Tursiops Aduncus Research Articles

Diversity, Distribution, and Density of Marine Mammals Along the Saudi Waters of the Arabian Gulf: Update From a Multi-Method Approach

Despite the important role of marine mammals in marine ecosystems and the imperative for their conservation, there is still a great lack of information on the diversity, distribution, and density of these animals in the Saudi waters of the Arabian Gulf. To fill this gap, an integrative data-collection approach including fishermen’s questionnaires, opportunistic sighting reports, and directed boat-based surveys, was undertaken between 2016 and 2020, leading to the first scientific report of marine mammal diversity, distribution, and density in the region. The results of the different approaches carried out during the study confirmed a high diversity of cetaceans on the west coast of the study area, with bottlenose dolphins (Tursiops aduncus), humpback dolphins (Sousa plumbea) and dugongs (Dugong dugon) as the most common species. While the two dolphin species were found to be widely distributed in both coastal and offshore waters,D. dugonappears to occur exclusively in coastal waters in the southern part of the study area, mainly in the Gulf of Salwah. The presence of both species of dolphins increased during the summer months and in the vicinity of the numerous oil and gas facilities in this region. The distribution of the observed dolphins was found mostly within a 10–20 km radius around each facility. Other cetacean species observed less frequently in the area include Bryde’s whale (Balaenoptera edeni), killer whale (Orcinus orca), common dolphin (Delphinus delphis) and finless porpoise (Neophocaena phocaenoides). Regarding the density of marine mammals in the region, boat-based surveys confirmed the results of fishermen’s questionnaires and reports of opportunistic sightings, with bottlenose and humpback dolphins being the most abundant species. These results provide a baseline for policies oriented to the conservation of mammals in the Saudi waters of the Arabian Gulf.

Age‐related changes to the speckle patterns on wild Indo‐Pacific bottlenose dolphins

AbstractAge estimating wild dolphins using noninvasive methods will improve our understanding of their ontogeny. Speckles appear on the ventral through to the lateral areas of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) as they age. Age‐related changes in the speckle density and shape were examined using type classification. Speckles first appeared on the ventral area of the genital area at approximately 6.5 years. They increased in two specific directions, from the genital area to the jaw and from the ventral side to the lateral side. The speckle shape changed with aging from a dot‐shape to oblong. Individuals aged over 35 years possessed more speckles than those aged 24–26 years. The oldest age category of dolphins in this study was over 35 years. The speckling area similarly increased with age for all individuals. Therefore, the results suggest that speckle condition can be used to estimate age. The relationship between speckling area and age showed no significant sexual dimorphism except near the genital slit area. There was no speckle area around the genital slit which differed in shape between the sexes. Therefore, speckle patch shape may be a useful sex confirmation tool.

Distribution and Habitat Preferences of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) Inhabiting Coastal Waters With Mixed Levels of Protection

Assessments of species distributions are crucial for informing conservation and management action. In this study, we used ensemble modelling to explain the distribution of Near Threatened Indo-Pacific (IP) bottlenose dolphins (Tursiops aduncus) in coastal waters at the North West Cape (NWC), Western Australia (WA), an area encompassing a marine protected area (MPA) and adjacent unprotected coastal waters. Analyses used dolphin sighting data collected during boat-based surveys conducted from 2013 to 2015 and 2018 to 2019. Overall, the distribution of IP bottlenose dolphins was best explained by distance to coast (up to 2,000 m) and distance to boat ramp (up to 7,000 m). Areas of high probability of occurrence for dolphins extended from the tip and down the eastern side of the NWC and overlapped with designated sanctuary zones as well as waters beyond the boundaries of the Ningaloo Marine Park (NMP). Distribution and habitat preferences varied slightly with season. In autumn, dolphin distribution was best explained by distance to coast and water depth with a higher likelihood of observing dolphins 1,000–2,000 m from the coast and in water depths of 7–10 m deep. During winter months, distance to coast (1,000–2,000 m) and sea surface temperature (SST) (21.5–23.5°C) were the most important explanatory variables, with presence in coastal lagoons to the west of the NWC more likely than other seasons. During spring, areas of moderate to high probability of dolphin occurrence were mainly located outside the NMP, with marine park zone (outside the NMP and Sanctuary zones within the NMP, the two zones with the highest probability of IP bottlenose dolphin occurrence) and water depth (waters 7–13 m deep) best explaining dolphin distribution. This study highlights the importance of inshore areas of the NWC for IP bottlenose dolphins and the potential vulnerability of this species to increasing and cumulative anthropogenic stressors associated with these areas. Results of this study should be considered in future zoning reviews and adaptive management efforts of the NMP allowing for effective management of this Near Threatened species.

