The underwater wreckers destroy dams and piers
Zoologists caught a specimen of the crab inhabiting southern seas in the Volga water area for the first time. It is a mystery for scientists how this specimen could get to this area.
Lecturer Vladimir Nazarenko from the Ulyanovsk State Teacher's Training University says that the crab was caught in the right-bank sector of the Volga River in the Ulyanovsk region. A fisherman from the Itil collective farm caught it with an ordinary seine with 5 cm meshes at a depth of 8 meters. Some time ago such finds were usually handed over to museums or given to scientists for further study. However, when Assistant Professor from the University's zoology department Vadim Zolotukhin confirmed that the crab was exotic, the fisherman refused to part with the "precious" catch. The man stuffed the crab and made it a wonderful detail of the interior.
Chinese crabs were first caught in Volga several years ago. Catch of such crabs were reported from the Russian city of Volgograd, from Saratov region (these are regions situated on the Volga River banks). As of now, the number of crabs caught and officially registered in the Saratov region is over 100. Recently, an exotic specimen has been caught in Ulyanovsk. Vladimir Nazareno says, it is not ruled out that fishermen managed to catch crabs long time ago; they told stories about some strange animal, neither a crayfish nor a frog, that was caught with a net.
What is the hairy-legged Chinese crab? The color of the animal is fawn; the shell is 7 centimeters long while fishermen say that crabs may be of a bucket size in the Far Eastern waters; the swing of its legs is up to 20 centimeters. The crab is called hairy-legged because of the numerous hairs on the legs. It inhabits deep-water areas, eats carrion remains of fishes, shellfish and other water organisms. There is less information in Russia about the mode of living of the hairy-legged crabs; all literature on the subject is in Chinese.
According to one version, the Chinese crab could get to Russia from the Baltic region where these animals are artificially bred. They could use the Baltic Channel, a system of lakes and storage ponds to get to Volga; this is an open route. Other people suppose that some jester probably bough a crab in China and set it free into the Great Russian river. It is not ruled out that a crab could stick to the bottom of a tanker and traveled together with the ballast water (each vessel has tanks for water ballast; they are filled with water depending upon the vessel's weight). The tanks are usually filled in ports where vessels start and poured out at the terminus. So, any sea organisms can get into rivers with the sea ballast waters.
When Saratov scientists first studied the crab caught in Volga, they were sure that the Chinese crab wouldn't get acclimatized in the river water. However, as it turned out, the exotic animal feels rather good in these latitudes; it comes across its worst enemy, the crawfish, very seldom. Crawfish prefers shallow water of the river, while crabs inhabit the depth of 10-15 meters. Theoretically, it is only the cat-fish that poses a real threat to the Chinese crab. In fact, it is a rather hard task to catch the exotic animal; even experienced poachers need special equipment to catch it in Volga.
Is it good or bad that Volga is now inhabited with crabs? On the one hand, the delicacy would cost less in the Ulyanovsk region as compared with the crab meat delivered from the Far East. The meat would be in great demand there, especially that it abounds in vitamins.
On the other hand, scientists fear that the sea animal may damage the frail balance of the Kuibyshev Reservoir. The Chinese crab may eat up the fish population in Volga. What is more, it is the carrier of a dangerous disease, crawfish plague. Crabs are also known as destroyers of artificial dams and piers, as they live in holes they dig themselves.
There are instances saying about great damage to the environment caused by animals that were transferred from their habitual habitat to a new place. In the 1980s, the bivalve Dreissena polymorpha of Caspian origin got into the US Great Lakes. Now Americans have to spend up to $400 million on clearing water intakes, including nuclear power plants from dreissena incrustations. Poisonous aquatic plants got somehow from European seas to Australia. Now farmers breeding shellfish are suffering great losses because of these poisonous plants.
The same way as the Colorado beetle has spread about Eurasia, the pipe-fish and different kinds of goby got into the Volga River from the Caspian Sea. The goby are a serious problem for ichthyologists, as the small fish eats up the spawn of food fish. It is incredible but last year a shark Squalus acanthias was caught in Volga near the city of Astrakhan. And it is not ruled out that the shark could spread further along the river. Even piranha was caught in the Surskiye Lakes! Probably some people set the fish from an aquarium hoping they may get acclimatized in the river water.
All "guests" now inhabiting Volga are closely studied by scientists; it is highly likely that number of animals and organisms that got into Volga from other places may even increase in the future.