Survival and Causes of Mortality of Head‐Started Western Pond Turtles on Pierce National Wildlife Refuge, Washington

Abstract

The western pond turtle (Actinemys marmorata) is a species of conservation concern over much of its range and is listed as endangered in Washington State. From 2000 to 2004, we used radiotelemetry to document survival and mortality factors of head‐started western pond turtles (n = 68) released into Pierce National Wildlife Refuge in southwestern Washington. Survival estimates for first year and older turtles ranged from 86% to 97% and overlapping confidence intervals indicated no detectible differences among age classes or among years. Subadult turtles released at ≥90‐mm carapace length apparently avoided capture by most aquatic predators, indicating that terrestrial predators should be the focus of research and management where predation on larger age‐classes is a concern. High annual survival combined with the documented nesting by ≥7‐year‐old female head‐started turtles in Washington suggest that recruitment of adults is being achieved; however, head‐starting is only practical as an interim solution and strategies for effective removal of aquatic predators must be developed and implemented where natural recruitment is inadequate to maintain populations.

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 ).…”

Post-Emergence Behavior of Hatchling Western Pond Turtles (Actinemys marmorata) in Western Oregon

“…We hypothesize that delayed emergence in western pond turtles is a response to unfavorable environmental conditions that also influence overwinter behavior by adults. Remaining in the nest from fall to spring largely coincides with the temporal pattern of overwintering for most of the adult populations in the central to northern portion of their range (Holland, 1994;Reese and Welsh, 1997;Vander Haegen et al, 2009), suggesting that hatchlings emerging in the fall would often be selected against.…”

A question of scale: Replication and the effective evaluation of conservation interventions

“…Elasticity analyses of population models show that adult female survivorship has the highest impact on population growth rates, and several authors have interpreted these results to mean that efforts to increase juvenile recruitment are better spent on protecting adults (Congdon et al 1993;Heppell et al 1996;Heppell 1998;Mitrus 2005;Enneson and Litzgus 2008). These criticisms tend to focus on headstarting in isolation, without consideration for concurrent mitigation of the initial causes of population declines (Dodd and Seigel 1991;Frazer 1992;Heppell 1998;Meylan and Ehrenfeld 2000;Vander Haegen et al 2009;Smeenk 2010;Crawford et al 2014). Models incorporating multiple conservation actions may be more realistic and may lead to more successful management plans for threatened populations.…”

“…As with other types of intervention, definitions of success vary considerably among headstarting projects, though they are largely segregated into the attainment of either short-or long-term goals (Bell et al 2005), reproducing (Vander Haegen et al 2009), and apparently altering the age structure of a population (Spinks et al 2003). Details of rearing techniques may not be described in the literature (e.g., Haskell et al 1996;Mogollones et al 2010;Bona et al 2012), and few studies explicitly compare success of headstarted individuals to wild individuals (but see Spinks et al 2003;Mitrus 2005).…”