Vulnerability of a top marine predator in one of the world’s most impacted marine environments (Arabian Gulf)

Knowledge of the habitat use of wildlife in highly impacted areas is essential to identify areas of biological importance and to implement appropriate conservation measures. The Arabian Gulf represents one of the most extreme marine environments and is considered one of the regions in the world with the greatest anthropogenic impact. Information on the habitat use and abundance of marine top predator species is, however, lacking, despite being a prerequisite for effective planning of conservation measures. Here, we provide novel information for the Indo-Pacific bottlenose dolphin (Tursiops aduncus) in the Arabian Gulf (Abu Dhabi, United Arab Emirates). Data from 80 daily surveys conducted between June 2014 and November 2019 were used both to assess correlates of bottlenose dolphin habitat use and relative density and to calculate mark-recapture abundance estimates. This study confirms the strong adaptability and tolerance of this top marine predator to extreme environmental conditions within a highly heterogeneous and impacted marine habitat. The observed preferences for areas with less human pressure were likely a result of the interactions of environmental factors with prey availability and human disturbance. This study also provides the first abundance estimates for a bottlenose dolphin population in the Arabian Gulf. Our findings support the call for increased marine-protected areas and the creation of transboundary conservation areas in the region. Regional connectivity should be of value to marine predators whose wide distribution and vulnerability to human activities means that alteration of their habitats can result in population declines and eventual local or regional extinctions.

Cetacean Research and Citizen Science in Kenya

In 2011, several non-governmental and government agencies established the Kenya Marine Mammal Network (KMMN) to provide a platform for the consistent collection of data on marine mammals along the Kenyan coast, identify areas of importance and engage marine users and the general public in marine mammal conservation. Prior to the KMMN, relatively little was known about marine mammals in Kenya, limiting conservation strategies. The KMMN collects data nationwide through dedicated surveys, opportunistic sightings and participative citizen science, currently involving more than 100 contributors. This paper reviews data on sightings and strandings for small cetaceans in Kenya collated by the KMMN. From 2011 to 2019, 792 records of 11 species of small cetaceans were documented. The most frequently reported inshore species were the Indo-Pacific bottlenose dolphin and Indian Ocean humpback dolphin. Offshore species, included killer whales, short-finned pilot whale and long-snouted spinner dolphin. Indo-Pacific bottlenose dolphins, long-snouted spinner dolphins, striped dolphins and Risso’s dolphins were recorded through stranding reports. The efforts of the KMMN were disseminated through international meetings (International Whaling Commission, World Marine Mammal Conference), national status reports, outreach and social media. Data has also supported the identification of three IUCN Important Marine Mammal Areas and one Area of Interest in Kenya. Further research is needed to improve estimates of cetacean abundance and distribution, particularly in unstudied coastal areas, and to assess the extent of anthropogenic threats associated with fisheries, coastal and port development, seismic exercises and unregulated tourism. The expansion of the network should benefit from the participation of remote coastal fishing communities, government research agencies, tourism and seismic operations, among others. The KMMN demonstrated the value of dedicated and citizen science data to enhance marine mammal conservation strategies to boost awareness and eco-tourism and to bring the public and science closer together, promoting research and effective conservation efforts.

