Perccottus glenii Dybowski, 1877

13. Possible population control

      The r-strategy of reproduction of rotan at the first stages of development of new reservoirs in the Yaroslavl area (Volga system) was observed. It becomes mature on the first-second year of life and it's fecundity here is higher, than in natural area. It promotes fast augmentation of number and suppression of indigenous species. The population number is regulated mainly via food resources, cannibalism and predators (Shlyapkin, Tikhonov, 2001).

      In the basin of Lake Baikal pike may be the regulator of rotan numbers. It acts as such regulator in water bodies of the delta of the Selenga River, however its numbers are low. Alternatively, larger populations of rotan may well have developed more rapidly in the delta of the Selenga River in the absence of predation. Clearly, the focus of the two main shallow-water piscivores on rotan has reduced predation on endemic fishes although it seems unlikely that this will offset the losses of the juvenile endemic fishes to predation by the rotan. Maintaining vigorous populations of Eurasian perch and northern pike may well be an effective strategy for limiting the size of rotan populations. It is possible to increase its numbers and temporary fish rearing stations and already existing fish rearing stations. The natural reproduction of pike was affected to a large extent by dynamics of water level in Lake Baikal in the period of spawning (April - May). The natural fluctuations of the level of Lake Baikal influenced by its regulation by dam of the power station (1958). Before that minimum water level in its annual dynamics falls on April. After regulation and raising of the level by one meter seasonal minimum shifted to May. However the annual physiological cycle of pike, genetically determined, remained invariable. Decline of water level in May leads to a considerable decline of spawning areas. Therefore regime of Irkutsk Power Station function should provide minimum level of water in April as before the regulation (Litvinov, O'Gorman, 1996; Bolonev et al., 2002).

      Litvinov and O'Gorman (1996) suppose that elimination of rotan from Lake Baikal is clearly not possible since attempts to eliminate exotic fishes after they have established reproducing populations are rarely successful.

      The experiments (Zaloznykh, 1984) have shown that of all species of weed fishes rotan is the most resistant one to lime chloride and ammonia water. 100% death of rotans occurs when concentration of lime chloride is 0.3 g per 1 l of water at exposure of not less than 6 hours. In actual practice this may be done in only small pools. In processing of [бочагов] and catchment canals ammonia water works well. At water temperature of 7-8 degrees and pH 9.0 100% death of rotans occurred in 1 hour 5 minutes after 1 ml of ammonia water was diluted in one pool.

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© N.G.Bogutskaya, A.M.Naseka, 2002
© Zoological Institute RAS, 2002