Inland Fisheries

3.4.7 Conclusion

Because dams tend to be constructed to enhance socio-economic development activities, they tend to attract people and industry. Subsequently, river ecosystems containing dams must contend with secondary environmental pressures such as increases in pollution as well as increased exploitation and extraction of their resources (primarily water, fish, and substrates), that are independent from and in addition to the direct influences of dams and reservoirs on the physical and biological dimensions of the system. Determining the impact of dams on river ecosystems and their associated fisheries depends on spatial and temporal scales of interest. If spatial scales are sufficiently large (planetary, continental, perhaps regional and biome), and temporal scales are sufficiently long (decades, centuries, millennia), placing a dam on a river does little more than increase atmospheric water vapour (through evaporation from the reservoir), reduce long term stream flows downstream, desiccate terrestrial environments, salinate surrounding areas, and shift bio-energetic processes (some of which can lead to floral and faunal extinction at various scales of resolution). We cannot assign the terms “good” or “bad” to any of these phenomena. They simply reflect anthropogenic activity on this planet. However, if we look at smaller spatial and shorter temporal scales, (which we obviously cannot neglect since we have to make decisions that have bearings on the present and future human generations and also on present and future living aquatic resources) we have to keep in mind that dams and their reservoirs (which can under certain circumstances help to better nourish people and make their livelihoods more sustainable) can - if wrongly placed - also lead to significant declines of fisheries and to extinction of aquatic species.

Given sufficient time, geophysical and climatic forces will override and erode the physical influences of dams, and evolutionary forces will alter how life forms interact with the resulting environments. Caution is warranted to avert potential negative impacts from dams with respect to fisheries and associated human interactions with these and other river resources. Such caution underscores the reality that people are depending on us, the scientists, the resource managers, the decision makers, to be right.