Signature whistles in free‐ranging populations of Indo‐Pacific bottlenose dolphins,Tursiops aduncus

Common bottlenose dolphins (Tursiops truncatus) use individually distinctive signature whistles which are highly stereotyped and function as contact calls. Here we investigate whether Indo‐Pacific bottlenose dolphins (T. aduncus) use signature whistles. The frequency trace of whistle contours recorded from three genetically distinct free‐ranging populations was extracted and sorted into whistle types of similar shape using automated categorization. A signature whistle identification method based on the temporal patterns in signature whistle sequences of T. truncatus was used to identify signature whistle types (SWTs). We then compared the degree of variability in SWTs for several whistle parameters to determine which parameters are likely to encode identity information. Additional recordings from two temporarily isolated T. aduncus made during natural entrapment events in 2008 and 2009 were analyzed for the occurrence of SWTs. All populations were found to produce SWTs; 34 SWTs were identified from recordings of free‐ranging T. aduncus and one SWT was prevalent in each recording of the two temporarily isolated individuals. Of the parameters considered, mean frequency and maximum frequency were the least variable and therefore most likely to reflect identity information encoded in frequency modulation patterns. Our results suggest that signature whistles are commonly used by T. aduncus.     

Sonographic evaluation of thyroid morphology during different reproductive events in female Indo‐Pacific bottlenose dolphins,Tursiops aduncus

Thyroid morphology and function are likely affected by the cyclic hormonal environment during different reproductive events in females. The present study was undertaken to evaluate the variation of thyroid morphology at different reproductive events (anestrus, estrus, lactation, and pregnancy) in a captive group of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) measured using sonography. Sonographic examinations of the thyroid gland and ovaries in nine sexually mature female subjects were performed weekly for 2.5 yr. A generalized linear mixed model was used to estimate the effects of the reproductive events for thyroid volume. Reproductive event was found to be a significant predictor for thyroid volume measurement and significant variation in thyroid volume was found between different reproductive events. A significantly larger thyroid volume in lactating females was observed when compared with estrous and anestrous females, possibly due to the high energy requirements and milk production during lactation. Taken together, thyroid volume variation during different reproductive events in female dolphins should be considered so as to obtain a diagnostically meaningful assessment when conducting routine examinations.     

Phylogenetic placement and population structure of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) off Zanzibar,Tanzania, based on mtDNA sequences

Phylogenetic placement of bottlenose dolphins from Zanzibar, East Africa and putative population differentiation between animals found off southern and northern Zanzibar were examined using variation in mtDNA control region sequences. Samples (n= 45) from animals bycaught in fishing gear and skin biopsies collected during boat surveys were compared to published sequences (n= 173) of Indo‐Pacific bottlenose dolphin, Tursiops aduncus, from southeast Australian waters, Chinese/Indonesian waters, and South African waters (which recently was proposed as a new species) and to published sequences of common bottlenose dolphin, Tursiops truncatus. Bayesian and maximum parsimony analyses indicated a close relationship between Zanzibar and South African haplotypes, which are differentiated from both Chinese/Indonesian and Australian T. aduncus haplotypes. Our results suggest that the dolphins found off Zanzibar should be classified as T. aduncus alongside the South African animals. Further, analyses of genetic differentiation showed significant separation between the T. aduncus found off northern and southern Zanzibar despite the relatively short distance (approximately 80 km) between these areas. Much less differentiation was found between southern Zanzibar and South Africa, suggesting a more recent common evolutionary history for these populations than for the northern and southern Zanzibar populations.     

