Fusion of Communities, the Response of Estuarine Bottlenose Dolphins to Population Decline in the Gulf of Guayaquil, Ecuador

Socio-ecological and conservation aspects of a small community of bottlenose dolphins Tursiops truncatus (Odontoceti: Delphinidae) in Santa Elena, Ecuador. A resident community of bottlenose dolphins (Tursiops truncatus) has been studied irregularly between 2005 and 2018 around the tip of the Santa Elena Peninsula, Ecuador (2°11'S, 81°0.7'W). Opportunistic sightings and systematic surveys from the beach and at sea from a boat were carried out along 40 km of coast, accounting for 917.2 km of tracking by car from land and 707.4 km of boat tracking by sea. Average group size was 5.31 dolphins/group (SD= 1.97, range 1-10), with no significant changes throughout the study period. From land, however, the group size was underestimated 32% on the average. This small dolphin community currently has only nine individuals, including six adults, one immature and two calves. The relative abundance ranged between 0.03 dolphins/km in the northwestern part and 0.32 dolphins/km in the south, where dolphins concentrate their activities, possibly because human activities are less intense. Dolphins were generally distributed in the first 200 m from the shore, reaching up to 1,200 in the northern shallower part and where port and tourist activities concentrate. The dolphins’ speed was significantly higher when they were followed from a boat at close range (5.87 km/h) than when they were monitored from the beach (2.9 km/h) (P < 0.01), which suggests that boat tracking had an effect on dolphin´s movements. Pairwise cluster analysis showed that animals from this community show high rates of association among each other (average 0.67, range 0.01-1.0), indicating this is highly cohesive population unit. Dolphins also showed high level of residence (average occurrence index = 0.62). During the study, two main threats were identified, a gillnet fishery in the southwestern part and an intense fishing boat traffic in the northwestern. This coastal bottlenose dolphin community is the smallest of this species ever reported in the Gulf of Guayaquil, probably is a remnant of a larger population that would be in process of extinction. Most of the study area is currently part of a coastal-marine protected area created in 2008, which offers an opportunity for the recovery and conservation of this dolphin community. Given the fragility of this population unit, we recommend to environment authorities addressing potential threats by eliminating gillnets, implementing an exclusion zone for fishing gear and fishing boat traffic of 1 km width from the shore and limit the speed of any type of vessel to 10 knots within the reserve.

Investigations of population structure across multiple niche dimensions can identify discrete management units within populations. This study examined social, spatial and isotopic niche partitioning in Indo‐Pacific bottlenose dolphins (Tursiops aduncus) across ca. 600 km2 of coastal and estuarine waters in south‐western Australia, to evaluate whether estuarine dolphins should be treated as a discrete management unit. Photo‐identification data and tissue samples were collected in 2016 and 2017 in a study area covering the Peel‐Harvey Estuary (PHE) and adjacent coastal waters. A total of 1,038 dolphin groups were encountered, and 481 individuals were identified. Tissue samples for stable isotope (δ13C and δ15N) analyses were collected from 96 individuals. Social structure and complexity analyses were conducted, full and core activity spaces were identified, and their size estimated for identified social communities. Differences in stable isotope composition among individuals and communities were examined. A socially, spatially and isotopically distinct dolphin community occurred in the PHE. The coastal waters contained four socially and spatially, but not isotopically, distinct communities as well as a substantial number of dolphins (n = 185) that were sighted infrequently and therefore were not assigned to any community. Individuals formed three levels of relationships; the majority (78%) were weak association relationships (mean half‐weight index 0.006). The estuarine community had significantly higher mean δ13C and significantly lower mean δ15N values than any of the coastal communities. There is a strong scientific basis for treating the PHE dolphin community as a discrete management unit. The estuarine and coastal communities occupied different social environments, with coastal individuals sharing space with more transient individuals. This study shows the value of integrating information from multiple niche dimensions when identifying management units, and the need to consider all encountered individuals in management planning.

