Matang Mangroves and Coastal Waters IMMA

Criterion A – Species or Population Vulnerability

Indo-Pacific humpback dolphins (Sousa chinensis) (hereafter referred to as humpback dolphins) and Indo-Pacific finless porpoises (Neophocaena phocaenoides) (hereafter referred to as finless porpoise) are listed as VU on the IUCN Red List of Threatened Species (Jefferson et al. 2017; Wang and Reeves, 2017), whereas Irrawaddy dolphins (Orcaella brevirostris) are listed as EN (Minton et al. 2017). However in Malaysia, all three species are further listed as Marine Endangered Species and protected under the Fisheries Act 1985 and Fisheries (Control of Endangered Species) Regulation (Amendment) 2008. The main fishing gear inshore that entangles humpback dolphins and Irrawaddy dolphins are gillnets, driftnets and trammel nets, whereas trawls were the more fatal bycatch gear offshore that entangled mostly finless porpoises (Kuit & Ponnampalam, 2021; Figure 3).

Criterion B: Distribution and Abundance

Sub-criterion B2: Aggregations

Systematic research from 2013 – 2016 in the area within the IMMA measuring 1152 km² and effort amounting 110 survey days across 11 surveys has found that there were 763 Irrawaddy dolphins (CV = 13%, 95% CI = 588-990) and 600 finless porpoises (CV = 27%, 95% CI = 354-1016) in the surveyed area. The mark-recapture estimate based on photographs of left side of dorsal fins was 426 humpback dolphins (CV = 34%, 95% CI = 222–817) in the surveyed area (Kuit et al., 2021). The annual abundance estimates of humpback dolphins ranged between 171 (95% CI =148-208) in 2014–2015 and 81 (95% CI = 67-98) in 2015–2016, likely due to the presence of offshore individuals that moved in and out of the study area (Kuit et al., 2021). The estuarine strata were inhabited by 68 inshore humpback dolphins (95% CI = 63-73) in 2013–2014 to 87 (95% CI = 78-97]) dolphins in 2014–2015 (Kuit et al., 2021). These animals are present year-round in Matang’s estuaries and coastal waters. Group sizes of humpback dolphins ranged from 1 – 40 individuals (n = 124), whereas group sizes of Irrawaddy dolphins ranged from 1 – 32 individuals (n = 254) (Kuit, 2021). Irrawaddy dolphins in Matang coastal waters were observed to aggregate in large groups of >10 individuals and engage in herding behaviour (Kuit 2021). Photo-identification data show that the inshore humpback dolphins in the IMMA range across the five estuaries that feed into Matang’s coastal waters, with many individual dolphins displaying high site fidelity. Further offshore, approximately 10 km onward, finless porpoises were recorded in groups of 1 -10 individuals (n = 102) (Kuit et al., 2019).

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

Systematic research from 2013 – 2016 in the area within the IMMA has found that 59% (n = 73) of the total number of humpback dolphin sightings (n = 124) contained calves (including neonates) (Kuit, 2021).  Sightings of humpback dolphins containing neonates constituted 1.6% (n = 2) of the species’ total sightings. In January 2017, a female humpback dolphin that washed ashore dead in Matang was found to be pregnant with a near-term foetus (MareCet, unpublished data). Irrawaddy dolphin sightings that contained calves (including neonates) made up 28.7% (n = 73) of the total number of the species’ sightings (N = 254). Sightings of Irrawaddy dolphin groups containing neonates constituted 28% (n = 70) of the species’ total sightings (N = 254). Of the 254 Irrawaddy dolphin groups sighted in the IMMA, 1.2% (n = 3) were recorded engaging in herd mating and sexual behaviour. Of the 128 humpback dolphin groups observed, 3.1% were recorded engaging in sexual behaviour (MareCet, unpublished data). In December 2013, a female finless porpoise that was accidentally bycaught in a trawl net was found to be pregnant with a near-term foetus (MareCet, unpublished data).

Sub-criterion C2: Feeding Areas

Systematic research effort across 2013 – 2016 within the IMMA, has found that humpback dolphins engaging in feeding or foraging behaviour constituted 74.3% (n = 95) of the total species’ sightings (N = 128). Of the 95 humpback dolphin sightings categorised as feeding, 30.0% (n = 29) were of direct observations of the dolphins preying on marine catfish (Kuit et al. 2015). Stomach contents recovered from humpback dolphins found dead stranded in Matang contained remains of coastal fish and cephalopod species known to occur in the area (Kuit et al. 2015). Irrawaddy dolphins groups observed in the IMMA were found engaging in feeding or foraging behaviour in 50.8% (n = 129) of the species’ total sightings (N = 254) (Kuit et al. 2015).