Failure in the Colonization of a New Area by Indo-Pacific Bottlenose Dolphins (Tursiops aduncus), Japan

Failure in the Colonization of a New Area by Indo-Pacific Bottlenose Dolphins (Tursiops aduncus), Japan

Identifying optimal wavelengths to maximise the detection rates of marine fauna from aerial surveys

Aerial surveys are increasingly used for assessing the presence and abundance of many large faunal species. However, detection rates often suffer significant sightability errors. Using sensors that capture thermal infrared can sometimes improve the detectability of fauna by increasing the contrast of target animals against their surrounds. However, there are several situations where this does not work well. Submerged fauna in marine environments are one example, and where the detection error can be substantial. To identify what wavelength selection might enhance detectability rates beyond standard cameras, we used a drone-based hyperspectral sensor to measure the reflectance of 64 animals and their corresponding surrounds. Fauna included white sharks (Carcharodon carcharias), bottlenose dolphins (Tursiops aduncus), and various other species of ray (Rhinoptera neglecta, Aetobatus narinari, Rhynchobatus australiae) and fish (Seriola lalandi). Data were analysed using Generalized Additive Mixed-Models (GAMM) to compare the difference in spectral reflectance between fauna and their surrounds. The GAMMs showed little difference between submerged fauna groups, but indicated that a band of wavelengths between 514 and 554 nm provided the greatest contrast between fauna and their surrounding backgrounds. This was also consistent across the range of environmental conditions. We contend that restricting the spectral input to a standard high-resolution camera, or focusing on the channels that accentuate the green colours in post-processing, will likely result in increased accuracy in the detection of submerged fauna. This approach may also be applied to fauna surveys in other landscapes, particularly where the use of thermal sensors is not appropriate.

Cognitive enrichment device provides evidence for intersexual differences in collaborative actions in Indo-Pacific bottlenose dolphins (Tursiops aduncus).

Social living, long lifespan and advanced cognitive skills provided favourable conditions for the development of pro-social behaviours and cooperative activities in cetacean. Dolphins have been observed to collaborate for various purposes, finding food, finding mates or raising and teaching younger individuals. This study investigated the potential impact of demographic factors (sex and age), social factors (relatedness and group size), and individual experience in a cooperative problemsolving task. A cognitive enrichment device was tested with 22 dolphins in 11 group settings. The device consisted of a tube, containing ice and fish, sealed by two caps with rope handles and designed to be operated by pairs of dolphins. The investigation focused on the differences in trial outcome (success rate of cooperative opening of the device) and on cooperative play (dolphin pairs engaging in synchronous swim with the device). From the five potential factors, sex showed the highest impact. Cooperative openings were more than four times more frequent in males than in females (75% vs 17%, respectively), and cooperative play was exclusively displayed by adult males. Given the strong correlation between cooperative opening and cooperative play, we argue the two behaviours can be regarded as parts of a cooperative action chain. This study provides the first evidence for intersexual differences in collaborative actions in dolphins under systematic testing conditions.

Possible limitations of dolphin echolocation: a simulation study based on a cross-modal matching experiment

Dolphins use their biosonar to discriminate objects with different features through the returning echoes. Cross-modal matching experiments were conducted with a resident bottlenose dolphin (Tursiops aduncus). Four types of objects composed of different materials (water-filled PVC pipes, air-filled PVC pipes, foam ball arrays, and PVC pipes wrapped in closed-cell foam) were used in the experiments, respectively. The size and position of the objects remained the same in each case. The data collected in the experiment showed that the dolphin’s matching accuracy was significantly different across the cases. To gain insight into the underlying mechanism in the experiments, we used finite element methods to construct two-dimensional target detection models of an echolocating dolphin in the vertical plane, based on computed tomography scan data. The acoustic processes of the click’s interaction with the objects and the surrounding media in the four cases were simulated and compared. The simulation results provide some possible explanations for why the dolphin performed differently when discriminating the objects that only differed in material composition in the previous matching experiments.

Whole genomes reveal multiple candidate genes and pathways involved in the immune response of dolphins to a highly infectious virus.

