Boundaries

This ecoregion comprises Sarawak (Malaysia) and Brunei on the island of Borneo, as well as the Nantuna Islands. It excludes higher elevations to the southeast, which form the Borneo Highlands [743] ecoregion. It is also bordered by Northeastern Borneo [744] in the northeast and Kapuas [741] in the southwest. The basins in this ecoregion drain into the South China Sea.

Terrestrial habitats

Terrestrial ecoregions in Northwestern Borneo include the Borneo montane rain forests [IM0103], Borneo lowland rain forests [IM0102], Borneo peat swamp forests [IM0104], and Sunda Shelf mangroves [IM1405] (WWF 2001).

Description of endemic fishes

The 26 endemics include several species of Carinotetraodon and two species each of Encheloclarias, Pangio, and Rasbora. There are also two endemic genera, Paedocypris and Parawaous.

Justification for delineation

For Southeast Asia, delineations were determined using a bottom-up approach that employed both published and unpublished field data and expert assessment (Abell et al. 2008). The data for this ecoregion is fragmentary, with large areas that have yet to be surveyed. Therefore, it is possible that this ecoregion could be split into several ecoregions once better information is known (M. Kottelat pers. comm. 2006).

Level of taxonomic exploration

Although checklists exist for the whole ecoregion and ecological studies exist for some basins, the data set is still fragmentary (M. Kottelat pers. comm. 2006).