Diving pattern and behavioral response to vessel traffic of Indo-Pacific humpback dolphins (Sousa chinensis) in Xiamen, China: implications for conservation

Little is known about the Australian snubfin (Orcaella heinsohni) and Indo-Pacific humpback (Sousa chinensis) dolphins (‘snubfin’ and ‘humpback dolphins’, hereafter) of north-western Australia. While both species are listed as ‘near threatened’ by the IUCN, data deficiencies are impeding rigorous assessment of their conservation status across Australia. Understanding the genetic structure of populations, including levels of gene flow among populations, is important for the assessment of conservation status and the effective management of a species. Using nuclear and mitochondrial DNA markers, we assessed population genetic diversity and differentiation between snubfin dolphins from Cygnet (n = 32) and Roebuck Bays (n = 25), and humpback dolphins from the Dampier Archipelago (n = 19) and the North West Cape (n = 18). All sampling locations were separated by geographic distances >200 km. For each species, we found significant genetic differentiation between sampling locations based on 12 (for snubfin dolphins) and 13 (for humpback dolphins) microsatellite loci (F ST = 0.05–0.09; P<0.001) and a 422 bp sequence of the mitochondrial control region (F ST = 0.50–0.70; P<0.001). The estimated proportion of migrants in a population ranged from 0.01 (95% CI 0.00–0.06) to 0.13 (0.03–0.24). These are the first estimates of genetic diversity and differentiation for snubfin and humpback dolphins in Western Australia, providing valuable information towards the assessment of their conservation status in this rapidly developing region. Our results suggest that north-western Australian snubfin and humpback dolphins may exist as metapopulations of small, largely isolated population fragments, and should be managed accordingly. Management plans should seek to maintain effective population size and gene flow. Additionally, while interactions of a socio-sexual nature between these two species have been observed previously, here we provide strong evidence for the first documented case of hybridisation between a female snubfin dolphin and a male humpback dolphin.

The Indo-Pacific humpback dolphin (Sousa chinensis) can be divided into two morphological types: (1) west of India, plumbea-type humpback dolphins are dark gray or almost black in color, with a defined “hump” and (2) east of India, in Southeast Asia and Australia, chinensis-type humpback dolphins do not possess a “hump” and are often white or very light in color, with or without blue-gray spots and freckles. Plumbea-type humpback dolphins inhabit coastal waters, bays, and estuaries typically within 0.5 km of the coast, in waters less than 15 m deep. School sizes are small (< 25), although schools of up to 100 have been sighted off Oman. Diurnal patterns and seasonal and tide-related changes in behavior are observed, which have been attributed to changes in seawater temperature and, ultimately, the availability of prey. Feeding behavior tends to be correlated with rocky reefs and rocky shores. Social and sexual behavior, as well as births, occur year-round, but with seasonal peaks (October-May). The acoustic behavior of the plumbea-type humpback dolphin is little known although clicks of 20-25 kHz, “screams” from 3 to 20 kHz, and whistles from 3 to 25 kHz have been reported. Interactions between plumbea-type humpback dolphins and a variety of non-cetacean species have been reported, and in Zanzibar mixed groups of humpback and bottlenose dolphins are common. Plumbea-type humpback dolphins typically display aversive reactions to boat traffic. Chinensis-type humpback dolphins are primarily coastal and estuarine, almost exclusively estuarine in the northern parts of their range. Australian dolphins off the Great Barrier Reef were observed at considerable distances offshore (up to 55 km), but always close to shallow water. Inhabited water depth is usually less than 10 m. School sizes resemble those of plumbea-type humpback dolphins, although groups of up to 44 have been observed. The home ranges of individual animals are more compact and less coastal than plumbea-type humpback dolphins, varying both by season and year. Seasonal changes in distribution observed in Hong Kong are linked to changes in hydrography of the Pearl River. Diurnal and tide-related changes in behavior also have been noted. Feeding is the predominant behavior noted for chinensis-type humpback dolphins in Hong Kong, which is frequently associated with estuarine mixing zones and trawling activities. Social behavior occurs year-round, but peaks during the same period as calf conception. Calves primarily are born between January and August, with peaks in April/May and August. Epimeletic behavior has been reported in chinensis-type humpback dolphins. Chinensis-type humpback dolphins have been recorded producing whistles of between 1.2 and 16 kHz, and broadband harmonic pulses and low frequency, narrow band “grunts.” The spectra of broadband click pulses ranged from 30 to 200 kHz. The sounds produced by these humpback dolphins can be as low as 600 Hz and coincide with frequencies produced by many types of boat traffic. In Moreton Bay, Australia, humpback dolphins often are observed in mixed groups with bottlenose dolphins (Tursiops truncatus), although humpback dolphins do not associate with finless porpoises (Neophocaena phocaenoides) in Hong Kong. Associations with fishing trawlers have been noted in China and Australia. Increased dive durations as a result of increased shipping density and avoidance of high-speed vessels have been recorded in Hong Kong. In addition ship-strikes have been a documented cause of mortality in this area. Chinensis-type humpback dolphins often are present in areas of high shipping traffic densities and, thus, impacts of boat traffic on this species are a cause for concern. Despite some very detailed studies in discrete areas (e.g., South Africa and Hong Kong), little is known about the ecology and behavior of either

