Heavy metals, gastrointestinal polymer-related materials, and gut microbiome in an Indo-Pacific bottlenose dolphin (Tursiops aduncus) recovered from a fisheries bycatch-related event in the East China Sea.

Systematic recording of marine mammal strandings provides useful data on species occurrence, distribution, abundance, and threats, especially in regions with limited information like southern Iran. This study reports on strandings data collected by the Iran National Stranding Network across four coastal provinces bordering on the Persian Gulf and Oman Sea over the ten-year period from 2010 to 2020. A total of 167 stranding events involving 177 individuals were documented, comprising 14 marine mammal species: 11 odontocetes, two mysticetes and a dugong. The most commonly stranded species was the Indo-Pacific finless porpoise (Neophocaena phocaenoides) (n = 38), followed by Indo-Pacific bottlenose dolphins (Tursiops aduncus) (n = 23), and Indian Ocean humpback dolphins (Sousa plumbea) (n = 23). The greatest number of strandings occurred in the Hormozgan (47%) and Bushehr (37%) provinces, which have the longest coastlines. Stranding reports were nearly twice as frequent during the colder boreal winter (October–March) than the warmer spring and summer months (April–September). Over 65% of the records with enough information to allow analysis (n = 104/167) bore signs of fisheries interactions. Given the challenges of conducting boat-based research in Iran, stranding data are invaluable for understanding marine mammal populations, and expanding the stranding network is crucial for conservation efforts.

Symbolic encoding of bottlenose dolphin signature whistles: A lightweight method for representation and comparison

Two Cases of Early Orphan Survival in Indo‐Pacific Bottlenose Dolphins ( <i>Tursiops aduncus</i> ) From the Adelaide Dolphin Sanctuary, South Australia

Cooperation between unrelated individuals across social groups is a hallmark of human societies, underpinning our species' unique capacity for cultural transmission and large-scale cooperation. Although long considered rare among non-human animals, recent findings from bonobos and Indo-Pacific bottlenose dolphins demonstrate that members of both species will provide costly help to unrelated out-group conspecifics with no immediate return, revealing that such cooperation can also arise outside the human lineage. In this review, we synthesize current knowledge on the occurrence, mechanisms and drivers of between-group cooperation in these two species. Despite differences in evolutionary history and social structure, both species share convergent traits-such as protracted development, social flexibility, advanced socio-cognitive abilities and absence of range defence-probably fundamental for the emergence of costly cooperation across groups. We highlight future research priorities, including the ontogeny and stability of between-group relationships, behavioural and cognitive mechanisms supporting partner choice across groups and resilience of these relationships to demographic and ecological change. By integrating insights from these two model systems and placing them within a broader phylogenetic perspective, we outline emerging evolutionary and mechanistic frameworks for understanding the origins, maintenance and function of between-group cooperation, providing comparative perspectives on the evolutionary roots of human ultrasociality.

Per- and polyfluorinated alkyl substances (PFAS), metals, and metalloids were analysed in liver of 42 Indo-Pacific bottlenose dolphins (Tursiops aduncus) and 28 common dolphins (Delphinus delphis) from South Australia (SA). Dolphins sampled between 1993 and 2015 (20T. aduncus) were screened for eleven PFAS, while those sampled between 2021 and 2023 (22T. aduncus and 28 D. delphis) were analysed for twenty-nine PFAS, and eighteen metals and metalloids. Twenty-one PFAS were identified overall, with PFOS comprising ~ 80% of ∑PFAS. Average ∑PFAS concentrations were similar among T. aduncus and D. delphis during 2021-2023. ∑PFAS was significantly higher in Adelaide Dolphin Sanctuary (ADS) T. aduncus (0.4-5.2 compared to < 2.7mg/kg ww elsewhere). A decreasing trend in ∑PFAS, primarily driven by PFOS, was observed over time. A preliminary risk assessment based on tentative critical concentrations and hazard quotients indicated a reduced potential risk of adverse effects from PFOS exposure over time. Reductions may be due to regulatory efforts. ADS T. aduncus also exhibited significantly higher lead (0.13-1.9mg/kg dw) and tin (0.15-1.1mg/kg dw). In other SA regions, a low Selenium: Mercury ratio in 50% of T. aduncus, alongside Hg concentrations up to 2350mg/kg dw, highlights a toxicity concern. This study is unique in being the first in Australia to report changes in hepatic PFAS in dolphins over time. It underscores the importance of contaminant load reassessments to understand bioaccumulation. Findings will help to understand contaminant threats to human, wildlife, and environmental health.

