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Jefferson T.A.,Clymene Enterprises | Hung S.K.,Hong Kong Cetacean Research Project | Robertson K.M.,Southwest Fisheries Science Center | Archer F.I.,Southwest Fisheries Science Center
Marine Mammal Science | Year: 2012

We studied life history characteristics of the Hong Kong/Pearl River Estuary population of Indo-Pacific humpback dolphins (Sousa chinensis), based on data from 120 specimens stranded between 1995 and 2009, 40 individuals biopsied at sea, and a long-term (14+ yr) photo-identification study. Ages were determined for 112 specimens by thin-sectioning teeth and counting growth layer groups. Estimated length at birth was 101 cm. Longevity was at least 38 yr, and there was little difference in growth patterns of males and females. Growth was described by a Bayesian two-phase Gompertz model; asymptotic length was reached at 249 cm. The tooth pulp cavity filled at an average of 18.5 yr of age. Physical maturity was reached at between 14 and 17 yr of age, apparently a few years after attainment of sexual maturity. Maximum lengths and weights of about 268 cm and 240 kg were attained. Females appear to lose all their spots by 30 yr, although males may retain some spotting throughout life. Calving occurred throughout the year, with a broad peak from March to June. Of 60 females monitored at sea for >14 yr of the study, none were documented to have more than three calves, suggestive of low reproductive output or low calf survival. © 2011 by the Society for Marine Mammalogy.


PubMed | Oceanwide Science Institute, Clymene Enterprises, Hong Kong Cetacean Research Project and Texas A&M University
Type: Journal Article | Journal: The Journal of the Acoustical Society of America | Year: 2016

Long-term passive acoustic monitoring (PAM) was conducted to study Indo-Pacific humpback dolphins, Sousa chinensis, as part of environmental impact assessments for several major coastal development projects in Hong Kong waters north of Lantau Island. Ecological acoustic recorders obtained 2711 days of recording at 13 sites from December 2012 to December 2014. Humpback dolphin sounds were manually detected on more than half of days with recordings at 12 sites, 8 of which were within proposed reclamation areas. Dolphin detection rates were greatest at Lung Kwu Chau, with other high-occurrence locations northeast of the Hong Kong International Airport and within the Lung Kwu Tan and Siu Ho Wan regions. Dolphin detection rates were greatest in summer and autumn (June-November) and were significantly reduced in spring (March-May) compared to other times of year. Click detection rates were significantly higher at night than during daylight hours. These findings suggest high use of many of the proposed reclamation/development areas by humpback dolphins, particularly at night, and demonstrate the value of long-term PAM for documenting spatial and temporal patterns in dolphin occurrence to help inform management decisions.


Sims P.Q.,Oregon State University | Vaughn R.,University of Texas Medical Branch | Hung S.K.,Hong Kong Cetacean Research Project | Wursig B.,University of Texas Medical Branch
Journal of the Acoustical Society of America | Year: 2012

Vocalizations of Indo-Pacific humpback dolphins (Sousa chinensis) in west Hong Kong waters were described from 12 recordings in 2010. A broadband hydrophone system recorded sounds. Vocalizations were characterized as broadband click trains, burst pulses, and narrowband frequency modulated sounds, including whistles generally similar to those of some other delphinid cetaceans. A comparison of results to previous humpback dolphin sound descriptions for Moreton Bay, Australia found broad similarities except for the apparent absence of quacks and grunts in the present study, which are of low frequency and thus were possibly masked by anthropogenic and other low frequency noise in the Hong Kong habitat. © 2012 Acoustical Society of America.


Dungan S.Z.,Trent University | Hung S.K.,Hong Kong Cetacean Research Project | Wang J.Y.,FormosaCetus Research and Conservation Group | Wang J.Y.,Trent University | White B.N.,Trent University
Canadian Journal of Zoology | Year: 2012

The way human activities impact animal populations can depend on social structure, which is important to understand in social species such as cetaceans. We investigated association patterns in Indo-Pacific humpback dolphins (Sousa chinensis (Osbeck, 1765)) inhabiting the Pearl River Estuary near Lantau Island, Hong Kong, using a 10-year data set for 88 individuals. Our analyses revealed two social communities. Each had its own region of core use, to the north and to the west of the island, but their overall ranges partially overlapped northwest of Lantau. The northern community had a fission- fusion structure characterized by short-term associations, while the western community had more long-term associations. Mixed-community groups included calves more often than exclusive groups, so between-community associations may arise from common habitat usage, by females especially, in the overlap area. Recent range extensions by the northern community into the west are likely a response to habitat destruction north of Lantau. This suggests ease of movement between the north and the west is necessary for northern-community dolphins to access suitable habitat, and gives new concern to construction projects planned for the region. We emphasize our study as an example of how sociobiological information can be important in understanding human impacts on animal populations.