Previous studies suggest that the common bottlenose dolphin population in the Croatian Adriatic Sea is structured into distinct local communities. However, their home ranges and levels of interaction remain unknown.Dedicated boat‐based surveys were conducted seasonally, in three adjacent study sites from 2013 to 2017. Photo‐identification data were used to identify distinct local communities by relating the social structure descriptors to the home ranges of individual animals, and to determine the community home ranges and identify the levels of interactions between them.The overlaps between the home ranges of individuals (50 and 95% kernel density estimators [KDE]) were positively correlated to association strengths between them. Three distinct communities were identified by the hierarchical cluster analysis. The individuals' 95% KDE home range overlaps and association strengths were significantly higher within the three communities than between them, indicating both social and spatial segregation.The 95% KDE home ranges of the communities showed very low to no overlap. The individuals ranged mainly centrally within the home range of their respective community. The probabilities of movement, expressed as lagged identification rates, were significantly higher within than between community home ranges. However, 37 out of 1024 identified individuals were observed in more than one community home range, indicating that the communities are not isolated.Four out of the six Sites of Community Importance currently in place within the Croatian Adriatic Sea lie within the home ranges of the three local bottlenose dolphin communities. Once these sites are declared as Special Areas of Conservation, the management scheme will need to accommodate for differences in the spatial and social ecology of these communities, and environmental and anthropogenic factors acting upon them. The results of this work provide baseline information for such tailored management.

The common bottlenose dolphin, Tursiops truncatus, is widely distributed along the western coast of South America. In Ecuador, a resident population of bottlenose dolphins inhabits the inner estuarine area of the Gulf of Guayaquil located in the southwestern part of the country and is under threat from different human activities in the area. Only one genetic study on South American common bottlenose dolphins has been carried out to date, and understanding genetic variation of wildlife populations, especially species that are identified as threatened, is crucial for defining conservation units and developing appropriate conservation strategies. In order to evaluate the evolutionary link of this population, we assessed the phylogenetic relationships, phylogeographic patterns, and population structure using mitochondrial DNA (mtDNA). The sampling comprised: (i) 31 skin samples collected from free-ranging dolphins at three locations in the Gulf of Guayaquil inner estuary, (ii) 38 samples from stranded dolphins available at the collection of the “Museo de Ballenas de Salinas,” (iii) 549 mtDNA control region (mtDNA CR) sequences from GenBank, and (iv) 66 concatenated sequences from 7-mtDNA regions (12S rRNA, 16S rRNA, NADH dehydrogenase subunit I–II, cytochrome oxidase I and II, cytochrome b, and CR) obtained from mitogenomes available in GenBank. Our analyses indicated population structure between both inner and outer estuary dolphin populations as well as with distinct populations of T. truncatus using mtDNA CR. Moreover, the inner estuary bottlenose dolphin (estuarine bottlenose dolphin) population exhibited lower levels of genetic diversity than the outer estuary dolphin population according to the mtDNA CR. Finally, the estuarine bottlenose dolphin population was genetically distinct from other T. truncatus populations based on mtDNA CR and 7-mtDNA regions. From these results, we suggest that the estuarine bottlenose dolphin population should be considered a distinct lineage. This dolphin population faces a variety of anthropogenic threats in this area; thus, we highlight its fragility and urge authorities to issue prompt management and conservation measures.

Lobomycosis-like disease (LLD) is a chronic granulomatous skin disorder that affects Delphinidae worldwide. LLD has been observed in common bottlenose dolphins Tursiops truncatus from the Gulf of Guayaquil, Ecuador, since 1990. Although exogenous factors such as salinity and pollution may play a role in the pathogenesis of this disease in estuarine and coastal dolphin communities, we hypothesized that demography and social behaviour may also influence its epidemiology. To address this issue, the role of social behaviour in the distribution and prevalence of LLD was assessed through hierarchical cluster analysis and spatial distribution analysis in 7 dolphin communities inhabiting the inner estuary. Individuals with LLD lesions were observed in 5 of the 7 dolphin communities, with 13 of the 163 (8%) animals being positive, all adults. Among 8 dolphins of known sex, LLD affected mostly males (86%), who usually were found in pairs. Prevalence was low to moderate (5.1-13%) in dolphin communities where low-rank males had LLD. Conversely, it was high (44.4%, n = 9) in a small community where a high-rank male was infected. LLD affected both dolphins in 2 of the 4 male pairs for which large time series data were available, suggesting horizontal transmission due to contact. Thus, association with LLD-positive males seems to be an important risk factor for infections. Additionally, low-rank males had larger home ranges than high-rank males, indicating that low-status LLD-affected dolphins are likely responsible for the geographic dissemination of the disease in this population.

