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Some dolphin species produce signature whistles, which may allow the identification of individual dolphins using passive acoustic monitoring (PAM). Identifying individuals by their sounds may enhance the opportunities for monitoring and addressing biological and ecological questions about these species. Here, we explored the potential of signature whistles to investigate ecological aspects of a resident bottlenose dolphin population. Using a limited data set, with few individuals recognized by signature whistles, combined with spatial capture‐recapture (SCR) methods, we investigated how effective such approach is describing spatial use patterns and estimating density for this population. The data were collected using 4–6 stationary bottom‐moored recorders. Since only eight signature whistles were identified, our density estimate may represent a subset of the entire population. However, even with only a few signature whistles identified, our results confirmed the center of the core area used by these dolphins as the area with the highest encounter probability. In addition, our results provided evidence that these dolphins have the same spatial use pattern at night as during the day. This study shows that SCR analysis of signature whistle data can improve our ecological knowledge and understanding of dolphin populations. [ABSTRACT FROM AUTHOR]

The small population paradigm assumes that populations with low numbers of individuals intrinsically have a high probability of extinction. The small population of Lahille's bottlenose dolphins Tursiops truncatusgephyreus that specializes in foraging with artisanal fishers in Laguna, southern Brazil, faces human pressures including bycatch in fishing gear. The viability of this population was modelled over 30 and 100 years under different levels of bycatch, including the current scenario of two bycatches every year, two scenarios with higher incidence of bycatches and three management scenarios. The sensitivity of predicted growth rates to fixed‐proportion and observed‐variation changes in life history parameters was explored.The current scenario predicted a declining population (r = −0.014; λ = 0.986) with a high probability of extinction in the long term (PE = 0.71). A small increase in bycatches would result in a marked increase in the probability of extinction. Management scenarios seem promising, but only the zero‐bycatch management scenario would make the difference between a declining and an increasing population.As expected for slow‐growing species, population growth rate was most sensitive to proportional changes in adult female and juvenile survival. However, considering observed variation in vital rates, population dynamics were most influenced by variation in reproductive rates.To determine the highest priority for management action, another simulation was made of how additional threat scenarios of recognized human activities (i.e. bycatch influencing adult survival and increased underwater noise or pollution influencing calf survival) would affect population dynamics. Population growth rate was very sensitive to changes in adult bycatch (especially females), as expected, and only subtly sensitive to a reduction in calf survival.The current level of bycatch is unsustainable. Bycatch needs to be eliminated to maximize the probability of long‐term persistence of this dolphin population. However, this population's persistence could be threatened by natural variation in reproductive rates. [ABSTRACT FROM AUTHOR]

Sympatric species are expected to differ in ecological requirements to minimize niche overlap and avoid competition. Here we assess the trophic interactions among three coexisting dolphin species from southern Brazil: the franciscana dolphin (Pontoporia blainvillei), the Guiana dolphin (Sotalia guianensis), and the Lahille's bottlenose dolphin (Tursiops truncatus gephyreus). We evaluated temporal variation in carbon (δ13C) and nitrogen (δ15N) isotope values of bone collagen to examine potential dietary shifts resulting from increased fishing activity over the past three decades. We estimated the degree of niche overlap among these species and the contribution of potential prey sources to their diet. δ15N values were consistent among species and across years, while δ13C values increased for Guiana dolphins and decreased for bottlenose dolphins, suggesting changes in diet and/or foraging habitats through time. The similar δ13C and δ15N values and the high niche overlap between Guiana and bottlenose dolphins indicate that these species are primarily feeding on demersal prey. The franciscana diet is primarily composed of pelagic prey, resulting in a lower niche overlap in comparison with the other dolphin species. Our study provides further information about the foraging ecology of this unique dolphin community in southern Brazil with implications for its management and conservation. [ABSTRACT FROM AUTHOR]

Coastal and offshore ecotypes of common bottlenose dolphins have been recognized in the western South Atlantic, and it is possible that trophic niche divergence associated with social interactions is leading them to genetic and phenotypic differentiation. The significant morphological differentiation observed between these ecotypes suggests they represent two different subspecies. However, there is still a need to investigate whether there is congruence between morphological and genetic data to rule out the possibility of ecophenotypic variation accompanied by gene flow. Mitochondrial DNA (mtDNA) control region sequence data and 10 microsatellite loci collected from stranded and biopsied dolphins sampled in coastal and offshore waters of Brazil as well as 106 skulls for morphological analyses were used to determine whether the morphological differentiation was supported by genetic differentiation. There was congruence among the data sets, reinforcing the presence of two distinct ecotypes. The divergence may be relatively recent, however, given the moderate values of mtDNA nucleotide divergence (dA = 0.008), presence of one shared mtDNA haplotype and possibly low levels of gene flow (around 1% of migrants per generation). Results suggest the ecotypes may be in the process of speciation and reinforce they are best described as two different subspecies until the degree of nuclear genetic divergence is thoroughly evaluated: Tursiops truncatus gephyreus (coastal ecotype) and T. t. truncatus (offshore ecotype). The endemic distribution of T. t. gephyreus in the western South Atlantic and number of anthropogenic threats in the area reinforces the importance of protecting this ecotype and its habitat. [ABSTRACT FROM AUTHOR]

