Variation in Reproductive Output of the Red-crowned Roofed Turtle (Batagur kachuga) and the Three-striped Roofed Turtle (Batagur dhongoka) in the Chambal River of North India

Abstract

Abstract Characterizing variation in reproductive output is foundational to understanding the demography of a population and determining management strategies. Doing so is paramount when the species of interest is threatened with extinction. The red-crowned roofed turtle (Batagur kachuga) and the three-striped roofed turtle (Batagur dhongoka) are severely threatened by overharvesting and habitat loss. Despite their imperiled status, there are very few published studies on species ecology and life history to enable effective conservation; the 3 published studies that are available were completed nearly 3 decades ago. We herein provide information on variation in reproductive output for these turtles in the Chambal River of North India. Generalized linear models and analyses of variance were fitted to data on nesting density, fecundity, and egg volume. The number of nests showed an overall decline across 3 seasons (2007, 2008, and 2010) over a 4-yr duration with the highest number of nests observed in the middle of each nesting season. Peak nesting activity potentially occurs at lowest river depth or maximum availability of nesting habitat. The observed decline in the number of nests could be related to a decline in the nesting cohort or a geographic shift in suitable nesting habitat or changes in food resource availability and/or acquisition, leading to fewer females nesting. The number of nests in B. kachuga were significantly negatively correlated with total precipitation in the immediately preceding year. Presumably, total precipitation may affect the amount of nesting habitat available or availability of some other limiting resource. Reproductive output in both species varied as a function of fecundity rather than egg volume, implying that maturity occurs at larger body sizes for egg volume to be unconstrained, which would require relatively long generation times. Variation in clutch size could be tied to variable resource acquisition patterns, although total precipitation was not found to be an appropriate proxy. Potential variation in fecundity as a function of body size was not accounted for in the study. The study corroborated previous findings that B. kachuga lays larger and fewer eggs than B. dhongoka. These results contribute to understanding the life history of these poorly documented turtle species and toward informing conservation actions. Future studies over a larger spatial extent need to characterize nesting sites and nest-site fidelity and incorporate data from individual females.