We report on the intestinal helminth fauna of 15 bottlenose dolphins Tursiops truncatus and 6 short-beaked common dolphins Delphinus delphis from the western Mediterranean. Eight helminth species were found in bottlenose dolphin, i.e., the digeneans Synthesium tursionis, Brachycladium atlanticum, and Pholeter gastrophilus, the nematode Anisakis sp., and the cestodes Tetrabothrius forsteri, Diphyllobothrium sp., Strobilocephalus triangularis, and tetraphyllidean plerocercoids. Brachycladium atlanticum, S. triangularis , and tetraphyllidean plerocercoids are new host records. No T. forsteri had previously been reported in Mediterranean bottlenose dolphins. Three species of helminths were recorded in the common dolphin, i.e., the digenean Synthesium delamurei (which was a new host record), and the cestodes T. forsteri and tetraphyllidean plerocercoids. The intestinal helminth communities of bottlenose and common dolphins are depauperate, similar to that of other cetacean species, but those from bottlenose dolphins harbored a higher number of helminth species. This study supports the notion that oceanic cetaceans, such as common dolphins, have a comparatively poorer helminth fauna than that of neritic species, such as bottlenose dolphins, because the likelihood of parasite recruitment is decreased.

[The behaviour of four captive Indian Ocean bottlenose dolphins (Tursiops aduncus)-a bull, two cows (adult) and a female calf-was observed for a total of Io4.5 hours during regular 30 minute observation sessions, conducted on a random basis at all times of the day, between March and November, I970. Units of precopulatory and copulatory behaviour were defined and quantified together with concomitant whistle-phonation in relation to the time of day. The frequency of social interactions was significantly influenced by a diurnal cycle. Social behaviour was infrequent at night and in the early morning, but increased significantly to reach a peak at midday and in the early afternoon Whistle-phonation rarely occurred at night and was still infrequent in the early morning. The behavioural roles in courtship contexts were interchangable between age and sex classes and sexual partners adopted identical courtship display postures with equal frequency. Free-ranging bottlenose dolphins were studied in three areas along the eastern Cape coast: Algoa Bay (34°S.25°E.), the Tsitsikamma Coastal National Park (34°S.23°E.), and Plettenberg Bay (34°S. 23°E.) Bottlenose dolphins were sighted on 122 occasions and were observed for a total of 79.7 hours between Janary I970 and May I97I. A systematic watch during all daylight hours was maintained for dolphins during three seasonal field trips to Plettenberg Bay. The dolphins entered the Bay mainly in the early morning and in the late afternoon. Feeding procedures and co-ordinated herding of food-fish by schools of bottlenose dolphins was described. The units of social behaviour scored in captivity, including mating attempts by bulls, were also observable under free-ranging conditions. Feeding was most frequent in the early morning and in the late afternoon. Mating behaviour was first seen after the initial feeding peak in the early morning and, whereas it was still apparent in the early afternoon, it declined again near the secondary peak of feeding activity at I700 hours, These findings were substantially confirmed by combining the data on feeding and mating activity obtained from all three study areas., The behaviour of four captive Indian Ocean bottlenose dolphins (Tursiops aduncus)-a bull, two cows (adult) and a female calf-was observed for a total of Io4.5 hours during regular 30 minute observation sessions, conducted on a random basis at all times of the day, between March and November, I970. Units of precopulatory and copulatory behaviour were defined and quantified together with concomitant whistle-phonation in relation to the time of day. The frequency of social interactions was significantly influenced by a diurnal cycle. Social behaviour was infrequent at night and in the early morning, but increased significantly to reach a peak at midday and in the early afternoon Whistle-phonation rarely occurred at night and was still infrequent in the early morning. The behavioural roles in courtship contexts were interchangable between age and sex classes and sexual partners adopted identical courtship display postures with equal frequency. Free-ranging bottlenose dolphins were studied in three areas along the eastern Cape coast: Algoa Bay (34°S.25°E.), the Tsitsikamma Coastal National Park (34°S.23°E.), and Plettenberg Bay (34°S. 23°E.) Bottlenose dolphins were sighted on 122 occasions and were observed for a total of 79.7 hours between Janary I970 and May I97I. A systematic watch during all daylight hours was maintained for dolphins during three seasonal field trips to Plettenberg Bay. The dolphins entered the Bay mainly in the early morning and in the late afternoon. Feeding procedures and co-ordinated herding of food-fish by schools of bottlenose dolphins was described. The units of social behaviour scored in captivity, including mating attempts by bulls, were also observable under free-ranging conditions. Feeding was most frequent in the early morning and in the late afternoon. Mating behaviour was first seen after the initial feeding peak in the early morning and, whereas it was still apparent in the early afternoon, it declined again near the secondary peak of feeding activity at I700 hours, These findings were substantially confirmed by combining the data on feeding and mating activity obtained from all three study areas.]

