2003 Volume 5 Issue 2 Pages 71-86
Habitat use, abundance-habitat relationships and assemblage composition of tropical freshwater fishes were surveyed in streams running through primary and secondary (deforested 9-20 years prior to the survey by slash-and-burn agriculture) forests in the Rayu River watershed, Sarawak, Borneo. Five species (Puntius kuchingensis, P. binotatus, Rasbora sarawakensis, R. caudimaculata, and Hemirhamphodon kuekenthali), of which habitat use was investigated, exhibited distinct diel habitat shifts between midstream and channel margin. Their abundances were related to habitat variables with the exception of P. binotatus. Puntius kuchingensis decreased with the increase of eroded banks. The abundance of R. caudimaculata increased downstream, while R. sarawakensis was less abundant in streams without riffle habitats. Hemirhamphodon kuekenthali was absent from high-gradient streams. Both habitat characteristics and fish assemblage composition differed distinctly between the primary-and secondary-forest streams. The secondary-forest streams were characterized by sandy substrates and eroded banks, suggesting a long persistence of sedimentation caused by the past deforestation. Macrognathus maculatus, Betta akarensis and P. kuchingensis appeared to be susceptible to sedimentation effects. Our data provide circumstantial evidence of the impact of past deforestation on fish assemblages in the Rayu River watershed.
