Post‐release movement and survivorship of head‐started gopher tortoises

Abstract

Gopher tortoise (Gopherus polyphemus) populations are declining throughout their range and recovery requires management intervention to alleviate losses. Population augmentation strategies may prove useful in recovery of depleted populations once threats are mitigated. We head‐started and soft‐released hatchlings produced from robust donor populations and evaluated their post‐release survivorship and movement for the first year following their release. During 2014 and 2015, we head‐started and released 145 tortoises, of which we radio‐tracked a subset of 41 individuals, from 2 cohorts at 2 release areas within Yuchi Wildlife Management Area in Burke County, Georgia, USA. Movement and mortality of gopher tortoises was highest in the first month after release but declined soon after. Estimated annual survivorship of our first cohort was 60.6%. Annual survivorship of our second cohort was low (7.1%) at the southeast release area but much higher (75.0%) at the northwest release area because of spatial variation in predation. Although survivorship was variable, site fidelity remained high throughout the study and no tortoise moved >122.0 m from its release location. Initial results suggest that head‐starting could prove effective as a population recovery tool, but that release strategy and predator mitigation, especially within the first month, are critical to success. © 2018 The Wildlife Society.

Benefits of Head‐starting for Blanding's Turtle Size Distributions and Recruitment

“…Head‐starting has been used extensively to augment existing populations and re‐establish extirpated populations of turtles more generally (Burke and citations therein, Caillouet et al , Peñaloza et al , Shaver and Caillouet , Tuberville et al , Jensen et al ). Although outcomes have been less widely monitored and reported than desirable (Burke ), case studies demonstrating growth and survival of head‐starts (Vander Haegen et al , Masin et al , Michell and Michell , Tuberville et al , Quinn et al ), recruitment of reproductive adults (Vander Haegen et al , Masin et al , Shaver and Caillouet ), and shifts in size distribution (Peñaloza et al ) similar to what we report for Blanding's turtles are accumulating. Future refinements to the use of head‐starting will benefit from studies of phenotypic effects of head‐starting (Geist et al ), disease status of head‐starts (Smith ), behavior following release (Hazard et al ), and genetic consequences of head‐starting (Dresser et al , Jensen et al ).…”

Behavior, growth, and survivorship of laboratory-reared juvenile gopher tortoises following hard release

“…Minimum survivorship of hard-released yearlings documented here appears on par with that of younger, albeit larger, individuals soft-released in other investigations (Tuberville et al 2015, Quinn et al 2018). Tuberville et al (2015) documented 0.35 minimum first-year survivorship and 0.88 minimum secondyear survival for gopher tortoises soft-released at 6-9 mo of age, and Wilson (1991) documented annual survival of about 0.45 for small wild juveniles (age = 1-4 yr).…”

“…The gopher tortoise Gopherus polyphemus is a threatened herbivore of the southeastern USA (McCoy et al 2006, Smith et al 2006, USFWS et al 2013) that relies on self-constructed burrows for predator avoidance and thermoregulation (Douglass & Layne 1978, Pike & Grosse 2006. In addition to conserving and restoring semi-open upland habitats, such as longleaf pine Pinus palustris savannas (Diemer 1986, Smith et al 2006, USFWS et al 2013, biologists across multiple states (Mississippi, Georgia, South Carolina, Florida) are investigating the management value of head-starting, a process whereby hatchlings are reared in captivity and released after having grown to larger sizes at which they are presumably less vulnerable to predators (Tuberville et al 2015, Quinn et al 2018. Release methods for juvenile gopher tortoises, either animals raised in captivity for head-starting or laboratory research, include 'soft release,' where individuals are provided starter burrows and/or penned to limit movements and interactions with predators, or 'hard release,' where tortoises are simply released without additional measures (Holbrook et al 2015, Tuberville et al 2015, Quinn et al 2018.…”

“…Hard release requires minimal resources and could facilitate novel ecological research, but its efficacy remains unclear with gopher tortoises. In a preliminary study, Quinn (2016) hard-released 10 captive-reared yearling gopher tortoises and found that 8 survived at least 2 mo, a promising result, as small wild juveniles experience intense predation pressure (Wilson 1991), and mortality can be high following soft release (Holbrook et al 2015, Tuberville et al 2015, Quinn et al 2018.…”

Translocation for conservation: Neonates are less suitable than adults

“…However, head‐starting projects may be a more viable option for reducing juvenile mortality and increasing success of potential translocations. Head‐starting has proven effective in reptile species such as the tuatara ( Sphenodon punctatus ; Nelson et al 2002; Jarvie et al 2015) and gopher tortoise, ( Gopherus polyphemus ; Quinn et al 2018). However, there are monetary costs involved in captive husbandry and risks of habituation to captivity the longer individuals are raised in captivity (Seddon et al 2007).…”