Endocrine-Disrupting Chemical Exposure Induces Adverse Effects on the Population Dynamics of the Indo-Pacific Humpback Dolphin.

Cetaceans play a pivotal role in maintaining the ecological equilibrium of ocean ecosystems. However, their populations are under global threat from environmental contaminants. Various high levels of endocrine-disrupting chemicals (EDCs) have been detected in cetaceans from the South China Sea, such as the Indo-Pacific humpback dolphins in the Pearl River Estuary (PRE), suggesting potential health risks, while the impacts of endocrine disruptors on the dolphin population remain unclear. This study aims to synthesize the population dynamics of the humpback dolphins in the PRE and their profiles of EDC contaminants from 2005 to 2019, investigating the potential role of EDCs in the population dynamics of humpback dolphins. Our comprehensive analysis indicates a sustained decline in the PRE humpback dolphin population, posing a significant risk of extinction. Variations in sex hormones induced by EDC exposure could potentially impact birth rates, further contributing to the population decline. Anthropogenic activities consistently emerge as the most significant stressor, ranking highest in importance. Conventional EDCs demonstrate more pronounced impacts on the population compared to emerging compounds. Among the conventional pollutants, DDTs take precedence, followed by zinc and chromium. The most impactful emerging EDCs are identified as alkylphenols. Notably, as the profile of EDCs changes, the significance of conventional pollutants may give way to emerging EDCs, presenting a continued challenge to the viability of the humpback dolphin population.

Estimation of Per- and Polyfluorinated Alkyl Substance Induction Equivalency Factors for Humpback Dolphins by Transactivation Potencies of Peroxisome Proliferator-Activated Receptors.

The potential risks of per- and polyfluoroalkyl substance (PFAS) accumulation in nearshore dolphins are not well understood. Here, transcriptional activities of 12 PFAS on peroxisome proliferator-activated receptors (PPAR-α, -ß/δ, and -γ) in Indo-Pacific humpback dolphins (Sousa chinensis) were evaluated. All PFAS activated scPPAR-α in a dose-dependent manner. PFHpA exhibited the highest induction equivalency factors (IEFs). The order of IEFs for other PFAS was as follows: PFOA > PFNA > PFHxA > PFPeA > PFHxS > PFBA > PFOS > PFBuS ≈ PFDA ≫ PFUnDA and PFDoDA (not activated). The total induction equivalents (∑IEQs, 5537 ng/g wet weight) indicated that more attention should be paid to investigating contamination levels in dolphins, especially in PFOS (82.8% contribution to the ∑IEQs). The scPPAR-ß/δ and -γ were not affected by any PFAS, except for PFOS, PFNA, and PFDA. Furthermore, PFNA and PFDA could induce higher PPAR-ß/δ and PPAR-γ-mediated transcriptional activities than PFOA. Compared to human beings, PFAS might be more potent PPAR-α activators in humpback dolphins, suggesting that the dolphins may be more susceptible to the adverse effects of PFAS. Our results may be instructive for understanding the impacts of PFAS on marine mammal health due to the identical PPAR ligand-binding domain.

Ranging pattern development of a declining delphinid population: A potential cascade effect of vessel activities.

It is generally accepted that vessel activity causes various behavioral responses of cetaceans and undermines individual fitness. Whether or how it can lead to a demographic response of populations remains rarely examined. In the northern Beibu Gulf, China, vessel activities have sharply increased in the past two decades, while abnormal demographic dynamics was recently noted for the resident Indo-Pacific humpback dolphins. The present study first examined the humpback dolphins' utilization distribution (UD) from 2003 to 2019. Habitat suitability was then modeled with the sighting data collected before the most recent population reduction. Finally, we tried to disentangle the anthropogenic driver of dolphin demography by cross-referring the spatiotemporal development of dolphins' UD, vessel activities, and habitat suitability. Our results showed that the dolphins' UD shrank substantially during the port expansion in the early 2010s, and we suggest that the consequential increase in vessel activities might impose extra marine stressors on the resident humpback dolphins. To reduce the boat interaction, the dolphins steadily shifted their core area to a less suitable area in the east during 2015-2017, when unnaturally low survivals were recorded. Afterward, the dolphin core area partially shifted back to the more suitable area in the west, which corresponded to the improving dolphin survival in 2018. Our finding suggested that the vessel activity may be responsible for the dolphin displacement, while staying in the less suitable area may further lead to a more severe and acute demographic consequence on the population. The underlying and indirect impact of vessel activities as disclosed by the present study is particularly important for port management, marine planning, and conservation practice regarding coastal cetaceans, especially for those resident and endangered populations inhabiting the urbanized coastal areas.

