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Lingham-Soliar T, Bloodgood J, Rothschild B, Bouveroux T. Survival of an Indian Ocean humpback dolphin Sousa plumbea in the wild despite chronic osteologic pathologies. DISEASES OF AQUATIC ORGANISMS 2022; 154:49-57. [PMID: 37318384 DOI: 10.3354/dao03729] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Skeletal examination of a female adult Indian Ocean humpback dolphin Sousa plumbea from South Africa suggested a chronic disease process. It manifested as erosions and pitting of the atlanto-occipital articulation as well as circumferential hyperostosis and ankylosis of some of the caudal vertebrae, findings rarely recorded together in the same animal. The character of the erosive process and vertebral fusion appeared chronic, and further findings of underdevelopment of the fluke, sternum and left humerus with remodeling of the periarticular region of the left scapula may support initiation of the process early in life. Because such chronic pathology would have affected the individual's locomotion and foraging abilities, we also postulate how this individual survived until its demise in a human-derived environmental hazard. Ecological and socio-behavioral aspects observed in S. plumbea, including habitat preference for inshore and shallow waters, small social group aggregations and feeding cooperation, may have contributed to its ability to survive.
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Affiliation(s)
- Theagarten Lingham-Soliar
- Nelson Mandela University, Institute for Coastal and Marine Research, Port Elizabeth 77000, South Africa
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2
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Mohsenian N, Methion S, Moshiri H, Hassan SK, Afkhami S, Tollab MA, Sadeh M, Braulik GT, López BD. Abundance estimation, group dynamics, and residence patterns of Indian Ocean humpback dolphin (Sousa plumbea) in the Dayer-Nakhiloo Marine National Park, Northern Persian Gulf, Iran. EUR J WILDLIFE RES 2022. [DOI: 10.1007/s10344-022-01565-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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Lampert S, Ingle RA, Jackson JA, Gopal K, Plön S. Low mitochondrial genetic diversity in the Indian Ocean humpback dolphin Sousa plumbea in South African waters. ENDANGER SPECIES RES 2021. [DOI: 10.3354/esr01147] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The Indian Ocean humpback dolphin Sousa plumbea has been described as South Africa’s most endangered marine mammal due to its low abundance, reliance on coastal habitats with increasing anthropogenic threats and high rates of mortality from bycatch in bather protection nets (BPNs). Although the species has been well studied in South Africa, only a single study has examined its molecular ecology to date, and its population structure remains poorly understood. However, understanding population structure is vital for the conservation and management of a species. To address these research gaps for S. plumbea in South African waters, we analysed the mitochondrial D-loop of 157 museum skin and tooth samples collected between 1963 and 2017 from across the species’ geographic range in South Africa. Our data show that the humpback dolphin has extremely low mitochondrial diversity (haplotype diversity, HD = 0.47; nucleotide diversity, π = 0.2%) with only 3 haplotypes identified, which is comparable to the Critically Endangered Māui dolphin Cephalorhynchus hectori maui and the Critically Endangered Mekong population of Irrawaddy dolphin Orcaella brevirostris. Mitochondrial genetic diversity has not changed significantly in the last 50 yr, despite the high levels of bycatch in BPNs over this time period. Furthermore, we found no evidence of differentiation between dolphins from the KwaZulu-Natal Coast and the Cape South Coast (Western Cape and Eastern Cape). The extremely low mitochondrial diversity we found adds to the growing body of evidence that the humpback dolphin is becoming increasingly vulnerable and that urgent conservation efforts are required for the survival of the species.
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Affiliation(s)
- S Lampert
- Department of Molecular and Cell Biology, University of Cape Town, Rondebosch 7700, South Africa
| | - RA Ingle
- Department of Molecular and Cell Biology, University of Cape Town, Rondebosch 7700, South Africa
| | - JA Jackson
- British Antarctic Survey, Cambridge CB3 0ET, UK
| | - K Gopal
- Natural Science Collections Facility (South African National Biodiversity Institute), Pretoria 0186, South Africa
- Department of Natural History, Iziko South African Museums, Cape Town 8001, South Africa
| | - S Plön
- Bayworld Centre for Research and Education (BCRE), Port Elizabeth 6013, South Africa
- Division of Medical Virology, Department of Pathology, Stellenbosch University, Cape Town 7505, South Africa
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Abstract
Humpback dolphins (Sousa spp.) are obligate shallow-water and resident species, and they typically live in fission-fusion societies composed of small-sized groups with changeable membership. However, we have scant knowledge of their behavioral ecology, starting with potential factors influencing inter-population variability of their group sizes. Here, we compiled a new global dataset of humpback dolphin group sizes based on 150 published records. Our data indicated an inter-specific consistency of group-living strategy among the 4 species in the Sousa genus, as these species preferred living in small-sized groups with a mean size of mostly no more than 10, a minimum size of single individual or small pairs, and a maximum size of several tens or ≈100. In addition, we clearly showed the geographic variations in group sizes of humpback dolphins at a global scale. We found that the geographic variations in humpback dolphin group sizes were primarily associated with the latitude, sea surface temperature, and abundance. To conclude, our findings provide insights into social dynamics and socioecological trade-offs of humpback dolphins, and help better understand how these resident animals adapted to their shallow-water habitats from the perspectives of biogeography and socioecology.
