Malampaya Sound IMMA

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). 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 – 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 Potential 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. 2018).