Ecoregional Assessment of Biological Diversity in East Kalimantan

East Kalimantan Ecoregional Assessment: Chapter 2 – Target Ecological Systems
molesta and Eichhornia crassipes, Mimosa pigra and Polygonum barbatum). The first three
species dominate the larger Semayang, Jempang and Melintang lakes, while P. barbatum
dominates Perian Lake. Total plant coverage in the Mahakam Lakes varied between 15 % -
90 %. Lake Tawar, with a surface area of 10.3 ha, was most densely covered by water
hyacinth (90%) - this lake is now very difficult to enter because this plant blocks its inlet.
Most floating plants are regularly flushed out of the lakes during heavy rains and enter the
Mahakam River.
Unna Chokkalingam (pers. com.) stated that the Mahakam Lakes frequently silt up and river
channels expand and change coarse remarkably. In dry periods, large parts of them are
exposed and people plant rice in their centers. They also cut branches and place them over
parts of the lake to “shade-fish”; this is said to greatly enhance the catch success for the
fishermen. Conservation of these lakes is just as dependent on protecting the upper catchment
areas where so much of the soil erosion and sedimentation comes from, as it is restoration
and protection of the lakes themselves.
Danielle Kreb (pers. com.) observed that the high density of gillnets used in Lake Semayang
and Lake Melintang causes physical obstruction to the movement of Pesut, thereby reducing
available habitat for this critically endangered dolphin species. This threat, together with high
sedimentation caused by devegetation of the surrounding shorelines, has probably resulted in
the elimination of these lakes as primary habitat for Pesut, as reported by Tas'an and
Leatherwood (1984).
Pesut occasionally move into the southern central waters of Lake Samayang. The impression
is that this lake and the other Mahakam lakes are not particularly important for the Pesut,
which is found elsewhere along the coast of Kalimantan. However, without more information
on the ecology or their specific use of the lakes it would be premature to dismiss the
importance of these lakes. It is possible for example; that births occur in the calmer waters of
the lakes and that these areas are in fact very important in the life histories of the Pesut- even
if only for short periods of their life cycles. [See section below entitled “Pesut Conservation
Issues” for additional information.]
Gönner (2000) states that the Middle Mahakam Area remains a crucial breeding and
migration site for many bird species. Between 1988 and 1999, he reports a total of 90 bird
species around Lake Jempang, including important breeding populations of various herons
and the Lesser Adjutant (Leptoptilos javanicus). He also recorded what appears to be the first
breeding record in Borneo of the Little Tern (Sterna albifrons). He states that, despite the
enormous damage of recent forest fires, most of the 90 species of birds were found in the
swamps and waterways of the Middle Mahakam area, including 12 heron species, 2 stork
species, 2 duck species, 6 crake/rail species, 23 wader species and 4 tern species
The appearance of visiting wading birds during the autumn migration depends on the water
level of the Mahakam lakes. Significant numbers (mainly of Wood Sandpipers Tringa
glareola) were only observed in extremely dry years (1993 and 1997), when the lakes had
virtually disappeared. Vast mudflats and grasslands provided excellent feeding habitats for
plovers, sandpipers and stilts. The shallow lakes also attracted large numbers of Whiskered
51