The restoration of the ecological functions (as habitats for fish spawning and waterbird feeding) of the mouths of the two larger semi-permanent streams that discharge into Lake Mikri Prespa (Action C3) was planned and carried out within LIFE15 NAT/GR/000936 – Prespa Waterbirds project. Accumulation of sediments at certain sites and overgrowth by helophytes, mainly common reeds, resulted in that the little spring water flows were too shallow and full of obstructing stems so fish could not enter from the lake to the stream to spawn. Additionally, due to a previously constructed weir in the Mikrolimni stream, there was an observed seasonal discontinuation of flow between the stream and the lake under specific conditions. In the period October 2018–April 2019 works were carried out for unclogging and deepening the streambed which allowed the unhampered flow of water from the two streams to the lake and a monitoring program followed to assess the success of these interventions. The aim of monitoring was to verify if following the works some fish species were able to enter the streams to spawn. The method initially chosen was the fortnightly simple qualitative electro-fishing sampling at six predefined stations, marked in the field, at each stream, from mid - April to end July. During the first two sampling sessions only very few fish of small sizes were caught and this lead to reconsider the probability that the bulk of fish might enter streams to spawn only during the night time as it was already known to occur in the Agios Germanos stream. In order to test this, and as the electrofishing method cannot be applied at night, subsequent sampling sessions we carried out using fyke nets during the night. In total with both methods six fish species were captured: Pseudorasbora parva, Economidicthys pygmaeus, Chalcalburnus belvica, Chondrostoma prespense, Lepomis gibbosus, Squalius prespensis. Five species were recorded through electro-fishing and three through fyke nets. Out of the six potamodromous fishes expected to occur in the streams only four were captured, but not Barbus prespensis and Cobitis meridionalis. In addition to the endemic species Squalius prespensis was also recorded, for which it is the first time evidence was collected that some fish spawn in the streams of the Lake Mikri Prespa. The main conclusion derived from the monitoring data was that various fish species enter in considerable numbers the two streams to spawn. When entering, their gonads are developed and ready to release eggs or/and sperm and there is some hatching success. Substantial differences were observed between the two streams regarding species occurrence, numbers and average length of captured individuals. In Mikrolimni stream four species were recorded with 1550 individuals, but the two large-bodied species were absent (the endemics Chondrostoma and Squalius), whilst in the Lefkona stream all six species were captured with much higher average length (mainly due to presence of the two larger species) but in much lower numbers (51 individuals). Conclusively, in the next monitoring period (2020) it is suggested to use only the method of fyke nets during the night, because it was shown to be the most appropriate monitoring tool for the kind of evidence necessary (presenceabsence of spawning fish), particularly for the endemic fishes such as Chalcaburnus belvica, Squalius prespensis and Chondrostoma prespensis
Action D1. Fish monitoring in stream mouths - 2019 (in Greek, with English summary)