EDP Baixo Sabor: Bivalvia - Compensatory Measures Program (measure MC10), Exploration Phase (2015-2020).

A total of 60 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, 10 intervention stations for MC10.7 in river Sabor and 10 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, July or August, 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.

Specifically for the translocation zones (MC10.6), individuals were marked during the translocations in order to estimate survival rates. A total of 7505 individuals of U.delphinus (of which 999 marked), 1059 individuals (1000 marked) of Potomida littoralis and 269 (161 marked) of Anadonta anatina was translocated from the flooded areas in Sabor river to the upstream reception sites in 2013 (Biota, 2013). These populations were then followed after 2015. The dataset includes the available information on the number of the specimens of each of the target species marked in 2013 and recaptured in 2015 and afterwards. Multiple recaptures (ie., specimens found in more than a year and/or site, were identified by the respective marking number (a uppercase letter designating the species – U, P or A-, the order number of marking, and the year of the first recapture in brackets, if applicable (e.g.: P747 (2015) or U987).