Tail fluke loss in cetaceans compromises locomotion and impairs social functioning, posing serious welfare challenges. Rehabilitation strategies that address both physical performance and behavioral reintegration are essential for improving quality of life in affected individuals. This study evaluated the outcomes of a structured, two-phase rehabilitation program applied to Sami, an adult Indo-Pacific bottlenose dolphin (Tursiops aduncus) that underwent tail-fluke amputation, with an emphasis on locomotor function, behavioral adaptation, and long-term welfare. The rehabilitation protocol comprised two phases. Phase 1 focused on restoring vertical tail-beat locomotion through a combination of range-of-motion exercises and the use of a custom-designed prosthetic tail fluke. Swimming performance was quantitatively assessed using biologging devices under three conditions: without tail flukes, with the prosthetic tail, and in healthy conspecifics. Phase 2 introduced structured cohabitation with familiar individuals to promote social reintegration. Behavioral data were collected before and after rehabilitation to evaluate affiliative engagement and activity patterns. While maximum swim speed remained lower than in healthy individuals, propulsion per stroke significantly improved with prosthetic use. Notably, the subject dolphin retained species-typical vertical tail-beat motion even after prosthesis discontinuation, indicating motor pattern adaptation. Post-rehabilitation, affiliative behavior increased to 17% of total observed activity-more than twice that of a healthy control-while resting behavior markedly declined. No aggression or abnormal behaviors were observed. This study demonstrates that a welfare-centered, multi-phase rehabilitation framework can effectively promote both functional recovery and social reengagement in dolphins with severe caudal injuries. The long-term retention of adaptive locomotor and social behaviors highlights the potential of integrative approaches to enhance the quality of life in physically compromised cetaceans.

Dolphin whistles represent a primary mode of social communication, characterized by complex frequency modulations. Accurate estimation and tracking of whistle fundamental frequency ( f0) are crucial for understanding dolphin behavior and social interactions. Nevertheless, passive acoustic monitoring (PAM) of dolphins is compromised by marine ambient noise, which degrades f0 tracking accuracy and reduces PAM system effectiveness. To address these challenges, a three-stage approach for dolphin whistle f0 tracking, refered to as enhanced segmented adaptive Gaussian process regression, is proposed. First, a whistle enhancement algorithm based on improved local mean decomposition, effectively suppressing background noise interference, is proposed. Second, a framewise frequency estimation method using a nonlinear least squares (NLS) estimator, accelerated through Toeplitz-plus-Hankel matrix formulation for rapid computation, is developoed. Finally, segmented adaptive Gaussian process regression with Matérn Kernel (ν=3/2) approach to efficiently track the NLS-estimated frequency points is proposed. This method demonstrates suppressing measurement noise while restoring missing whistle f0 points. By leveraging the finite differentiability of the Matérn-3/2 kernel, this method achieves an optimal equilibrium between preserving local trajectory fidelity and maintaining global trend characteristics. Experimental validation using whistle signals from two Tursiops aduncus demonstrates that our proposed f0 tracking method achieves superior accuracy under different signal-to-noise ratios compared to existing approaches.