Hoffman J.M.,Trent University | Ponnampalam L.S.,University of Malaya | Araujo C.C.,CetAsia Research Group | Wang J.Y.,CetAsia Research Group | And 2 more authors.
Journal of the Acoustical Society of America | Year: 2015

Differences in the acoustic variables of whistles emitted by Indo-Pacific humpback dolphins (Sousa chinensis) from two coastal locations along western Peninsular Malaysia were investigated. Duration, frequency, and frequency modulation variables were extracted from and used to characterize recordings of free-ranging humpback dolphins that were made using a broadband towed hydrophone. A total of 960 whistles from Matang Mangroves and 823 whistles from Langkawi Island were used in analyses. The whistles of Malaysian humpback dolphins covered frequencies from 1231 to 27 120 Hz with durations from 0.010-1.575 s. Significant multivariate differences were found in whistles emitted between locations. Significant differences were also found between dolphins of the two locations in their whistle duration, frequency modulation, and all frequency variables except for minimum frequency, which is likely under morphological constraints. The differences in whistles may be related to adaptations to the local acoustic habitat or unique whistles may have developed due to social interactions within each location, or broader scale differences resulting from geographic separation between the locations. © 2015 Acoustical Society of America.


Wang J.Y.,CetAsia Research Group | Wang J.Y.,Trent University | Yang S.C.,FormosaCetus Company Ltd | Hung S.K.,Hong Kong Cetacean Research Project
Zoological Studies | Year: 2015

Background: Subspecies recognition can affect how people (scientists and non-scientists alike) view organisms and thus has important implications for research on, as well as the conservation of, these entities. Recently, a small group of Indo-Pacific humpback dolphins was discovered inhabiting the waters off central western Taiwan. This geographically isolated population possesses pigmentation patterns that are subtly, but noticeably, different from their nearest conspecifics in the neighbouring waters of the Jiulong River Estuary and Pearl River Estuary of mainland China. Due to this population’s low and declining numbers and the numerous threats it faces, it was assessed as critically endangered by the Red List of Threatened Species of the International Union for Conservation of Nature. The purpose of this study is to examine the degree of differentiation of the Taiwanese population to determine if subspecies recognition is warranted. Results: Analysis of the degree of differentiation in pigmentation patterns revealed nearly non-overlapping distributions between dolphins from Taiwanese waters and those from the Jiulong River + Pearl River estuaries of mainland China (the nearest known populations). The Taiwanese dolphins were clearly diagnosable from those of the Jiulong River + Pearl River estuaries under the most commonly accepted ‘75% rule’ for subspecies delimitation (with 94% of one group being separable from 99+% of the other). Evidence of geographical isolation and behavioural differences also provided additional support for the distinctiveness of the Taiwanese dolphins. Conclusions: Together, the evidence strongly demonstrated that the Taiwanese humpback dolphin population is differentiated at the subspecies level and on an evolutionary trajectory that is independent from that of dolphins from adjacent waters of mainland China (i.e. Jiulong River + Pearl River estuaries). As a result, the taxonomy of Sousa chinensiswas revised to include two subspecies: the Taiwanese humpback dolphin, Sousa chinensis taiwanensis subsp. nov., and the Chinese humpback dolphin, Sousa chinensis chinensis (the nominotypical subspecies). These subspecies are described, and the holotype and paratype specimens for S. c. taiwanensis are established. © 2015 Wang et al.