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Affiliation(s)
- Mingming Liu
- Marine Mammal and Marine Bioacoustics Laboratory, Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya, China.,University of Chinese Academy of Sciences, Beijing, China.,School of Biological Sciences, University of Aberdeen, Aberdeen, UK
| | - Mingli Lin
- Marine Mammal and Marine Bioacoustics Laboratory, Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya, China
| | - David Lusseau
- School of Biological Sciences, University of Aberdeen, Aberdeen, UK.,National Institute of Aquatic Resources, Technical University of Denmark, Lyngby, Denmark
| | - Songhai Li
- Marine Mammal and Marine Bioacoustics Laboratory, Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya, China.,Tropical Marine Science Institute, National University of Singapore, Singapore
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Edmonds NJ, Al-Zaidan AS, Al-Sabah AA, Le Quesne WJF, Devlin MJ, Davison PI, Lyons BP. Kuwait's marine biodiversity: Qualitative assessment of indicator habitats and species. MARINE POLLUTION BULLETIN 2021; 163:111915. [PMID: 33360724 DOI: 10.1016/j.marpolbul.2020.111915] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 11/27/2020] [Accepted: 12/03/2020] [Indexed: 06/12/2023]
Abstract
The tropical waters of the Northern Arabian Gulf have a long history of maritime resource richness. High levels of biodiversity result from the complex matrix of coastal habitats, coral reefs and sea grass beds that characterise the region. Insight into the ongoing health of such habitats and the broader Kuwait maritime environment can be gauged by the status of indicator species found within these habitats. Here we review information on the occurrence, distribution and threats to key marine habitats and associated indicator species to provide an updated assessment of the state of the Kuwait's marine biodiversity. Critical evaluation of historic data highlights knowledge gaps needed inform the focus of future monitoring and conservation efforts. This assessment is designed to evaluate performance against environmental policy commitments, while providing a solid foundation for the design of comprehensive marine ecosystem management strategies.
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Affiliation(s)
- N J Edmonds
- Centre for Environment, Fisheries, Aquaculture Science (Cefas), Pakefield Road, Lowestoft, Suffolk NR33 0HT, United Kingdom.
| | - A S Al-Zaidan
- Kuwait Environment Public Authority (KEPA), P.O. Box: 24395, Safat 13104, Kuwait
| | - A A Al-Sabah
- Kuwait Environment Public Authority (KEPA), P.O. Box: 24395, Safat 13104, Kuwait
| | - W J F Le Quesne
- Centre for Environment, Fisheries, Aquaculture Science (Cefas), Pakefield Road, Lowestoft, Suffolk NR33 0HT, United Kingdom
| | - M J Devlin
- Centre for Environment, Fisheries, Aquaculture Science (Cefas), Pakefield Road, Lowestoft, Suffolk NR33 0HT, United Kingdom
| | - P I Davison
- Centre for Environment, Fisheries, Aquaculture Science (Cefas), Pakefield Road, Lowestoft, Suffolk NR33 0HT, United Kingdom
| | - B P Lyons
- Cefas, Weymouth Laboratory, Barrack Road, Weymouth, Dorset DT4 8UB, UK; British Embassy at the State of Kuwait, P.O. Box 2, Safat 13001, Kuwait
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Amaral AR, Chanfana C, Smith BD, Mansur R, Collins T, Baldwin R, Minton G, Parra GJ, Krützen M, Jefferson TA, Karczmarski L, Guissamulo A, Brownell RL, Rosenbaum HC. Genomics of Population Differentiation in Humpback Dolphins, Sousa spp. in the Indo-Pacific Ocean. J Hered 2020; 111:652-660. [PMID: 33475708 DOI: 10.1093/jhered/esaa055] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2020] [Accepted: 11/30/2020] [Indexed: 11/13/2022] Open
Abstract
Speciation is a fundamental process in evolution and crucial to the formation of biodiversity. It is a continuous and complex process, which can involve multiple interacting barriers leading to heterogeneous genomic landscapes with various peaks of divergence among populations. In this study, we used a population genomics approach to gain insights on the speciation process and to understand the population structure within the genus Sousa across its distribution in the Indo-Pacific region. We found 5 distinct clusters, corresponding to S. plumbea along the eastern African coast and the Arabian Sea, the Bangladesh population, S. chinensis off Thailand and S. sahulensis off Australian waters. We suggest that the high level of differentiation found, even across geographically close areas, is likely determined by different oceanographic features such as sea surface temperature and primary productivity.
