Capture-recapture abundance estimate of Guiana dolphins in southeastern Brazil

Abstract

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.

Photo‐identification as a tool to study small‐spotted catshark Scyliorhinus canicula

“…To manage elasmobranch species sustainably and design efficient conservation programmes, accurate information on the population dynamics of these marine predators is necessary. The first step to estimate the population size, and thus understand the population dynamics of a particular species, is to identify the different individuals of a population (Bradshaw et al, 2007;Freitas-Nery, 2012). Marine biologists use a great variety of methods for marking and identification purposes, from simple and passive methods, such as external tags, to active methods like electronic tags (Hammerschlag et al, 2011).…”

Short Note: Performance of Computer-Assisted Photographic Matching of Guiana Dolphins (Sotalia guianensis)

“…We performed boat-based surveys between August 2005 and December 2011 in Sepetiba Bay, southeastern Brazil, where one of the largest populations of Guiana dolphins, estimated to be thousands of individuals (Flach et al, 2008a;Nery & Simão, 2012), is found. Sighted groups of dolphins were slowly approached and followed, while an attempt was made to take pictures of all group members, with no preference, using a digital SLR camera Canon 40D equipped with a 100 to 400 mm lens (Flach, 2006).…”

20 years of research on the Guiana dolphin population of Sepetiba Bay, southeastern Brazil: What has changed?

“…While the changes observed in the Guiana dolphins of Sepetiba Bay are associated with human‐induced rapid environmental change, it is important to note that possible demographic changes caused by the morbillivirus outbreak, as well as the differences between the time series in sampling effort, may have had a major influence on the results of the present study. Abundance estimates from 2002 to 2006, when Sepetiba Bay was considered to be a closed population, indicate that the bay was inhabited by 1000–1269 individuals (Flach, Flach & Chiarello, 2008; Nery & Simão, 2012). In a subsequent estimate, in 2012, also considering it a closed population, Flach (2015) reported a population of between 588 and 1004 individuals.…”

“…The population also had a large proportion of groups with calves, which used the bay primarily to breed and feed (e.g. Erber & Simão, 2004; Flach, Flach & Chiarello, 2008; Nery & Simão, 2012; Oliveira et al, 2013).…”