Degrees of residence of Guiana dolphins (Sotalia guianensis) in Ilha Grande Bay, south-eastern Brazil: a preliminary assessment

Abstract

Applying the photo-identification technique, we took pictures of dolphins' dorsal fins, looking for natural markings on them. A total of 17,969 photographs were taken, from which was created a databank of 462 distinct dolphins. Individuals showed different degrees of residency in the bay. More than 50% of the catalogued dolphins were considered non-residents and/or showed a low degree of residence. The average interval between resightings was 35 + 27.4 days. Animals without markings (calves and juveniles) accounted for 45% (N ¼ 2917) of photographs taken. These results indicate that this population has a fluid structure including different individuals over time. We suggest a possible relationship between the presence of some individuals and local resource availability, such as prey and protected areas.

Behavioral event occurrence differs between behavioral states in Sotalia guianensis (Cetarctiodactyla: Delphinidae) dolphins: a multivariate approach

“…Our sampling occurred in the western part of the bay, which includes shallow areas (<10 m) inhabited by a S. guianensis population (LODI 2003). Sotalia guianensis inhabits this part of the bay throughout the year, and 63.9% of the population presents some kind of residency (ESPÉCIE et al 2010). Groups include up to 18 individuals and may include offspring (TARDIN et al 2013a, b).…”

Sensitivity analysis of residency and site fidelity estimations to variations in sampling effort and individual catchability

“…Two main concerns relate to studies of residency and site fidelity: 1), no biases are accounted for sampling conditions, and 2), most studies use different definitions to assess 1 or both parameters. Methodological variations among studies are expected and this research provides alternatives to either assess the biases or standardize the results; however, there is a need to unify the criteria used for determination of residency for results to be directly comparable among studies (e.g., Möller et al, 2002;Fury and Harrison, 2008;Espécie et al, 2010). Therefore, we put forward 4 criteria to standardize residency determination: 1), individual recapture rates (r i ) must be higher than 25%; 2), Fisher's curve must be asymptotic for at least 10% of the study duration (e.g., Baker et al, 2006); 3), residency must be assessed over short periods, minimizing the possibilities of violating assumptions of closed and stable populations (e.g., migrations, seasonal and/or annual environmental oscillations), and 4), as most studies circumscribe their calculations in natural or arbitrary periods, the optimum number of residency categories (NRC) should be established empirically according to Balmer et al (2008):…”

Modelling habitat use by the Guiana dolphin, Sotalia guianensis, in south‐eastern Brazil: Effects of environmental and anthropogenic variables, and the adequacy of current management measures

“…Non‐systematic routes were followed at a mean velocity of 10 km/h from the port at Tarituba (Figure ). When dolphins were sighted, the boat's speed was reduced to approximately 5 km/h and focal group follows (Mann, ) were conducted at a minimum distance of 50 m according to the protocol of previous studies (Espécie, Tardin, & Simão, ; Tardin, Espécie, Lodi, & Simão, ). Point locations of the dolphin groups were recorded using a GARMIN VISTA CX GPS device.…”