Wildlife species are challenged by various infectious diseases that act as important demographic drivers of populations and have become a great conservation concern particularly under growing environmental changes. The new era of whole genome sequencing provides new opportunities and avenues to explore the role of genetic variants in the plasticity of immune responses, particularly in non-model systems. Cetacean morbillivirus (CeMV) has emerged as a major viral threat to cetacean populations worldwide, contributing to the death of thousands of individuals of multiple dolphin and whale species. To understand the genomic basis of immune responses to CeMV, we generated and analysed whole genomes of 53 Indo-Pacific bottlenose dolphins (Tursiops aduncus) exposed to Australia's largest known CeMV-related mortality event that killed at least 50 dolphins from three different species. The genomic data set consisted of 10,168,981 SNPs anchored onto 23 chromosome-length scaffolds and 77 short scaffolds. Whole genome analysis indicated that levels of inbreeding in the dolphin population did not influence the outcome of an individual. Allele frequency estimates between survivors and nonsurvivors of the outbreak revealed 15,769 candidate SNPs, of which 689 were annotated to 295 protein coding genes. These included 50 genes with functions related to innate and adaptive immune responses, and cytokine signalling pathways and genes thought to be involved in immune responses to other morbilliviruses. Our study characterised genomic regions and pathways that may contribute to CeMV immune responses in dolphins. This represents a stride towards clarifying the complex interactions of the cetacean immune system and emphasises the value of whole genome data sets in understanding genetic elements that are essential for species conservation, including disease susceptibility and adaptation.

Elevated Calf Mortality and Long-Term Responses of Wild Bottlenose Dolphins to Extreme Climate Events: Impacts of Foraging Specialization and Provisioning

As demands for wildlife tourism increase, provisioning has become a popular means of providing up-close viewing to the public. At Monkey Mia, Shark Bay, Australia, up to five adult female Indo-Pacific bottlenose dolphins (Tursiops aduncus) visit a 100 m stretch of beach daily to receive fish handouts. In 2011, a severe marine heatwave (MHW) devastated seagrass and fish populations in Shark Bay. Offspring survival declined precipitously among seagrass specialists (dolphins that forage disproportionately in seagrass habitat). As all provisioned dolphins at the site are seagrass specialists, we examined how provisioned and non-provisioned seagrass specialists responded to the MHW. Using 27 years of data we compare habitat use, home range size, calf mortality, and predation risk between provisioned and non-provisioned females and their offspring before and after the MHW. Our results show that provisioned females have extremely small home ranges compared to non-provisioned females, a pattern attributable to their efforts to remain near the site of fish handouts. However, weaned offspring (juveniles) born to provisioned females who are not provisioned themselves also had much smaller home ranges, suggesting a persistent maternal effect on their behavior. After the MHW, adult females increased their use of seagrass habitats, but not their home range size. Provisioned females had significantlylowercalf mortality than non-provisioned females, a pattern most evident pre-MHW, and, in the first 5 years after the MHW (peri-MHW, 2011–2015), calf mortality did not significantly increase for either group. However, the ecosystem did not recover, and post-MHW (2016–2020), calf mortality was substantially higher, regardless of provisioning status. With few survivors, the impact of the MHW on juvenile mortality post-weaning is not known. However, over three decades, juvenile mortality among offspring of provisioned vs. non-provisioned females did not statistically differ. Thus, the survival benefits accrued to calves in the provisioned group likely cease after weaning. Finally, although shark attack rates on seagrass specialists did not change over time, elevated predation on calves cannot be ruled out as a cause of death post-MHW. We discuss our results as they relate to anthropogenic influences on dolphin behavioral plasticity and responses to extreme climate events.