An Indo-Pacific humpback dolphin (Sousa chinensis) severely injured by vessel collision: live rescue at sea, clinical care, and postmortem examination using a virtopsy-integrated approach.

BACKGROUND: Vessel collision induces blunt and sharp force traumas to aquatic animals and is a leading anthropogenic impact affecting cetaceans worldwide. Vessel collision is an important threat affecting vulnerable coastal cetaceans such as the Indo-Pacific humpback dolphins (Sousa chinensis) which reside in coastal waters of Hong Kong amongst heavy marine traffic. CASE PRESENTATION: A severely injured subadult S. chinensis was sighted in the waters off southwestern Hong Kong with four gaping incision wounds on its dorsum. It was in poor body condition and seemed unable to use the fluke effectively. The deepest wound located at the caudal peduncle near the base of the fluke and exposed the underlying fractured caudal vertebrae. The dolphin was monitored in the field over three weeks and eventually captured for medical intervention as veterinary assessment indicated progressive and life-threatening deterioration. During rehabilitation, the dolphin demonstrated initial signs of improvement over the first 36 hours as supported by diagnostic tests but then deteriorated rapidly. It was humanely euthanised after three days of rehabilitation. Postmortem investigation was carried out using virtopsy (postmortem computed tomography and magnetic resonance imaging) and conventional necropsy, with special attention to the traumatic musculoskeletal injuries caused by vessel collision and also revealed acute gastrointestinal compromise and respiratory disease that further hampered the rehabilitation. CONCLUSION: In cetaceans, the prognosis for recovery from injuries caused by vessel collision depends on the extent, location, and gravity of the injuries (i.e., superficial, deep, penetrating, blunt vs. sharp, fresh vs. septic), as well as the health status of the individual and its ability to respond to the insult. Injuries extending deep into the vertebral column may lead to delayed death and associated welfare issues. The prognosis of this case was likely poor given the severity and location of the injuries, but the attempted rehabilitation and postmortem investigation provided valuable insights for clinical management if similar cases are encountered in the future. Being able to non-invasively assess and document traumatic injuries and other pathologies, diagnostic imaging is particularly useful in the clinical assessment and postmortem investigation (virtopsy) of cases with vessel-induced injuries.

Severe mutilation of a Critically Endangered Taiwanese humpback dolphin Sousa chinensis taiwanensis by fishing gear.

Direct observations of the causes of injuries to cetaceans are rare events. For very small and declining populations, such events may be even less likely to be observed because of the few individuals that remain. A long-term monitoring program using photographic identification of individuals resulted in the documentation of an individual Taiwanese humpback dolphin Sousa chinensis taiwanensis that survived a harmful interaction with fishing gear. An adult female that was accompanied by a young calf sustained massive damage to several tissue types on her dorsal surface. From the injuries, it is clear that the animal had suffered intense trauma that likely caused pain for several months as the fishing gear sliced through its dorsal hump and fin. Given the incredible mutilation, the animal is likely compromised at some level and probably continues to experience ongoing pain. This case, along with observations of other individuals in this population bearing serious injuries or being entangled in fishing gear, is direct evidence that the impacts of local fisheries on this subspecies are almost certainly unsustainable.

Conservation Status of the Australian Humpback Dolphin (Sousa sahulensis) Using the IUCN Red List Criteria.

Australian humpback dolphins (Sousa sahulensis) were recently described as a new species endemic to northern Australia and potentially southern New Guinea. We assessed the species conservation status against IUCN Red List Criteria using available information on their biology, ecology and threatening processes. Knowledge of population sizes and trends across the species range is lacking. Recent genetic studies indicate Australian humpback dolphins live in small and relatively isolated populations with limited gene flow among them. The available abundance estimates range from 14 to 207 individuals and no population studied to date is estimated to contain more than 104 mature individuals. The Potential Biological Removal method indicates populations are vulnerable to even low rates of anthropogenic mortality. Habitat degradation and loss is ongoing and expected to increase across the species range in Australia, and a continuing decline in the number of mature individuals is anticipated. Considering the available evidence and following a precautionary approach, we considered this species as Vulnerable under IUCN criterion C2a(i) because the total number of mature individuals is plausibly fewer than 10,000, an inferred continuing decline due to cumulative impacts, and each of the populations studied to date is estimated to contain fewer than 1000 mature individuals. Ongoing research efforts and recently developed research strategies and priorities will provide valuable information towards the future conservation and management of Australian humpback dolphins.

