Humpback Dolphins Research Articles

Spatio-temporal distribution and habitat preferences of cetaceans in Algoa Bay, South Africa

Increasingly, baseline knowledge of habitat preferences and movement patterns of marine species is required to inform anthropogenic developments. The aim of this study was to determine baseline spatio-temporal distribution and habitat preference of cetaceans in the coastal waters of Algoa Bay. Areas of potential conflict with anthropogenic activities were also assessed. Monthly sea-based surveys were conducted between June 2008 and May 2011. A total of 500 cetacean sightings comprising six species were recorded in 106 surveys. Tursiops aduncus (Indo-Pacific bottlenose dolphin), Sousa plumbea (Indian Ocean humpback dolphin), Delphinus capensis (long-beaked common dolphin) and Balaenoptera brydei (Bryde's whale) were observed year-round, while Eubalaena australis (southern right whale) and Megaptera novaeangliae (humpback whale) were recorded from May to December. A large portion of sightings were associated with a Marine Protected Area and shipping zones. Eubalaena australis, T. aduncus and S. plumbea were found inshore (water depths < 12 m), while the other species were associated with deeper waters. Tursiops aduncus were most commonly seen (233 sightings). Megaptera novaeangliae were sighted often in austral winter, with 113 sightings. Only nine D. capensis sightings were recorded. Spatial distributions of species were corrected for search effort to identify habitat preferences. A number of key observations were made, including opportunistic foraging in M. novaeangliae, and the expansion of nursery grounds for E. australis, to include Algoa Bay. Four preferred habitat areas are proposed, providing important information for conservation and management of cetaceans in Algoa Bay. The spatial approach can be used to inform future relevant management decisions elsewhere.

Noise impact assessment on Indo-Pacific Humpback Dolphin in the habitat of the East Taiwan Strait during the first two pile driving activities of demonstration offshore wind farm

Foundation piles of the first two wind turbines were driven off the coast of Miaoli, Taiwan in 2016. However, that area is also the habitat of the critically endangered Eastern Taiwan Strait (ETS) population of Indo-Pacific humpback dolphin (Sousa chinensis). To assess potential noise effects from pile driving on the humpback dolphins, we collected underwater noise data during the construction and found that the sound pressure level (Lrms) at 750m was less than 180dB re 1μPa and the peak sound pressure (Lpk, flat) was less than 190 dB re 1μPa. We also presented recommendations of noise and marine mammal monitoring for future pile driving activities. It includes an exclusion zone of radius 750m from the piling location and the peak sound pressure (Lpk, flat) not to exceed 190~220 dB re 1μPa at 750 m distance, and an observation zone extends to 1500m radius where both marine mammal observers and passive acoustic monitoring are posted. [This work was sponsored by Ministry of Science and Technology of Taiwan (105-3113-E-002 -002 -CC2), Taiwan Bureau of Energy and Industrial technology Research Institution (05HZT56002), and U.S. Marine Mammal Commission’s Research and Conservation Grant.]

The research on the optimal bionic waveform design

In this paper, the authors address the design of optimal waveform for target detection and parameter estimation based on the features analysis of the whistle of Indo-pacific humpback dolphins. A set of types of waveforms exist in the sequence of whistle calls. Considering the perfect performance of non-linear frequency modulated and multi-harmonics structure in anti-range sidelobe and anti-reverberation, several fusion schemes of several kinds of waveforms are explored and fusion results are studied analytically and from simulation. It is concluded that the bionic harmonic fused signal shows good time resolution, and improve the performance of suppressing reverberation. Research result provides nice reference and application value in underwater sonar based on bionic acoustic signal.

Indo-Pacific humpback dolphins (Sousa chinensis) in Hong Kong: Modelling demographic parameters with mark-recapture techniques.

