No abstract

ABSTRACT. The resident population of estuarine dolphin, Sotalia guianensis (P.J. van Bénéden, 1864), in Norte Bay, Santa Catarina, southern Brazil, was studied from 2000 to 2003. Systematic one-day cruises were undertaken aboard a 5 m sail boat equipped with an outboard motor. Applying the focal-group method, information such as geographical position, predominant behavioural patterns, group size, cohesion index and the presence of calves, were registered at every five-minute interval, totalling 198 hours of direct observation of the dolphins. The estuarine dolphin used preferential areas for each behavioural pattern. The mean group size was approximately 29 individuals, and the presence of calves occurred throughout the entire year, but with a significant increase in the warm seasons. The frequency of behavioural patterns and group size varied according to season and time of day, and were strongly associated. The frequency of moving behaviours increased in the cold seasons and along the day. The seasonal variation in the moving behaviours suggest the requirement of a larger area in the cold seasons, probably related to seasonal fluctuations in the abundance of dominant prey items. Higher group sizes were observed while dolphins were foraging. The cohesion index also varied according to the behaviour. Our results showed that group organization and behavioural patterns of this estuarine dolphin population are probably linked to daily and seasonal environment cycles, and also possibly to the condition of being at the furthest southern limit of distribution of the species.

This study represents the first attempt to study the population dynamics of Guiana dolphins (Sotalia guianensis), by evaluating a set of demographic parameters. The population of the Caravelas River estuary, eastern Brazil, was systematically monitored through a long-term mark-recapture experiment (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009). Abundance estimates revealed a small population (57-124 dolphins), comprised of resident dolphins and individuals that temporarily leave or pass through the study area. Temporary emigration from the estuary to adjacencies (␥ = 0.33 ± 0.07 SE) and return rate (1 − ␥ = 0 .67) were moderate and constant, indicating that some dolphins use larger areas. Survival rate ( = 0.88 ± 0.07 SE) and abundance were constant throughout the study period. Power analysis showed that the current monitoring effort has high probability of detecting abrupt population declines (1 − ␤ = 0.9). Although the monitoring is not yet sensitive to subtle population trends, sufficient time to identify them is feasible (additional 3 yr). Despite such apparent stability, this population, as many others, inhabits waters exposed to multiple human-related threats. Open and closed population modeling applied to photo-identification data provide a robust baseline for estimating several demographic parameters and can be applied to other populations to allow further comparisons. Such synergistic efforts will allow a reliable definition of conservation status of this species.

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.

No abstract

Table of Contents Supplement 1 Stratification by geographic regions Supplement 2 Detection curves for each year Supplement 3 Model building and selection procedure Supplement 4 Growth rate by geographic strata Supplement 5 Review of documents reporting the population growth rates for humpback whales Supplement 6 Explanatory variables used in the meta-analysis Literature cited in the supplementary material

Site fidelity and movements were studied for humpback whales photo‐identified from 1989 to 2006 in the Abrolhos Bank, southwestern Atlantic, Brazil. A total of 2,612 individuals were identified, 374 of which were observed on more than one occasion. The cumulative number of identified whales has increased since 1989. Recapture rate was low and varied among different years. A total of 33 whales was observed using the Abrolhos Bank for longer than 10 yr, up to a maximum of 16 yr. Our data suggest that different whales show distinct movement rates. Some whales used a large extent of the Abrolhos Bank region. Opportunistic photo‐identification data (on the scale of the Brazilian coast from 4° to 23°S) revealed important information about stock identity. The longest distance between within‐season resightings was over 600 km, while one whale was observed in two locations separated by more than 1,400 km in different years. Long‐range movements within and between seasons support the single stock hypothesis for humpback whales wintering off the Brazilian coast.

For the first time we report on an aggressive interaction between wild bottlenose dolphins (Tursiops truncatus) and estuarine dolphins (Sotalia guianensis) observed in Baía Norte, southern Brazil. Three bottlenose dolphins aggressively herded a Sotalia guianensis calf, which was the main target of the aggressive and threatening behaviours of the bottlenose dolphins. Another two to four adult S. guianensis were involved in the interaction and were constantly chased by the bottlenose dolphins. After approximately two hours, the bottlenose dolphins left the calf and the area, and no dead or wounded animals were seen afterwards. We provide a detailed spatial and temporal description of the interaction, and discuss the potential causes of this event.