Social Structure, Habitat Use and Injuries of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) Reveal Isolated, Coastal, and Threatened Communities in the South Pacific

Understanding population structure and habitat use of poorly known cetacean species is a first step toward scientifically informed management decisions. In the southern range of New Caledonia (South Pacific), a long-term dataset of Indo-Pacific bottlenose dolphins (Tursiops aduncus) encounters primarily during winter seasons 1997 to 2019 (473 group observations) was used to assess social structure, habitat use and potential threats. A total of 338 individuals were photographically identified, forming three distinct communities in the south-west lagoon, the south lagoon and the Isle of Pines. Mark-recapture histories revealed that the three communities were weakly connected and might be considered as independent management units. Suitable habitats were estimated with presence-only distribution models relative to topographic and seabed substrate predictors. Habitat suitability increased with proximity to coasts or reefs, at shallow depth, and over muddy bottom. These habitats had various levels of protection and were used by humans, mostly in the south-west lagoon. External injuries were interpreted to determine natural interactions and potential anthropogenic threats. The prevalence in injuries did not vary among the three areas. A substantial proportion of injuries related to propeller hits was reported, representing a total of 16.7% (34 of 204) of all injuries observed on dolphins. The three communities of Indo-Pacific bottlenose dolphins revealed in the southern part of New Caledonia are particularly vulnerable due to their insularity, their coastal habitat use and the low levels of connectivity found among them. In a context of increasing maritime traffic, fishing and recreational activities, this study provides a useful baseline to the urgent assessment of the conservation status of dolphins in New Caledonia.

Inconsistency Between Socio-Spatial and Genetic Structure in a Coastal Dolphin Population

Identifying population structure and boundaries among communities of wildlife exposed to anthropogenic threats is key to successful conservation management. Previous studies on the demography, social and spatial structure of Indo-Pacific bottlenose dolphins (Tursiops aduncus) suggested four nearly discrete behavioral communities in Perth metropolitan waters, Western Australia. We investigated the genetic structure of these four communities using highly polymorphic microsatellite markers and part of the hypervariable segment of the mitochondrial control region. Overall, there was no evidence of spatial genetic structure. We found significant, yet very small genetic differentiation between some communities, most likely due to the presence of highly related individuals within these communities. Our findings of high levels of contemporary migration and highly related individuals among communities point toward a panmictic genetic population with continuous gene flow among each of the communities. In species with slow life histories and fission-fusion dynamics, such asTursiopsspp., genetic and socio-spatial structures may reflect different timescales. Thus, despite genetic similarity, each social community should be considered as a distinct ecological unit to be conserved because they are exposed to different anthropogenic threats and occur in different ecological habitats, social structure being as important as genetic information for immediate conservation management. The estuarine community, in particular, is highly vulnerable and appropriate conservation measures are needed in order to maintain its connectivity with the adjacent, semi-enclosed coastal communities.

Long-Term Demographic and Spatio-Temporal Trends of Indo-Pacific Bottlenose Dolphin (Tursiops aduncus) Bycatch in Bather Protection Nets off KwaZulu-Natal, South Africa

Bather protection nets have been in place off the coast of KwaZulu-Natal (KZN), South Africa, since the 1950’s. Besides sharks, they also catch a number of other marine vertebrates, including dolphins, the majority of which are Indo-Pacific bottlenose dolphinsTursiops aduncus. Previous analyses of dolphin bycatch in the nets indicated the potential impacts on the local populations, but a lack of information on population structure has to-date hindered a more detailed assessment. A recent re-assessment of the status and population delineations ofT. aduncusoff South Africa prompted a re-examination of demographic, spatial, and temporal patterns of its catches in bather protection nets over a 36-year period (January 1980 to December 2015). In total, 1169 dolphins were caught, including a slightly greater number of females and juveniles than other sex-classes, raising concern about the potential long-term effects on population demographics. More dolphins were caught off the North than the South coast. Temporal trends indicate that the bycatch during June and July every year (peak Sardine Run period) as a percentage of overall dolphin bycatch has been steadily decreasing from 39.8% in 1980 to 13% in 2015. A large inter-annual fluctuation can be seen, probably as a result of the inter-annual intensity of the Sardine Run. Although our results do not indicate a long-term decline of the individual populations as previously predicted, revised abundance estimates and data on the demographics and movement patterns of the animals are urgently required to accurately assess the impact of bycatch on the Indo-Pacific bottlenose dolphin populations off KZN and to advise conservation and management decisions going forward.