From fireflies to fiddler crabs and anurans to apes, males from across the animal kingdom perform synchronous displays in the mating context. Most do so in competition for mates, but few species synchronise signal production cooperatively. For example, synchrony in humans is cooperative; where interpersonal synchrony increases affiliation, cooperative ability, and group cohesion. Interestingly, multi-level alliances of male Indo-Pacific bottlenose dolphins in Shark Bay, Western Australia, also engage in cooperative synchrony. Adult males form pairs or trios to cooperatively herd single oestrus females, during which males perform elaborate synchronous displays. These displays comprise synchronous turns, leaps, and surfacing bouts around the female, but the function remains equivocal. Here, we used drone mounted video coupled with 40 years of behavioural data to investigate what social factors influence the performance of these synchronous displays by male dolphins. We found that males perform synchronous displays for longer after engaging in affiliative contact behaviour, and that those with weaker social bonds engaged in more precise synchrony with each other. Aligning with recent research on vocal synchrony in this population, we provide evidence that male dolphins use synchrony to both maintain and strengthen their social bonds. These findings suggest that dolphins have converged with humans on the use of synchronous displays to sustain multiple social bonds in nested, complex social systems.

ABSTRACT Skin lesions are valuable indicators of individual and population health in cetaceans. To understand the occurrence of skin and mucosal lesions among dolphins inhabiting South Australian waters, this study employs opportunistic sampling of deceased dolphins during 2021–2024. A total of 52 dolphins, comprising 23 Indo‐Pacific bottlenose dolphins ( Tursiops aduncus ) and 29 common dolphins ( Delphinus delphis ), underwent thorough macroscopic, microscopic, and ancillary diagnostics of identified lesions. Thirty‐three individuals displayed 115 skin and 12 mucosal lesions. The most common skin lesion sites were the head (23%–34%), peduncle (25%–26%), and lateral surfaces (17%–19%). A negative association was found between body condition and the number of infectious skin lesions in T. aduncus . Tattoo Skin Disease was identified in 13% of D. delphis skin lesions and 29% of T. aduncus skin lesions. Additional etiologies of skin lesions included bacteria (including Erysipelothrix rhusiopathiae , Mycobacterium marinum , Vibrio spp.), protozoa, physiological, and trauma‐related (propeller strike and shark bite). Opportunistic bacterial ulcerative dermatitis occurred predominantly in dolphins from the Adelaide Dolphin Sanctuary. Novel findings include the identification of herpesvirus in oral/genital papillomas, cutaneous lesions from an erysipelas‐infected animal, and M. marinum skin abscessation, not previously reported in free‐ranging Australian cetaceans. This study complements live‐animal observational studies and provides diagnostic insight into dolphin skin lesions, supporting their use as population and ecosystem health indicators.

Long-term host parasite dynamics in eight odontocete species from south-eastern South Africa

Although tool use offers obvious benefits to the user, the role of costs in the spread of tool use has received scant attention. Sponge tool use is a foraging technique restricted to a small subpopulation of bottlenose dolphins ( Tursiops aduncus ) in Shark Bay, Australia, that carry basket sponges on their beaks to probe the seafloor and flush out camouflaged fish, widening the search area and protecting the beak from abrasion. While most instances of animal tool use extend the phenotype, we hypothesized that sponges interfere with echolocation, particularly reception of echoes along the lower jaw. To evaluate how echolocation signals change while travelling through sponge tissue, we simulated echolocation using finite-element analysis based on digital models of sponge species ( Echinodictyum mesenterinum and Ircinia spp.). We find that acoustic properties of the echolocation signal are changed in the presence of Ircinia spp. and, to a lesser extent, E. mesenterinum . Given distortions vary with each sponge, dolphins must adaptively and flexibly compensate during neural signal processing. This explains why sponging takes so long to learn, is strictly vertically transmitted and does not spread to others despite close association with tool users. Taken together, these findings provide a compelling look at the underlying intrinsic and extrinsic forces shaping tool use in wild populations.