The Behavioural Ecology of Indo-Pacific Humpback Dolphins in Hong Kong.

Fewer than 200 Indo-Pacific humpback dolphins (Sousa chinensis) occur in Hong Kong waters (though these are part of a much larger population in the Pearl River Estuary), with a decrease in the past about 10 years. They have partially overlapping individual ranges (mean=100km(2)), and two partially overlapping communities. Seasonal occurrence is higher in June-November than December-May, approximate wet and dry monsoon seasons, respectively. Group sizes tend to average three dolphins, a decrease from the past decade. Feeding often occurs in abruptly changing water depths and off rocky natural shores. The area immediately north of Hong Kong International Airport is largely used for travelling between locations to the west, east and further north. The area around Lung Kwu Chau Island in northwest Hong Kong is a "hot spot" for foraging and socializing. The area off Fan Lau, southwest Lantau Island, is largely used for foraging. A former foraging "hot spot" was located around the Brothers Islands east of the airport, now reduced, possibly due to increases in high-speed ferries (HSFs) and other activities. Sound recordings of dolphins from bottom-mounted hydrophones suggest that northwestern Hong Kong waters are used more at night than in daytime. Sexual activity and calving occur throughout the year, with a peak in late spring to autumn (wet monsoon season). Humpback dolphins communicate acoustically with each other and probably passively listen to prey in murky waters, and anthropogenic noises may be masking communication and affecting prey location. Increasing sounds of shipping, HSFs and industrial activities are likely to alter dolphin habitat use patterns and overall behaviours beyond the present already affected status.

Biology and Conservation of the Taiwanese Humpback Dolphin, Sousa chinensis taiwanensis.

The humpback dolphins of the eastern Taiwan Strait were first discovered scientifically in 2002 and since then have received much research attention. We reviewed all information published in peer-reviewed scientific journals on these dolphins and where appropriate and available, peer-reviewed scientific workshop reports and graduate theses were also examined. Recent evidence demonstrated that this population warranted recognition as a subspecies, Sousa chinensis taiwanensis. It is found in a highly restricted and linear strip of coastal waters along central western Taiwan. Numbering fewer than 80 individuals and declining, five main threats (fisheries interactions, habitat loss and degradation, loss of freshwater to estuaries within their habitat, air and water pollution, and noise) threaten the future existence of this subspecies. These dolphins have cultural and religious importance and boast the highest level of legal protection for wildlife in Taiwan. However, despite enormous efforts by local and international non-governmental groups urging immediate conservation actions, there have been no real government efforts to mitigate any existing threats; instead, some of these threats have worsened. Based on recent studies, we suggest the IUCN Red List status be revised to Critically Endangered CR 2a(ii); D for the subspecies.

Observations on Australian Humpback Dolphins (Sousa sahulensis) in Waters of the Pacific Islands and New Guinea.

The Australian humpback dolphin, Sousa sahulensis, has recently been described to occur in northern Australian coastal waters. However, its distribution in adjacent waters of the Pacific Islands and New Guinea remains largely unknown. Although there have been few studies conducted on inshore dolphins in these regions, the available information records humpback dolphins primarily from the Kikori Delta in Papua New Guinea, and Bird's Head Seascape in West Papua. Research in southern Papua New Guinea indicates that humpback dolphins are indeed S. sahulensis, based on cranial and external morphometrics, external colouration and the preliminary genetic analysis presented here. A similar situation exists for the Australian snubfin dolphin, Orcaella heinsohni, where it is assumed that the species also occurs along the Sahul Shelf coastal waters of northern Australia and New Guinea. There are anecdotal reports of direct catch of Australian humpback dolphins for use as shark bait, coastal development is increasing, and anthropogenic impacts will continue to escalate as human populations expand into previously uninhabited regions. Future research and management priorities for the Governments of the Pacific Islands and Indonesia will need to focus on inshore dolphins in known regional hotspots, as current bycatch levels appear unsustainable.

