Movhera Foz Tua: Bivalvia – Ecological Monitoring Program (PME) and Compensatory Monitoring Program (PMC, MC12N), Exploration Phase (2021-2023).

Study Extent

The study was carried out in 36 fixed stations covering the upper Tua river above the AHFT dam reservoir, the mouth of river Tinhela and the lower partes of rivers Tuela and Rabaçal, up to 60 km to the nord of the reservoir.

Sampling

A total of 36 sampling stations were established in the upper part of river Tua, in the mouth of river Tinhela, and in the lower stretches of rivers Tuela and Rabaçal, in accordance with the needs of the PME and each sub-measure of the MC12N: 21 stations (7 impact and 14 controls) for the PME (incuding 15 shared as controls with the MC12N), in rivers Tua, Tinhela, Tuel and Rabaçal, 10 stations (5 intervention, 5 controls) for MC12N1, in rivers Tua, Tinhela Tuela and Rabaçal, 10 stations (5 intervention, 5 controls) for MC12N2, in rivers Tua and Tuela, and 10 stations (5 intervention, 5 controls) for MC12N3, in rivers Tuela and Rabaçal. In 2023, station TUA_A1 was abandoned due to security issues and replaced by a new station, TUA_A5. Each sampling station was visited once a year by two teams of 2 persons, in the late spring/summer months (June or July, depending of the year. In 2023, due to consistent adverse weather conditions in the established sampling period, the sampling was delayed until early September). For the PME, sampling was carried out through random search, using snorkeling and aquascopes or telescopes of Kalfa, in areas less than 1 m depth and with good visibility, in a length of approximately 100 m (protocol A, see below). The search had a duration not inferior to 2 hours per monitoring station, with a minimum time search of 30 minutes per operator. All mussels detected were identified and measured using a caliper (shell length). The handling of the mussels out of the water did not exceed 30 minutes, in order to minimize disturbance (Wilson et al., 2011). At the end of the process, each individual was returned to the approximate place of capture. This general methodology was adapted in function of the water turbidity and the structural complexicity of the habitat (e.g., in areas of reduced visibility and in places with overhanging branches the river bed, the only practical way of searching was by touch in the riverbed). The exact time of sampling was recorded in all stations, in order to obtain abundance estimates, both in relation to the length of river sampled and to the sampling effort. In fact, the variation in the sampling effort per station resulted, above all, from the differences in habitats in the sampling sections. So, river sections with less depth and with coarser or homogeneous substrates required less search time, compared to deeper sites, with a predominance of thinner substrates or with banks with roots or branches fallen to the river bed, which required a longer sampling time. Regarding the MC12N, the study focused only on the translocated species (Anodonta anatina, Potomida littoralis and Unio delphinus), as well as on the invasive species Corbicula fluminea. Two sampling protocols were used in parallel: one (protocol A) more expeditious, mainly aimed at determining patterns of occurrence (i.e., presence/absence data), and a quick density estimation, and another more detailed and logistically more complex (Protocol B), intended for a more robust estimation of densities and populational structure. Sampling from Protocol A was carried out as described above. The methodology of Protocol B was very similar, excpet that the searches were carried out in 10 linear transects across the river, speced every 10 meters. All marked individuals found (dead or alive) were reported and included in the dataset.

Quality Control

All individual identifications were performed by qualified technicians

Method steps

1. To be completed

The taxonomic coverage of this dataset spans 1 phylum, 1 class, 2 orders, 3 families 5 genera and 5 species. All individuals were identified to the species level.

1. Animalia
   rank: kingdom
2. Mollusca
   rank: phylum
3. Bivalvia
   rank: class
4. Unionida
   rank: order
5. Venerida
6. Unionidae
   rank: family
7. Margaritiferidae
   rank: family
8. Cyrenidae
   rank: family

The data was collected at 36 field stations in the Tua river sub-basin, including in rivers Tua (about 45 km from the mouth), Tinhela, Tuela and Rabaçal, in the municipalities of Alijó, Murça, Vinhais, Valpaços and Mirandela.