Foraging preferences of an apex marine predator revealed through stomach content and stable isotope analyses

Insights into the food habits of predators are essential for maintaining healthy predator populations and the functioning of ecosystems. Stomach content and stable isotope analyses were used to investigate the foraging habits of an apex predator, the Indo-Pacific bottlenose dolphin (Tursiops aduncus) in south-western Australia. A total of 2,594 prey items from 26 families were identified from the stomachs of 10 deceased stranded dolphins. Fish otoliths from stomach contents were used to identify fish to family or species level. Ninety-three percent of identified stomach contents were perciforme fishes, however, perciformes comprised only 30% of the catch during prey sampling. Gobiidae species, small fish generally <100 mm in total length, were the most prevalent family identified in dolphin stomachs, accounting for 82% of identified prey, yet Gobiidae accounted for 12.7% of the catch during prey sampling. For stable isotope analyses, tissue samples from 14 free-ranging dolphins were analyzed for nitrogen (δ15N) and carbon (δ13C) ratios. From stable isotope analyses and boat-based dolphin photo-identification surveys (n = 339, 2007–2011), results indicated niche differentiation between coastal and inshore (bay and estuarine habitat) dolphins. Carbon signatures showed that coastal dolphins had a more pelagic diet compared to a benthic diet observed in the inshore dolphins. Whereas, nitrogen signatures of inshore dolphins showed higher nitrogen levels than coastal dolphins, likely attributed to feeding on enriched prey typical of estuarian environments. Overall, these results indicated that bottlenose dolphins in the study area were selective foragers and that their foraging is specialized by the habitats most frequently used.

Prey Species and Foraging Behaviour of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) Around Mikura Island in Japan

Prey Species and Foraging Behaviour of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) Around Mikura Island in Japan

Seroprevalence of Antibodies Against Paracoccidioides Spp. in Captive Dolphins from Three Aquaria in Japan.

The skin disease paracoccidioidomycosis ceti occurs in several dolphin species globally. Infection by the unculturable fungi Paracoccidioides brasilensis or other Paracoccidioides spp. results in chronic cutaneous and granulomatous lesions. In this study we used immunohistochemistry to investigate the seroprevalence of antibodies to Paracoccidioides spp. in captive dolphins from three aquaria in Japan. We had previously reported that there were serological cross-reactions for Paracoccidioides spp. with related species in the order Onygenales. We hypothesized that the degree of serological cross-reactions for Paracoccidioides spp. might be lower in areas, such as Japan, where the fungal diseases coccidiodomycosis and paracoccidiodomycosis are not endemic. Sera from 41 apparently healthy dolphins, including 20 Atlantic bottlenose dolphins (BD: Tursiops truncatus), 6 Indo-Pacific bottlenose dolphins (IPBD: Tursiops aduncus), 2 F1 generation of a cross between BD and IPBD (F1), 3 Pacific white-sided dolphins (PWD: Lagenorhynchus obliquidens), 2 pantropical spotted dolphins (PSD: Stenella attenuata), 6 false killer whales (FKW: Pseudorca crassidens), and 2 rough-toothed dolphins (RTD: Steno bredanensis) were investigated. Sera from three dolphins with paracoccidioidomycosis ceti were used as a positive control. The yeast-form cells of Paracoccidioides spp. in the cutaneous tissue sample derived from the first Japanese paracoccidioidomycosis ceti case were used as the antigen for the immunohistochemistry. Of the 41 dolphins tested, 61.0% had antibodies against Paracoccidioides spp. This indicates that dolphins of several species in Japanese aquaria have likely been exposed to the pathogen Paracoccidioides spp.

Abundance of Indo-Pacific bottlenose dolphins (Tursiops aduncus) along the south coast of South Africa.

