Journal of Ethology

, Volume 36, Issue 2, pp 169–180 | Cite as

Factors influencing the behaviour of Irrawaddy dolphins Orcaella brevirostris (Owen in Gray, 1866) in Brunei Bay, Malaysia

  • Anisul Islam Mahmud
  • Saifullah Arifin Jaaman
  • Azmi Marzuki Muda
  • Hairul Masrini Muhamad
  • Xuelei Zhang
  • Felicita Scapini


The population of Irrawaddy dolphins in Brunei Bay, Malaysia is little studied. This study aimed at contributing information on how abiotic and other factors influence different aspects of their behaviour displayed at the water surface. Several behaviours, i.e. foraging, travelling, foraging behind trawler, milling and socializing were observed during boat-based line transect surveys (2013–2016). The behaviours of individuals and groups were filmed or noted, and the abiotic factors of the habitat were registered at the same time. The number of “travelling” individuals was negatively correlated with surface water salinity (p value = 0.04) and positively correlated with turbidity (p value = 0.01). Fisher’s exact test also revealed that the behaviours of dolphin groups significantly differed with the ranges of several abiotic factors, i.e. foraging behind trawler with depth (p value = 0.001), travelling with surface water salinity (p value = 0.05), travelling and foraging behind trawler with turbidity (p value = 0.04, 0.01). The results for foraging behind trawler differed significantly between the groups with calves and those without calves (χ2 test, p value = 0.04), where groups with calves were less likely to forage behind trawlers. Significant differences were observed among group sizes for travelling, milling and socializing (χ2 test, p value < 0.05), with large groups (11–20 individuals) more frequently foraging, milling and socializing, compared to smaller ones. The current study is the first behavioural observation for Irrawaddy dolphins in Brunei Bay and these findings will help researchers, conservationists, local marine park managers and policy makers in developing effective conservation and management plans for the area.


Irrawaddy dolphin Behaviour Abiotic factors Group size Brunei Bay 



The authors would like to give special thanks to the team of the Marine Endangered Species (MES) Program, INOS-UMT for the database. The corresponding author would also like to acknowledge the European Commission for providing a scholarship (2014–2016) under the Erasmus Mundus Masters Course in Tropical Biodiversity and Ecosystems (TROPIMUNDO). Thanks to Eléonore R. A. Viez (BEVT, ULB) for helping in data analysis, and Miro Kolenic for language revision. Also thanks to Mr. Ismail (boatman) and his family members for cooking for us during the survey periods. Authors give thanks to the Sarawak Forestry Department for giving permission to conduct research on biological resources in Sarawak waters [Permit No. NCCD.907.4.4(JLD.11)-35]. Thanks to three anonymous reviewers for their comments for improving the manuscript.


The study was funded by the Ministry of Education (MOE) Malaysia, Higher Institution Centre of Excellence (HICOE) Grant Scheme (2013–2015) of INOS-UMT; FIO-UMT surveys for marine mammals and sea turtles in the bay of Brunei, 2015–2018 project and the China-ASEAN maritime cooperation fund.

Compliance with ethical standards

Conflict of interest

The authors of different universities originally produced this research article, and there is no overlap with other articles published or in press in journals, books or conference proceedings, or in preparation, and all co-authors agreed to submit to this journal. Thanks to three anonymous reviewers for their valuable comments for improving the manuscript. The authors declare that they have no conflict of interest.


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Copyright information

© Japan Ethological Society and Springer Japan KK, part of Springer Nature 2018

Authors and Affiliations

  • Anisul Islam Mahmud
    • 1
    • 2
  • Saifullah Arifin Jaaman
    • 2
  • Azmi Marzuki Muda
    • 2
  • Hairul Masrini Muhamad
    • 3
  • Xuelei Zhang
    • 4
  • Felicita Scapini
    • 1
  1. 1.Dipartimento di BiologiaUniversità degli Studi di Firenze (UNIFI)FlorenceItaly
  2. 2.Institute of Oceanography and Environment (INOS)Universiti Malaysia Terengganu (UMT)Kuala TerengganuMalaysia
  3. 3.Key Laboratory of Underwater Acoustics and Marine Information Technology, Department of Applied Marine Physics and Engineering, College of Ocean and EarthXiamen UniversityXiamenChina
  4. 4.First Institute of OceanographyState Oceanic AdministrationQingdaoChina

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