Assessment of the Conservation Status of the Indian Ocean Humpback Dolphin (Sousa plumbea) Using the IUCN Red List Criteria.

Indian Ocean humpback dolphins (Sousa plumbea) are obligate shallow-water dolphins that occur exclusively in the near-shore waters of the Indian Ocean, from South Africa to the Bay of Bengal. They have a narrow habitat preference, restricted distribution and do not appear very abundant across any part of their range. There is no estimate of total species abundance; all populations that have been quantitatively evaluated have been small in size, usually fewer than 200 individuals. Fishing, dredging, land reclamation, construction blasting, port and harbour construction, pollution, boat traffic and other coastal development activities all occur, or are concentrated within, humpback dolphin habitat and threaten their survival. Although data are far from sufficient to make a rigorous quantitative assessment of population trends for this species, the scale of threats is large enough over a significant enough portion of the range to suspect or infer a decline of at least 50% over three generations, which qualifies it for listing on the IUCN Red List as Endangered. The issue primarily responsible is incidental mortality in fisheries, but the loss and degradation of habitat is likely a contributing factor. None of the threats have been adequately addressed in any part of the species' range, even though threat levels are increasing virtually everywhere.

The Natural History and Conservation of Indian Ocean Humpback Dolphins (Sousa plumbea) in South African Waters.

Although most knowledge on the biology of Sousa plumbea has primarily come from South African waters, a number of research gaps remain on the natural history and status of the species in the region. Research on two populations in South African waters for which some historical data exist may aid in highlighting long-term changes in the biology and natural history of this little known coastal delphinid. Recent studies on the age, growth and reproduction of animals incidentally caught in shark nets in Richards Bay, KwaZulu-Natal, yielded a lower maximum age estimate of 24 (previously 46) growth-layer-groups (GLGs), sexual maturity of 7.5 and 8 GLGs in males and females (previously 12-13 and 10 GLGs, respectively), an ovulation rate of 0.2 and a 5-year calving interval (previously 0.3 and 3-year calving interval) than previously reported. These differences may be due to a difference in the interpretation of GLGs between observers or a predominance of young males being caught in the shark nets. Stomach content analysis revealed a change in the relative proportions of the main prey items over the past 25 years, but no difference in species richness or diversity was found between the sexes. No change in trophic level was recorded between 1972 and 2009. Field studies in Algoa Bay, Eastern Cape, conducted 16 years apart indicated a decline in the mean group size (from 7 to 3 animals), a decline in the maximum group size (from 24 to 13 animals), an increase in solitary individuals (15.4-36%), and a change in behaviour from predominantly foraging (64-18%) to mainly travelling (24-49%). The observed changes are suggestive of a change in food availability, resulting in a range shift or a potential decline in numbers. These studies indicate the importance of long-term studies to monitor population changes and their possible causes. A number of threats, such as shark nets, pollution (noise and chemical), and coastal development and disturbance, to the humpback dolphin populations in South Africa have been identified. Urgent action is required to ensure continued existence of the species in South African waters.

Ecology and Conservation Status of Indian Ocean Humpback Dolphins (Sousa plumbea) in Madagascar.

The Indian Ocean humpback dolphin (Sousa plumbea) has been studied in several range states in the Southwest Indian Ocean, however little information exists on populations in Madagascar. Here, we review available literature and describe a study on S. plumbea conducted between 2004 and 2013 on the west coast of Madagascar, involving boat-based field surveys in the southwest and northwest regions, and interview surveys with local fishers from villages along most of the west coast. Field surveys in the southwest region of Anakao/St. Augustine Bay revealed low encounter rates and mean group size, and markedly declining trends in both from 1999 to 2013. Conversely, in the northwest region around Nosy Be and Nosy Iranja, encounter rates were higher, as were mean group sizes, suggesting an apparently more abundant and less impacted population. Interview surveys revealed by-catch of coastal dolphins along the entire west coast, including S. plumbea, as well as other species. Directed hunting, including drive hunts of groups of dolphins, was reported primarily in the southern regions, in the range of the Vezo Malagasy ethnicity; however, there was evidence of hunting starting in one area in the northwest, where hunting dolphins is normally considered taboo for the predominant Sakalava ethnicity. Thus, the conservation status of S. plumbea in Madagascar appears to be spatially heterogeneous, with some areas where the local population is apparently more impacted than others. Conservation measures are recommended to mitigate further decline in the southwest of Madagascar, while protecting habitat and ensuring resilience in the northwest.

