“Currently, the number of crayfish is decreasing, but the current level of stocks still exceeds the level recorded in 2007-2010,” the zoologist said.

According to the specialist, the low-water and dry years of 2020 and 2021 were very difficult for crayfish. Many reservoirs, especially in the eastern part of the Rostov region, have become very shallow or completely dry. The area of ​​crayfish habitats has been greatly reduced everywhere. In some places the crayfish died completely, in some places they buried themselves in the silt or concentrated in the watered part of the reservoir. All this made the crayfish more vulnerable to predation, fishing and removal by humans.

“At the same time, every cloud has a silver lining. The drying out of the reservoir bed and natural “flying” contributed to the aerobic healing of the silt soils. We see that in the fall of 2021, under the influence of heavy precipitation, the reservoirs were filled with water, which, against the background of the previous natural “flight”, will lead to an outbreak in the productivity of these reservoirs. This will also be beneficial for the reproduction and restoration of the number of crayfish. We will be able to see the effect of this by 2023-2024,” says Sergei Dudkin .

The zoologist noted that crayfish populations, like populations of all living organisms, are characterized by population fluctuations that are initiated by both natural and anthropogenic factors. Natural ones include the spread of viral, bacterial or parasitic zoonoses, in particular, crayfish plague, which is dangerous for crayfish, and the fairly common rusty spot disease. Anthropogenic factors include pollution of water bodies, ingress of insecticides from surrounding agricultural lands, and excessive harvest by both commercial and illegal and unreported fishing. Unfortunately, the impact of illegal and unreported fishing on crayfish populations remains high throughout.

“In all water bodies where crayfish live, their numbers are determined by the dynamic balance between replenishment, which depends on the initial number of females of reproductive age and on the reproductive potential of the local population, and consumption, death at different stages of the life cycle from consumption by predators (many fish use crayfish in food, and for catfish all size groups of crayfish are a favorite food; crayfish are consumed by some birds, mammals – otters, raccoons), cannibalism, diseases, and removal by humans. Moreover, the last factor is one of the most powerful,” said Sergei Dudkin.

The number of crayfish is determined only in those reservoirs where industrial crayfish fishing takes place. In the Rostov region, these are the Tsimlyanskoye, Veselovskoye, Ust-Manychskoye and Proletarskoye (inter-dam section only) reservoirs, the bed and reservoirs of the Don River floodplain in the area below the Tsimlyanskoye hydroelectric complex dam, the Sal River with all its tributaries (Kara-Sal, Djurak-Sal and others). All other reservoirs, river beds, ponds, reservoirs, and lakes are not commercial, which means that industrial crayfish fishing is not carried out in them. Crayfish are caught there either by amateur fishermen or by groups of illegal poachers.

According to the specialist, of the commercial reservoirs, the highest number of crayfish is observed in the Veselovsky Reservoir – there are about 250 thousand specimens of commercial size (more than 9 cm in length) with a total biomass of about 33 tons. However, this is also the largest crayfish-fishing reservoir in terms of area.

Throughout the Rostov region, the highest abundance is created by the narrow-toed crayfish Astacus leptodactilus, also called the Kuban crayfish by some researchers. In the east and northeast of the region, common crayfish or thick-clawed crayfish can also be found. However, its numbers are small and everywhere it is replaced by the narrow-toed crayfish, which is more resistant to pollution of water bodies.