Similajau-Kuala Nyalau Coastline IMMA
Size in Square Kilometres
1 235 km2
Qualifying Species and Criteria
Irrawaddy dolphin – Orcaella brevirostris
Criterion A; B (1)
Finless porpoise – Neophocaena phocaenoides
Criterion A; B (1)
Indo-Pacific Humpback dolphin – Sousa chinensis
Criterion A; B (1)
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The Similajau to Kuala Nyalau coastline encompasses approximately 455 km2 of coastal waters in the Bintulu district, Sarawak, Malaysian Borneo. While a few small rivers empty into this stretch of coastline, it does not include any major estuaries or bays. It does encompass the coastal waters of Similajau National Park, a terrestrial park increasingly hemmed in by oil palm plantations, a major industrial park and a liquefied natural gas plant. Research conducted over a period of six years reveals that Irrawaddy dolphins, finless porpoises and humpback dolphins are frequently sighted along this coastline. Photo-identification studies indicate a high rate of site fidelity for Irrawaddy dolphins that appear to be resident year-round, while finless porpoises were encountered more frequently here than in any other study site in Sarawak. Observations of Irrawaddy dolphin and finless porpoise calves and feeding behaviour demonstrate that these coastal waters are important habitat for both species.
Description of Qualifying Criteria
Criterion A – Species or Population Vulnerability
Finless porpoises and Irrawaddy dolphins are both species known to be restricted to nearshore coastal waters throughout their ranges, which in both cases are limited to Southeast Asia. Irrawaddy dolphins have recently been re-assessed as Endangered on the IUCN Red List of Threatened Species (Minton et al. 2017), and the assessment points out that the locally occurring population in Similajau to Kuala Nyalau represents one of the very few entirely coastal as opposed to riverine or estuarine ecotypes of Irrawaddy dolphins to have been studied in detail. Their distribution is always within the 10 m contour line suggesting an obligatory nearshore distribution (Peter et al. 2017). The introduction of oil palm plantations and a large-scale industrial park is likely to have significant impacts on the water quality and level of human activity in the area’s nearshore waters. Fishing activities are likely to become more intense in the area around and to the north of the fishing village as the waters around the industrial park are occupied by a jetty and deep-water port as well as high levels of industrial vessel traffic. As of 2017 four strandings had been reported in the fishing village, two of which were attributed to fisheries bycatch. 16% (n=4.8) of fishermen interviewed in the village reported having been involved in an incident of bycatch in the past seven years and the Irrawaddy dolphins and humpback dolphins were the species most commonly bycaught. As fishing and coastal development continue to expand, the 25 km long national park may serve as a small refuge for coastal cetaceans.
Criterion B: Distribution and Abundance
Sub-criterion B1: Small and Resident Populations
Finless porpoises were observed regularly throughout all times of year and all years that surveys were conducted in the Similajau to Kuala Nyalau area, indicating a high likelihood of residence. Irrawaddy dolphins were also observed during every survey period, and photo-identification studies revealed a high-degree of site fidelity among some identified individuals, with less than 15 km between sighting locations over a period of six years (Peter et al. 2017). Both line-transect and mark-recapture estimates indicate a population size of fewer than 300 Irrawaddy dolphins (Peter et al. 2017), and unpublished line transect estimates for finless porpoises are in a similar range: 107 individuals (CV 35.5%, 95% CI 54-213).
Irrawaddy dolphin juveniles and calves were observed during 33 of the 77 sightings of Irrawaddy dolphins from March to September of the survey year. In the months of March, June and August, a mother-calf pair of finless porpoises was seen between Tanjung Payung, the northernmost boundary of the survey area and Tanjung Similajau, adjacent to the industrial zone. Depths in this area range from 2.4-6.7 m. Humpback dolphin calves were also recorded in the same areas in 2009, 2012 and 2013 (Sarawak Dolphin Project, unpublished data). Direct observations of feeding (chasing fish at the surface), or probable feeding behaviour (as indicated by deep fluke-up dives, the presence of fish at the surface of the water, or dolphins surfacing with mud on their bodies) was recorded during 44.2% of all Irrawaddy dolphin sightings recorded between 2008 and 2013 (n= 34, Peter et al., 2017). Furthermore, Irrawaddy dolphins were regularly observed in close proximity to fishing boats and fishing nets during 28.6% of encounters (n=22, Peter et al., 2016). Finless porpoise behaviour was difficult to classify in the area, as sightings were often limited to one or two brief surfaces before they were no longer detectable. However, the finless porpoises were seen to be feeding during three of 80 encounters and humpback dolphins also exhibited similar feeding behaviour during two of four encounters. 71% of the fishermen interviewed (n=21) reported that all three species of cetaceans feed on discarded fish such as anchovies (Sarawak Dolphin Project, unpublished data).
Minton, G., Peter, C. and Tuen, A.A. 2011. ‘Distribution of small cetaceans in the nearshore waters of Sarawak’. Raffles Bulletin of Zoology, 59: 91–100.
Minton, G., Smith, B.D., Braulik, G., Kreb, D., Sutaria, D. and Reeves, R. 2017. ‘Orcaella brevirostris. The IUCN Red List of Threatened Species 2017’. e.T15419A50367860. [online]. Available at
Peter, C., Zulkifli Poh, A.N., Ngeian, J., Tuen, A.A. and Minton, G. 2016. ‘Identifying Habitat Characteristics and Critical Areas for Irrawaddy Dolphin, Orcaella brevirostris: Implications for Conservation’. In: I Das, A.A. Tuen (eds.) Naturalists, Explorers and Field Scientists in South-East Asia and Australasia, pp 225-238. Switzerland: Springer.
Peter, C., Tuen, A.A., Zulkifli Poh, A.N., Ngeian, J. and Minton, G. 2017. ‘Population estimates and range of movement of Irrawaddy dolphins (Orcaella brevirostris) in Similajau, Bintulu, Malaysian Borneo’, paper delivered at the 22nd Biennial Conference on the Biology of Marine Mammals, Halifax, Canada, 24 October 2017.
Tregenza, N.J.C. and Collet, A.S. 1998. ‘Common Dolphin Delphinus delphis bycatch in pelagic trawl and other fisheries in the Northeast Atlantic.’ Report of the International Whaling Commission, 48: 452-459
Zulkifli Poh, A.N., Peter, C., Tuen, A.A., Ngeian, J. and Minton, G. 2017. ‘Small cetaceans in Bintulu, East Malaysia in the shadow of coastal development’, paper delivered at the 22nd Biennial Conference on the Biology of Marine Mammals, Halifax, Canada, 26 October 2017.