Sains Malaysiana 50(11)(2021): 3159-3169

http://doi.org/10.17576/jsm-2021-5011-01

 

 

Seasonal Occurrence, Distribution and Group Size of Irrawaddy Dolphins (Orcaella brevirostris) in the Bay of Brunei, Brunei Darussalam

(Kejadian Bermusim, Taburan dan Saiz Kumpulan Ikan Lumba-lumba Irrawaddy (Orcaella brevirostris) di Teluk Brunei, Brunei Darussalam)

 

FARAH DAYANA HAJI ISMAIL1, NURLISA AZIZUL1, SAIFULLAH ARIFIN JAAMAN1*, AZMI MARZUKI MUDA1, MOHD VOL MOMIN2, BOHARI ABDULLAH2, XUELEI ZHANG3 & HAIRUL MASRINI MUHAMAD4

 

1Institute of Oceanography and Environment, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu Darul Iman, Malaysia

 

2Sakam Enterprise, Unit 17C, 2nd Floor, Bgn. Ben Kassim & Hjh Zaliha, Spg 440, Kg. Sungai Tilong, Jalan Muara BC3315, Brunei Darussalam

 

3Marine Ecology Research Center, First Institute of Oceanography (FIO), Ministry of Natural Resources, Qingdao 266061, China

 

4Key Laboratory of Underwater Acoustics & Marine Information Technology, Department of Applied, Marine Physics & Engineering, College of Ocean and Earth, Xiamen University, China

 

Received: 2 November 2019/Accepted: 11 March 2021

 

ABSTRACT

The uniqueness of the Bay of Brunei makes it an ideal place to be inhabited by Irrawaddy dolphins. However, the increasing potential impacts of anthropogenic factors and environmental changes on the dolphins are alarming. The objectives of this study were to determine the seasonal occurrence and distribution, and to estimate the group size of Irrawaddy dolphins in the Bay of Brunei. Surveys were conducted between January 2016 and April 2018. The total distance surveyed was 2,439.2 km in 189.13 h (survey effort = 13,081.93 km.h). Forty-nine groups of Irrawaddy dolphins were recorded with a sighting rate of 0.37 per 100 km.h. Thirteen of the groups were observed with calves. Overall, the group size ranged between 1 and 15 individuals with a mean of 4.5 individuals (SD = 3.3). There was no statistical significance in the number of dolphin sightings between four different monsoon seasons (Northeast, Southwest, April Inter-monsoon, and October Inter-monsoon) (χ2 = 5.66, df = 3, p > 0.05). The number of sightings and number of individuals suggest that Irrawaddy dolphins are residents of the Bay of Brunei and are in need of a conservation management plan. 

 

Keywords: Bay of Brunei; distribution; group size; Irrawaddy dolphin; occurrence

 

ABSTRAK

Keunikan Teluk Brunei menjadikan ia sebagai tempat yang ideal untuk didiami oleh ikan lumba-lumba Irrawaddy. Kesan peningkatan faktor antropogen dan perubahan alam sekitar terhadap ikan lumba-lumba bagaimanapun membimbangkan. Objektif kajian ini adalah untuk menentukan corak kehadiran, taburan dan menganggarkan saiz kumpulan ikan lumba-lumba Irrawaddy di Teluk Brunei. Tinjauan telah dijalankan dari Januari 2016 hingga April 2018. Jumlah jarak yang ditinjau ialah 2,439.2 km pada 189.13 jam (usaha tinjauan = 13,081.93 km.j) dengan kadar penglihatan 0.37 setiap 100 km.j. Jumlah keseluruhan penemuan yang direkodkan adalah 49 dan telah didapati bahawa 13 daripada penemuan tersebut mempunyai kehadiran ikan lumba-lumba kecil. Secara keseluruhannya, saiz kumpulan adalah antara 1 hingga 15 individu dengan purata 4.5 individu (SD = 3.3). Bilangan penemuan ikan lumba-lumba di antara keempat-empat musim monsun (Monsun Timur Laut, Monsun Barat Daya, peralihan monsun April dan peralihan monsun Oktober adalah secara statistiknya tidak signifikan2 = 5.66, df = 3, p> 0.05). Jumlah penemuan dan bilangan individu menunjukkan bahawa ikan lumba-lumba Irrawaddy menghuni kawasan tersebut dan pelan pengurusan pemuliharaan spesies merupakan keperluan di Teluk Brunei.

