Abstract
The objective of this study was to estimate the abundance of Sotalia guianensis in Sepetiba Bay, southeastern Brazil, based on photographic identification of animals. Estimates of population size were obtained using capture-recapture models for a closed population. Photo-identification data were analyzed using a model-fitting approach in the computer programs CAPTURE and MARK, and the Schnabel and Schumacher-Eschmeyer estimators were used to calculate the abundance of individuals with natural marks. These estimates were corrected to include unmarked individuals using data of the proportion of identifiable individuals in this population. During the surveys conducted between April 2006 and April 2007, a total of 9990 photographs of dolphins were taken and, of these, 2567 images were of sufficient quality for analysis; 382 dolphins were identified and catalogued from distinctive nicks and notches on their dorsal fins and, among them, 153 dolphins were photographed on more than one occasion. The resulting abundance estimates, corrected to account for the proportion (0.47) of unmarked dolphins in the population, showed an overlap among estimators ranging from 1004 to 1099 individuals. This is the largest estimated abundance for a population of S. guianensis reported to date using the capture-recapture technique.
Highlights
The Guiana dolphin (Sotalia guianensis) is a small dolphin that inhabits estuarine and bay areas along the Atlantic coast of Central and South America (Silva and Best 1994, Flores 2002)
En Brasil hay pocas estimaciones de abundancia de S. guianensis con métodos de captura-recaptura (Pizzorno 1999, Santos y Zerbini 2006) y técnicas de muestreo a distancia (Cremer et al 2006, Flach et al 2008a)
The population of Guiana dolphin in Sepetiba Bay occurs in large groups
Summary
The Guiana dolphin (Sotalia guianensis) is a small dolphin that inhabits estuarine and bay areas along the Atlantic coast of Central and South America (Silva and Best 1994, Flores 2002). Considering its relatively wide range, little information concerning the population ecology of this species is available. It is classified as an inadequately known species by the International Union for Conservation of Nature (IUCN) (Secchi 2010), and is considered a threatened species in Brazil (Machado et al 2005). El delfín Guiana (Sotalia guianensis) es un pequeño delfín que habita estuarios y bahías a lo largo de la costa del Atlántico de Suramérica y América Central (Silva y Best 1994, Flores 2002). Trabajos anteriores encontraron que la bahía de Sepetiba, en la costa sureste de Brasil, abriga una población
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