Abstract. Sobri MF, Jaaman SA, Mohamed Z, Muda AM, Rashid MASA, Zhang X. 2022. Identifying the hotspot area of Indo Pacific humpback (Sousa chinensis) and Irrawaddy (Orcaella brevirostris) dolphins in Matang waters, Perak, Malaysia. Biodiversitas 23: 6106-6113. The Indo-Pacific humpback (Sousa chinensis) and Irrawaddy (Orcaella brevirostris) dolphins are commonly found in Matang waters, Perak, Malaysia. The area, filled with healthy mangrove forest cover and many estuaries, is not only frequented by the dolphins for its daily activities but also extensively used by locals for artisanal fishing, charcoal production and organizing ecotourism activities. There could be a high risk of human-dolphin interactions, hence determining habitat use and identifying critical habitats or "hot spots" for the dolphins in the area is important. In this study, a series of dedicated boat sighting surveys were conducted from March 2019 to January 2021 between Kuala Gula and Kuala Jarum Mas. The total survey effort was 3325.76 km, 44 days and 239.38 hours. A total of 69 dolphin sightings were made, consisting of 40 Indo-Pacific humpback dolphins and 29 Irrawaddy dolphin observations, respectively. During each sighting, every dolphin's behaviors were categorized as: foraging, socializing, evasive, and travelling, and the survey area was classified into four blocks. The results indicated that different dolphin species have different hotspot areas. For Indo-Pacific humpback dolphins, the hotspot area was Kuala Sangga, while the Irrawaddy dolphin's hotspot area was outside Kuala Larut, and there was a small overlap between the two dolphins' hotspots. Among the recorded behaviors (n: 281) for both dolphins, the most dominant was foraging (72.24%), followed by socializing (17%), evasive (7%), and travelling (4%). The sighted foraging behavior for both dolphin populations was dominant, indicating the hot spots were major foraging grounds for the two dolphin populations. This study shows the importance of Matang waters as a conservation area for the species and warrants further studies of dolphin population ecology to be conducted.

First evaluation of quantitative fatty acid signature analysis (QFASA) in dolphins

Passive acoustic monitoring (PAM) is increasingly being adopted as a non-invasive method for the assessment of ocean ecological dynamics. PAM is an important sampling approach for acquiring critical information about marine mammals, especially in areas where data are lacking and where evaluations of threats for vulnerable populations are required. The Indo-Pacific humpback dolphin (IPHD, Sousa chinensis) is a coastal species which inhabits tropical and warm-temperate waters from the eastern Indian Ocean throughout Southeast Asia to central China. A new population of this species was recently discovered in waters southwest of Hainan Island, China. An array of passive acoustic platforms was deployed at depths of 10–20 m (the preferred habitat of humpback dolphins), across sites covering more than 100 km of coastline. In this study, we explored whether the acoustic data recorded by the array could be used to classify IPHD echolocation clicks, with the aim of investigating the spatiotemporal patterns of distribution and acoustic behavior of this species. A number of supervised machine learning algorithms were trained to automatically classify echolocation clicks from the different types of short-broadband pulses recorded. The best performance was reported by a cubic support vector machine (Cubic SVM), which was applied to 19,215 5-min recordings (∼4.2 TB), collected over a period of 75 days at six locations. Subsequently, using spectrogram visualization and audio listening, human operators confirmed the presence of clicks within the selected files. Additionally, other dolphin vocalizations (including whistles, buzzes, and burst pulses) and different sound sources (soniferous fishes, snapping shrimps, human activities) were also reported. The detection range of IPHD clicks was estimated using a transmission loss (TL) model and the performance of the trained classifier was compared with data synchronously collected by an acoustic data logger (A-tag). This study demonstrates that the distribution and habitat use of a coastal and resident dolphin species can be monitored over a large spatiotemporal scale, using an array of passive acoustic platforms and a data analysis protocol that includes both machine learning techniques and spectrogram inspection.

