Temporal changes in an alligator snapping turtle (Macrochelys temminckii) population

Abstract

Context Monitoring populations of long-lived species requires continuous long-term efforts. This is especially applicable for species that have experienced declines range-wide. Aims Our study assessed the current status of a population of wild Macrochelys temminckii and compared the present results to those from a survey conducted nearly a decade ago. Methods Trapping in 2010–2011 was conducted on two creeks within the refuge, during the months of May–July. Capture data were compared with data collected by similar methods in 1997–2001. Key results The population structure of M. temminckii was dominated by juveniles, with few large adults or small juveniles detected and a missing size class was evident. Retrospective analysis of 1997–2001 data revealed that the population was likely to be in decline even then, despite high capture rates. Conclusions The M. temminckii population showed significant declines that indicated that the population had experienced stressors of unknown origin. The status of M. temminckii at the refuge is concerning, given the protection afforded this remnant population. Implications Short-term data from 1997–2001 indicated a healthy M. temminckii population, whereas longer-term data showed that the population has declined, resulting in significant demographic changes. Continued monitoring will be necessary to develop management recommendations and track the impact of implemented management practices. Longer-term monitoring of long-lived vertebrates is required to identify population trends.

Population Structure and Body Size of the Suwannee Alligator Snapping Turtle (Macrochelys suwanniensis) in Northern Florida

“…The number of adults in a heavily harvested population in Louisiana was 1.1 times the number of juveniles (Boundy and Kennedy 2006). Adults in Arkansas populations (0.72:1-1.2:1; Trauth et al 1998;Howey and Dinkelacker 2013) and in an Oklahoma population (0.42:1-0.97:1; Riedle et al 2008;East et al 2013) were approximately equal to or lower than the number of juveniles. Adults in a Missouri population significantly decreased between 1993-1994 (5.2:1) and 2009 (1.2:1; Lescher et al 2013).…”

Establishing Reference Demography for Conservation: A Case Study ofMacrochelys temminckiiin Spring Creek, Georgia

“…Because adults typically comprise 70% of freshwater turtle population structure (Bury 1979), and because other studies of Macrochelys have found juvenile-dominated structure, biased sex ratios, or both, we tested whether the observed ratios of adults:juveniles and males:females deviated from 1:1 with Pearson's chi-square (v 2 ) tests. Because a population of M. temminckii experienced a shift in population structure that was consistent with a population decline over a comparable time period as our study (East et al 2013), we tested for changes in size of adult males and adult females in Spring Creek across the study period using linear regression. For these analyses, we evaluated statistical significance with alpha set at 0.05.…”

“…Mark-recapture studies permitting estimation of demographic parameters for M. temminckii have been performed at two other sites: a 2-yr study at East Fork Cadron Creek, Arkansas (hereafter, the Arkansas population, Howey et al 2013) and a 14-yr study at Sequoyah National Wildlife Refuge, Oklahoma (hereafter, the Oklahoma population; East et al 2013). To understand the comparative viability, population structure, and extinction probability of the population in Spring Creek relative to the two western populations, we input estimates of juvenile and adult female survival (phi) and population structure from the Arkansas and Oklahoma populations into the population transition model from Spring Creek and measured k, stable population structure, and generation time for the Arkansas and Oklahoma populations.…”

“…We parameterized juvenile and female survival as 0.80 (0.40-0.96 95% confidence interval [CI]) and 0.88 (0.42-0.99), respectively, for the Arkansas population (Howey and Dinkelacker 2013) and as 0.46 (0.11-1.00) and 0.31 (0.05-0.78), respectively, for the Oklahoma population (East et al 2013). Abundance of juveniles and adult females for each population were input as initial values-for Spring Creek, we input an average of the two population estimates from our results section, assuming a 1:1 juvenile sex ratio; for Arkansas, we used the total population estimate and observed juvenile:adult and female:male ratios to estimate the starting population size (90 juveniles, 90 females; Howey and Dinkelacker 2013); and for the Oklahoma population, we used the population estimates for 1997-2001 by East et al (2013;31 juveniles, 31 females), assuming a 1:1 sex ratio of juveniles and adults. In the absence of data for the hatchling stages, abundance of the hatchling age class was set at zero for the initial population size of each matrix.…”

“…In the Flint River, Georgia, a river exploited by commercial collectors at an estimated rate of 3-4 tons of live turtles per day in the early 1970s (Pritchard 1989), capture rates of M. temminckii were among the lowest anywhere in the state, suggesting that historic commercial collection heavily depleted the population (Jensen and Birkhead 2003). In general, populations appear to be declining in many areas, and the distribution of M. temminckii appears to be shrinking in the northern and western extent of its range, such as in Missouri (Lescher et al 2013), Oklahoma (Riedle et al 2005;East et al 2013), Kentucky (Baxley et al 2014), and Illinois (Bluett et al 2011 A challenge with previous studies is that marked Macrochelys are rarely recaptured during subsequent sampling efforts. Mark-recapture data from repeated observations of individuals through time can inform models that account for imperfect detection (Lebreton et al 1992;Mazerolle et al 2007) and estimate vital rates of populations (e.g., survival, abundance, population structure) and individuals (e.g., growth).…”