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Affiliation(s)
- Ana R Amaral
- Sackler Institute for Comparative Genomics, American Museum of Natural History, New York, NY.,Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências Universidade de Lisboa, Campo Grande, Lisboa, Portugal
| | - Cátia Chanfana
- Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências Universidade de Lisboa, Campo Grande, Lisboa, Portugal
| | - Brian D Smith
- Wildlife Conservation Society, Ocean Giants Program, Bronx, NY
| | - Rubaiyat Mansur
- Wildlife Conservation Society, Ocean Giants Program, Bronx, NY
| | - Tim Collins
- Wildlife Conservation Society, Ocean Giants Program, Bronx, NY
| | | | - Gianna Minton
- Megaptera Marine Conservation, The Hague, The Netherlands
| | - Guido J Parra
- Cetacean Ecology, Behaviour and Evolution Lab, College of Science and Engineering, Flinders University, Adelaide, SA, Australia
| | - Michael Krützen
- Evolutionary Genetics Group, Department of Anthropology, University of Zurich, CH Zurich, Switzerland
| | | | - Leszek Karczmarski
- Division of Cetacean Ecology and Division of Comparative Behavioural Ecology, Cetacea Research Institute, Lantau, Hong Kong.,Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Hatfield, Pretoria, South Africa
| | - Almeida Guissamulo
- Universidade Eduardo Mondlane, Museu de Historia Natural, Praca Travessia do Zambeze, Maputo, Mozambique
| | - Robert L Brownell
- NOAA Fisheries, Southwest Fisheries Science Center, La Jolla Shores Drive, La Jolla, CA
| | - Howard C Rosenbaum
- Sackler Institute for Comparative Genomics, American Museum of Natural History, New York, NY.,Wildlife Conservation Society, Ocean Giants Program, Bronx, NY
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Affiliation(s)
- Songhai Li
- Marine Mammal and Marine Bioacoustics Laboratory, Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Sanya, 572000, China.
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Bouveroux T, Kirkman SP, Conry D, Vargas-Fonseca OA, Pistorius PA. The first assessment of social organisation of the Indian Ocean humpback dolphin (Sousa plumbea) along the south coast of South Africa. CAN J ZOOL 2019. [DOI: 10.1139/cjz-2018-0244] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Indian Ocean humpback dolphin (Sousa plumbea (G. Cuvier, 1829)) is the most endangered marine mammal species in South Africa, and the overall decline of its abundance and group size may affect the social organisation of the species, potentially accentuating its vulnerability. Understanding the social organisation is therefore particularly relevant to conservation efforts. From photo-identification surveys along the south coast of South Africa from March 2014 to June 2015, we quantified association patterns and investigated the social organisation of Indian Ocean humpback dolphins using the half-weight index, social cluster, and network analyses. During the 101 surveys conducted and 553 h of survey effort, 98 sightings of dolphins were recorded and 65 individuals identified. Using individuals seen at least three times, this study reveals that the social network is well differentiated, as strong social divisions exist between individuals that seem to be split into four distinctive social clusters. Network strength was low; approximately half of the associations were low to moderate, whereas some individuals were strongly associated, especially between four pairs of individuals. Although this study is based on a limited number of individuals, our study nevertheless suggests that the atypical strong social bonds recorded here could result from behavioural responses following the decline in group size and abundance.