A Review of the Status of the Indian Ocean Humpback Dolphin (Sousa plumbea) in Pakistan.

Limited historical and new information on Indian Ocean humpback dolphins, Sousa plumbea, in Pakistan are reviewed. Although present along most of the coast, S. plumbea concentrates in the mangrove-lined creek system of the Indus Delta (Sindh), Miani Hor (Sonmiani Bay), Kalmat Lagoon, Gwadar and the Dasht River estuary (Gwater Bay, Jiwani). Other areas of distribution comprise the Karachi coast, Kund Malir, Ormara and Pasni. In the Indus Delta, 46 small-boat surveys conducted monthly (minus July and October) in 2005-2009, documented 112 sightings (439 individuals) in major creeks, smaller channels and nearshore waters. Group sizes ranged from 1-35 animals (mean=3.92±4.60). Groups of 1-10 animals composed 91% of total (27.9% single animals). An encounter rate of 0.07-0.17 dolphins km(-1) lacked a significant trend across survey years. A discovery curve remained steep after 87 dolphins were photo-identified, suggesting the population is vastly larger. In Sonmiani Bay, Balochistan, during 9 survey days in 2011-2012, group sizes ranged from 1-68 animals (mean=11.9±13.59; n=36), totalling 428 dolphins. Incidental entanglements, primarily in gillnets, pollution (especially around Karachi), overfishing and the ship breaking industry in Gaddani, pose major threats. Incidental catches occur along the entire Pakistani coast. Of 106 stranded cetaceans, 24.5% were S. plumbea. Directed takes in Balochistan, driven by demand for bait in shark fisheries, have reportedly declined following dwindling shark stocks. Habitat degradation threats include depletion of prey and increased maritime traffic. Domestic sewage and solid waste pollution are predominant on the Balochistan coast, especially at Miani Hor, Kund Malir, Ormara, Kalmat Lagoon, Pasni, Gwadar and Jiwani. An exhaustive habitat assessment combined with appropriate fishery management is the only way to safeguard the future of S. plumbea in Pakistan.

Broad-scale impacts of coastal mega-infrastructure project on obligatory inshore delphinids: A cautionary tale from Hong Kong.

Inshore marine habitats experience considerable anthropogenic pressure, as this is where many adverse effects of human activities concentrate. In the rapidly-changing seascape of the Anthropocene, Hong Kong waters at the heart of world's fastest developing coastal region can serve as a preview-window into coastal seas of the future, with ever-growing anthropogenic footprint. Here, we quantify how large-scale coastal infrastructure projects can affect obligatory inshore cetaceans, bringing about population-level consequences that may compromise their long-term demographic viability. As a case in point, we look at the construction of world's longest sea crossing system and broad-scale demographic, social and spatial responses it has caused in a shallow-water delphinid, the Indo-Pacific humpback dolphin (Sousa chinensis). Soon after the infrastructure project began, dolphins markedly altered their home range near construction sites such that these waters no longer functioned as dolphin core areas despite the apparent presence of prey, indicating that anthropogenic impacts outweighed foraging benefits. The contraction of key habitats has in turn led individuals to interact over spatially more constricted area, reshaping their group dynamics and social network. Although there was no apparent decline in dolphin numbers that could be detected with mark-recapture estimates, adult survival rates decreased drastically from 0.960 to 0.904, the lowest estimate for these animals anywhere across the region to date, notably below the previously estimated demographic threshold of their long-term persistence (0.955). It is apparent that during an advanced stage of this coastal infrastructure project, dolphins were under a major anthropogenic pressure that, if sustained, could be detrimental to their long-term persistence as a viable demographic unit. As effective conservation of species and habitats depends on informed management decisions, this study offers a valuable lesson in environmental risk assessment, underscoring the implications of human-induced rapid environmental change on obligatory inshore delphinids-sentinels of coastal habitats that are increasingly degraded in fast-changing coastal seas.

Machine-learning based detection of marine mammal vocalizations in snapping-shrimp dominated ambient noise.

