Mersing Archipelago IMMA

Size in Square Kilometres

1 244 km2

Qualifying Species and Criteria

Dugong – Dugong dugon

Criterion A; B (2); C (1, 2); D (1)

Marine Mammal Diversity 

Neophocaena phocaenoides, Orcaella brevirostris, Sousa chinensis, Tursiops aduncus, Delphinus delphis tropicalis

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The Mersing Archipelago is a cluster of tropical islands and rocky outcrops situated off the east coast of the state of Johor, Peninsular Malaysia. These islands have a rich geological history, and host high marine biodiversity and ecosystems that include mangroves, coral reefs and verdant seagrass meadows. Since 1994, these islands’ surrounding waters up to 2 nautical miles from the lowest watermark have been gazetted as Marine Parks. Tourism is the main economic activity, while artisanal and commercial fishing communities are found along the adjacent mainland coast. Of particular significance in this IMMA is the seagrass meadows, especially those found on the leeward sides of Sibu and Tinggi cluster of islands which constitute a significant critical habitat for dugongs (Dugong dugon) in Peninsular Malaysia. Ongoing research on the dugongs since 2014 has revealed a small but reproductive population that feed on the seagrasses in the meadows, breed and socialise in this IMMA year-round.

Description of Qualifying Criteria

Criterion A – Species or Population Vulnerability

Dugongs are listed as VU on the IUCN Red List of Threatened Species, and the species is also listed as a Marine Endangered Species under the Malaysian Fisheries Act 1985 and Fisheries (Control of Endangered Species) Regulation (Amended) 2008. Furthermore, the Mersing Archipelago is the only place in Peninsular Malaysia where dugong occurrence is frequent and reliable. The population is small and there have been at least 19 dugong deaths recorded between 2015 and 2022, most of which were of calves/juvenile individuals (MareCet, unpublished data). A bycatch risk assessment on dugongs at Sibu and Tinggi Islands revealed that the species was most likely to be impacted by the use of gillnets in the surrounding waters (Hines et al., 2020).

Criterion B: Distribution and Abundance

Sub-criterion B2: Aggregations

Systematic aerial surveys were conducted three times a year from 2014 to 2016 covering total search effort of 23,790 km over 145 hours (Ponnampalam, 2017). A total of 642 dugong sightings were made over the course of the surveys with group size ranging from solitary animals to large herds of more than 40 animals (maximum count of 43 in a single sighting) (Ponnampalam, 2017).  Although dugongs have a wide global range, populations are often small and fragmented throughout its range. While this population do not represent a large proportion of the entire global population of the species, it is the only population around Peninsular Malaysia where regular occurrences of the species have been observed.  These herds are usually inclusive of mother-calf pairs. These aggregations were observed mainly in the mornings, concentrated mainly in a small area south of Sibu Island (Ponnampalam, 2017).

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

The area around Sibu island, especially to the southwest, is considered to be an important nursing ground where most dugong mother-calf pairs were observed (24% of all dugong groups sighted during aerial surveys were of mother-calf pairs/contained mother-calf pairs) (Ponnampalam et al., 2014, 2015, Ponnampalam 2017).

Sub-criterion C2: Feeding Areas

The seagrass meadows in the area, especially those around Sibu Island are known dugong feeding grounds due to documented presence of many feeding trails during surveys throughout the year (Heng et al. 2022; Ponnampalam, 2017) (Figure 2).

Criterion D: Special Attributes  

Sub-criterion D1: Distinctiveness

The seagrass meadows in the area especially those of Tinggi Island and the area south of Mentigi and Nanga Kecil and Nanga Besar Islands are identified as dugong ‘vocal hotspots’ where dugong vocalizations were often detected (Ichikawa et al. 2015 ; Ponnampalam, 2017). The ‘vocal hotspot’ is believed to be an area for daily communication and social cohesion for the dugongs using the area.

Supporting Information

Heng, H.W.K., Ooi, J.L.S., Affendi, Y.A., Kee Alfian, A.A. and Ponnampalam, L.S. 2022. Dugong feeding grounds and spatial feeding patterns in subtidal seagrass: A case study at Sibu Archipelago, Malaysia. Estuarine, Coastal and Shelf Science 264: 107670. Available at:

Hines, E., Ponnampalam, L.S., Junchompoo, C., Peter, C., Vu, L., Huynh, T., Caillat, M., Johnson, A.F., Minton, G., Lewison, R. and Verutes, G.M. 2020. Getting to the bottom of bycatch, a GIS-based toolbox to assess the risk of marine mammal bycatch. Endangered Species Research. Available at:

Ichikawa, K., Akamatsu, T., Ponnampalam, L., Alfian, K. and Arai, N. 2015. ‘Heterogeneous movement of dugongs between a vocal hotspot and a seagrass bed in Johor, Malaysia’. Abstracts of the 3rd Design Symposium on Conservation of Ecosystem (SEASTAR2000)’, Kyoto, Japan, 15 March 2015.

Jaaman, S.A. and Mohamed, C.A.R. 2014. ‘Marine mammals in the waters of east coast Johor, Malaysia’. ASM Science Journal 8(2): 143-149. Available at:

Kili, K.A. 2016. ‘Johor seeks best way to protect dugong’, The Star Online, 19 May, accessed 22 October 2018. Available at:

Ooi, J.L.S., Kendrick, G.A., Van Niel, K.P. and Affendi, Y.A. 2011. ‘Knowledge gaps in tropical Southeast Asian seagrass systems’. Estuarine, Coastal and Shelf Science 92: 118–131. Available at:

Ponnampalam, L.S. 2017. ‘A three-pronged approach for overcoming knowledge barriers on the ecology and status of dugongs in Johor, Malaysia – Towards critical habitat protection’.  Narrative Report #3: Year 3 (Final) Progress Report of PEW Fellowship in Marine Conservation (2014 – 2017).  Report submitted to The PEW Charitable Trusts.

Ponnampalam, L.S., Fairul Izmal, J.H., Adulyanukosol, K., Ooi, J.L.S. and Reynolds III, J.E. 2015. ‘Aligning conservation and research priorities for proactive species and habitat management: the case of dugongs Dugong dugon in Johor, Malaysia’. Oryx 49(4): 743-749. DOI:10.1017/S0030605313001580

Ponnampalam, L.S., Fairul Izmal, J.H., Ichikawa, K., Akamatsu, T., Kee Alfian, A.A., Wetzel, D. and Reynolds III, J. 2014. ‘A multi-pronged approach for overcoming knowledge barriers on the ecology and status of dugongs (Dugong dugon) in Johor, Malaysia: Towards critical habitat protection’. In: Wan Musthapa, W. F. Z., Nik Rosely, N. F. and Othman, A. S. (eds.) Johor Nature Heritage, pp 101-112. School of Biological Sciences, Universiti Sains Malaysia, Penang, Malaysia.

Said, M.Z., Komoo, I., Mohamad, E.T., Ali, C.A., Ahmad, N., Abd Wahid, M.E. and Rajimin, M.F. 2021. Geological, biological, cultural and local wisdom
heritage a key element of Mersing Geopark development. Bulletin of the Geological Society of Malaysia 71: 89 – 98. Available at:

The Star. 2016. Johor allocates RM1mil to set up dugong sanctuary, The Star Online, 15 May, accessed 24 October 2018. Available at:


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