially available traps to date (2015), and examine the ability of realized detection and capture probabilities to achieve benchmark levels of precision in occupancy and capture-mark-recapture studies.

Suggested Citation

Halstead, B.J., Skalos, S.M., Casazza, M.L., and Wylie, G.D., 2015, Realized detection and capture probabilities for the giant gartersnake (Thamnophis gigas) using modified floating aquatic funnel traps: U.S. Geological Survey Open-File Report 2015-1200, 36 p., http://dx.doi.org/10.3133/ofr20151200.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Executive Summary
  • Introduction
  • Detection Probabilities 
  • Capture Probabilities
  • Summary 
  • Acknowledgments 
  • References Cited
  • Glossary 
Publication type Report
Publication Subtype USGS Numbered Series
Title Realized detection and capture probabilities for giant gartersnakes (Thamnophis gigas) using modified floating aquatic funnel traps
Series title Open-File Report
Series number 2015-1200
DOI 10.3133/ofr20151200
Year Published 2015
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Western Ecological Research Center
Description iv, 36 p.
Time Range Start 2013-06-14
Time Range End 2013-11-30
Country United States
State California
Other Geospatial Sacramento Valley
Online Only (Y/N) Y
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
Additional publication details