Indo-Pacific humpback dolphins (Sousa chinensis) inhabiting Hong Kong waters are thought to be among the world's most anthropogenically impacted coastal delphinids. We have conducted a 5-year (2010–2014) photo-ID study and performed the first in this region comprehensive mark-recapture analysis applying a suite of open population models and robust design models. Cormack-Jolly-Seber (CJS) models suggested a significant transient effect and seasonal variation in apparent survival probabilities as result of a fluid movement beyond the study area. Given the spatial restrictions of our study, limited by an administrative border, if emigration was to be considered negligible the estimated survival rate of adults was 0.980. Super-population estimates indicated that at least 368 dolphins used Hong Kong waters as part of their range. Closed robust design models suggested an influx of dolphins from winter to summer and increased site fidelity in summer; and outflux, although less prominent, during summer-winter intervals. Abundance estimates in summer (N = 144–231) were higher than that in winter (N = 87–111), corresponding to the availability of prey resources which in Hong Kong waters peaks during summer months. We point out that the current population monitoring strategy used by the Hong Kong authorities is ill-suited for a timely detection of a population change and should be revised.

Preliminary sex differentiation of Indo‐Pacific humpback dolphins (Sousa chinensis) in the Pearl River estuary and eastern Taiwan Strait using scarring of dorsal fins

Preliminary sex differentiation of Indo‐Pacific humpback dolphins (<i>Sousa chinensis)</i> in the Pearl River estuary and eastern Taiwan Strait using scarring of dorsal fins

Distribution and Habitat Characteristics of the Indo-Pacific Humpback Dolphin (Sousa chinensis)in the Northern Beibu Gulf, China

Studies on the distribution and habitat characteristics of the Indo-Pacific humpback dolphin (Sousa chinensis) indicate a general preference toward estuarine environments. However, quantitative connections between this preference and estuarine characteristics are seldom investigated. Distribution of the humpback dolphin in the northern Beibu Gulf, China, was evaluated through systematically designed surveys and was compared to oceanographic characteristics from on-board measured and remotely sensed variables. The humpback dolphins' core distribution zone, measured by the 50% kernel density estimate (50% KDE), was confined to the Dafengjiang River Estuary in a 50.23 km(2) area, with a steep-edged underwater sand bar below and locally high chlorophyll-a concentration. The surface salinity distribution showed an eco-cline environment in which riverine runoff mixes with sea water in the 50% KDE. We found significant relationships between distribution probability and two oceanographic variables: (1) water depth and (2) chlorophyll-a concentration. This associates the distribution preference of humpback dolphins with regional productivity and biodiversity peaks that may facilitate prey aggregation. As humpback dolphins inhabit comparable environments in other locations throughout their range, the oceanographic features of the 50% KDE may help to provide proxies to identify other key habitats over a broader spatial scale.

Stereotyped Whistles May Be First Evidence to Suggest the Possibility of Signature Whistles in an InjuredIndo-Pacific Humpback Dolphin (Sousa chinensis

Stereotyped Whistles May Be First Evidence to Suggest the Possibility of Signature Whistles in an InjuredIndo-Pacific Humpback Dolphin (Sousa chinensis

Threshold of long-term survival of a coastal delphinid in anthropogenically degraded environment: Indo-Pacific humpback dolphins in Pearl River Delta

Defining demographic and ecological threshold of population persistence can assist in informing conservation management. We undertook such analyses for the Indo-Pacific humpback dolphin (Sousa chinensis) in the Pearl River Delta (PRD) region, southeast China. We use adult survival estimates for assessments of population status and annual rate of change. Our estimates indicate that, given a stationary population structure and minimal risk scenario, ~2000 individuals (minimum viable population in carrying capacity, MVPk) can maintain the population persistence across 40 generations. However, under the current population trend (~2.5% decline/annum), the population is fast approaching its viability threshold and may soon face effects of demographic stochasticity. The population demographic trajectory and the minimum area of critical habitat (MACH) that could prevent stochastic extinction are both highly sensitive to fluctuations in adult survival. For a hypothetical stationary population, MACH should approximate 3000-km2. However, this estimate increases four-fold with a 5% increase of adult mortality and exceeds the size of PRD when calculated for the current population status. On the other hand, cumulatively all current MPAs within PRD fail to secure the minimum habitat requirement to accommodate sufficiently viable population size. Our findings indicate that the PRD population is deemed to become extinct unless effective conservation measures can rapidly reverse the current population trend.