 

Kata kunci: Ikan lumba-lumba Irrawaddy; penemuan; saiz kumpulan; taburan; Teluk Brunei

 

REFERENCES

Atkins, S., Pillay, N. & Peddemors, V.M. 2004. Spatial distribution of Indo-Pacific Humpback Dolphins (Sousa chinensis) at Richards Bay, South Africa: Environmental influences and behavioural patterns. Aquatic Mammals 30(1): 84-93.

Baird, I.G. & Mounsouphom, B. 1997. Distribution, mortality, diet and conservation of Irrawaddy Dolphins (Orcaella brevirostrisGray) in Lao PDR. Asian Marine Biology 14: 41-48.

Baird, I.G. & Mounsouphom, B. 1994. Irrawaddy dolphins in Southern Lao PDR and northeastern Cambodia. Natural History Bulletin of the Siam Society 42: 159-175.

Bali, J., Jaaman, S.A., Saleh, E., Munsang, T., Tisen, O. & Ganyai, T. 2017. Distribution, abundance and density of Irrawaddy Dolphin (Orcaella brevirostris) in Rajang River of Sarawak, East Malaysia. Malaysian Applied Biology 46: 105-114.

Barros, N.B., Jefferson, T.A. & Parsons, E.C.M. 2004. Feeding habits of Indo-Pacific humpback dolphins (Sousa chinensis) stranded in Hong Kong. Aquatic Mammals 30(1): 179-188.

Beasley, I., Phay, S., Lor, K.S. & Yim, S. 2003. Mekong Dolphin Conservation Project (Unpublished report). James Cook University, Australia; Department of Fisheries, Cambodia and the Wildlife Conservation Society, Cambodia Program.

Beasley, I., Chooruk, S. & Piwpong, N. 2002. The status of the Irrawaddy dolphin, Orcaella brevirostris, in Songkhla Lake, Southern Thailand. Raffles Bulletin of Zoology Supplement 10: 75-83.

Elkin, J. 1992. Observations of marine animals in the coastal waters of western Brunei Darussalam. Brunei Museum Journal 7: 74-87.

Fury, C.A. & Harrison, P.L. 2011. Impact of flood events on dolphin occupancy patterns. Marine Mammal Science 27(3): 185-205.

Gibson-Hill, C.A. 1950. The whale, porpoises and dolphins known in Sarawak waters. The Sarawak Museum Journal 5: 288-296.

Gibson-Hill, C.A. 1949. The whale, porpoises and dolphins known in Malayan waters. The Malayan Nature Journal 4: 44-61.

Hashim, N.A.N. & Jaaman, S.A. 2011. Boat effects on the behavior of Indo-Pacific Humpback (Sousa chinensis) and Irrawaddy Dolphin (Orcaella brevirostris) in Cowie Bay, Sabah, Malaysia. Sains Malaysiana40(12): 1383-1392.

Hines, E., Strindberg, S., Junchompoo, C., Ponnampalam, L., Ilangakoon, A., Jackson-Ricketts, J. & Monanunsap, S. 2015. Line transect estimates of Irrawaddy dolphin abundance along the eastern Gulf Coast of Thailand. Frontiers in Marine Science. doi:  10.3389/fmars.2015.00063.

Jaaman, S.A. & Bali, J. 2011. Marine mammals of Borneo. In Malaysia's Marine Biodiversity: Inventory and Current Status, edited by Kamarruddin, I., Mohamed, C.A.R., Rozaimi, M.J., Kee-Alfian, B.A.A., Fitra, A.Z. & Lee, J.N. Putrajaya: Department of Marine Park Malaysia. pp. 47-69.

Jaaman, S.A., Muda, A.M., Abdul-Raman, A., Bali, J., Munsang, T.K. & Muhamad, H.M. 2016. Surveys of marine mammals in the Bay of Brunei, Malaysia. In Scientific Expedition to Brunei Bay, edited by Suratman, S. Penerbit UMT: Universiti Malaysia Terengganu. pp. 151-174.