A subset of the bottlenose dolphin Tursiops truncatus gephyreus population in Laguna, southern Brazil, specialize in foraging cooperatively with fishermen. In this study, we describe reproductive parameters for these dolphins and investigate whether this specialized tactic generates reproductive advantages for females that frequently engage in this unusual behavior. We analyzed photo-identification data collected during 233 boat-based surveys during 2007–2009 and 2013–2017. From 27,808 high-quality photographs, we identified and tracked the fate of 24 reproductive females and 45 of their calves. Calving was found to be seasonal, with most births occurring in late spring/summer. The average crude birth rate was 0.09, and estimated fecundity was 0.17. The mean inter-birth interval was 2.09 (for all calves) or 2.43 years (for surviving calves only). Survival to 1 and 2 years estimated by the Kaplan–Meier method was 0.78 (95% CI 0.65–0.92) and 0.65 (95% CI 0.51–0.83), respectively—which represents a survival rate in the second year of 0.83. We investigated the potential influence of birth timing, resource availability, and maternal foraging tactic, home range size and frequency of interaction with fishermen on calf survival. Timing of birth was a significant predictor of calf survival. Giving birth close to the local mullet season would provide lactating females with increased seasonal prey resources, leading to increased calf survival. Due to our sample size (n = 9 cooperative and 15 non-cooperative females), we could not conclude whether or not the cooperative foraging tactic influences calf survival and female reproductive success. We emphasize the importance of long-term monitoring of populations to understand regional life history characteristics and provide accurate information for viability analyses. [ABSTRACT FROM AUTHOR]

A small population of coastal bottlenose dolphins (Tursiops truncatus gephyreus) inhabits the inland waters of Laguna, southern Brazil. A subset of this population interacts with artisanal fishermen. This specialized foraging tactic structures dolphin society into 'cooperatives' (participants of the interaction) and 'non‐cooperatives' (non‐participants).Between 2012 and 2015, a bridge was constructed in Laguna over an important core area for dolphins. Photo‐identification and georeferenced data collected on boat surveys, conducted both before and during bridge construction, were used to evaluate changes in both 'cooperative' and 'non‐cooperative' dolphin distribution.Changes in dolphin distribution were analysed with kernel densities and hurdle models. A grid of 120 cells of area 1 km2 was used to model dolphin distribution, and the minimum distance from the grid cell centre to the bridge and to the area of gillnet use were defined as explanatory variables of human activities. Habitat descriptors (depth and distance) from the lagoon margin were also considered in the model procedure.Dolphin distribution patterns shifted between periods. A core area used by 'non‐cooperative' dolphins near the bridge construction works disappeared. The effects of habitat descriptor and anthropogenic activity on dolphin distribution also differed between periods. Before bridge construction, the abundance of 'non‐cooperative' dolphin was higher close to the bridge area (p < 0.05). During bridge construction, the presence of 'cooperative' and 'non‐cooperative' dolphins decreased significantly with the distance from gillnet fishing activity (p < 0.01 and p < 0.001 respectively).This study highlights the importance of accounting for individual variations in response when assessing the effects of a habitat disturbance, or when implementing conservation plans. [ABSTRACT FROM AUTHOR]

Recent years have seen an increasing interest in individual behavioral variation. However, the implications of such variation for population dynamics are often unknown. We studied the dynamics of a bottlenose dolphin (Tursiops truncatus gephyreus) population from southern Brazil, where some individuals forage cooperatively with artisanal fishermen. We fitted mark‐recapture models to 10 yr of photo‐identification data to investigate the influence of this foraging specialization on dolphins' population parameters, controlling for sex and ranging behavior. We estimated adult survival to be high (0.949 ± 0.015 SE), weakly influenced by home range size, sex or the frequency of interaction with fishermen. The slightly higher survival probability for individuals with smaller home ranges could stem from the benefits of reduced spatial requirements implied by the specialized foraging. Foraging also influenced the probability of resighting individuals, and there was no temporary or permanent emigration. Abundance fluctuated slightly over the years from 54 (95% CI = 49–59) to 60 (95% CI = 52–69) individuals, with no evident population trend. Despite such apparent population stability, we confirm this population remains small and geographically isolated which may threaten its viability and the viability of its unusual, localized foraging specialization. Our study also illustrates how accounting for individual variation can portray animal population dynamics more realistically. [ABSTRACT FROM AUTHOR]