Demographic characteristics of Australian humpback dolphins reveal important habitat toward the southwestern limit of their range

The paucity of information on the recently described Australian humpback dolphin Sousa sahulensis has hindered assessment of its conservation status. Here, we applied capturerecapture models to photo-identification data collected during boat-based surveys between 2013 and 2015 to estimate the abundance, site fidelity and residence patterns of Australian humpback dolphins around the North West Cape (NWC), Western Australia. Using Pollock's closed robust design, abundance estimates varied from 65 to 102 individuals, and POPAN open modelling yielded a super-population size of 129 individuals in the 130 km2 study area. At approximately 1 humpback dolphin per km2, this density is the highest recorded for this species. Temporary emigration was Markovian, suggesting seasonal movement in and out of the study area. Hierarchical clustering showed that 63% of individuals identified exhibited high levels of site fidelity. Analysis of lagged identification rates indicated dolphins use the study area regularly, following a movement model characterised by emigration and re-immigration. These density, site fidelity and residence patterns indicate that the NWC is an important habitat toward the southwestern limit of this species' range. Much of the NWC study area lies within a Marine Protected Area, offering a regulatory framework on which to base the management of human activities with the potential to impact this threatened species. Our methods provide a methodo logical framework to be used in future environmental impact assessments, and our findings represent a baseline from which to develop long-term studies to gain a more complete understanding of Australian humpback dolphin population dynamics.

Long‐term changes in the distribution and core habitat use of a coastal delphinid in response to anthropogenic coastal alterations

Abstract The influence of anthropogenic habitat loss on animal distribution and core habitat use can be particularly strong in animals with narrow habitat selectivity, such as the Indo‐Pacific humpback dolphin (Sousa chinensis), a delphinid species that specifically inhabits coastal and estuarine waters. This study measured the extent of habitat loss in the waters around Xiamen City, China, where intense environmental changes and coast utilization have occurred in the past 40 years. The extent of occurrence and the core habitat of the humpback dolphin were measured based on sighting records from censuses conducted in different years. A Landsat image series revealed a permanent 119.95 km2 loss of coastal waters to land reclamation, coastal modification and harbour construction from 1973 to 2013. The distribution of the humpback dolphin showed a significant shift from inshore to offshore waters and away from artificial shorelines. Though the extent of occurrence appears to change minimally, a significant shift in the core habitat from the original coastal habitats into mid‐channel waters was observed in the eastern Xiamen Bay. These results imply multiple consequences of anthropogenic coastal alterations for the humpback dolphin: the elimination of vital habitats, changes in habitat use preferences, and the partitioning of the social structure of the population. The need to adjust current protected area designations along with adequate measures to restore habitat quality and population connectivity, both locally and regionally, are considered.

Reconstruction of the forehead acoustic properties in an Indo-Pacific humpback dolphin (Sousa chinensis), with investigation on the responses of soft tissue sound velocity to temperature.

Computed tomography (CT) imaging and ultrasound experimental measurements were combined to reconstruct the acoustic properties (density, velocity, and impedance) of the head from a deceased Indo-Pacific humpback dolphin (Sousa chinensis). The authors extracted 42 soft forehead tissue samples to estimate the sound velocity and density properties at room temperature, 25.0 °C. Hounsfield Units (HUs) of the samples were read from CT scans. Linear relationships between the tissues' HUs and velocity, and HUs and density were revealed through regression analyses. The distributions of the head acoustic properties at axial, coronal, and sagittal cross sections were reconstructed, suggesting that the forehead soft tissues were characterized by low-velocity in the melon, high-velocity in the muscle and connective tissues. Further, the sound velocities of melon, muscle, and connective tissue pieces were measured under different temperatures to investigate tissues' velocity response to temperature. The results demonstrated nonlinear relationships between tissues' sound velocity and temperature. This study represents a first attempt to provide general information on acoustic properties of this species. The results could provide meaningful information for understanding the species' bioacoustic characteristics and for further investigation on sound beam formation of the dolphin.