ABSTRACT The bottlenose dolphin is one of the most extensively distributed cetaceans, yet research in Asia, particularly in China, remains limited, leaving an information gap on the species' distribution and population abundance. From 2019 to 2022, surveys were conducted in the surrounding waters of the Nan Peng Archipelago waters, during which 14 groups of Indo‐Pacific bottlenose dolphins ( Tursiops aduncus ) were recorded across 15 survey trips. A total of 205 marked individuals were cataloged through photo‐identification. The likelihood of re‐sighting individuals across years was low (3.41%), and the cumulative individual identification curve remains in the growth phase, indicating that many individuals are likely yet to be identified. Additionally, species distribution models (SDMs) were used to predict the potential distribution of bottlenose dolphins around the Taiwan Strait, and the results indicated that this region may be identified as a distributional hotspot of this species. Our study underscores the importance of the Taiwan Strait as a critical habitat for Indo‐Pacific bottlenose dolphins.

ABSTRACT Investigating the foraging ecology and trophic interactions of threatened marine predators is critical to assess how community changes due to anthropogenic activities will affect predator–prey relationships. Two species of threatened coastal dolphins, the Indian Ocean humpback dolphin ( Sousa plumbea ) and the Indo‐Pacific bottlenose dolphin ( Tursiops aduncus ), occur off Nosy Be, north‐western Madagascar, in a region where artisanal fisheries are ecologically and socioeconomically important. Here, we investigated the feeding ecology of these two coastal dolphins and their trophic interactions with four other odontocetes using bulk stable carbon and nitrogen isotope analysis ( δ 13 C and δ 15 N). Humpback dolphins had significantly enriched δ 13 C values, reflecting a preference for coastal/benthic prey. Bottlenose dolphins had a broader isotopic niche, suggesting a broader range of prey and foraging habitats. The overlap in isotopic niche of all six odontocete species was limited, indicating partitioning of resources and habitats. Bayesian mass‐balance isotopic mixing models revealed that humpback dolphins forage primarily on reef planktivores (38.9%) and inner reef mesopredators (20.5%), while bottlenose dolphins had a broader diet, including reef‐associated (15%–32%) and pelagic prey (12%–23%). Our study reveals that the reliance on inshore prey by humpback dolphins may place them in competition with coastal fisheries.

Environmental DNA (eDNA) serves as a non-invasive tool for monitoring the presence of specific organisms in challenging or hard-to-access areas. We attempted non-invasive monitoring of Korean cetacean species by extracting eDNA from the western and southern seas of the Republic of Korea, as well as around Jeju Island. In the present study, we focused on two representative cetaceans of the Korean Sea: the narrow-ridged finless porpoise (Neophocaena asiaeorientalis sunameri) and oceanic dolphins (Family Delphinidae). When selecting polymerase chain reaction primers, mitochondrial DNA (mtDNA) of N. asiaeorientalis and microsatellite Slo4 of oceanic dolphins were identified as the most effective gene sequences in high abundance in low concentration eDNA samples, using tissue samples for eDNA detection of the target species. A total of 139 samples were collected, and eDNA was detected from finless porpoises (Neophocaena sp.) in 94 samples (68%) and from oceanic dolphins in 50 samples (36%). Significantly, eDNA revealed the considerable presence of finless porpoise around Jeju Island, despite a lack of visual confirmation. In the Yellow Sea, eDNA primarily detected the presence of common dolphin (Delphinus delphis), orca (Orcinus orca), and Indo-Pacific bottlenose dolphin (Tursiops aduncus). Indo-Pacific bottlenose dolphins were identified along the coast of Jeju Island. The value of this research lies in being the first attempt to explore cetacean eDNA across various species in Korea. Further cetacean eDNA research should focus on developing metabarcoding primers capable of detecting a greater variety of cetacean species and primers for detecting specific porpoise species. This study will serve as a valuable reference for future studies.