Jackson-Ricketts, J. 2016. Diet, life history, habitat, and conservation of Irrawaddy dolphins (Orcaella brevirostris) in the Gulf of Thailand (Doctoral dissertation) (Unpublished). https://escholarship.org/uc/item/19q2k06f.

Jefferson, T.A. 2000. Population biology of the Indo-Pacific hump-backed dolphin in Hong Kong waters. Wildlife Monographs 144: 1-65.

Jefferson, T.A. & Hung, S.K. 2004. A review of the status of the Indo-Pacific humpback dolphins (Sousa chinensis) in Chinese Waters. Aquatic Mammals 30(1): 149-158.

Jefferson, T.A., Webber, M.A. & Pitman, R.L. 2008. Marine Mammals of the World: A Comprehensive Guide to Their Identification. London: Academic Press. pp. 153-155.

Jiang, Y., Liu, Z., Yang, C., , L., Yu, X., Huang, L., Zhang, X., Yang, Z., Yang, G., Sun, L., Jaaman, S.A. & Muda, A.M. 2020. High-frequency whistles of Irrawaddy dolphins (Orcaella brevirostris) recorded in Brunei Bay. Marine Mammal Science 2020: 1-12. doi: 10.1111/mms.12681.

Jiang, Y., Zhang, X., Yang, Z., Jaaman, S.A., Xu, Q., Muda, A.M. & Muhamad, H.M. 2019. Preliminary analysis of echolocation signals produced by fleeing Irrawaddy dolphins (Orcaella brevirostris). Acta Oceanologica Sinica -English Edition- 38(1): 85. doi: 10.1007/s13131-019-1373-y.

Junchompoo, C., Monanunsap, S. & Penpein, C. 2013. Population and conservation status of Iirawaddy Dolphins (Orcaella brevirostris) in Trat Bay, Trat Province, Thailand. Proceedings of the Design Symposium on Conservation of Ecosystem (The 13th SEASTAR2000 Workshop). doi: 10.13140/2.1.5183.3601.

Khalifa, M.A., Kamal, M.M., Adiwilaga, E.M. & Sunuddin, A. 2014. Preliminary study on the distribution of Irrawaddy Dolphin, Orcaella brevirostris, in Banten Bay. Open Journal of Marine Science 4(4): 338-343.

Kreb, D., Budiono & Syachraini. 2007. Status and conservation of Irrawaddy Dolphins Orcaella brevirostris in the Mahakam River of Indonesia. In Status and Conservation of Freshwater Populations of Irrawaddy Dolphins, WCS Working Paper 31, edited by Smith, B.D., Shore, R.G. & Lopez, A. Bronx, New York: Wildlife Conservation Society. pp. 53-66.

Krützen, M., Beasley, I., Ackermann, C.Y., Lieckfeldt, D., Ludwig, A., Ryan, G.E., Bejder, L., Parra, G.J., Wolfensberger, R. & Spencer, P. 2018. Demographic collapse and low genetic diversity of the Irrawaddy dolphin population inhabiting the Mekong River. PLoS ONE 13(1): e0189200. https://doi.org/10.1371/journal.pone.0189200.

Kuit, S.H., Ponnampalam, L., Ng, J., Chong, V. & Then, A. 2019. Distribution and habitat characteristics of three sympatric cetacean species in the coastal waters of Matang, Perak, Peninsular Malaysia. Aquatic Conservation: Marine and Freshwater Ecosystems. https://doi.org/10.1002/aqc.3121.

Lim, P.E. 1992. Water quality in the coastal areas of Brunei Darussalam: Status, management issues and recommendations.  In The Coastal Resources of Brunei Darussalam: Status, Utilization and Management, edited by Silvestre, G.T., Matdanan, H.J.H., Sharifuddin, P.H.Y., De Silva, M.W.R.N. & Chua, T.E. ICLARM Conference. Proceeding. pp. 91-108.