The taxonomy of Tursiops truncatus in the western South Atlantic is not resolved. Two different hypotheses have been proposed: (1) offshore and coastal ecotypes with a parapatric distribution, and (2) two species, T. truncatus and T. gephyreus, living in sympatry. To test these hypotheses, we examined a total of 100 physically mature skulls and 35 vertebral columns from the suggested overlap zone in southern Brazil. In all skulls, 24 measurements, four alveoli counts and two categorical variables were analyzed. Vertebral formula was determined and five measurements were taken from selected vertebrae. Multivariate analyses were conducted for skull and vertebral data. Results revealed the presence of two well-separated groups. Specimens of Group1 had smaller skulls and shorter body lengths, but more vertebrae, than Group2. The morphological characteristics of each group corresponded well with two ecotypes of common bottlenose dolphins reported in other ocean basins. Therefore, we assigned the specimens of Group1 to the offshore ecotype, and Group2 to the coastal ecotype. Differences in the geographic locations and ratio of strandings supported the parapatric hypothesis. The significant morphological differentiation observed suggests the presence of different subspecies, but an additional independent line of evidence is needed to hypothesize whether they represent different species. [ABSTRACT FROM AUTHOR]

A subgroup of a population of Tursiops truncatus in southern Brazil is known for a cooperative behavior with artisanal fishermen whereby the dolphins shoal fish towards net-casting fishermen. Combining photo-identification data collected between September 2007 and 2009 with mark-recapture and Pollock's robust design models, we assessed abundance within seasons and survival and temporary emigration rates of dolphins between seasons. We also reanalyzed a previous data set collected during 1989-1991, and Cormack-Jolly-Seber models were applied to estimate survival rates for each of the study periods. The abundance of marked 'cooperative' dolphins varied between seasons from 18 (CI: 17-24) to 21 (CI: 20-24). The total abundance varied from 59 in the winter of 2008 (CI: 49-72) to 50 in the autumn of 2009 (CI: 40-62). The annual adult survival was estimated to be 0.917 (CI: 0.876-0.961), close to that estimated from data collected in the 1990s (0.941; CI: 0.888-0.998). The emigration probability was low (0.031; CI: 0.011-0.084) and different capture probabilities between the 'cooperative' and 'noncooperative' dolphins indicated a degree of behavioral segregation. The precision of our estimates is likely to provide sufficient power to detect population change, but we recommend a precautionary management approach to protect this vulnerable dolphin community and its unique cooperative feeding tradition. [ABSTRACT FROM AUTHOR]

The article discusses a study about the presence of lobomycosis-like disease (LLD) in wild bottlenose dolphins Tursiops truncatus of Laguna in southern Brazil. Researchers identified 47 adult dolphins and 10 calves, seven of which showed some form of epidermal lesion while 5 had evidence of LLD. The growth of the lesion at a slow but constant rate on the adult was observed during the first few months of observation, while also noted are the rapid increase of the growth rate and the appearance of the first lesions on the calf in the 14th month. Findings suggested that there is a need to monitor both the health of cetaceans and the quality of their habitat.

An individual reaction to natural threats, such as the presence of predators or aggressors, can shape the social behaviour of an entire population. In southern Brazil, two coastal Delphinid species, Guiana dolphin (Sotalia guianensis) and Lahille's bottlenose dolphin (Tursiops truncatus gephyreus) co-occur on a regional scale. However, within Baía Norte, there is a clear spatial segregation between these dolphins at a fine-scale that, combined with records of bottlenose dolphins displaying agonistic behaviours towards Guiana dolphins, raised the hypothesis that such aggressive behaviours may contribute to shape this segregated distribution. Here, to investigate this hypothesis, we carried out a controlled exposure experiment in which surface behavioural responses of Guiana dolphins were evaluated before, during and after acoustic playbacks of bottlenose dolphins. Through aerial footages, collected with an unmanned aerial vehicle, we accessed significant behavioural responses of Guiana dolphins in terms of group organization and behavioural states. During playbacks, we observed a decrease in the cohesion index between individual Guiana dolphins and an increase in group synchrony, indicating that individuals coordinate their movements to aggregate when exposed to playback. In addition, time spent in foraging behaviours decreased significantly during playbacks, suggesting that foraging activities are interrupted, and individuals start to travel. These results demonstrate that Guiana dolphins perform a collective escape behaviour when facing bottlenose dolphins, a potential aggressor, reinforcing the hypothesis that such defensive behaviour is mediating the spatial segregation between these dolphins' populations. [Display omitted] • Fear effect can be generated by non-trophic aggressive interactions. • Social and spatial organization modulated by the presence of a larger species. • Fear motivated behaviour are determinant for small coastal delphinids ecology. • Controlled exposure experiment using drones and playbacks in a natural environment. • Behavioural interactions may shape Guiana dolphins' distribution. [ABSTRACT FROM AUTHOR]