Sampling rare and elusive species: Florida east coast diamondback terrapin population abundance

Abstract

The Florida east coast terrapin (Malaclemys terrapin tequesta) is a rare and potentially endangered species that is difficult to survey because of poor detection probability and a patchy distribution. Like many rare species sampling programs, we apply a density and multistate occupancy sampling approach that considered the impacts of imperfect detection. We separated the detection process into availability of the animal within the sampling area (e.g., coming to surface) and perceptibility (actually seeing it). Our study employed a density estimation approach originally developed for birds, which combined time to detection and distance sampling within a Bayesian N-mixture model. Our study also estimated two abundance occupancy states (few and many terrapins). We were able to estimate large differences in terrapin densities between sites through functions of site-specific environmental covariates (water depth, distance to mangrove, and distance to land). The detection probability was poor (0.28) for the few terrapin occupancy state, but was much greater for many (0.75). The time to detection and distance-sampling approach for this aquatic animal should be useful for other aquatic organisms that regularly surface. Terrapins were generally available to be sighted within four minutes but detection declined rapidly to a low probability of terrapin detection >30 m. The approach of estimating density as a function of habitat covariates to identify habitat associations can provide an effective method that combined with adaptive sampling should be useful to investigate the distribution of terrapins in open water.

Amazonian run‐of‐river dam reservoir impacts underestimated: Evidence from a before–after control–impact study of freshwater turtle nesting areas

“…Although still incipient, studies show that boat surveys can be used to monitor freshwater turtle abundances at a local scale (e.g. 6 km surrounding islands in Florida: Breininger et al, 2019) and more widely (e.g. P. unifilis populations along > 50 km of rivers in Bolivia: Coway‐Gómez, 2007; Yapu‐Alcázar et al, 2018; and Peru: Norris et al, 2011; Pitman et al, 2011).…”

Amazonian run-of-river dam reservoir impacts underestimated: Evidence from a Before-After Control-Impact study of freshwater turtle nesting areas

“…Although still incipient, studies show that boat surveys can be used to monitor freshwater turtle abundances at a local scale [e.g. 6 km surrounding islands in Florida (Breininger et al, 2019)] and more widely [e.g. P. unifilis populations along > 50 km of rivers in Bolivia (Coway-Gomez, 2007;Yapu-Alcázar et al, 2018) and Peru (Norris et al, 2011;Pitman et al, 2011)].…”

An easily implemented single‐visit survey method for intermittently available and imperfectly detectable wildlife applied to the Florida east coast diamondback terrapin (Malaclemys terrapin tequesta)

“…The number of individuals at sample plots ( s ) were generated as random draws from a Poisson distribution with the mean selected from (0.5, 1, 2) based on densities observed in a previous study (Breininger et al, 2019). The availability of individuals p a was constant for all individuals during each replicate count period and was chosen from (0.2, 0.4, 0.6, 0.8).…”