Movhera - Elétricas do Norte, S.A. Foz-Tua: Fishes – Ecological Monitoring Program [2021-2023]

Study Extent

The data were collected along the Tua lower valley (Northeast Portugal), up to 52 kms from the mouth, and in its main tributaries, in the municipalities of Alijó, Carrazeda de Ansiães, Murça, Vila Flor, Valpaços and Mirandela.

Sampling

The capture methods employed were electric fishing, for lothic environments, and gill nets, for lenthic environments, in this case complemented with electric samples in the nearby banks. In the lothic environments, the fieldwork was carried out according to the standardized protocol established by the National Water Authority (INAG), namely the “Manual for the biological assessment of water quality in river systems according to the Water Framework Directive - Sampling and analysis protocol for fish fauna” (INAG, 2008). Thus, the specimens were captured alive by electric fishing, identified down to the species level and measured (total length). Sampling was carried out from downstream to upstream, with a strict adherence to the INAG protocol, which defines the minimum lenght of the section to be sampled (20 times the width of the river and never less than 100 m or, in rivers >30 m wide, a section in length 10 times the width of the river), with the electric equipment properly adjusted (voltage and amperage) to the electrical conductivity of the water (previously determined), thus allowing to increase the efficiency of the fishing while avoiding injuries and mortality of the fish. After capture, the fish were handled carefully and kept, until processing, inside boxes with plenty of water and oxygenation ensured by portable aerators. All measures were taken to avoid have densities raised inside the boxes, thus preserving the good physical condition of the fish until they were returned to the aquatic environment. Fish sampling in the reservoir also followed the directives of the National Authority for Water (INAG, 2009). Standardized gill nets (Standard CEN 14757:2005) were used in two sampling points, 200/300 m and 1200/1300 meters away from the dam (Stations 1 and 2, respectively). At each sampling points, 4 benthic nets and a surface pelagic net were cast, covering a total of 690 m2 (360 m2 of benthic and 330 m2 of surface netting). One surface and four depth classes were used (0-6 meters, 6-12 (m), 12-20 (m), 20-35 (m) and the fourth near the bottom, respectively), but in this dataset the benthic classes were amalgamated. In each sampling point in the reservoir, the monofilament were cast perpendicularly to the bank, and in order to cover all classes of existing depth, with the helpof a four-stroke motorized boat. The nests were released at the end of the day and collected at the beginning of the next day, staying in the water throughout the night, for an approximate period of 14 hours. After the launch of gill nets, placement locations were recorded using GPS. During sampling, the welfare of the captured specimens was ensured by depositing them in plastic buckets with portable oxygenators, which were kept in shelters at cover of direct sun exposure. The usual safety measures for working with electrofishing were strictly followed. The captured individuals were identified up to the species, and measured (total length in mm) with the aid of an ichthyometer. After these procedures, the native specimens were returned to their habitat in the vicinity of the capture sites with suitable conditions; at the request of the Institute of Conservation of Nature and Forestry (ICNF), exotic individuals were eliminated.

Quality Control

All identifications were performed by qualified technicians

Method steps

1. To be completed

The taxonomic coverage of this dataset spans 1 phylum, 1 class, 4 orders, 7 families, 15 genera and 15 species.

1. Animalia
   rank: kingdom
2. Chordata
   rank: phylum
3. Actinopterygii
   rank: class
4. Cypriniformes
   rank: order
5. Perciformes
   rank: order
6. Salmoniformes
   rank: order
7. Siluriformes
   rank: order
8. Cobitidae
   rank: family
9. Cyprinidae
   rank: family
10. Poeciliidae
    rank: family
11. Centrachidae
    rank: family
12. Percidae
    rank: family
13. Salmonidae
    rank: family
14. Ictaluridae
    rank: family

The data were collected along the River Tua (Northeast Portugal) and its main tributaries, up to 52 kms from the mouth, in the municipalities of Alijó, Carrazeda de Ansiães, Murça, Vila Flor, Valpaços and Mirandela.