Revealing capture sites and movements by strontium isotope analyses in bones of Caiman yacare in the Beni river floodplain, Bolivia

Abstract

Studying the distribution of organisms and their movements is fundamental to understand population dynamics. Most studies indicated that crocodilians do not move around much but several studies demonstrated that some species showed movement patterns. Detection of these movements along the individual life is still a challenge. In this study we analyzed the variation of strontium isotopic ratio (87Sr/86Sr) in the femur bones of 70 Caimanya care individuals caught in 16 sites located in five hydrological sectors of the Beni river floodplain in Bolivia. Our results demonstrated for the first time that such a methodology could yield indications about the capture sites and reconstruct individual life history. Analyses of the outer part of the femur of 70 individuals showed that capture sites could be differentiated between sectors and even between sites or groups of sites in each sector. Studies of complete 87Sr/86Sr profiles along the femur, representing the individuals entire life, were performed on 33 yacares. We found that most of the individuals did not show any significant isotopic variation throughout their lives. This absence of variation could result from a high fidelity to the birth site, and/or from an insignificant isotopic variation between the water bodies through which the animal has potentially moved. However, 24% of the analyzed individuals presented significant variations that can be considered as movements between different habitats. Based on the observed low proportion of moving yacares, we advocated that each water body should be considered an individual management unit.