Mark‐resight abundance and survival estimation of Indo‐Pacific bottlenose dolphins,Tursiops aduncus,in the Swatch‐of‐No‐Ground,Bangladesh

A mark‐resight analysis under Pollock's robust design was applied to Indo‐Pacific bottlenose dolphins Tursiops aduncus in the Swatch‐of‐No‐Ground (SoNG) submarine canyon, Bangladesh, during the winter seasons of 2005–2009. Information from sightings of photo‐identified individuals (1,144) and unmarked individuals generated abundance estimates of 1,701 (95% confidence interval [CI]= 1,533–1,888), 1,927 (95% CI = 1,851–2,006), 2,150 (95% CI = 1,906–2,425), and 2,239 (95% CI = 1,985–2,524) individuals for seasons 1–4, respectively. This makes the population among the largest assessed of the species. Overall apparent survival was estimated as 0.958 (95% CI = 0.802–0.992). Interseasonal probabilities of transitioning to an unobservable state were estimated as 0.045, 0.363, and 0.300 for years 1–2, 2–3, and 3–4, respectively, and the overall probability of remaining in an unobservable state was 0.688. These probabilities, together with an apparent increase in abundance during the study period, indicate that the identified dolphins are part of a larger superpopulation moving throughout a more extensive geographic area. Of the photo‐identified dolphins, 28.2% exhibited injuries related to entanglements with fishing gear. This implies a strong potential for fatal interactions that could jeopardize the conservation status of the population, which otherwise appears favorable.     

Home range size of adult Indo‐Pacific bottlenose dolphins (Tursiops aduncus) in a coastal and estuarine system is habitat and sex‐specific

This study examined sex‐specific differences in home range size of adult Indo‐Pacific bottlenose dolphins off Bunbury, Western Australia. We applied a new kernel density estimation approach that accounted for physical barriers to movements. A Bayesian mixture model was developed to estimate a sex effect in home range size with latent group partitioning constrained by association data. A post hoc analysis investigated group partitioning relating to the proportion of time spent in open vs. sheltered waters. From 2007 to 2013, photographic‐identification data were collected along boat‐based systematic transect lines (n = 586). Analyses focused on adult dolphins of known sex (sighted ≥ 30 times; n = 22 males and 34 females). The 95% utilization distributions of males varied between 27 and 187 km² (; 94.8 ± 48.15) and for females between 20 and 133 km² (65.6 ± 30.9). The mixture model indicated a 99% probability that males had larger home ranges than females. Dolphins mostly sighted in open waters had larger home ranges than those in sheltered waters. Home ranges of dolphins sighted in sheltered waters overlapped with areas of highest human activity. We suggest that sex differences in home ranges are driven by male mating strategies, and home range size differences between habitats may be influenced by prey availability and predation risk.     

Activity budget of inshore Indo‐Pacific bottlenose dolphins (Tursiops aduncus): A critical evaluation of methods and comparison among other populations

Activity budgets are widely used to compare behavior patterns but sampling methods vary, rendering comparisons difficult. The two main methods used are instantaneous and continuous sampling. Their comparability was examined by applying them to data obtained from bottlenose dolphins in the Port River estuary, South Australia. They gave comparable results for activity budgets, but instantaneous sampling did not detect most of the behavioral events. Individual differences in behavior and/or follow duration influenced results. Variability in activity definitions and categories among studies makes comparative analysis difficult. Comparison of the Port River dolphin's activity budget with other inshore populations indicated the former spent more time feeding and resting, and less time traveling. The greater feeding time seemed to be due to small prey size rather than reduced abundance or unpredictable distribution. The reduced traveling time, possibly the result of low predation pressure and/or evenly distributed prey, gave them more time to rest. They traveled mostly at 2.5 kn or less, consistent with studies from other shallow areas. Most feeding was individual, probably on demersal species. Surface feeding incorporated physical barriers rather than cooperative behavior. Activity durations ranged from 2 s to 2.9 h, with mean durations varying from 7.8 to 22.9 min.     