The Pearl River Delta (PRD) region on the southeast coast of China is among the largest and most populated metropolitan regions of the world, subjecting the Indo-Pacific humpback dolphins (Sousa chinensis) inhabiting coastal waters of this region – apparently the largest population of this species – to intense anthropogenic pressure. In this 5-year study (2011-2015), we applied mark-recapture techniques to quantify population parameters of humpback dolphins in the main body of the extensive estuarine system of the Pearl River, the Lingding Bay (LB), the most urbanized and industrialized part of PRD. The super-population size was estimated at 928 individuals (95% CI=823-1046), which however over-represents the latest number of extant animals. Annual estimates fluctuated between 708 and 750 dolphins, and likely reflect most accurately the latest/current number of humpback dolphins in waters of LB. Both the overall and annual estimates generated by our study are considerably lower than previously published abundance estimates. Apparent survival rates were generally low, estimated at 0.943 (SE = 0.008, 95% CI = 0.929-0.958) and 0.815 (SE = 0.025, 95% CI = 0.766-0.866) for adults and juveniles, respectively. In conjunction with limited recruitment, they may have led to a substantial decline in population numbers over the past two decades. Notably, dolphins exhibited heterogeneous apparent survival rates across the complex anthropogenic seascape of LB. Adult individuals that use Hong Kong waters as their primary habitat exhibited 6.2% higher survival rates than those in other parts of LB. This difference tripled (19.2%) for juveniles, a likely expression of their susceptibility to environmental and/or anthropogenic stresses. We suggest that the difference in survival is largely due to heterogeneous anthropogenic stressors that vary spatially across the estuary, among which habitat loss, pollution, and declining prey resources appear to be the primary threats. Based on our latest findings, we call for a strategic conservation planning with the highest priority given to preserve the remaining key dolphin habitats in Hong Kong waters, and to quantify and mitigate the impacts of major stressor(s) in Guangdong (mainland China) waters. Given the encroachment of ever-more-intense human activities on the coastal habitats of humpback dolphins, understanding their demographic response and the underlying mechanisms of the population processes may prove instrumental in the formulation of a conservation management strategy that can secure their continuous survival.

Long-term increase in mortality of Indo-Pacific humpback dolphins (Sousa chinensis) in the Pearl River Estuary following anthropic activities: Evidence from the stranded dolphin mortality analysis from 2003 to 2017

The northern Beibu Gulf is one of the major habitats for the Indo-Pacific humpback dolphin (Sousa chinensis) in China. In this habitat, the core distribution zone of humpback dolphins was confined to the Sanniang Bay (SNB) and Dafengjiang River Estuary (DRE) areas. In our present research, the sediments of 14 sampling sites across the SNB and DRE waters were collected and further conducted for microbiomic and environmental analysis to explore the ecosystem characteristics of major humpback dolphin habitats in Northern Beibu Gulf. The environmental condition includes ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3--N), dissolved reactive phosphorus (DRP), sulfur content in the form of sulfuric acid (SO42--S), Fe, and heavy metals (including Cu, Zn, Cd, Pb, and As). The composition of the bacterial community was characterized by 16S ribosomal DNA analysis of the V3-V4 regions using the Illumina-based sequencing platform. The environmental characteristic of the nutrient elements and heavy metals indicated that SNB suffered more anthropogenic impact than DRE. The comparably higher concentration of NH4+-N, NO3--N, DRP, Pb, and Cd in the SNB region was detected. The comparably higher nutrients in the SNB may have resulted in higher biomass and lower dissolved oxygen (DO) profile, which was further proved by Landsat thermal image data. The microbiome analysis showed that the DRE region was oligotrophic and SNB reflected an anaerobic environment in the sediments. Environmental factors rather than the spatial distance determined the similarity of bacterial community among different sites. Ecological associations between environmental, oceanographic, and bacterial characteristics were illustrated, which exhibited strong mutual associations. Our findings presented a feasibility that integrates empirical and remote sensing data to distinguish ecological features and evaluate ecosystem healthiness for the humpback dolphin habitats.