Skull shape analysis provides useful information on wildlife ecology and potential local adaptations. Common bottlenose dolphins (Tursiops truncatus) often differentiate between coastal and offshore populations worldwide, and skull shape analyses can be particularly useful in this context. Here we quantify skull shape variation between coastal populations from the Gulf of Guayaquil (Ecuador) and the Mediterranean Sea, compared to offshore specimens from multiple oceans. We analysed skull shape differences using 3D models from museum specimens through geometric morphometrics (3DGM). Two complementary landmark approaches included single-point semi-landmarks in homologous features, as well as pseudo-landmarks placed automatically. Results show skull shape distinction between both coastal populations and offshore specimens. Offshore specimens showed little differentiation between distinct locations. Skull shape patterns mostly diverged in the shape and length of rostrum, as well as the shape of the ascending processes of the maxilla, pterygoids, and occipital bones. However, both coastal populations differed in the patterns and direction of change of those features and were also morphologically distinct. Our results are consistent with local data on site fidelity and social structure in the coastal populations. Skull shape changes suggest divergent feeding and sound production patterns are potential drivers, probably specific to the local environment of each community.

Marine mammal (MM) observations were carried out during seismic survey of a 37 km 2 area in water depths ranging from 37-58 m in the Gulf of Guayaquil in May- June 2013. Twenty-one encounters with individual MMs or groups of MMs were recorded during 216 hours of observer effort. Bottlenose dolphins were most frequently seen, but observers also recorded the presence of striped dolphins and of humpback and killer whales and of sea lions. This short paper presents companion meteorological observations and considers the influence of weather and other environmental conditions on the frequency of the MM encounters.

Data from behavioural observations and acoustic recordings of free-ranging bottlenose dolphins (Tursiops truncatus) were analysed to determine whether signature whistles are produced by wild undisturbed dolphins, and how whistle production varies with activity and group size. The study animals were part of a resident community of bottlenose dolphins near Sarasota, Florida, USA. This community of dolphins provides a unique opportunity for the study of signature-whistle production, since most animals have been recorded during capture-release events since 1975. Three mother-calf pairs and their associates were recorded for a total of 141.25 h between May and August of 1994 and 1995. Whistles of undisturbed dolphins were compared with those recorded from the same individuals during capture-release events. Whistles were conservatively classified into one of four categories: signature, probable signature, upsweep or other. For statistical analyses, signature and probable signature whistles were combined into a 'signature' category; upsweep and other whistles were combined into a 'non-signature' category. Both 'signature' and 'non-signature' whistle frequencies significantly increased as group size increased. There were significant differences in whistle frequencies across activity types: both 'signature' and 'non-signature' whistles were most likely to occur during socializing and least likely to occur during travelling. There were no significant interactions between group size and activity type. Signature and probable signature whistles made up ca. 52% of all whistles produced by these free-ranging bottlenose dolphins.

Over the last 20 years, significant habitat shifts have been documented in some populations of cetaceans. On Little Bahama Bank (LBB) there are sympatric communities of resident Atlantic spotted dolphins (Stenella frontalis) and bottlenose dolphins (Tursiops truncatus), monitored since 1985. The size and social structure (three clusters: Northern, Central, Southern) have been stable among the spotted dolphin community with little immigration/emigration, even after large demographic losses (36%) following two major hurricanes in 2004. In 2013 an unprecedented exodus of over 50% (52 individuals) of the spotted dolphin community was documented. The entire Central cluster and a few Northern and Southern individuals relocated 161 km south to Great Bahama Bank (GBB), also home to two sympatric resident communities of spotted dolphins and bottlenose dolphins. During the late summer of 2013 and the summers of 2014 and 2015 both sites were regularly monitored but no former LBB dolphins returned to LBB. Uncharacteristic matriline splits were observed. Social analyses revealed random associations for those spotted dolphins and very little integration between spotted dolphins that moved to GBB (MGBB) and those dolphin resident to GBB (RGBB). Male alliances among spotted dolphins were present, with some altered patterns. On LBB, the operational sex ratio (OSR) was reduced (.40 to .25). OSR for MGBB and RGBB dolphins were similar (.45 and .43). A significant steady decrease in sea surface temperature and chlorophyll a (a proxy for plankton production) occurred on LBB leading up to this exodus. Similar trends were not present over the same period on GBB. The sudden large-scale shift of spotted dolphins from LBB to GBB in association with the gradual decline in certain environmental factors suggests that a possible “tipping point” was reached in prey availability. This study provides a unique view into social and genetic implications of large-scale displacement of stable dolphin communities.