Mahmud, A.I. 2016. Population estimation and behavioural patterns of Irrawaddy dolphins, Orcaella brevirostris(Owen in Gray 1866) in the Brunei Bay, Malaysia (Master’s thesis, Erasmus Mundus Master Course in Tropical Biodiversity and Ecosystem).

Mahmud, A.I., Jaaman, S.A., Muda, A.M., Muhamad, H.M., Zhang, X. & Scapini, F. 2018a. Factors influencing the behaviour of Irrawaddy dolphins Orcaella brevirostris (Owen in Gray, 1866) in Brunei Bay, Malaysia. Journal of Ethology. doi: 10.1007/s10164-018-0549-9.

Mahmud, A.I., Jaaman, S.A., Muda, A.M., Muhamad, H.M., Zhang, X. & Scapini, F. 2018b. Population estimation, distribution, and habitat preference of Irrawaddy dolphins Orcaella brevirostris (Owen in Gray, 1866) in the Brunei Bay, Malaysian waters. Wildlife Biology 2018(1). doi: 10.2981/wlb.00383.

Marsh, H., Lloze, R., Heinsohand, G.E. & Kasuya, T. 1998. Irrawaddy dolphin Orcaella brevirostris (Gray, 1866). In Handbook of Marine Mammals, Vol 4, edited by Ridgway, S.H. & Harrison, R.J. London: Academic Press. pp. 101-118.

Ministry of Industry and Primary Resources. 2015. 5th National Report to the Convention on Biological Diversity, Brunei Darussalam. https://www.cbd.int/doc/world/bn/bn-nr-05-en.pdf.

Minton, G., Smith, B.D., Braulik, G.T., Kreb, D., Sutaria, D. & Reeves, R. 2017. Orcaella brevirostris (errata version published in 2018). The IUCN Red List of Threatened Species.  http://dx.doi.org/10.2305/IUCN.UK.20173.RLTS.T15419A50367860.en.

Muhamad, H.M., Xu, X., Zhang, X., Jaaman, S.A. & Muda, A.M. 2018. Whistle description of Irrawaddy dolphins (Orcaella brevirostris) in Bay of Brunei, Sarawak, Malaysia. The Journal of the Acoustical Society of America 143(5): 2708. https://doi.org/10.1121/1.5036926.

Muhamad, H.M., Xu, X., Zhang, X., Jaaman, S.A., Muda, A.M., Ismail, F.D. & Azizul, N. 2020. Echolocation clicks of Irrawaddy Dolphins (Orcaella brevirostris) during foraging in the Bay of Brunei, Malaysia. Acoustics Australia 48: 201-210. doi:10.1007/s40857-020-00183-5.

Owen, R. 1866. On some Indian Cetacea collected by Walter Elliot. Transactions of Zoological Society of London 6(1): 17-47.

Pattnaik, A., Sutaria, D., Khan, M. & Behera, B.P. 2007. Status and conservation of Irrawaddy Dolphins Orcaella brevirostris in Chilika Lagoon of India. In Status and Conservation of Freshwater Populations of Irrawaddy Dolphins, edited by Smith, B.D., Shore, R.G. & Lopez, A. WCS Working Papers 1530-4426. pp. 90-109.

Perrin, W., Dolar, M.L.L. & Alava, M.N.R. 1996. Report of the Workshop on the Biology and Conservation of Small Cetaceans and Dugongs of Southeast Asia, Dumaguete, 27-30 June 1995. UNEP(W)EAS WG 1/2. United Nations Environment Programme, Bangkok.

Pilleri, G. & Gihr, M. 1974. Contribution to the knowledge of the cetaceans of southwest and monsoon Asia (Persian Gulf, Indus Delta, Malabar, Andaman Sea and Gulf of Siam). Investigations on Cetacea 5: 95-149.

Ponnampalam, L., Hines, E., Monanunsap, S., Ilangakoon, A., Junchompoo, C., Adulyanukosol, K. & Morse, L. 2013. Behavioral observations of coastal Irrawaddy dolphins (Orcaella brevirostris) in Trat Province, Eastern Gulf of Thailand. Aquatic Mammals 39(4): 401-408. doi: DOI:10.1578/AM.39.4.2013.401.