Passive acoustics is an effective method for monitoring marine mammals, facilitating both detection and population estimation. In warm tropical waters, this technique encounters challenges due to the high persistent level of ambient impulsive noise originating from the snapping shrimp present throughout this region. This study presents the development and application of a neural-network based detector for marine-mammal vocalizations in long term acoustic data recorded by us at ten locations in Singapore waters. The detector's performance is observed to be impeded by the high shrimp noise activity. To counteract this, we investigate several techniques to improve detection capabilities in shrimp noise including the use of simple nonlinear denoisers and a machine-learning based denoiser. These are shown to enhance the detection performance significantly. Finally, we discuss some of the vocalizations detected over three years of our acoustic recorder deployments using the robust detectors developed.

Skin Marks in Critically Endangered Taiwanese Humpback Dolphins (Sousa chinensis taiwanensis).

As long-lived apex predators, Indo-Pacific humpback dolphins (Sousa chinensis) are key indicators of marine coastal environmental health. Skin marks can be observed on dorsal body surfaces that are visible during mark-recapture studies that rely on photo-identification (photo-ID) methods. Skin mark prevalence may be an indicator of environmental or anthropogenic stressors in the ecosystem, which may lead to individual and/or population-level health concerns. The prevalence of marks of anthropogenic origin was assessed in the Critically Endangered S. chinensis taiwanensis population along the coasts of central Taiwan. Fifty, twenty-eight, and thirty-four individuals were identified in 2018, 2019, and 2021, respectively. At least one category of injuries was observed in 47 of 57 distinctive individuals (82%), and adults showed a higher prevalence of deep injuries than the other coloration stages. At least one category of skin lesion was observed in 33 of 57 distinctive individuals (58%), and high prevalence of skin lesions was found in mature individuals. Given the difficulty in taking direct observations, skin mark prevalence is proposed as a proxy for estimating habitat health and anthropogenic stressors upon S. chinensis taiwanensis. The moderate-to-high prevalence of skin marks in this study was designated as a warning of risks. This study provides important updated information for the assessment of the health and survival of this population. More effective management measures are urgently needed to reverse the observed population decline.

Multilocus DNA metabarcoding diet analyses of small cetaceans: a case study on highly vulnerable humpback dolphins and finless porpoises from the Pearl River Estuary, China.

Accurate diet identification of top predators is crucial to fully understand their ecological roles. Compared to terrestrial animals, gathering dietary information from cetaceans is notoriously difficult. Here, we applied a multilocus metabarcoding approach to investigate the diet of vulnerable Indo-Pacific humpback dolphins and Indo-Pacific finless porpoises from the Pearl River Estuary (PRE), China. Our analyses identified 21 prey fish species from the 42 humpback dolphin stomachs, as well as 10 species of fish and 1 species of cephalopod from the 13 finless porpoise stomachs. All of the taxa were assigned to the species level, highlighting that the multimarker approach could facilitate species identification. Most of the prey species were small- and medium-sized fishes that primarily fed on zooplankton. The calculated similarity index revealed a moderated dietary overlap between the 2 cetaceans, presumably due to the feeding of the 2 predators in association with fishing vessels in the PRE. A more diverse diet was observed in humpback dolphins in the closed fishing season compared to the fishing season, implying the influence on the dolphin diet due to the availability of commercial fishery resources. However, according to the results of species rarefaction curves, our findings on the feeding habits of the 2 cetaceans are still limited by insufficient sample size and therefore should be interpreted with caution. This study represents a first attempt to apply the multilocus DNA metabarcoding technique in the diet analysis of small cetaceans, although more efforts are needed to improve this type of analysis.

High genetic differentiation of Indo-Pacific humpback dolphins (Sousa chinensis) along the Asian Coast of the Pacific Ocean.

The Indo-Pacific humpback dolphin (Sousa chinensis) is a vulnerable marine mammal species that inhabits shallow, coastal waters from Southeast China, southward throughout Southeast Asia, and westward around the Bay of Bengal to eastern India. Polymorphic microsatellites are useful for elucidating ecological and population genetics-related questions. Here, 18 new polymorphic microsatellites were developed from S. chinensis genomic DNA by Illumina MiSeq sequencing. Population genetic analyses were conducted on 42 S. chinensis individuals from three geographic locations, including the Xiamen Bay of China, the Western Gulf of Thailand, and Andaman Sea. Our microsatellite data revealed a strong and significant population structure among the three sampling regions (overall F ST = 0.371, p = .001). Pairwise mutual information index also demonstrated high levels of genetic differentiation between different region pairs (values range from 0.272 to 0.339, p < .001). Moreover, Structure analysis inferred three genetic clusters, with the high assignment probabilities of 95.92%, 99.47%, and 99.68%, respectively. Principal coordinate analysis plots of individuals divided entire genotypes into three clusters, indicating high level of genetic differentiation. Our results indicated the strong genetic structure in S. chinensis populations is a result of geographic distances. Other factors such as environmental variables, anthropogenic interference, and social behavior may also have contributed to population differentiation.

