Size Matters: the Influence of Trap and Mesh Size on Turtle Captures

Abstract

Methods used in wildlife ecology can influence population‐ and community‐level estimates, such as species richness, sex ratio, age and size structure, occupancy and detection probabilities, and community composition. Various trapping and sampling biases exist for freshwater turtles including bait and trap choice and survey technique. To date, no study has investigated the influence of hoop net and mesh size on various population‐ and community‐level estimates. Here, we use detection models to determine if trap and mesh size influence detection probability of nine species of freshwater turtles over 3 consecutive years (2016–2018) in west Tennessee. Additionally, we use multivariate models to determine if freshwater turtle community composition was influenced by hoop trap and mesh sizes. Our results indicated that there was a bias related to mesh size in detection probabilities and community composition. Smaller mesh sized traps were better at detecting smaller‐bodied turtle species, which then changed community species richness but not catch‐per‐unit‐effort estimates (i.e., abundance). Additionally, larger mesh sized traps were better at detecting common snapping turtles (Chelydra serpentina), which supports previous research. Our results suggest that researchers should account for the variation in detection probabilities by mesh size when conducting mark‐recapture and occupancy analyses. Moreover, erroneous inferences about population trends and changes in diversity within turtle communities through time could cause managers to misidentify population declines and conservation value of a site. © 2021 The Wildlife Society.

Should landscape variation in population status be assessed with individual‐ or population‐level indicators?

“…To evaluate abundance and occupancy, we modeled all species using a multi‐species N‐mixture and occupancy framework while accounting for imperfect detection (Kéry and Royle 2015, Ennen et al 2021, Gould and Peterman 2021). Despite recent concerns on the reliability of N‐mixture models (Barker et al 2018, Link et al 2018), evidence suggests that for small vertebrate species they remain a useful analytical tool for estimating relative abundance (Ficetola et al 2018, Costa et al 2019, Costa et al 2020).…”

Big Turtles Start Small: Trapping Juvenile Alligator Snapping Turtles in South Mississippi and Implications for Conservation

“…While there have been many surveys for alligator snapping turtles across their range (Baxley et al 2014, Bluett et al 2011, Boundy and Kennedy 2006, Folt et al 2016, Huntzinger et al 2019, Jensen and Birkhead 2003, Riedle et al 2005, Shipman and Riedle 2008), most surveys involved the use of large, baited hoopnets (>1 m in diameter), with only 1 study incorporating the use of slightly smaller hoops for capturing M. suwanniensis (60 cm diameter; Johnston et al 2015). Indeed, large hoopnets with large mesh sizes seem to be more adept at catching snapping turtle (Chelydridae) species (Ennen et al 2021, Gulette et al 2019). However, large traps preclude the capture of smaller turtles, or at least allow smaller turtles to enter and exit the trap without being detected (Gulette et al 2019).…”

Effects of hoop-net mouth opening on capture success of Rio Grande Cooters (<i>Pseudemys gorzugi</i>)

“…F or decades, the use of conventional hoop-net traps has been considered one of the most effective means of sampling aquatic turtles because they are lightweight, easy to move, and relatively easy to hide (Lagler 1943;Mali et al 2013Mali et al , 2014Gulette et al 2019). Factors such as bait type, trap mouth and mesh size, trapping duration, and trap placement can influence capture rates and estimates of community and population compositions and abundance (Mali et al 2014;Ennen et al 2021). Attraction of turtles to baited hoop-nets can differ by species, individual size, sex, behavior, previous capture history, individual bait preferences, and habitat characteristics (Mali et al 2012;Mali et al 2014;Gulette et al 2019).…”