Rodríguez-Vargas, L., Rajamani, L., Dolar, L. & Porter, L. 2019. Population size, distribution and daylight behaviour of Irrawaddy dolphins (Orcaella brevirostris) in Penang Island, Malaysia. Raffles Bulletin of Zoology 67: 671-683.

Ross, G.J.B. 2002. Humpback dolphins, Sousa chinensis, S. plumbea, and S. teuszi. In Encyclopedia of Marine Mammals, edited by Würsig, B., Perrin, W. & Thewissen, J.G.M. San Diego: Academic Press. pp. 585-589.

Silvestre, G.T. & Garces, L.R. 2004. Population parameters and exploitation rate of demersal fishes in Brunei Darussalam (1989-1990). Fish Research 69: 73-90.

Smith, B.D. 2004. Orcaella brevirostris (Ayeyarwady River subpopulation). 2004 IUCN Red List of Threatened Species. http://www.redlist.org/.

Smith, B.D. & Beasley, I. 2004a. Orcaella brevirostris (Mekong River subpopulation). 2004 IUCN Red List of Threatened Species. http://www. redlist.org/.

Smith, B.D. & Beasley, I. 2004b. Orcaella brevirostris (Songkhla Lake subpopulation). 2004 IUCN Red List of Threatened Species. http://www. redlist.org/.

Smith, B.D., Braulik, G., Strindberg, S., Ahmed, B. & Mansur, R. 2006. Abundance of Irrawaddy dolphins (Orcaella brevirostris) and Ganges River dolphins (Plantanista gangetica gangetica) estimated using concurrent counts made by independent teams in waterways of the Sundarbans mangrove forest in Bangladesh. Marine Mammal Science 22(3): 527-547. doi: 10.1111/j.1748-7692.2006.00041.x.

Smith, B.D., Jefferson, T.A., Leatherwood, S., Ho, D.T., Thuoc, C.V. & Quang, L.H. 1997. Investigation of Marine Mammals in Vietnam. Asian Marine Biology 14: 145-172.

Stacey, P.J. & Hvenegaard, G.T. 2002. Habitat use and behavior of Irrawaddy Dolphin (Orcaella brevirostris) in the Mekong River of Laos. Aquatic Mammals 28(1): 1-13.

Stacey, P.J. & Leatherwood, S. 1997. The Irrawaddy dolphin, Orcaella brevirostris: A summary of current knowledge and recommendations for conservation action. Asian Marine Biology 14: 195-214.

Sutaria, D. & Marsh, H. 2011. Abundance estimates of Irrawaddy dolphins in Chilika Lagoon, India, using photo‐identification based mark-recapture methods. Marine Mammal Science 27: 338-348.

Tisen, O.B. 2011. Pilot Project: Financial Incentive for Dugong Management. United Arab Emirate: UNEP. 

Tubbs, S.E., Keen, E., Jones, A.L. & Thap, R. 2020. On the distribution, behaviour and seasonal variation of Irrawaddy dolphins (Orcaella brevirostris) in the Kep Archipelago, Cambodia. Raffles Bulletin of Zoology 68: 137-149.

Wang, J.Y., Yang, S. & Liao, H. 2001. Species composition, distribution and relative abundance of cetaceans in the waters of Southern Taiwan: Implications for conservation and eco-tourism. Journal of the National Parks of Taiwan 11(2): 136-158.

Wang, X., Wu, F., Turvey, S.T., Rosso, M. & Zhu, Q. 2016. Seasonal group characteristics and occurrence patterns of Indo-Pacific humpback dolphins (Sousa chinensis) in Xiamen Bay, Fujian Province, China. Journal of Mammalogy 97(4): 1026-1032.

Weber, M. 1923. Die Cetaceen der Siboga-Expedition. Vorkommen und Fang der Cetaceen im Indo-Australischen Archipel. Siboga-Expeditie 58. Leiden: E.J. Brill. pp. 1-38. pls I-III.

Weir, C.R. 2009. Distribution, behavior and photo-identification of Atlantic humpback dolphins Sousa teuszii off Flamingos, Angola. Journal of Marine Science 31(3): 319-331.

 

*Corresponding author; email: saifullahaj@umt.edu.my