Baixo Sabor: Fishes – Ecological Monitoring Program [2012]

The capture method employed was electric fishing and the samples were taken during the day, by a team of three to four elements, using a portable device with a gasoline generator set with pulsed direct current output, fixed with generator (to operate from the margin or from a vessel) or back transport with an explosion engine or battery, with the recommended characteristics: 200-1000V, power 0.8 - 2.5 KVA.

The methodology adopted depended also on the depth of the section to be sampled. In small watercourses, fishing was carried out from the margin, in the upstream downstream direction, with the rapid immersion of the anode with the current already on, and the operator taking care to avoid denounce its presence. In larger water courses, harvest was carried out by two operators walking slowly upstream the initial point, describing a zigzag between the 2 margins, covering all habitats and fleeing the sheltered fishes.

In conditions prone to promote a high escape behavior (high transparency water with low shelter conditions), the operators only unloaded the current after a period of immobilization with the electrodes already in the water (minimum 20 – 30 seconds). In these cases, and in all situations where most fish tended to escape upstream avoiding capture, an attempt was made, whenever possible, to previously close the section at the ends with fine mesh net, in order to increase the efficiency of fishing.
The harvested specimens were handled carefully. Sampling was carried out in several periods lasting no more than 30 minutes to avoid fish mortality. 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, or in a net apparatus plunged into the sampled water course, in a place not subjected to electric current . The usual safety measures for working with electrofishing were strictly followed.

The identification of the specimens up to the species was carried out on the spot, based on external characters. Small specimens that did not yet differ specific external characters were identified at the gender level. All individuals whose length was greater than 40 mm were measured with a 1 mm precision. Those below that threshold were not measured, and only their number was recorded. If the number of specimens were very high in a given sample, only a sub-sample of 50 individuals was measured. After these procedures, all specimens were returned to their habitat in the vicinity of the capture sites with suitable conditions without current (INAG, 2008).

In the original dataset the single individual of the genus Cobitis captured was assigned to Cobitis calderoni, but the identification is doubtful because the species is not expected to occur in the Sabor watershed.