Indo-Pacific humpback dolphins Sousa chinensis face multiple anthropogenic threats in the coastal waters of Langkawi and the adjacent Perlis–Kedah mainland in north-west Peninsular Malaysia. The area is recognized by the IUCN as an Important Marine Mammal Area and harbours a significant population of humpback dolphins. Understanding their social structure is crucial for identifying conservation units to guide targeted management to preserve the species’ ecological processes, particularly for a species in the data-deficient Southeast Asia region. Association patterns and network analysis from a decade of photo-identification surveys (2010–2020) revealed a fission–fusion society defined by frequent changes in group membership and size, and characterized by loose associations between individuals. Association strength was generally low, although some non-random long-term associations persisted for 5 months to several years. Unusually large groups of humpback dolphins (81–204 individuals) were often observed, comprising travelling mother–calf pairs and functioning as nursery groups. The grouping plasticity and social dynamics reflect the species’ survival strategies in response to local environmental conditions, notably resource availability and predation pressure. Most importantly, our findings confirm that the humpback dolphin population in this region constitutes a stable and well-connected single conservation unit, necessitating coordinated protection by different governmental administrators across the extensive study area. The insights from our study should inform tailored management strategies for humpback dolphins and promote early detection of anthropogenic threats that may impact social-ecological processes and the overall survival of the population.

Reserve planning based on the investigation of the core habitat distribution of wild cetaceans is a powerful conservation strategy for protecting target species. However, studies on core habitats and their variations at the large-scale distribution of cetaceans are limited. In this study, we conducted a seven years (2015-2021) boat-based field observation surveys with highly applicable and generalized methods to analyze the habitat changes and how these changes influenced the largest known Indo-Pacific humpback dolphin (Sousa chinensis) population in the Pearl River Estuary (PRE), China. Our findings revealed that there is 3204 km2 of dolphin habitat in the PRE, and dolphin distribution preferences are related to nutrients and biological resources. The decreasing trend of dolphin sighting rates in most areas (73.2%) indicated that the dolphin habitat had declined, and the annual habitat decline rate (2.83%; 95% confidence interval: 0.58%-5.08%) was consistent with the population decline rate. The annual habitat decline rate in the hypoxic zone revealed that low dolphin sighting rates from March to October in the hypoxic zone was 0.43% faster than that in the non-hypoxic zone, indicating long-term sustained effects of summer hypoxia on the dolphin population. Existing reserves have partially prevented habitat decline. However, more than 82.3% of the habitat has not been effectively protected and encounters the threats of pollution and hypoxic stress. This study offers new scientific evidence for developing effective monitoring strategies for humpback dolphin populations in the PRE, and also help establish spatial planning and management measures for reserve habitats.

Place‐based management can be an effective conservation tool to protect cetaceans from anthropogenic pressures. The spatial use of the world's second largest population of the threatened Indo‐Pacific humpback dolphins (Sousa chinensis) is not well‐documented, which makes it challenging to designate protected areas for this population.To address this knowledge gap and to test the efficacy of an existing dolphin protected area (Zhanjiang Leizhou Bay Municipal Humpback Dolphin Nature Reserve, ZLBMHDNR), boat‐based surveys were conducted to document dolphin occurrence from 2015 to 2018, covering an area of 1221 km2in the eastern waters off Zhanjiang, China. In total, 253 dolphin group sightings were obtained during 174 survey days.Spatial analysis showed that humpback dolphins aggregated in threecore‐use areaswith higher sighting density within the survey area. Furthermore,intermediate‐useandbroad‐use areaswere identified that could be essential for the movements of humpback dolphins among thesecore‐use areas.The spatial usage of humpback dolphins was compared inside and outside the ZLBMHDNR. Results suggest that the ZLBMHDNR is insufficient to encompass a significant portion of dolphin habitat. The ZLBMHDNR (21 km2) is not large enough, and thus it should be expanded for effective place‐based conservation management in this region.For developing a protected area network, important dolphin habitats identified in this study should be protected as a single management unit. Additionally, mitigation of anthropogenic pressures is needed to be taken into consideration as conservation initiatives in the study area.This study provides support for a more science‐informed protected area network, and highlights the necessity of implementing place‐based conservation and management for the world's second largest humpback dolphin population.

