J. Mar. Biol. Ass. U.K. (2007), 87, 207–212 Printed in the United Kingdom Journal of the Marine Biological Association of the United Kingdom (2007) doi: 10.1017/S0025315407055683 Residence and site fidelity of Sotalia guianensis in the Caravelas River Estuary, eastern Brazil Between April 2002 and April 2005, 210 estuarine dolphin groups were sighted, with 58 animals individually identified. Fifteen dolphins were photo-identified just once, while only two animals were sighted in 15 different months. Some individuals showed long-term residence (more than 3 y). Residence rates showed heterogeneity in the dolphin’s permanence of the estuary, with 60% of the individuals with low numbers (<10) and only 7% showing high values for residence (maximum=45.9). Continued resightings of some dolphins support the regular use of the study area by the animals, despite some individuals that, after a long time without resightings were registered again. Individual range analysis showed that dolphins shared the same common area, the Caravelas River Estuary. A marked fluctuation in the number of photo-identified dolphins was observed in the study area, revealed by the high number of individuals with just a few resightings. The majority of the dolphins (60%) present a yearly residence pattern, as observed in other areas, suggesting that a few individuals show high fidelity for the area, while many other dolphins move constantly between different areas for unknown reasons. INTRODUCTION The term ‘residence’ may be interpreted as the time spent by an animal in a certain geographical area (Wells & Scott, 1990; Wells, 1991); however, the term has been employed by researchers in different ways according to the parameters used to measure the residence of individually identified dolphins (Wells & Scott, 1990; Ballance, 1992; Simões-Lopes & Fabián, 1999; Hardt, 2005). Site fidelity is defined as the tendency of an animal to occupy an area or to return to a previously occupied area over some period of time (White & Garrot, 1990). The estuarine dolphin (Sotalia guianensis) was recently separated from the tucuxi dolphin (Sotalia fluviatilis) based on cranial characteristics (Monteiro-Filho et al., 2002) and genetic divergence (Cunha et al., 2005; Caballero et al., in press). The species inhabits coastal and shallow waters of South and Central America, from southern Brazil to Honduras (Silva & Best, 1996). Along its coastal habitats, the species is subject to a variety of human activities that threaten its conservation, such as fishing operations, boat traffic and habitat destruction (Reeves et al., 2003; Lodi, 2003). According to the IUCN, however, the species is classified as Data Deficient (Reeves et al., 2003) which reinforces the importance of conducting long-term studies about their ecology, such as residence patterns. In the Caravelas River Estuary, S. guianensis has been studied since 2002 by the Humpback Whale Institute, that develops research and conservation activities in the region. It has been demonstrated that estuarine dolphins are present all year round, in mean groups of 3–4 individuals, mainly engaged in foraging behaviour in the river mouth of the estuary (Rossi-Santos et al., 2003; Rossi-Santos, 2006). Some studies used photo-identification to study diverse aspects of the biology of S. guianensis, such as abundance (Pizzorno, 1999), residence and site fidelity (Flores, 1999; Link, 2000; Simão et al., 2000; Santos et al., 2001; Hardt, 2005), individual home-range (Flores & Bazzalo, 2004; Hardt, 2005), population structure (De Oliveira, 2006), individual behaviour (De Jesus, 2004), and others. The majority of these studies were concentrated in the southern and south-eastern Brazilian coast, with few studies developed in the eastern and north-eastern coast of Brazil. The few exceptions include the studies developed at Pipa Beach, Rio Grande do Norte State, where at least 34 estuarine dolphins were identified (Link, 2000; De Jesus, 2004). The present study aims to describe residence and site fidelity patterns of individually-identified estuarine dolphins in the Caravelas River Estuary and adjacent waters, eastern coast of Brazil. MATERIALS AND METHODS Study area The study area included the Caravelas River Estuary (17°30'S–39°30'W) (Figure 1) and the coastal adjacent areas which are influenced by an estuarine-mangrove system, the second largest of the north-eastern coast of Brazil (Herz, 1991). This area is an extension of the Brazilian continental shelf, presenting warm and shallow waters, where a great Marcos R. Rossi-Santos* †∫ , Leonardo L. Wedekin* † and Emygdio L.A. Monteiro-Filho †‡ *Instituto Baleia Jubarte, Rua Barão do Rio Branco, 26, Caravelas-Bahia, Brazil, 45900-000. † Pós-Graduação em Zoologia, Universidade Federal do Paraná, Centro Politécnico, Curitiba–Paraná, Brazil. ‡ Instituto de Pesquisas Cananéia, Rua Tristão Lobo, 199. Centro, Cananéia–São Paulo, Brazil, CEP: 11990-000. ∫ Corresponding author, e-mail: marcos.rossi@baleiajubarte.com.br