To develop robust reference intervals for hematologic and serum biochemical variables by use of data derived from free-ranging bottlenose dolphins (Tursiops truncatus) and examine potential variation in distributions of clinicopathologic values related to sampling sites' geographic locations. 255 free-ranging bottlenose dolphins. Data from samples collected during multiple bottlenose dolphin capture-release projects conducted at 4 southeastern US coastal locations in 2000 through 2006 were combined to determine reference intervals for 52 clinicopathologic variables. A nonparametric bootstrap approach was applied to estimate 95th percentiles and associated 90% confidence intervals; the need for partitioning by length and sex classes was determined by testing for differences in estimated thresholds with a bootstrap method. When appropriate, quantile regression was used to determine continuous functions for 95th percentiles dependent on length. The proportion of out-of-range samples for all clinicopathologic measurements was examined for each geographic site, and multivariate ANOVA was applied to further explore variation in leukocyte subgroups. A need for partitioning by length and sex classes was indicated for many clinicopathologic variables. For each geographic site, few significant deviations from expected number of out-of-range samples were detected. Although mean leukocyte counts did not vary among sites, differences in the mean counts for leukocyte subgroups were identified. Although differences in the centrality of distributions for some variables were detected, the 95th percentiles estimated from the pooled data were robust and applicable across geographic sites. The derived reference intervals provide critical information for conducting bottlenose dolphin population health studies.

Identifying appropriate management units is vital for wildlife management. Here we investigate one potential management unit — resident communities of bottlenose dolphins — using information from ranging, occupancy, and association patterns. We identify a resident community of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in the Swan Canning Riverpark, Western Australia based on: ranging patterns, sighting rates, Lagged Identification Rates (LIR), and three measures of social affinity and structure (Simple Ratio Index, preferred dyadic association analyses, and Lagged Association Rates (LAR)). The analyses yielded an estimated ‘community size’ of 17–18 individuals (excluding calves). High seasonal sighting rates (> 0.75 sightings per season) and a long mean residence time (ca. nine years) indicated year-round residency. The model best-fitting the LIR (emigration and mortality) also supported this. The social structure of dolphins was species-typical, characterized by significant dyadic associations within agesex classes (permutation test; P < 0.001), stronger associations among adult males than among adult females (LAR males > LAR females), and temporally stable associations (LAR > null LAR). Constant companions or long-lasting association models best explained adult male and female LARs. While behavioural information identified a resident community in the Riverpark, genetic and demographic information is needed to assess its appropriateness as a management unit.

The social structure of coastal ecotype bottlenose dolphins, Tursiops truncatus, is largely unknown as they inhabit regions far from shore. This study reports on a community of bottlenose dolphins ≥ 27 km from Grand Bahama Island (May‐September, 1993–2002). Resident and non‐resident dolphins occurred in the area. Some dolphins traveled over 320 km between communities; others showed long‐ term site fidelity up to 17 yr. Average group size was 3–5, and was significantly larger with calves present and significantly smaller when traveling. The half‐weight index was used to determine coefficients of association (COA) for individuals of known sex annually and for pooled years. Permutation tests revealed non‐random associations and presence of preferred/avoided companions in all data sets. Annual COAs were low: female‐female χ= 0.31, male‐male χ= 0.30, and mixed‐sex χ= 0.26. Mother‐calf associations showed the highest values. Some males formed strong, long‐term bonds. Female COAs fluctuated with reproductive status. Using pooled data, COAs were lower and the same basic trends were evident. However, strong associations seen in the annual data were not evident in pooled data. Bottlenose dolphins that inhabit offshore, shallow water show many of the same social structure characteristics as in well‐studied coastal populations.

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.