Movhera Baixo Sabor: Bivalvia - Compensatory Measures Program (measure MC10), Exploration Phase (2021-2023)

Study Extent

The study was carried out in 40 (2021-2022) or 20 (2023) fixed stations covering the upper Sabor river above the AHBS dam reservoir, as well as in the mouths of rivers Maçãs and Angueira, up to 30 km to the north and 10 km to the east of the reservoir. In 2023, only the river Sabor upstream the Baixo Sabor dam and the lower vally of river Maçãs were surveyed. Sampling took place between June 2021 and July 2023.

Sampling

A total of 40 (2021-2022) or 20 (2023) sampling stations were established in the upper part of river Sabor and in the mouths of rivers Maçãs and Angueiras, in accordance with the needs of each sub-measure: 10 intervention stations for MC10.6 in river Sabor and in the mouth of river Maçãs and 10 (2021-2022) intervention stations for MC10.8 in river Sabor and in the mouth of rivers Maçãs and Angueira. Each set of intervention stations was matched by the same number of control stations, located as near as possible. Each sampling station was visited once a year in the summer months (June or July, depending of the year) by two teams of 2 persons. The sampling was carried out using standardized methods for this group of organisms. Whenever possible, the technique of snorkeling was used as it maximizes the results/effort ratio. Along the margins, due to the low depth of the water body, bivalves were sampled with the help of handmade View Finders and/or Calfa Spectacles. Semi-quantitative sampling (only specimens visible on the surface of the substrate) was used along a 50 m stretch of river at each sampling site.
Visibility conditions in some of the sampled locations forced the detection of mussels by touch, as an alternative to its visual location. Sampling was performed from downstream to upstream, in order to avoid disturbance of the sediment with the consequent reduction of visibility. It should be noted that in the deeper strata, where water turbidity did not allow the observation of the bed substrate, it was not possible to detect marked organisms, both those placed there or those that had eventually been dragged into these zones. The identification of the different species of river mussels was carried out mainly in situ, based on the different morphological features of the shell (identation, texture, color, sculpture, umbo height and location), and also in Concology. The specimens found were also counted and measured (length of shell), before being returned to the river. In the period 2021-2023 there were no new releases of Naiads, but efforts were made to find marked individuals. This dataset presented the identification of the recaptured specimen, using the same notation of the 2015-2020 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 class, 1 order, 2 families, 4 genera and 4 species. All individuals were identified to the species level.

1. Animalia
   rank: kingdom
2. Chordata
   rank: phylum
3. Mollusca
   rank: class
4. Unionida
   rank: order
5. Veneroida
   rank: order
6. Unionidae
   rank: family
7. Corbiculidae
   rank: family

The data was collected at 40 (2021-2022) or 20 (2023) field stations along the valleys of Lower Sabor, Maçãs and Angueira rivers (Northeast Portugal, Europe) in 2021-2022, or in the rivers Sabor and Maçãs in 2023, within the municipalities of Mogadouro, Macedo de Cavaleiros, Vimioso, Miranda do Douro and Bragança