Araujo C.C.,Federal University of Goais | Wang J.Y.,Trent University | Wang J.Y.,CetAsia Research Group | Hung S.K.,Hong Kong Cetacean Research Project | And 2 more authors.
Endangered Species Research | Year: 2014

The population of humpback dolphins Sousa chinensis that resides in the eastern Taiwan Strait (ETS) is geographically and genetically isolated from populations inhabiting the coastal waters of mainland China and appears to be facing unsustainable levels of human threats. Using VORTEX 9.99b, we modeled the viability of this Critically Endangered population under the present conditions as well as under realistic additional threat scenarios. We examined 6 different levels of bycatch mortality, 3 scenarios of habitat loss/degradation, and scenarios in which these threats were experienced together. Under the baseline (present) scenario, the population exhibited a decreasing growth rate and was predicted to be smaller than the initial population size in more than 76% of all model runs. In all scenarios with additional threats, the proportion of model runs in which population size was smaller than the initial size varied from 77.1 to 92.6%. Over the short term, fisheries-related mortality appears to have a more obvious impact on the population's trajectory than habitat loss/degradation. Even minimal increases in mortality from the current baseline levels will increase the probability of extinction of this population. Due to the fragile situation of ETS humpback dolphins, mitigation actions to reduce the current threats to this population are needed immediately. © Inter-Research 2014.


PubMed | CetAsia Research Group, Trent University, University of Malaya and Hong Kong Cetacean Research Project
Type: Comparative Study | Journal: The Journal of the Acoustical Society of America | Year: 2015

Differences in the acoustic variables of whistles emitted by Indo-Pacific humpback dolphins (Sousa chinensis) from two coastal locations along western Peninsular Malaysia were investigated. Duration, frequency, and frequency modulation variables were extracted from and used to characterize recordings of free-ranging humpback dolphins that were made using a broadband towed hydrophone. A total of 960 whistles from Matang Mangroves and 823 whistles from Langkawi Island were used in analyses. The whistles of Malaysian humpback dolphins covered frequencies from 1231 to 27120Hz with durations from 0.010-1.575s. Significant multivariate differences were found in whistles emitted between locations. Significant differences were also found between dolphins of the two locations in their whistle duration, frequency modulation, and all frequency variables except for minimum frequency, which is likely under morphological constraints. The differences in whistles may be related to adaptations to the local acoustic habitat or unique whistles may have developed due to social interactions within each location, or broader scale differences resulting from geographic separation between the locations.


Chen T.,CAS South China Sea Fisheries Research Institute | Hung S.K.,Hong Kong Dolphin Conservation Society | Hung S.K.,Hong Kong Cetacean Research Project | Qiu Y.,CAS South China Sea Fisheries Research Institute | And 2 more authors.
Mammalia | Year: 2010

To obtain critical information on distribution and abundance of Indo-Pacific humpback dolphins (Sousa chinensis) residing in the Pearl River Estuary (PRE), systematic line-transect surveys and photo-identification studies were conducted in the eastern and western sections of the estuary in 2005-2006 and 2007-2008, respectively. Dolphins in the eastern section occurred throughout Lingding Bay, whereas their distribution in the western section extended from the mouth of Modaomen to the channel between Shangchuan and Xiachuanislands. Variations in dolphin distribution during the wet and dry seasons were evident and probably associated with movements of their prey species. Photo-identification of individuals confirmed exchange of at least some individuals between the western and eastern sections of PRE, and thus dolphins from both areas almost certainly comprise a single population. Using line-transect analysis, the total population size of the PRE humpback dolphins was estimated to be 2555 during the wet season and 2517 during the dry season. However, these should be considered preliminary as the coefficients of variation in some survey areas were high. Further studies should focus on refining these estimates and working towards understanding the western boundary of the PRE population. © 2010 by Walter de Gruyter Berlin New York.


Marcotte D.,Concordia University at Montréal | Hung S.K.,Hong Kong Cetacean Research Project | Caquard S.,Concordia University at Montréal
Ocean and Coastal Management | Year: 2015

Indo-Pacific humpback dolphins have historically inhabited the northern waters off Lantau Island, Hong Kong; however their numbers have significantly decreased over the past decade, while human pressure has simultaneously increased. Based on a spatio-temporal analysis using a Geographic Information System (GIS), this study aims to assess the cumulative human impacts of local activities on this dolphin population since 1996. After introducing and discussing the multiple approaches, difficulties, and limitations to cumulative effects assessments (CEA), this paper outlines our proposed CEA methodology. Our methodology involves mapping and analysis of anthropogenic marine impacts in relation with historical dolphin distributions in the area. Local scale results show evidence of a relationship between the addition of new high-speed ferry (HSF) routes into the cumulative environment and the decrease in dolphins in a specific region known as the Brothers Islands. These results coincide with past research showing that whales and dolphins are significantly disrupted in the presence of high vessel traffic, which continues to grow in the northern waters off Lantau Island, Hong Kong and in many other places around the world. s © 2015 Elsevier Ltd.

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