Ecoregional Assessment of Biological Diversity in East Kalimantan

East Kalimantan Ecoregional Assessment: Chapter 2 – Target Ecological Systems
‣ Fishermen who work illegally with electric prods, frequently focus on Pesut feeding
grounds and use the presence of Pesut to identify favorable places to fish. Most of
these illegal fishermen are Banjar transmigrants and tend not to be local Kutai people
who have a stake in maintaining viable populations of these native fishes.
4. Pollution from gold mining upstream, which commenced about 1980. Because Pesut eat
fish and prawns that may spend part of their time upstream in the areas more
contaminated by mercury and arsenic, they are likely to have increased loads of these
heavy metals. The effect of these metals on reproduction and health of Pesut can only be
speculated upon at this time, but is likely to be detrimental to the health, productivity and
longevity of affected individuals.
5. Siltation in these lakes is caused not only by erosion from the Mahakam’s upper
catchment area (due to extensive logging since the early eighties), but also by the
accumulation of dead aquatic plants, which are over abundant in the lakes and whose
growth is supported by the high nutrient input to the water (eutrophication) from
agriculture, fish cage farming and settlements surrounding the lakes (Hardwinarto et al.
1999; Suryadiptra et al. (2002).
6. There has been a major increase in the amount of aquatic vegetation (mainly Eicchornia
crassipes and Mimosa pigra) in the lakes, which may have arisen from eutrophication
due to nutrient enrichment from fish farming in the rivers and lakes or from agricultural
activities surrounding the lakes. The presence of increased aquatic vegetation is in turn
increasing the rate of siltation in the lakes by trapping more suspended material in the
river. Not only does fish-farming lead to nutrient enrichment in the lakes but it probably
contributes directly to the physical siltation process, through large amounts of waste food
falling to the riverbed and being washed into the lakes (Suryadiptra et al. 2000).
7. Danielle Kreb (pers. com.) also strongly recommends the immediate establishment of
conservation areas in major Pesut habitat, namely, 1) the confluence area of Muara
Kaman and tributary Kedang Rantau, 2) the Pela tributary and southern part of Lake
Semayang, and 3) the confluence area of Muara Pahu and Kedang Pahu tributary until
Bolowan. She considers that, within these areas, it is important to increase awareness of
local residents, install speed limit regulation for speedboats, gillnet-setting regulations,
and step up active patrolling and law-enforcement of illegal fishing techniques and
dolphin catches. Additionally, Suryadiptra et al. (2000) indicate the need for an
integrated management plan for the Mahakam lakes and their upper catchment areas by
involving various/relevant stakeholders and to restore some of the lakes (e.g., Lakes
Tawar and Perian) by removing aquatic plants and sediment.
55