Malampaya Sound, Palawan, Philippines, is home to a small locally occurring subpopulation of Irrawaddy dolphins. The most recent population estimate is 35 individuals (CV = 22.9%), with bycatch rates greatly exceeding the potential biological removal rate. This subpopulation is restricted to the inner part of the sound and is listed as Critically Endangered on the IUCN Red List. Though Malampaya Sound has been a designated a Protected Landscape and Seascape since 2000, management of fisheries continues to be ineffective for enhancing the conservation of this species. Fishing effort continues to increase without meaningful enforcement of regulations, in a context of local communities that are highly dependent on fisheries for their livelihoods.
Description of Qualifying Criteria
Criterion A – Species or Population Vulnerability
The Irrawaddy dolphin, Orcaella brevirostris, recently declared Endangered on the IUCN Red List (Minton et al. 2017), is found only in the Indo-Pacific region. It tends to occur in small, patchy populations concentrated in and near estuaries and in semi-enclosed, protected bodies of water with freshwater inputs, such as bays, lagoons, and river systems (Stacey and Leatherwood, 1997; Stacey and Arnold, 1999). Five discrete subpopulations of Irrawaddy dolphins, including the Malampaya Sound subpopulation, have been assessed on the IUCN Red List separate from the species’ main assessment. All of these are designated as Critically Endangered. Several other subpopulations, which have not been assessed, have populations in the tens or hundreds of individuals. Several of these subpopulations occur in “ecological cul-de-sacs” – such as rivers or inlets – meaning that they do not have the option to move to more suitable, less impacted habitats in contiguous areas.
Until recently, the Critically Endangered Malampaya Sound subpopulation in Palawan was the only subpopulation known in Philippine waters (Dolar et al. 2009, Matillano pers. comm). Two more recently identified locally occurring populations in southern Palawan and in Iloilo and Guimaras Straits have yet to be assessed. Surveys in 2001 yielded a population estimate of 77, CV = 0.27 (lower 95% CI = 45, upper 95% CI = 130) (Smith et al. 2004); most recent population estimate from research in 2011-2012 is 35 individuals (CV = 22.9%, 95% CI: 22 to 55) (Whitty, 2016). Based on extensive interviews with fishers, cross-checked with limited official records, bycatch estimates for 2009 ranged from 2 to 6 dolphins; 2010, 6 to 11; 2011, 0 to 3 – though the study might not have captured entanglement events that occurred in the latter part of 2011, when the study was conducted (Whitty, 2016). These are minimum estimates, and indicate bycatch rates that far exceed the Probable Biological Removal threshold (Whitty, 2016). Surveys indicate extensive overlap in fishing grounds and dolphin habitat throughout the Inner Sound (Whitty, 2016).
Meaningful efforts to reduce bycatch are hampered by ineffective fisheries management, high dependence of local communities on fisheries as a livelihood, and lack of strong community-based groups working on environmental resources, in addition to continued influx of fishers and ever-increasing fishing effort. The main fishing gears responsible for Irrawaddy dolphin bycatch – crab gillnets and crab pots – are also among the most widely used gears. This renders this population extremely vulnerable.
Criterion B: Distribution and Abundance
Sub-criterion B1: Small and Resident Populations
As described under Criterion A, the Malampaya Sound subpopulation of Irrawaddy dolphins is small and under threat. A further consideration is that this subpopulation is resident to the Inner Sound, with no corridors to other suitable habitats nearby. Additionally, the southernmost portion of the Inner Sound is decreasing in depth due to sedimentation from rivers (Aquino et al. 2006), possibly decreasing accessible habitat.
Criterion D: Special Attributes
Sub-criterion D1: Distinctiveness
Given its geographic location, this population is most likely distinct from the other population of Irrawaddy dolphins in the Philippines, which are found in the lloilo and Guimaras Straits, although genetic studies have not been conducted. So far, comparison of photo-identified individuals between the two localities yielded no similarities (Dolar et al. in prep).
Aquino, M.T., Matillano, M.V., and Gamarsa, I. 2006. 2005 survey of the Irrawaddy dolphin population in Malampaya Sound, Taytay, Northern Palawan. World Wildlife Fund Report.
Dolar, M.L.L., Perrin, W.F., Gaudiano, J.P. and others. 2002. Preliminary report on a small estuarine population of Irrawaddy dolphins Orcaella brevirostris in the Philippines. Raffles Bull Zool: 155–60.
Dolar, M.L.L., Sabater, E.R. and de la Paz, M.E. (in prep). Distribution, population size and conservation status of Irrawaddy dolphins (Owen in Gray, 1866) in the Visayas, Philippines.
Dolar, M.L.L, Aquino, M.T., Sabater, E.R., Solis, E.F.D. and Perrin, W.F. 2009. Preliminary results on the ecology and conservation on a newly discovered population of Irrawaddy dolphins in Iloilo Strait, Philippines. 18th Biennial Conference on the Biology of Marine Mammals, 12-16 October 2009. Quebec City, Canada.
Gonzales, B.J. and Matillano, M.V. 2008. Irrawaddy dolphin conservation in the fisheries of Malampaya Inner Sound, Palawan, Philippines. Mem Fac Fish Kagoshima Univ Special Issue: 16–25.
Stacey, P.J. and Arnold, P.W. 1999. Orcaella brevirostris. Mammalian Species (American Society of Mammalogists) 616: 1-8.
Stacey, P. J. and Leatherwood, S. 199 7. The Irrawaddy Dolphin, Orcaella brevirostris: a summary of current knowledge and recommendations for conservation action. Asian Marine Biology 14 : 195–2 14.
Smith, B.D., Beasley, I., Buccat, M., and others. 2004. Status, ecology and conservation of Irrawaddy dolphins (Orcaella brevirostris) in Malampaya sound, Palawan, b 131–41.
Whitty, T.S. 2016. Multi-methods approach to characterizing the magnitude, impact, and spatial risk of Irrawaddy dolphin (Orcaella brevirostris ) bycatch in small-scale fisheries in Malampaya Sound, Philippines. Marine Mammal Science.
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