Spatiotemporal Trends of Heavy Metals in Indo-Pacific Humpback Dolphins (Sousa chinensis) from the Western Pearl River Estuary, China.

We assessed the spatiotemporal trends of the concentrations of 11 heavy metals (HMs) in the liver and kidney of Indo-Pacific humpback dolphins (Sousa chinensis) from western Pearl River Estuary (PRE) during 2004-2015. The hepatic levels of Cr, As, and Cu in these dolphins were among the highest reported for cetaceans globally, and the levels of Zn, Cu, and Hg were sufficiently high to cause toxicological effects in some of the animals. Between same age-sex groups, dolphins from Lingdingyang were significantly more contaminated with Hg, Se, and V than those from the West-four region, while the opposite was true for Cd. Generalized additive mixed models showed that most metals had significant but dissimilar temporal trends over a 10-year period. The concentrations of Cu and Zn increased significantly in recent years, corresponding to the high input of these metals in the region. Body-length-adjusted Cd levels peaked in 2012, accompanied by the highest annual number of dolphin stranding events. In contrast to the significant decrease in HM levels in the dolphins in Hong Kong waters (the eastern reaches of the PRE), the elevated metal exposure in the western PRE raises serious concerns.

Encounters with Indo-Pacific Humpback Dolphins (Sousa chinensis) Carrying Dead Calves in Sanniang Bay, Guangxi Province, China

Encounters with Indo-Pacific Humpback Dolphins (Sousa chinensis) Carrying Dead Calves in Sanniang Bay, Guangxi Province, China

Unsustainable human-induced injuries to the Critically Endangered Taiwanese humpback dolphins (Sousa chinensis taiwanensis)

The Critically Endangered Taiwanese humpback dolphin (Sousa chinensis taiwanensis) is endemic to inshore and estuarine waters of central western Taiwan. It numbers fewer than 75 individuals, is declining and faces a myriad of human threats. Data from a long-term photo-identification program on these dolphins allowed major injuries to be examined quantitatively. A large proportion (57.7%) of individuals had suffered major human-induced injuries that likely compromised their health, survivorship or reproductive potential and thus, the future of this subspecies. Considering major injuries as “takes”, the injury rate (1.13 dolphins/year) for the population was 8–8.5 times higher than its Potential Biological Removal rate. Observations of new injuries and fishing gear entanglements on several dolphins showed that fisheries continue to be the predominant cause of these major injuries. Unless immediate action is taken to reduce harmful fisheries, extinction is imminent for Taiwan's only endemic dolphin.

Effect of environmental conditions on cetacean entanglements: a case study from the Gold Coast, Australia

Entanglement of marine mammals in fishing gear is recognised worldwide and is a continuous management concern. Gill-net entanglement data from the Queensland Shark Control Program (QSCP) on the Gold Coast, Australia, from 1990 to 2012 were analysed in the present study. Environmental drivers that may affect entanglements of humpback whales (Megaptera novaeangliae) and common dolphins (Delphinus delphis) were selected. M. novaeangliae entanglements coincided with their annual migration, with the greatest occurrences in September. D. delphis were mostly entangled from March to November, with the greatest occurrences in June. For both species, entanglements primarily occurred when the wave height was between 0.5 and 1.25m, the wave power was between 0 and 5kWm–1 and the wind speed was between 12 and 19kmh–1. M. novaeangliae entanglements were significantly more likely to occur in low rainfall (&lt;6mmh–1), and D. delphis entanglements were more likely to occur during spring tides. There was a correlation between entanglements and the position of the East Australian Current’s (EAC) maximum velocity, with 73% of M. novaeangliae entanglements and 79% of D. delphis entanglements occurring when the EAC’s maximum velocity was west (shoreward) of its average position at 154°E. The present study provides the first set of possible management intervention targets associated with environmental conditions.

