Effect of habitat and seasonality on the densities of caiman in southern Pantanal, Brazil

Abstract

Studies of variation in the population densities of animals are of importance for at least two major reasons: (i) understanding the factors responsible for such variation contributes to general theory of population dynamics (Connell & Souza 1983, McArddle et al. 1990, Pimm & Redfearn 1988, Taylor 1961), and (ii) they provide basic data for management decisions relative to population exploitation or conservation (Caughley 1977, Clark 1976, May 1976). The yacare caiman (Caiman crocodilusyacare) was subject to illegal harvesting during the last three decades and was possibly the most exploited crocodilian in the world (Crawshaw 1987). More recently, legal exploitation of natural populations of yacare caimans has been permitted through a ranching system where eggs are collected in the wild and hatchlings are raised in captivity for commercial purposes. Another potential strategy for managing natural populations of caimans in the Pantanal is to establish a sustained yield-harvesting programme of larger caiman, which may be effective in promoting habitat conservation. However, in both cases accurate and precise methods to estimate populations size and/or trends are required to evaluate impacts (Webb & Smith 1987). Spotlight surveys have been widely used to monitor crocodilian populations and are precise and accurate in some habitats (Chabreck 1966, Glastra 1983). In the Pantanal, spotlight surveys have been of limited use because: (i) reaching remote areas by boat is logistically difficult; (ii) the wetlands are heavily vegetated such that crocodiles are difficult to see at night (Campos et al. 1995); and