Ecoregional Assessment of Biological Diversity in East Kalimantan

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East Kalimantan Ecoregional Assessment: Chapter 2 – Target Ecological Systems The population of Irrawaddy dolphins, Orcaella brevirostris, in the Mahakam River, known locally as Pesut, was recently listed as Critically Endangered, based on surveys in 1999-2000 that estimated the population of mature individuals to be less than 50 (Kreb, in press). Between 1995 and 2001, at least 37 dolphins were killed, primarily from entanglement in gillnets, but also from vessel collisions and illegal hunting (Danielle Kreb, pers. comm.; also see Kreb (2000) for details on the deaths recorded in 1997-1999). Previous estimates of Pesut in the Mahakam numbered about 100 individuals (Sowelo 1994), indicating a dramatic decline in their numbers. Danielle Krebs and Budiono (pers. com.) stated that in the Mahakam lake area, Pesut are distributed from about 180 km upstream from the mouth of the Mahakam River to an area near Muara Melak. They are focused around the area of Muara Pahu where they are found in greatest numbers primarily in deep pools located near confluences and meanders, and occasionally in appended lakes and connecting tributaries. These areas are also primary human fishing grounds and subject to intensive motorized vessel traffic. However, Pesut frequently make daily movements from this focal area upstream. Usually these daily movements are made by groups of about five individuals and they frequently are only about a kilometer in distance. Sometimes, though, individuals will travel as far as 30 km upstream. Most of these movements away from the focus area are shortly after the rainy season commences. At these times Pesut move in very directional ways to areas that are large sanctuary pool areas for fish. It is speculated that Pesut take advantage of these initial opportunities to feed in high-density fish areas. After the first flush of waters, Pesut do not appear to focus on these ‘pooled places” again. On occasion, a small group of Pesut has been observed trapped in clearer water in the Ratah River, between two areas of rapids. Rivers are major landscape determinants and provide broad corridors for species that have wide local movement patterns, such as birds and bats that travel through these landscapes pollinating plants and dispersing their seeds. A common East Kalimantan bat species, Eonycteris, travels distances each night as far as 80 km in Malaysia as they move from their inland roost sites to feed in coastal mangroves (Start and Marshall1976). However, while rivers serve as conduits for mobile fauna to traverse the landscapes, they are also major geographic barriers to the distribution of some species. For example, the boundaries defining the distribution of subspecies of the Bornean Gibbon, and other gibbons tend to be large rivers. In fact, seas and rivers separate the nine species of gibbon from each other. In the case of the Bornean Gibbon, most of East Kalimantan is inhabited by the subspecies H. m. abbotti, while in the northern part of Berau this subspecies is replaced by H. m. funereus. However, H. m. abbotti appears to hybridize with the White-handed Gibbon, H. agilis, in its contact zone at the headwaters of the Barito River (Mather 1992). Lakes Surrounding the middle Mahakam region there are at least 32 (total 76 according to Bappeda I Kaltim, 1982) lakes that can be detected from the map at a scale of 1:50,000, their sizes ranging from around 1.2 hectares up to 15,000 hectares (Jempang). About 18% (totaling 89,719 ha) of all the natural lakes in Indonesia Borneo are located in the Kutai District, East 49
East Kalimantan Ecoregional Assessment: Chapter 2 – Target Ecological Systems Kalimantan (Salmani 1987 in Moersid and Christensen 1987); almost 10% (totaling 48,000 ha) are located in the middle Mahakam area alone. Some of the lakes are rounded, most are slightly rounded to elliptical, and the rest slightly irregular in shape. Their average depth varies between 0.40 – 3.00 meters, which classifies them all as shallow lakes. Because of their shallowness and exposure to wind, it can be deduced that all the Mahakam lakes are susceptible to mixing and would support high nutrient re-suspension in the water. This mixing process can be of great importance to the primary productivity of the lakes as well as to the fish yields. The surface area of most of these lakes changes from time to time. During an average dry season, surface areas may shrink by 80-96% from their maximum areas during the rainy season. In extremely dry seasons some lakes dry completely (Suryadiptra et al. 2002). Suryadiptra et al. (2000) report that the Mahakam lakes are very rich in biodiversity. A recent study by Wetlands International – Indonesia Program of the 11 Mahakam lakes located in the southern part of the Mahakam River, found the following numbers of species: approximately 86 fishes, 125 birds, 25 mammals, 12 large reptiles, four amphibians and 300 tree species. Some of these animals are listed as endangered in the IUCN Red Data Book (such as the Storm’s Stork Ciconia stormii); listed under Appendix I and II of CITES (eg. Leptoptilos javanensis, Citra indica, Callagur borneoensis) and also protected under the Indonesian regulations (Act number 7/1999) such as lesser mouse deer (Tragulus javanicus) and Sambar deer (Cervus unicolor). Suryadiptra et al. (2000) states that the recorded 260 bird species from the lakes and nearby forests of the middle Mahakam area make the lakes a unique place of great ecological interest. Particularly notable are the 12 species of heron, important tern populations and thousands of migrating shorebirds. Suryadiptra et al. (2000) further observe that at least 40% of Kalimantan’s land mammal species are still found in the area adjacent to the lakes. The Ohong River (52 km long) and Perian River (72 km long) with its swamp forest vegetation form the center of the richest biodiversity in the Mahakam lakes, including a large population of Proboscis monkeys and seven of Borneo’s eight Hornbill species. Two crocodile species (Tomistoma schlegeli and Crocodylus sp.) are still found in the Ohong River area. In East Kalimantan, the major lakes are located in the Middle Mahakam region. These are the mixed-water lakes of Jempang (14,600 ha, 7-8 m deep); Semayang (10,300 ha, ~5m deep) and the black water lake, Melintang (8,900 ha, 4-6 m deep). They are, in actuality, a vastly enlarged part of the Mahakam River and its tributaries, which meander through them, continuously depositing silt and shifting its course. These lakes contain much the same fauna and flora as found in the rivers that feed them (MacKinnon et al.1996). Most are very shallow, with water levels typically fluctuating between 4-6 meters, with two high-water periods between October and May. (MacKinnon et al.1996). Suryadiptra et al. (2000) reported that there are at least 86 aquatic plant species and genera in the Middle Mahakam Lake area. These are dominated by floating weeds (e.g., Salvinia 50
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Ecoregional Assessment of Biological Diversity in East Kalimantan

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