Group size is a key social trait influencing population dynamics of group-living animals. The Indo-Pacific humpback dolphins (IPHDs), Sousa chinensis, a shallow water delphinid species, display a fission-fusion social system. Yet little is known about how social organization of this species vary with temporal scales and behavioral state. In this study, we sampled group size estimates from the world’s second largest population of humpback dolphins (Sousa spp.), which inhabit the eastern waters of Zhanjiang, China. IPHD group sizes changed seasonally and inter-annually, but not with tidal phases. Group sizes also changed with behavioral state of IPHD groups and with number of mother-calf pairs present. IPHDs formed larger groups in the autumn than in other seasons, which might be related to seasonal changes in food availability and reproductive cycle. Of the groups observed, we recorded the presence of mother-calf pair in 85 groups (i.e., nursery groups: 47 ones with one pair, 25 ones with two pairs, and others with three pairs). Notably, nursery groups were about 2–4 times larger than non-nursery groups. In addition, group sizes greatly increased with the number of mother-calf pairs. Living in relatively large groups, more protection, food, and resources might be available for IPHD mothers and calves, and such social strategy provide higher reproduction efficiency and survival success for this species. During our observations, feeding (45.5%) and traveling (25.2%) represented the majority of IPHD’s behavioral budget, while socializing (8.4%) and resting/milling (6.8%) were not frequently observed. Resting/milling groups were approximately 50% smaller than feeding, traveling, or socializing groups, while the latter three types had a similar mean group size. Large groups when IPHDs foraged, traveled, or socialized, might provide more added group benefits. For the first time, our findings clearly revealed intra-population variability in IPHD group sizes across different behavioral and temporal variables, and provided a better understanding of IPHDs’ adaptations to various biological processes and ecological constraints.

Humpback Dolphins: A Brief Introduction to the Genus Sousa.

Cetacean-watching tourism has become an economically important recreation industry, but can compromise cetacean viability and hence tourism sustainability. While current management tactics pay much attention on industrialized cetacean-watching tourisms, impacts of tours operated by motorized boats in inshore waters are seldom discussed. This study investigated the spatial and temporal activities of dolphin-watching tours in Sanniang Bay, China, where tours specifically focus on Indo-Pacific humpback dolphins (Sousa chinensis). The primary boat-dolphin interaction directly overlaps with a core habitat of humpback dolphins. Average tour duration was shorter than 40 min and approximately one third of time was spent on following dolphins. Monthly tour activities were extremely high in February, early May, August, and October that corresponded to Chinese national festivals. An eastward shift of primary interaction site during high-tour-activity months implies a long-term tour impacts on habitat use of humpback dolphins in northern Beibu Gulf. We urge a collaboration and coordination between boat captains, tour managers, maritime administrative, academic teams, and NGOs to systematically collect tour statistics in Sanniang Bay, including daily tour and visitor numbers, encounter duration and locations, and unsustainable maritime activities. As eco-tourisms targeting humpback dolphins and other coastal cetaceans adopting small motorized boats are rapidly growing in southeastern Asia, management guidelines involving codes of conduct, allowable daily trips, and sustainable tourism tactics are urgently needed before the tourism becomes industrialized and economically oriented. Variables and statistics presented in this study can provide a baseline proxy to help design management guidelines to minimize unsustainable impacts on the target animals.

Directional communication plays a pivotal role in enabling odontocetes to maintain group coordination and social interactions. The fundamental frequency, number of harmonics, and their relative energy distribution in whistles exhibit temporal variation. This study investigated the whistles produced by the Indo-Pacific humpback dolphins (Sousa chinensis) in Xiamen Bay, China. Using computed tomography scanning data, we developed a numerical model of the species and used finite element modeling to examine the beam patterns at both fundamental and harmonic frequencies of whistles, ranging from 3.9 to 64.9 kHz, which corresponds to directivity indices (DIs) between 2.2 and 16.2 dB. We weighted the beams at the fundamental frequencies and harmonics based on their energy distribution to derive composite beam patterns at specific time stamps, allowing us to investigate temporal variations in the corresponding DI within individual whistles. The time-varying properties of DIs were analyzed for various whistle types, including constant, upsweep, downsweep, convex, and sine. Given that harmonics are integer multiples of the fundamental frequency, their contours exhibit similar shapes, whereas the composite DI showed more complexity. These findings indicate that the proportion of energy between the fundamental frequency and harmonics is a key determinant of whistle directivity in Indo-Pacific humpback dolphins.