Sexual maturity and estimated fecundity in female Indo‐Pacific bottlenose dolphins (Tursiops aduncus) from South Australia: Combining field observations and postmortem results

Knowledge of life history of bottlenose dolphins in Australia is limited, with no studies comparing field and postmortem data from the same region. Carcasses of 88 opportunistically collected females (1987–2015) were studied, including eight observed for up to 23 yr before death. Ovaries were weighed and number of corpora determined grossly. Nineteen mammary glands were examined histologically. Relative age was determined using developmental features and body length, estimated age by tooth incremental lines, and physical maturity by epiphyseal fusion. Age at sexual maturation was 7.17 yr (6–>14 yr) at body lengths of 191–209 cm. Physical maturation occurred at 12–17 yr, and body lengths of 195–233 cm. An Exponential model provided the best fit for age at body length, with an asymptote at 214 cm. Combined ovary weight increased between birth and sexual maturation, with significantly more corpora in the left ovary. Corpora increased with age and appeared to persist throughout life. For mature females, 95% had ≤ 11 corpora. Number of corpora was consistent with number of calves for females with known life histories. Estimated interbirth period was about 4 yr. Three females with abnormal reproductive features were either chronically diseased and/or had high heavy metal burdens.     

Habitat and resource partitioning among Indo‐Pacific bottlenose dolphins in Moreton Bay,Australia

Investigating resource partitioning among mobile marine predators such as cetaceans is challenging. Here we integrate multiple methodologies (analyses of habitat use, stable isotopes and trace elements) to assess ecological niche partitioning amongst two genetically divergent sympatric subpopulations (North and South) of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) in Moreton Bay, Australia. Comparisons of the mean locations (latitude, longitude) and environmental variables (distance from sandbanks, distance from shore and water depth) observed at sightings of biopsy‐sampled individuals indicated that the North subpopulation occurred in the northwestern bay in significantly deeper water than the South subpopulation, which was found in southeastern nearshore waters and closer to sandbanks. Ratios of stable carbon and nitrogen isotopes in skin samples suggested that North dolphins foraged on higher trophic level prey in relatively more pelagic, offshore habitats, while South dolphins foraged on lower trophic prey in more nearshore, demersal and/or benthic habitats. Habitat partitioning was also reflected in higher blubber concentrations of most of the 13 measured trace elements, in particular lead, in the coastal South compared to the more pelagic North dolphins. These findings indicate that genetic subpopulations of bottlenose dolphins in Moreton Bay are adapted to different niches.     

Synchrony,leadership, and association in male Indo-pacific bottlenose dolphins (Tursiops aduncus)

Male Indo-pacific bottlenose dolphins in Shark Bay, Western Australia, have converged with humans in the formation of nested male alliances and the use of synchrony in alliance behavior. Further, the strength of association among allied male dolphins varies and the stability of alliances correlates with the rate that males consort with estrus females (and is thus a possible indicator of dominance). To examine the possibility that synchrony reflects alliance association strength and dominance relationships, we analyzed videotapes from focal follows of two groups of males that reflect the range of alliance size and the strength of association between individuals in the population. We examined two variables: leadership during synchronous behaviors, based on which animal in a synchronously surfacing pair surfaced first, and the degree of synchrony, based on temporal differences in synchronous surfacing. We predicted that closer associates would exhibit a greater degree of synchrony and that one dolphin in a dyad would consistently lead. Contrary to our predictions, the degree of synchrony was inversely related to strength of association within alliances. This surprising result suggests that individuals with less secure bonds may strive more to achieve synchrony. We found no evidence of leadership during synchronous surfacing or between synchrony and other behavioral variables. Proximate mechanisms for synchronous behavior, such as entrainment and mutual motor imitation (“the mirror game” paradigm), may inhibit leadership in this context. Our results show that synchrony during surfacing is not a useful behavior to examine for dominance relationships in wild dolphins but it may be a useful tool to examine variation in alliance relationships.     