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Affiliation(s)
- Thibaut Bouveroux
- Department of Zoology, Nelson Mandela University, P.O. Box 77000, 6031, Port Elizabeth, South Africa
- Marine Apex Predator Research Unit, Coastal and Marine Research Institute, Nelson Mandela University, P.O. Box 77000, 6031, Port Elizabeth, South Africa
| | - Stephen P. Kirkman
- Department of Environmental Affairs, Branch Oceans and Coasts, 8001, Cape Town, South Africa
| | - Danielle Conry
- Department of Zoology, Nelson Mandela University, P.O. Box 77000, 6031, Port Elizabeth, South Africa
- Marine Apex Predator Research Unit, Coastal and Marine Research Institute, Nelson Mandela University, P.O. Box 77000, 6031, Port Elizabeth, South Africa
| | - O. Alejandra Vargas-Fonseca
- Department of Zoology, Nelson Mandela University, P.O. Box 77000, 6031, Port Elizabeth, South Africa
- Marine Apex Predator Research Unit, Coastal and Marine Research Institute, Nelson Mandela University, P.O. Box 77000, 6031, Port Elizabeth, South Africa
| | - Pierre A. Pistorius
- Department of Zoology, Nelson Mandela University, P.O. Box 77000, 6031, Port Elizabeth, South Africa
- Marine Apex Predator Research Unit, Coastal and Marine Research Institute, Nelson Mandela University, P.O. Box 77000, 6031, Port Elizabeth, South Africa
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9
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Braulik G, Wittich A, Macaulay J, Kasuga M, Gordon J, Davenport TRB, Gillespie D. Acoustic monitoring to document the spatial distribution and hotspots of blast fishing in Tanzania. MARINE POLLUTION BULLETIN 2017; 125:360-366. [PMID: 28958441 DOI: 10.1016/j.marpolbul.2017.09.036] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Revised: 09/14/2017] [Accepted: 09/18/2017] [Indexed: 06/07/2023]
Abstract
Destructive fishing using explosives occurs in a number of countries worldwide, negatively impacting coral reefs and fisheries on which millions of people rely. Documenting, quantifying and combating the problem has proved problematic. In March-April 2015 231h of acoustic data were collected over 2692km of systematically laid transects along the entire coast of Tanzania. A total of 318 blasts were confirmed using a combination of manual and supervised semi-autonomous detection. Blasts were detected along the entire coastline, but almost 62% were within 80km of Dar es Salaam, where blast frequency reached almost 10blasts/h. This study is one of the first to use acoustic monitoring to provide a spatial assessment of the intensity of blast fishing. This can be a useful tool that can provide reliable data to define hotspots where the activity is concentrated and determine where enforcement should be focused for maximum impact.
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Affiliation(s)
- Gill Braulik
- Wildlife Conservation Society, Tanzania Program, Zanzibar, Tanzania; Scottish Oceans Institute, University of St Andrews, St Andrews, Fife, UK.
| | | | - Jamie Macaulay
- Scottish Oceans Institute, University of St Andrews, St Andrews, Fife, UK
| | - Magreth Kasuga
- Wildlife Conservation Society, Tanzania Program, Zanzibar, Tanzania
| | - Jonathan Gordon
- Scottish Oceans Institute, University of St Andrews, St Andrews, Fife, UK
| | | | - Douglas Gillespie
- Scottish Oceans Institute, University of St Andrews, St Andrews, Fife, UK
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10
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Karczmarski L, Huang SL, Chan SCY. Threshold of long-term survival of a coastal delphinid in anthropogenically degraded environment: Indo-Pacific humpback dolphins in Pearl River Delta. Sci Rep 2017; 7:42900. [PMID: 28230056 PMCID: PMC5322318 DOI: 10.1038/srep42900] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Accepted: 01/17/2017] [Indexed: 11/09/2022] Open
Abstract
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.
