|Entering the deep and wide "Yperchilistis" - a semi-artificial channel of the Sperchios; north of the natural meandering channel.|
Early May 2014
The WFD field monitoring electrofishing teams and the KRIPIS project ichthyologists met at the Sperchios Delta for a special kind of sampling.
We used a traditional fisher’s boat with a four-person team to sample two +500 m sites along the lowest stretches of the river, near its river-mouth, within the Sperchios Delta. At this time of the year the river is in freshet and its freshwaters are not being funneled yet into the cotton and rice fields. After about the tenth of May much of the lower river’s main channel is diverted. A drastic change is said to take place in the lower river distributaries and the river mouth (higher salinities etc.).
The two main distributaries of the river are unusual and different. The first and largest is 'heavily modified' by being totally straightened and fed by polluted waters from a dis-functioning Sewage Treatment Plant of Lamia (it is called the "Yperchilistis"). The result is a eutrophic lowland canal-like river; however the channel is deep (+2 m) and water is fresh and flowing fast at a conductivity of only 400 μS/cm during early May. The second river is the original meandering natural channel. It is very degraded by reduced water flow and incredible silting-in of the original channel. Water is very slowly flowing (despite the freshet), and the silted-in conditions are shallow (about 1 m or so). The river channel is still meandering but the increased salinity has killed much of the deciduous trees (dead poplars were seen). Conductivity was 1200 μS/cm in Early May.
The channeled river was full of fish, especially large-sized freshwater fishes, particularly dominated by the Greek Barbel (Luciobarbus graecus). 12 fish species were found in total. My opinion was that younger fishes were seen in smaller numbers. The second morphologically more “natural channel” had less fish, dominated by mugilids (Grey-mullets). Freshwater species were much scarcer as was the presence of smaller freshwater fishes (several Rutilus sp. Sperchios were found). Total species count: Only 6 species in the 'natural' but degraded channel.
Sampling the lowermost parts of large rivers in Mediterranean areas especially areas affected by increased salinity and pollution should be done in mid spring – before river fresh waters are channeled away to water agricultural crops. It is an interesting time to see where the fish are during this time. Later in the summer - conditions degrade drastically and it is probably impossible to sample using electrofishing methods.
Some photos of our work below. I thank Vassilis Tachos, Dimitris Kommatas, Alkis Economou, Elena Oikonomou, Leonidas Vardakas and Nikos Koutsikos great participation. The local fisherman, Vassilis Routzos guided us well.