Microplastics in the endangered Indo-Pacific humpback dolphins (Sousa chinensis) from the Pearl River Estuary, China.

Microplastic pollution is a growing concern worldwide. Despite numerous studies showing the occurrence of microplastics in low-trophic level aquatic organisms, microplastic ingestion and contamination in cetaceans, especially those from Asian waters, has been rarely recorded. Here, we investigated stomach microplastic pollution in twelve Indo-Pacific humpback dolphins stranded along the Pearl River Estuary (PRE), China. We also compared microplastic abundances in dolphins stranded near populated urban areas (ZH, n = 6) with those stranded near rural areas (JM, n = 6). Microplastics were detected in all samples, with abundance ranging widely from 11 to 145 items individual-1 (mean ± SD, 53 ± 35.2). Major microplastics were polypropylene and polyethylene fibers, with the size mostly ranging from 1 to 5 mm and the dominant colors of white or transparent. Humpback dolphins from ZH (73 ± 36.8 items individual-1) exhibited a significantly higher average microplastic abundance than those from JM (33 ± 18.3 items individual-1, p < 0.05). In particular, the highest microplastic concentration was identified in the dolphin (SC-ZH01) stranded near the mouth of the Pearl River, whereas the dolphin (SC-JM04) collected at the rural site contained the lowest concentration of microplastics, suggesting the important influence of land-based human activities on the accumulation of microplastics in the PRE. The identification of varied microplastic polymers indicated their complex source scenarios. This study suggests that, as one of top predators in the potential microplastic food chains, this cetacean species could likely serve as an endpoint biomonitoring species of microplastic pollution in the PRE or other similar estuarine ecosystems. Our results highlight the need for more studies towards better understanding the potential impacts of microplastics on this endangered species.

Bioaccumulation of legacy organic contaminants in pregnant Indo-Pacific humpback dolphins (Sousa chinensis): Unique features on the transplacental transfer.

The placental transfer and congener composition of organic contaminants (OCs) in Indo-Pacific humpback dolphins have been little studied. In the present study, 16 polycyclic aromatic hydrocarbons (PAHs), 18 organochlorine pesticides (OCPs), and 28 polychlorinated biphenyl (PCB) congeners were analyzed in muscle, lung, liver, kidney, and blubber tissues from three mother-fetus pairs of this species stranded along the Pearl River Estuary, China. For PCBs, tetra-, penta-, hexa-, and hepta-chlorobenzene congeners were dominant in all the analyzed samples. Among them, hexachlorobenzene congeners showed the highest level in most dolphin mother-fetus tissue samples. The concentrations of PCBs and OCPs in adult females were higher in the detoxification organs (liver and kidneys) than in the muscles and lungs, whereas muscle tissues in fetuses generally exhibited higher PCBs and OCPs levels than the livers and kidneys. The most abundant PAHs in the four tissues were those with lower molecular weights, which were also the most water-soluble and bioavailable. Negative correlations between the octanol/water partition coefficients (log KOW) and the fetus/mother ratios for PCB congeners revealed that the transfer of PCBs may be determined by their lipid solubility. OCPs and PCBs with low molecular weights and low log KOW values would be more likely to accumulate in the dolphin liver, lung, kidney and muscle tissues. Furthermore, OCs with low molecular weights and low log KOW values were more concentrated in the fetal blubber, lung, and liver tissues than in their respective mothers. The ubiquitous existence of OCs in the mother-fetus pairs strongly suggested that these contaminants could pass through the placenta and partition in fetal tissue. The high transfer efficiency of PAHs and PCBs indicated that the placenta might not be an efficient barrier for these pollutants. PCBs levels in both mother and fetus dolphins could cause immunosuppression.