Estimating factors influencing the detection probability of semiaquatic freshwater snails using quadrat survey methods

Hydrobiologia
By:  and 

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Abstract

Developing effective monitoring methods for elusive, rare, or patchily distributed species requires extra considerations, such as imperfect detection. Although detection is frequently modeled, the opportunity to assess it empirically is rare, particularly for imperiled species. We used Pecos assiminea (Assiminea pecos), an endangered semiaquatic snail, as a case study to test detection and accuracy issues surrounding quadrat searches. Quadrats (9 × 20 cm; n = 12) were placed in suitable Pecos assiminea habitat and randomly assigned a treatment, defined as the number of empty snail shells (0, 3, 6, or 9). Ten observers rotated through each quadrat, conducting 5-min visual searches for shells. The probability of detecting a shell when present was 67.4 ± 3.0%, but it decreased with the increasing litter depth and fewer number of shells present. The mean (± SE) observer accuracy was 25.5 ± 4.3%. Accuracy was positively correlated to the number of shells in the quadrat and negatively correlated to the number of times a quadrat was searched. The results indicate quadrat surveys likely underrepresent true abundance, but accurately determine the presence or absence. Understanding detection and accuracy of elusive, rare, or imperiled species improves density estimates and aids in monitoring and conservation efforts.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Estimating factors influencing the detection probability of semiaquatic freshwater snails using quadrat survey methods
Series title Hydrobiologia
DOI 10.1007/s10750-017-3415-9
Volume 808
Issue 1
Year Published 2018
Language English
Publisher Springer
Contributing office(s) Coop Res Unit Atlanta
Description 9 p.
First page 153
Last page 161