Dams facilitate fish invasions

NUS researchers have established an association between dam construction and the increase in the proportion of non-native species in freshwater fish communities.

Dams are expected to become more commonplace with the intensifying demand for hydroelectricity and potable water. They have been shown to impact aquatic species both directly and indirectly, the critically endangered Chinese sturgeon being one prominent example. However, at the community level (i.e. multiple species), the effects of dam construction are less well-characterised and published findings can be conflicting.

To address this pertinent issue, Prof Darren YEO Chong Jinn and Ph.D. student LIEW Jia Huan, both from the Department of Biological Sciences at NUS, together with Dr TAN Heok Hui from the Lee Kong Chian Natural History Museum conducted a global meta-analysis to summarise findings reporting changes in freshwater fish communities as a result of dam construction. The team found that damming was associated with an increase in the proportion of alien species in fish communities, although net fish species richness and abundance did not change significantly.

Findings made by this group contribute to a mounting body of evidence suggesting that reservoirs represent an important invasion pathway. Data collected in this study also indicate that a probable mechanism underlying the findings is the initial local extinction of sensitive river-specialists, which are then subsequently replaced by more tolerant generalist alien fish species. The findings also showed how dam construction can be detrimental to aquatic communities even if overall changes in species richness and abundance do not reflect the repercussions.

At present, the data collected from this research highlight the role played by reservoirs in facilitating biological invasions. This can be expanded to other man-made habitats (e.g. canals) to better ascertain the contribution of human-mediated environmental changes to the establishment of alien species. Finally, postulations regarding the mechanisms underlying the invasion of alien species, post-damming, can serve as a basis for experimental studies to further our understanding of invasion biology.

Figure illustrates the putative mechanism underlying the role of reservoirs as pathways for the introduction of alien (i.e. non-native) species.

Figure shows some common alien fish invaders: peacock bass (Cichla orinocensis; upper left), flowerhorn hybrid cichild (upper right), Mozambique tilapia (Oreochromis mossambicus; bottom left), and bighead carp (Hypophthalmichthys nobilis; lower right). [Photo credit: Tan Heok Hui].

Reference

Liew, JH., Tan, HH., & Yeo DCJ. “Dammed rivers: impoundments facilitate fish invasions.” Freshwater Biology. 10.1111/fwb.12781