EDP Baixo Sabor: Fishes – Ecological Monitoring and Complementary Measures Programs [2015-2020]

A total of 68 sampling stations was used to perform both monitoring programs. Of these, 61 (lotic) were used for both the Ictiofauna PME and PMC (MC1 – “Compensation Habitat of the Vilariça Stream”, MC2 – “Recovery and Valuation of the Small Streams of the Sabor Basin” MC3 – “Valuation of the Riparian Corridor in the Upper Sabor and Maçãs Rivers” and MC10 – “General Plan of Protection and Valuation of Herpetofauna and Invertebrates of the AHBS”). No control points were established in the PME (simple survey monitoring), whereas several points were used as controls in the PMC (points with a “C” included in the name). A further 7 points for Ichtyofauna were used in the Aquatic Ecosystems Monitoring Program: four in lentic habitats (“7 PMEAS”, “9 PMEAS”, “14 PMEAS” and “15 PMEAS” ) and three in the respective lotic controls (“1 PMEAS”, “MAÇ PMEAS” and “C4 PMEAS”). Sampling took place once a year, in June and July, over the course of several days.

Sampling within the scope of PMC and at the control stations of the Aquatic Ecosystems Monitoring Program (lotic seasons) was carried out using the electrofishing method, following the guidelines contained in the standardized protocol, published by National Institute of Water (INAG) (INAG, 2008). Sampling was carried out from downstream to upstream of the waterline, with proper electrofishing equipment, adjusted (voltage and amperage) as a function of the electrical conductivity of the water (previously determined), thus allowing an increased efficiency of the fishing while avoiding fish injuries and mortality. After capture, the fish were handled carefully and kept, until processing, inside boxes with plenty of water and oxygenation ensured by portable aerators. High densities inside the boxes were avoided thus preserving the good physical condition of the fish until they were returned to the aquatic environment. All specimens captured were identified down to the species level (if possible) and measured (total length). The length of the section to be sampled was not the same for the Ichtyofauna PMC/PME and the Aquatic Ecosystems PM. In the first case, the INAG protocol (INAG, 2008) was strictly followed; in the second case, the length and duration of fishing followed the stipulated in the Lower Sabor’s Integrated Program of Environmental Monitoring (PIMA), in its 4th version, which consisted of the sampling of 50 m sections with an average depth of <1 m for 15 to 20 minutes.

In the reservoir stations (lentic habitats), the main technique of capture was by gillnets, complemented with electrofishing in the banks. The methodology followed the recommendations of the INAG for the sampling of the fish communities of lakes and reservoirs (INAG, 2009). Two sampling points were established in each reservoir: Feiticeiro (downstream) and Baixo Sabor (upstream). The effective fishing effort depended on the geomorphological characteristics of the two reservoirs. In the downstream reservoir, of lower depth and small dimension, the fishing effort adopted for each sampling point was three benthic nets and a surface pelagic net, totaling 600 m2 of fishing effort in each reservoir (corresponding to 270 m2 of benthic nets and 330 m2 of surface pelagic nets). Although the nets were launched at different depths, the data were aggregated in the present dataset, and only one value per sampling point/sampling time was used. In the upstream reservoir, more deeper and geomorphologically heterogeneous, the capture effort was increased, albeit respecting the two sampling points advised in the PIMA. In total, the two points were prospected using eight benthic and two pelagic nets, totaling a sampling area of 690 m2 (corresponding to 360 m2 of benthic nets and 330 m2 of surface pelagic nets). Sampling was also performed at different depths, but the individual depth data were aggregated for each sampling point, as above. In each sampling point, the monofilament nets were cast from a motorized boat perpendicularly to the bank and positioned in order to cover all chosen depths. They were released at the end of the day and collected at the beginning of the next, remaining throughout the night, for an approximate duration of 14 hours. The position of the nets were recorded with a GPS device. All specimens captured were handled carefully, and the fish were kept on the boat in plastic containers of appropriate dimensions with water and aeration. After identification and measurement, the specimens were returned to the water.

In addition to the gillnets, electrofishing sampling, carried out from a boat, was used to characterize the fish communities in the banks of the reservoirs. The characteristics of the electric current (amperage and voltage) were defined according to the water physio-chemical conditions, namely its conductivity. In the vicinity of each monitoring station (place where the nets were launched) electrofishing was carried out in three stretches of bank about 50 m in length for 10 minutes in habitats with different characteristics, intending to be representative of the heterogeneity of existing habitats in the coastal zone of the reservoir.