Erratum: The Survival of a Flukeless Juvenile Dolphin (Tursiops aduncus) in the Wild

Social learning, information transmission and culture play vital roles in the lives of social animals, influencing their survival, reproduction and ability to adapt to changing environments. However, the effect of anthropogenic disturbances on these processes is poorly understood in free-living animals. To investigate the impact of anthropogenic disturbance on social learning and information transmission, we simulated individual removal from contact networks derived from long-term behavioural datasets. We simulate the effects of individual removal on network efficiency and social learning for three group-living species—yellow baboons (Papio cynocephalus), African savanna elephants (Loxodonta africana) and Indo-Pacific bottlenose dolphins (Tursiops aduncus). We reveal how removals of key network positions reduce network efficiency. However, groups with high levels of innovation may cope with changing social network structures. These findings highlight the importance of protecting key individuals to preserve group structure and the role of innovation in possibly mitigating the fitness costs of removals. Identifying and safeguarding individuals that drive innovation can reduce a group’s susceptibility to anthropogenic threats and promote cultural resilience in social animals in a changing world. These emerging trends contribute to a growing understanding of the role of conservation interventions in protecting critical individuals in group-living animals.This article is part of the theme issue ‘Animal culture: conservation in a changing world’.

Bottlenose dolphins were often found in zoos and aquariums. Dolphin calves have a higher mortality rate in the first month after birth as they are unable to eat and breathe properly. The inability to thrive can affect growth until adulthood. This research was being conducted to better understand the nursing and breathing patterns of a bottlenose dolphin calf. Data were collected by observing the behaviour of a post-partum dolphin calf for 24 hours over 3 months (90 days). The behaviours observed were the calf's nursing (frequency, daily duration, and duration of suckling) and breathing (frequency). The results showed a decrease in the frequency of suckling and an increase in the duration of suckling, which indicated that the calf was becoming more successful at suckling. A constant decrease in respiratory frequency indicated a healthy growing calf due to an increase in lung capacity. These results indicated that the feeding and respiratory behaviour patterns of normally developing bottlenose dolphin calves showed a decrease in feeding frequency and an increase in feeding duration, as well as a decrease in respiratory frequency per week. Further studies on the feeding and respiratory behaviour of bottlenose dolphin calves.

ABSTRACTThis study examined association patterns, social clustering, and temporal stability of Indo‐Pacific bottlenose dolphins off the North West Cape (NWC), Western Australia. Over 6 years, boat‐based surveys collected photo‐identification data, enabling repeated sampling, sighting history construction, and associate identification. Among the 344 adult dolphins identified, 116 were sighted at least five times and used in association analyses. A strong correlation (r = 0.86 ± 0.01 SE) between true and estimated association indices, along with a high coefficient of variation (S = 1.92 ± 0.9 SE), indicates a highly differentiated society with diverse relationships among individuals. Generalized affiliation indexes, social network metrics, and lagged association rates revealed predominantly loose, short‐term associations within a well‐connected but non‐clustered social network. These fluid association patterns are likely related to the open and transient nature of this population, where individuals move in and out of the study area. These movements provide opportunities for social interactions among different individuals, and members of different groups may fission for varying periods of time. Findings from this study provide a solid baseline for future studies looking at the sociogenetic structure of this population and the environmental and social factors driving their fluid social system.

Bottlenose dolphins produce individually distinctive signature whistles (SWs) to broadcast identity. Stability of the SW frequency contour is essential to preserve identity information; however, SWs could carry additional information which requires variability. We used acoustic recordings from provisioned free-swimming Indo-Pacific bottlenose dolphins at Moreton Island (Mulgumpin), Australia, collected in 2002 and 2017-2018, to assess the long-term (15-year) stability in SWs, and if variability of acoustic parameters increases with whistle complexity. Stability was assessed by analyzing basic contour parameters (minimum and maximum frequency, duration, etc.) and visually. We quantified SW variability using two developed variability metrics. Complexity was defined using four developed metrics, and its effect on variability was tested. Our results demonstrated that SW contours remain highly stable over time, but minimum frequency decreased by 8.8%. SWs also showed different degrees of variability between individuals. Variability appeared to be higher in males than in females, possibly indicating differences in SW use in different social contexts. Furthermore, SWs with a greater level of frequency modulation varied more than less modulated whistles. We propose that SWs possess sufficient variation in their frequency contour to contain additional information, possibly related to social and behavioral context, while still maintaining their identity function.