Monitoring was carried out over many years on two experimental areas. Samples were collected based on the standard methodology by netting and low-impact electric fishing. There were three persons using one electric fishing device and three nets.

The only species collected on the monitoring areas was trout Salmo trutta labrax morpha fario Linnaeus, 1758.

In the summer-autumn 2013 no trout was found on the part of the river Mzymta adjacent to the JSC ”Krasnaya Polyana” ski complex (Table 1). The state of the trout population on this river section can be considered as unsatisfactory. When the species population was censured in April 2012, mature fish and young-of-the-year fish were identified which were washed off from the unharmed upstream river section. There was no trout on this river section at the end of 2012 and first half of 2013. The summer-autumn survey in 2013 has shown that the trout population density upstream of the river Mzymta, beyond the construction sites, is 1-2 individuals (0.5) per 10 m².

Table 1 – Dynamics of the trout population on the Mzymta section adjacent to the monitoring site

Monitoring was carried out on two experimental areas. Samples were collected based on the standard methodology by netting and low-impact electric fishing. There were three persons using one electric fishing device and three nets.

The only species collected on the monitoring areas was trout – Salmo trutta labrax morpha fario Linnaeus, 1758.

In the spring 2013, as before, no trout was found on the part of the river Mzymta adjacent to the JSC ”Krasnaya Polyana” ski complex (Table 1). The state of the trout population on this river section can be considered as unsatisfactory. When the species population was censured in April 2012, mature fish and young-of-the-year fish were identified washed off from the unharmed section upstream of the river.

The summer-autumn survey has shown that the trout population density upstream of the river Mzymta, beyond the construction sites, is 1-2 individuals (0.5) per 10 m2. In the low-water season, the water in the river is muddy, machinery is running in the river channel and nearby, and erosion processes are intensified in case of heavy precipitation. As a result, some parts of the river turn into a mudflow. The entire section of the Mzymta river adjacent to the JSC ”Krasnaya Polyana”ski complex stopped, for some time, to be a feeding and spawning area required for trout dwelling and reproduction. Part of the fish moved from the unsuitable sections higher up the river, while others were killed during flooding

Table 1 – Dynamics of the trout population on the Mzymta section adjacent to the monitoring site

The ichthyofauna of the ski complex JSC “Krasnaya Polyana”, as shown by the studies of previous years, is represented by a single fish species - trout (Salmo trutta labrax morpha fario Linnaeus, 1758.) In 2012 monitoring of trout was organized on two experimental areas. During the fishing in the summer 2012 no trout was found on the part of the river Mzymta adjoining the ski complex JSC “Krasnaya Polyana”, which suggests unsatisfactory situation with the species on this area. When the species population was censured in April 2012, mature fish and young-of-the-year fish was identified which was washed off from the environmentally safe section upstream of the Mzymta.

Upstream the river Mzymta, beyond the construction sites, trout normally occurs at 0.5-2 individuals (0.6) per 10 m2, which is in keeping with the background rates for the species, based on average many-years census data in the upper reach of the mountain rivers in the Sochi National Park.

Downstream of the construction sites of the ski complex “Roza Khitor””, “ Alpiko Service” and “Kransnaya Polyana” the water is muddy and resembles a debris flow. This was the case throughout 2012 due to the intensive operations of machinery in the streambed and on floodplain terraces of the river. The situation was aggravated during the heavy rainfall that enhanced erosion processes and the entire part of the Mzymta turned into a mudflow.

Therefore it has to be acknowledged that these sections of the Mzymta river temporarily stopped to be feeding and spawning areas required for trout dwelling and reproduction. Part of the fish moved from the unsuitable sections upstream, while others were killed during floods.

The trout population was decreasing from the first half of 2011 (most intensive construction activities in the river channel ) up to the total loss of the species on the monitoring areas in the second half of 2012. In other words, the loss of ichtiocenosis for the study part of the river Mzymta occurred in eighteen months.

Like in the previous years the ichthyofauna on the study areas was represented by one species only – trout (Salmo trutta labrax morpha fario).

The water turbidity as a result of erosion processes practically does not influence the trout. Among the adverse factors is withdrawal of the ballast substance from the river bed, which may lead to the physical death of juvenile fish.

On the monitoring areas the trout is a common species: 1-2 individuals per 10 m² and, on the average, 1 individual (fish of all linear size was accounted). These indicators were not much lower the autumn census of the population, which is probably due to easonal movementof trout and autumn falls. Generally, the condition of the trout on the parts of the Mzymta adjoining the “Karusel” complex can be assessed as satisfactory. During the censure of the species population in April 2011, both mature and juvenile fish was identified suggesting successful spawning of the previous years.

On the study areas the ichthyofauna is represented by one species only– trout (Salmo trutta labrax morpha fario Linnaeus), 1758.

The water turbidity as a result of erosion processes practically does not influence the trout. Among the adverse factors is withdrawal of the ballast substance from the river bed, which may lead to the death of juvenile fish.

On the monitoring areas the trout is a common species: 1-3 individuals per 10 m² and on the average 2 individuals (fish of all linear size was accounted). These indicators are not much higher the spring census of the population, which is probably due to spring movement of the trout. Generally the condition of the trout population on the parts of the Mzymta adjoining the JSC “Gornqaya Karusel” can be assessed as satisfactory. During the censure of the species population in October 2010, mature fish and young-of-the-year fish were identified suggesting its successful spawning and development.