Genetic evidence for sex-biased dispersal in resident bottlenose dolphins (Tursiops aduncus)

In most mammals males usually disperse before breeding, while females remain in their natal group or area. However, in odontocete cetaceans behavioural and/or genetic evidence from populations of four species indicate that both males and females remain in their natal group or site. For coastal resident bottlenose dolphins field data suggest that both sexes are philopatric to their natal site. Assignment tests and analyses of relatedness based on microsatellite markers were used to investigate this hypothesis in resident bottlenose dolphins, Tursiops aduncus, from two small coastal populations of southeastern Australia. Mean corrected assignment and mean relatedness were higher for resident females than for resident males. Only 8% of resident females had a lower probability than average of being born locally compared to 33% of resident males. Our genetic data contradict the hypothesis of bisexual philopatry to natal site and suggest that these bottlenose dolphins are not unusual amongst mammals, with females being the more philopatric and males the more dispersing sex.     

Largest reported groups for the Indo‐Pacific bottlenose dolphin (Tursiops aduncus) found in Algoa Bay,South Africa: Trends and potential drivers

This study investigates how group size of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) changes temporally, spatially, and/or with predominant behavior at two discreet sites along the Eastern Cape coastline of South Africa: Algoa Bay and the Wild Coast. The mean group size of bottlenose dolphins was large with an average of 52 animals. Significantly larger groups were observed in Algoa Bay ( = 60, range = 1–600) than off the Wild Coast ( = 32.9, range = 1–250). In Algoa Bay, the mean group size increased significantly over the study period, from an average 18 animals in 2008 to 76 animals in 2016. Additionally, the largest average and maximum group sizes ever reported both in South Africa and worldwide, were recorded in Algoa Bay (maximum group size = 600). Neither season nor behavior had a significant effect on mean group size at both sites. Similarly environmental variables such as the depth and substrate type also had no influence on group size. It remains unclear which ecological drivers, such as predation risk and food availability, are leading to the large groups observed in this area, and further research on abundance and distribution of both predators and prey is necessary.     

Habitat‐driven population structure of bottlenose dolphins,Tursiops truncatus,in the North‐East Atlantic

Despite no obvious barrier to gene flow, historical environmental processes and ecological specializations can lead to genetic differentiation in highly mobile animals. Ecotypes emerged in several large mammal species as a result of niche specializations and/or social organization. In the North‐West Atlantic, two distinct bottlenose dolphin (Tursiops truncatus) ecotypes (i.e. ‘coastal’ and ‘pelagic’) have been identified. Here, we investigated the genetic population structure of North‐East Atlantic (NEA) bottlenose dolphins on a large scale through the analysis of 381 biopsy‐sampled or stranded animals using 25 microsatellites and a 682‐bp portion of the mitochondrial control region. We shed light on the likely origin of stranded animals using a carcass drift prediction model. We showed, for the first time, that coastal and pelagic bottlenose dolphins were highly differentiated in the NEA. Finer‐scale population structure was found within the two groups. We suggest that distinct founding events followed by parallel adaptation may have occurred independently from a large Atlantic pelagic population in the two sides of the basin. Divergence could be maintained by philopatry possibly as a result of foraging specializations and social organization. As coastal environments are under increasing anthropogenic pressures, small and isolated populations might be at risk and require appropriate conservation policies to preserve their habitats. While genetics can be a powerful first step to delineate ecotypes in protected and difficult to access taxa, ecotype distinction should be further documented through diet studies and the examination of cranial skull features associated with feeding.     

Male reproductive success increases with alliance size in Indo-Pacific bottlenose dolphins (Tursiops aduncus)

1. Determining the extent of variation in male mating strategies and reproductive success is necessary to understand the fitness benefits of social and cooperative behaviour. 2. This study assesses the reproductive success of male Indo-Pacific bottlenose dolphins in a small embayment population where different behavioural strategies of males have previously been identified. Parentage for 44 sampled calves was examined using 23 microsatellite loci and one mitochondrial DNA marker. Our candidate parent pool of 70 males and 64 females contained individuals sampled from both the embayment and adjacent coastal populations. 3. A moderate level of polygyny was detected in our sample. We assigned paternity of 23 calves to 12 males at the strict 95% confidence level and an additional nine calves to two males at the 80% confidence level. The majority (92%) of successful males were identified as residents to the embayment, and 46% of offspring were located within the same social group or community as their father. 4. Our results suggest that the size of alliances was the best predictor of reproductive success for males in this population, while the strength of association among allied males, alliance stability and male ranging patterns had little influence. In line with predictions for male alliances formed between unrelated individuals, we found that reproductive skew within alliances was not large. 5. Together, our genetic and behavioural analyses demonstrate that alliance formation between male dolphins is a successful strategy to enhance reproductive output.     