New records of atlantic humpback dolphin (Souza teusziisouza), in Guinea, Nigeria, Cameroon and Togo underscore pressure from fisheries and marine bushmeat demand

De nouvelles données sur le Dauphin à bosse de l’Atlantique (Sousa teuszii) en Guinée, au Nigéria , au Cameroun et au Togo soulignent la pression des pêcheries et de la demande en viande d’origine marine. Le Dauphin à bosse de l’Atlantique (Sousa teuszii) est une espèce encore mal connue : sa biologie , sa distribution détaillée et l’existence de populations restent encore à préciser. Des suivis de terrain, des enquêtes et des observations opportunistes ont permis d’identifier plusieurs nouveaux spécimens, observés en mer ou retrouvés après leur capture, dans quatre pays, dont le Nigéria et le Togo où la présence de S. teuszii, bien que fortement suspectée, n’avait jamais été prouvée. De nouvelles données, provenant des îles Tristao et de l’estuaire du Río Nuñez en Guinée du nord, indiquent que les populations du Rio do Jéba-Bijagos (Guinée-Bissau) et Guinée du sud devraient être combinées dans une seule population Guinéenne. La population du golfe de Guinée, qui correspond à la population historique de S. teuszii, anciennement appelée «dauphins du Cameroun», s’étend au minimum du Togo au sud du Cameroun. Plusieurs spécimens prouvent que la mortalité de S. teuszii causée par des captures accidentelles ou ciblées est significative, répandue et difficilement quantifiable en raison des contrôles sporadiques qui sont réalisés. Ces captures sont préoccupantes en Guinée, au Nigéria et au Cameroun. Les dauphins sont capturés accidentellement dans des filets maillants de pêcheries artisanales littorales, puis consommés comme «viande de brousse marine». La commercialisation de ce type de viande étant croissante, les captures intentionnelles risquent aussi d’être encouragées. La rareté des observations et la petite taille des groupes dans le golfe de Guinée du nord indiquent des communautés de dauphins qui semblent plutôt en déclin. Des variations de répartition de l’espèce peuvent apparaître de novo le long des côtes fortement peuplées par l’Homme, après des décennies de prises accessoires, de compétition pour les ressources alimentaires, et de perte d’habitat suite à un développement côtier irréversible. Nous suggérons que le manque d’effort de suivi n’explique pas entièrement l’absence d’observations de S. teuszii sur les 1900 km de littoral allant du Ghana à la Sierra Leone, et particulièrement au Ghana où le suivi des petits cétacés est mieux documenté. La mise en œuvre d’une politique de conservation rigoureuse devient dès lors de plus en plus urgente. De nouvelles Aires Marines Protégées binationales et transfrontalières pourraient avoir des effets positifs et mesurables en termes de conservation en limitant la compétition pour les proies avec les pêcheries, en limitant les captures accidentelles dans les filets et en limitant la destruction des habitats. L’installation d’un groupe de travail ad hoc, à l’échelle de la région considérée, est recommandée afin d’identifier des mesures pratiques visant à éviter que le Dauphin à bosse de l’Atlantique, maintenant menacé, ne se dirige vers l’extinction.

Abundance Estimates of Indo-Pacific Humpback Dolphins (Sousa chinensis) in Kuching Bay, East Malaysia

Abundance Estimates of Indo-Pacific Humpback Dolphins (Sousa chinensis) in Kuching Bay, East Malaysia

Oceanographic drivers of population differentiation in Indo-Pacific bottlenose (Tursiops aduncus) and humpback (Sousa spp.) dolphins of the northern Bay of Bengal