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Affiliation(s)
- Leszek Karczmarski
- The Swire Institute of Marine Science and School of Biological Sciences, Faculty of Science, The University of Hong Kong, Cape d'Aguilar, Shek O, Hong Kong
| | - Shiang-Lin Huang
- The Swire Institute of Marine Science and School of Biological Sciences, Faculty of Science, The University of Hong Kong, Cape d'Aguilar, Shek O, Hong Kong
| | - Stephen C Y Chan
- The Swire Institute of Marine Science and School of Biological Sciences, Faculty of Science, The University of Hong Kong, Cape d'Aguilar, Shek O, Hong Kong
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Oceanographic drivers of population differentiation in Indo-Pacific bottlenose (Tursiops aduncus) and humpback (Sousa spp.) dolphins of the northern Bay of Bengal. CONSERV GENET 2016. [DOI: 10.1007/s10592-016-0913-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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12
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Weir CR, Wang JY. Vertebral column anomalies in Indo-Pacific and Atlantic humpback dolphins Sousa spp. DISEASES OF AQUATIC ORGANISMS 2016; 120:179-187. [PMID: 27503913 DOI: 10.3354/dao03026] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Conspicuous vertebral column abnormalities in humpback dolphins (genus Sousa) were documented for the first time during 3 photo-identification field studies of small populations in Taiwan, Senegal and Angola. Seven Taiwanese humpback dolphins S. chinensis taiwanensis with vertebral column anomalies (lordosis, kyphosis or scoliosis) were identified, along with 2 possible cases of vertebral osteomyelitis. There was evidence from several individuals photographed over consecutive years that the anomalies became more pronounced with age. Three Atlantic humpback dolphins S. teuszii were observed with axial deviations of the vertebral column (lordosis and kyphosis). Another possible case was identified in a calf, and 2 further animals were photographed with dorsal indents potentially indicative of anomalies. Vertebral column anomalies of humpback dolphins were predominantly evident in the lumbo-caudal region, but one Atlantic humpback dolphin had an anomaly in the cervico-thoracic region. Lordosis and kyphosis occurred simultaneously in several individuals. Apart from the described anomalies, all dolphins appeared in good health and were not obviously underweight or noticeably compromised in swim speed. This study presents the first descriptions of vertebral column anomalies in the genus Sousa. The causative factors for the anomalies were unknown in every case and are potentially diverse. Whether these anomalies result in reduced fitness of individuals or populations merits attention, as both the Taiwanese and Atlantic humpback dolphin are species of high conservation concern.
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Affiliation(s)
- Caroline R Weir
- Ketos Ecology, 4 Compton Road, Kingsbridge, Devon TQ7 2BP, UK
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13
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Jefferson TA, Curry BE. Humpback Dolphins: A Brief Introduction to the Genus Sousa. ADVANCES IN MARINE BIOLOGY 2015; 72:1-16. [PMID: 26555620 DOI: 10.1016/bs.amb.2015.04.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The delphinid genus Sousa has recently undergone a major revision, and currently contains four species, the Atlantic humpback (Sousa teuszii), Indian Ocean humpback (Sousa plumbea), Indo-Pacific humpback (Sousa chinensis), and Australian humpback (Sousa sahulensis) dolphins. Recent molecular evidence suggests that humpback dolphins in the Bay of Bengal may comprise a fifth species. These moderate-sized dolphin species are found in shallow (<30m), coastal waters of the eastern Atlantic, Indian, and western Pacific oceans. Abundance and trends have only been studied in a few areas, mostly in eastern Africa, China, and northern Australia. No global, empirically derived abundance estimates exist for any of the four species, but none appear to number more than about 20,000 individuals. Humpback dolphins feed mostly on small fishes, and sometimes shrimps; occur for the most part in small groups (mostly 12 or less); have limited nearshore movements; and in most parts of their range exhibit a fission/fusion type of social organization. Major threats that affect all the species are entanglement in fishing gear, and habitat degradation/destruction from various forms of coastal development. Impacts from vessel traffic (including behavioural disturbance and displacement, as well as mortality and morbidity from collisions with vessels) appear to be significant in most areas. Several other threats are apparently significant only in particular parts of the range of some species (e.g. high levels of organochlorine contaminants affecting Indo-Pacific humpback dolphins in Hong Kong). Direct hunting only occurs in limited areas and primarily on a small scale. Conservation actions so far have been limited, with most populations receiving little study and almost no management attention. Much more work is needed on humpback dolphin population status, threats, and how the major threats can be reduced or eliminated. Extinction risks for the four species and some populations are preliminarily re-assessed using the IUCN Red List criteria in the current volume. The results suggest that all four species in the genus are threatened at some level (suggested Red List status ranges from Vulnerable for S. chinensis and S. sahulensis to Critically Endangered for S. teuszii).
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Affiliation(s)
| | - Barbara E Curry
- Physiological Ecology and Bioenergetics Laboratory, University of Central Florida, Orlando, Florida, USA
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Plön S, Cockcroft VG, Froneman WP. The Natural History and Conservation of Indian Ocean Humpback Dolphins (Sousa plumbea) in South African Waters. ADVANCES IN MARINE BIOLOGY 2015; 72:143-162. [PMID: 26555625 DOI: 10.1016/bs.amb.2015.08.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
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.
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Affiliation(s)
- Stephanie Plön
- Coastal and Marine Research Institute, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa.
| | - Victor G Cockcroft
- Department of Zoology, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa
| | - William P Froneman
- Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa
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