Captive environment influences the composition and diversity of fecal microbiota in Indo-Pacific bottlenose dolphins,Tursiops aduncus

Captive environments impact the microbiota of captive animals; however, the comparison of microbiota between wild and captive dolphins has been poorly investigated. To explore the impact of a captive environment, we characterized the fecal microbiota of nine wild and four captive Indo-Pacific bottlenose dolphins, Tursiops aduncus, using a next-generation sequencing and revealed differences in the fecal microbiota between the analyzed groups. Statistical differences in abundances of the phyla Firmicutes and Proteobacteria were found between the wild and captive dolphins. Thirty-six genera (22.9% of the total genera detected in all dolphins) were shared between the groups, whereas 79 (50.3%) and 42 (26.8%) genera were found only in the wild or captive dolphins, respectively. Several pathogenic bacterial genera, including Morganella and Mycoplasma, were detected only in the captive dolphins, and the genus Lactobacillus was found only in the wild dolphins. LefSe and SIMPER analyses revealed that the genus Clostridium sensu stricto 1 was significantly more abundant in the captive dolphins than in the wild ones and contributed the most to the dissimilarity of fecal microbiota between the groups. Our results indicate that the captive environment impacts the fecal microbiota of dolphins and reinforces the importance of monitoring potentially pathogenic bacteria in captivity.     

Alliance membership and kinship in wild male bottlenose dolphins (Tursiops aduncus) of southeastern Australia

Bottlenose dolphins are one of only a few mammalian taxa where the males are known to cooperate within their social group in order to maintain mating access to single females against other males. Male bonds in bottlenose dolphins have been hypothesized as evolving through kinship and associated inclusive fitness effects. In this study we tested whether individually identified male bottlenose dolphins preferentially associate and form alliances with kin in a small coastal resident population of southeastern Australia using a combination of behavioural data, genetic sexing, sequences of the mitochondrial DNA control region and nuclear microsatellite markers. Males generally associated significantly more often than expected with one to three other males, with whom they jointly herded females for mating. Associations and alliance membership were not associated with either maternal kinship or genetic relatedness. The majority of male pairs within alliances were randomly related, although high relatedness values were found between males of different alliances in the resident population. These findings indicate that mechanisms other than kin selection may be foremost in the development and maintenance of cooperation between male bottlenose dolphins.     

Evaluating and minimising social stress in the care of captive bottlenose dolphins (Tursiops aduncus)

Stress can increase an organism’s susceptibility to disease. Thus, managing stress and its causes are important elements of captive care. Social factors such as changes in group dynamics, competition over resources, and unstable dominance hierarchies are potential stressors for highly social animals such as bottlenose dolphins (Tursiops sp). We present three case studies of mortality and illness in captive bottlenose dolphins and suggest that stress, resulting from social instability and ensuing aggressive interactions, is likely to have played a role in these health consequences. Stress is implicated by blood profiles, loss of appetite, and gastric ulcers, and social problems and instability are evident in the quantitative analysis of individual activity levels and association patterns. This is a unique study on marine mammals in that it demonstrates a correlation between quantitative behavioral indices and physiological measures of stress and health. Recommendations are made for the management of captive dolphins including regular quantitative assessment of behavior and associations and maintenance of appropriate groupings of age and sex classes. Behavioral records can be an important early indicator of health problems and may also serve as a useful tool for recognizing potentially stressful social changes and circumstances. Zoo Biol 21:5–26, 2002. © 2002 Wiley‐Liss, Inc.