The Bay of Bengal is one of the most productive ecosystems in the northern Indian Ocean and it harbours a rich community of cetaceans, including Indo-Pacific bottlenose (Tursiops aduncus) and humpback (Sousa spp.) dolphins. The taxonomy of these genera has been controversial, but within the Indian Ocean both seem to be divided into phylogenetically discrete units that range from the east to the west. Within the Sousa genus, S. plumbea is distributed in the western Indian Ocean while S. chinensis is distributed in the eastern Indian and western Pacific Ocean. T. aduncus has a discontinuous distribution throughout the Indo-Pacific Ocean and two different phylogenetic units are known to exist, one along the eastern African coast and another one in the eastern Indian and west Pacific Ocean. In this study we investigate the phylogeography of Indo-Pacific humpback and bottlenose dolphins in the northern Bay of Bengal. We sequenced the mitochondrial DNA control region for 17 bottlenose and 15 humpback dolphins and compared the results with previously published sequences within each genus. In both cases, we found that Bangladesh dolphins are genetically different from neighbouring populations. While the Bangladesh T. aduncus seem to be more closely related to the African T. aduncus form than the Pacific form, Sousa spp. seem to be more closely related to individuals from Australia. The genetic uniqueness of these populations has important evolutionary implications, due to their isolation, coastal distribution in a geographic cul-de-sac characterized by an extreme infusion, redistribution and recycling of biological productivity, and conservation implications since their survival is threatened in particular by fatal interactions with fisheries. We suggest that the particular and extreme oceanographic conditions found in the Bay of Bengal may be driving speciation in these dolphins and other marine megafauna.

Fine‐scale habitat use in Indo‐Pacific humpback dolphins, Sousa chinensis, may be more influenced by fish rather than vessels in the Pearl River Estuary, China

AbstractShifts in habitat use and distribution patterns in dolphins are often concerns that can result from habitat degradation. We investigated how potential changes to a habitat from human activity may alter dolphin distributions within Lingding Bay in the Pearl River Estuary, China, by studying the relationship between fish choruses, vessel presence and Indo‐Pacific humpback dolphin (Sousa chinensis) detection rates. Analyses revealed temporal and spatial variation within fish choruses, vessel presence and dolphin detection rates. After accounting for any temporal autocorrelation, correlations between fish choruses and dolphin detection rates were also found; however, no relationship between fish choruses and vessel presence or dolphin detection rates and vessel presence were observed. Furthermore, fewer dolphins were detected at sites where fish activity was less intense. Thus fish activity, rather than vessels, may be a key factor influencing the distribution of the dolphins within the estuary. These findings emphasize the risk of potential shifts in habitat use for Indo‐Pacific humpback dolphins due to detrimental changes to prey availability and dolphin feeding grounds from human activity, such as overfishing and coastal developments, within the estuary. This is a critical conservation issue for this dolphin population that is facing intense anthropogenic pressure.

The Trophic Significance of the Indo-Pacific Humpback Dolphin, Sousa chinensis, in Western Taiwan.

Indo-Pacific humpback dolphins (Sousa chinensis) have attracted considerable attention due to their critically endangered status and related conservation issues, but their trophic relationships and ecological significance in coastal ecosystems are poorly understood. For instance, this species is noticeably more abundant in the Xin-Huwei River Estuary (Ex) of Western Taiwan than in the nearby Zhuoshui River Estuary (Ez), though it is unclear why the distribution shows such partitioning. To explore this topic, we conducted field surveys seasonally for two years from 2012 to 2013 and constructed Ecopath models of Ex, Ez, and an offshore site (Dm) to compare energy flow within the food webs. Model comparisons showed that the availability of food resources was the main factor influencing the biomass of Indo-Pacific humpback dolphins. Specifically, its more frequent occurrence in Ex can be attributed to greater phytoplankton production and greater biomasses of macroinvertebrates and prey fish than in the other two areas. An increase in fishing activity might decrease the food availability and, consequently, the biomass of the dolphins. Although the decline in the dolphin population would increase the biomass of some prey fish species, local fishermen might not necessarily benefit from the decline due to the concurrent decrease of highly valued crabs and shrimp. Collectively, our work suggests that the Indo-Pacific humpback dolphin is a keystone species in tropical coastal waters of Taiwan, and thereby exhibit a disproportional large ecological impact given their relatively low abundance.