Population Dynamics of the Florida Softshell Turtle (Apalone ferox) in a Protected Spring Ecosystem

The Florida softshell turtle, Apalone ferox, is considered common and found in many different types of freshwater habitats throughout its range. However, despite its prevalence where it occurs, little is understood about the species' life history and population dynamics due to difficulties with capture and long-term marking. Building on a foundational study of the Florida softshell turtle at Wekiwa Springs State Park (WSSP) from 2007 to 2012, we present findings from an extended 16-year mark-recapture study spanning from 2007 to 2023. A total of 31 sampling events were conducted with a median of two capture events per year. Sampling events were spread over a median of 5 days each year (range, 2-11 days), with a total of 88 capture days. One hundred and twenty individual A. ferox were captured over 225 encounters. We estimated an average population size of 135.6 individuals using an annual Schumacher-Eschmeyer ratio estimator. Using a state-space Jolly-Seber model, we estimated that 204 individuals entered the population over the 16 years (the superpopulation), while the average current population size was 40 individuals. The median survival probability was 0.884 but the median detection probability was 0.10, reinforcing the perceived difficulty with capturing A. ferox. The continued influx of new juveniles, recapture of these individuals as adults, and strong female bias support the possibility that the WSSP and Rock Springs greater ecosystem functions as a potential nursery habitat for the Florida softshell. Though population estimates dropped 20% following a two-year sampling gap owing to the COVID-19 pandemic, the population is currently growing slowly and highlights the value of continued, long-term monitoring of elusive freshwater turtle species.