Evidence of fish community fragmentation in a tropical river upstream and downstream of a dam, despite the presence of a fishway

Context
Rapid human population growth has increased demand for water supply, food security, electricity, and flood mitigation worldwide. To address these challenges, governments have invested heavily in the expansion of water infrastructure. However, there is substantial evidence that globally, this infrastructure impacts aquatic ecosystems and can have a significant impact on the persistence of fish species. Despite being well understood globally, the impacts of dams on fish have been given scant attention in Indonesia. Thus, considerations for fish are rarely included in river development planning frameworks.

Methods
To document the impact of riverine barriers on Indonesian freshwater fish, we surveyed multiple sites, using three different kinds of gear (gillnets, castnets, and bait traps), upstream and downstream of Perjaya Dam in the Komering River.

Key results
The study revealed 13 of 36 species were found only downstream of the dam and five of 36 species were found only above the dam. There were significant differences in fish community composition between upstream and downstream regions using either fish abundance (Pseudo-F = 4.495, d.f. = 1, P < 0.05), species richness (Pseudo-F = 15.837, d.f. = 1, P < 0.05) or species diversity as the response metrics (Pseudo-F = 8.3256, d.f. = 1, P < 0.05).

Conclusions
The local extirpation of many species from upstream areas suggests that the Perjaya Dam hinders fish migration.

Implications
Despite containing a fishway, the results indicate that fish are not successfully recolonising upstream reaches.