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

Diserahkan: 2 November 2019/Diterima: 11 Mac 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 signifikan (χ² = 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

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*Pengarang untuk surat-menyurat; email: saifullahaj@umt.edu.my