Action D1. Fish monitoring in stream mouths - 2020

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.  

In the period November 2019–February 2020 unclogging works were repeated with vegetation mowing and streambed deepening to ensure the unhampered flow of water from the two streams to the lake and a monitoring program followed to assess the success of these interventions.

For fish, the aim of monitoring was to verify if, following the works, fish were indeed able to enter the streams to spawn. Already since last year we had chosen to use the sampling method of blocking the stream with fyke nets, every fortnight, for one and a half hour during the night, as fish only enter the streams in the night, and count caught fish.

In total, 1640 fish belonging to 5 species were caught:  Alburnus belvica, Chondrostoma prespense, Lepomis gibbosus, Squalius prespensis and Rutlilus prespensis. The latter species was caught for the first time in the streams.  Based on the results, the main conclusion of the monitoring was that various fish species enter indeed the streams to spawn in considerable numbers. In their vast majority their gonads were ready for reproduction.

Noteworthy differences were noted between the two streams, regarding the numbers, species and average size of the individuals captured in each one. At Mikrolimni stream 1565 individuals of 4 species were caught, whilst in the Lefkona stream 75 individuals of the 2 larger –sized species (Chondrostoma and Squalius) were caught.

Regarding the use of the stream mouths by waterbirds as feeding sites, the goal of monitoring had been to assess whether these two sites were indeed used by waterbirds after the maintenance works carried out in 2018, 2019 and 2020. These two sites were added in 2020 to the network of sampling sites under surveillance for assessing the use of feeding sites by waterbirds.

Despite their limited area (they are the smallest monitored sampling sites) the two stations (LM01-Mik Rema = Mikrolimni Stream Mouth and LM04-Lef Rema = Lefkona Stream Mouth) had the 3rd and 4th (among 16 sampling stations in total) higher records of waterbirds, with 5 species and 43 individuals and 9 species and 70 individuals, respectively, during April and May.

Furthermore, during the whole period of sampling (March-June) at the Lefkona Stream mouth 88% of total waterbird records were made in March-April, while, in contrast, at Mikrolimni stream mouth 97.5% of total waterbird records were made in May-June. This can be attributed to the differential patterns of temporal occurence of fish entering to spawn in these two streams.

Action D1. Fish monitoring in stream mouths – 2020 (in Greek, with English summary)