Is it safe to remove a dam at the risk of a sprawl by exotic fish species?

• Published in: The Science of the total environment Vol. 771; p. 144768
• Main Authors: Terêncio, D.P.S., Pacheco, F.A.L., Sanches Fernandes, L.F., Cortes, R.M.V.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.06.2021
• Subjects: Animals; Biodiversity; Dams; Ecosystem; Europe; Fishes; Invasive species control; Multicriteria analysis; Restoration ecology; Rivers; Stream connectivity; Europe; Stream connectivity; Dams; Invasive species control; Multicriteria analysis; Restoration ecology
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.144768

The longitudinal dimension of river connectivity has been significantly disrupted by barriers to compensate for water demand in the long periods of water scarcity in the Iberian Peninsula. The scale of this modification is widespread in the Portuguese part of Douro River network where, side to side with agriculture water demand, there is a constant increase in hydropower production. Thus, native species in Iberian freshwater systems, performing reproductive migrations along the rivers, are strongly affected by the amplification of fragmentation caused by the tremendous density of transversal obstacles in this river basin. We aimed to prioritize dam removal in the Portuguese part of Douro River, mainly considering obsolete barriers (small dams, weirs) based on a spatial multicriteria decision analysis (GIS-MCDA) based on a prioritization procedure. A diversity of parameters were used to prioritize (rank) the dam's suitability for removal, considering the losses of connectivity and fish biodiversity, habitat degradation, negative effects on water quality and ecological conditions, and socio-economic factors. Different weights were assigned to the different attributes in each criterion according to their importance. The analysis also included a significant constraint: the potential spreading of exotic invasive fish species if connection was reestablished through dam removal. This procedure started with the georeferencing of 1201 transversal obstacles that were further characterized for their relative permeability to fish migration. In conclusion the model used allowed to identify 158 priority barriers, as well as the 5 most fragmented tributaries, which means the most impacted by river regulation. In 8 cases the barriers were big dams (> 15 m), whereas in the remaining 150 were weirs. From a final rank of 20 most impacting structures, the MCDA results also identified two cases where potential removal could trigger the additional impact to native fish species related to the sprawl of alien populations. [Display omitted] •Georeferencing of 1201 obstacles and their characterization for fish migration permeability•Multicriteria decision analysis (GIS-MCDA) used to prioritize the removal of barriers.•Potential of exotic fish species spreading through dam removal•The modeling allowed to identify 158 priority barriers, 8 big dams (>15 m) and 150 weirs.•In the final rank of 20 most impacting structures, two cases have the risk of alien fishes sprawl.