Coastally distributed dolphin species are vulnerable to a variety of anthropogenic pressures, yet a lack of abundance data often prevents data-driven conservation management strategies from being implemented. We investigated the abundance of Indo-Pacific bottlenose dolphins (Tursiops aduncus) along the south coast of South Africa, from the Goukamma Marine Protected Area (MPA) to the Tsitsikamma MPA, between 2014 and 2016. During this period, 662.3h of boat-based photo-identification survey effort was carried out during 189 surveys. The sighting histories of 817 identified individuals were used to estimate abundance using capture-recapture modelling. Using open population (POPAN) models, we estimated that 2,155 individuals (95% CI: 1,873–2,479) occurred in the study area, although many individuals appeared to be transients. We recorded smaller group sizes and an apparent decline in abundance in a subset of the study area (Plettenberg Bay) compared to estimates obtained in 2002–2003 at this location. We recorded declines of more than 70% in both abundance and group size for a subset of the study area (Plettenberg Bay), in relation to estimates obtained in 2002–2003 at this location. We discuss plausible hypotheses for causes of the declines, including anthropogenic pressure, ecosystem change, and methodological inconsistencies. Our study highlights the importance of assessing trends in abundance at other locations to inform data-driven conservation management strategies of T. aduncus in South Africa.

Sexual maturity, seasonal estrus, and gestation in female Indo-Pacific bottlenose dolphins Tursiops aduncus inferred from serum reproductive hormones.

Reproductive hormones in serum concentrations of progesterone, estradiol, and testosterone in female Indo-Pacific bottlenose dolphins (Tursiops aduncus, n = 12) housed in Ocean Park Hong Kong were investigated in the present study. Results showed that, onset of puberty of captive Indo-Pacific bottlenose dolphins was at 5 years while sexual maturity was at 6. Average serum progesterone concentrations in non-pregnant sexually mature individuals was 0.33 (0.25-0.97) ng/mL (interquartile), significantly higher than in immature ones 0.26 (0.25-0.38) ng/mL. This study found significant difference in serum estradiol concentrations between individuals at the onset of puberty (9.5± 1.7 pg/mL, ±SD) and not (below detection limit 9 pg/mL). A slightly seasonal breeding pattern, with progesterone values tend to be higher from February to October (0.38 [0.25-1.07] ng/mL) was inferred. During pregnancy, serum progesterone concentrations range from 10.54 ± 8.74 ng/mL (indexed month post-conception [IMPC] 0) to 25.49 ± 12.06 ng/mL (IMPC 2), and display a bimodal pattern with 2 peaks in early- (25.49 ± 12.06 ng/mL, IMPC 2) and late-pregnancy (21.71 ± 10.25 ng/mL, IMPC 12), respectively. Serum estradiol concentrations can seldom be detected in early-pregnancy and increase constantly in mid- (9.45 ± 1.83 pg/mL) and late-pregnancy (11.88± 3.81 pg/mL), with a spike (15.45 ± 6.78 pg/mL) 1 month prior to delivery. Serum testosterone concentrations elevate significantly in IMPC 7 (0.36± 0.10ng/mL) compared to other months (0.16± 0.10ng/mL) of the year. The present study provides normal concentration profiles for some reproductive hormones in female Indo-Pacific bottlenose dolphins and can contribute to the breeding monitoring of this species. Also, our study would shed further light on the reproductive physiology of small cetaceans.

Occurrence of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) off the Wild Coast of South Africa using photographic identification

AbstractThe present study represents the first reported boat‐based photographic identification study of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) off the Wild Coast of southeast South Africa. This area is known for the annual sardine run, which attracts apex predators to the region during the austral winter. Dedicated photo‐identification surveys were conducted along this coast at three different study sites in February, June, and November of each year from 2014 to 2016. During 47 surveys, 136 bottlenose dolphin groups were encountered, an estimated 4,474 dolphins observed, and 2,149 individuals were identified. Although most individuals (N = 1,770, 82.4%) were only observed once, some were resighted 2–7 times (N = 379, 17.6%), with an average of 305 days (range: 88–705 days) between resightings. The majority of bottlenose dolphins were resighted within the same study site (N = 192), indicating some degree of residency. However, 65 individuals were observed at two different study sites, indicating individual movements along the coast. Our findings contrast earlier suggestions that bottlenose dolphins only use the Wild Coast during the sardine run, as we found large number of animals year‐round with some level of site fidelity. This highlights the importance of the Wild Coast to bottlenose dolphins and provides further information on their status off southeastern South Africa.