Abstract:

Age composition, length and weight indices of the roach populations (Rutilus rutilus L.) were analyzed and compared in water bodies with the different commercial fishery loading levels. Presence of fast-growing and slow-growing forms is inherent to cyprinid fish. In Dnieper reservoirs these forms are mixed and it is difficult to separate any one of them. It is assumed that selective elimination of fast-growing forms by commercial fishing may cause accumulation of slow-growing forms in populations. On that ground, water bodies with different levels of commercial fishery pressure have been chosen to test this hypothesis. For instance, Kremenchuk Reservoir was selected as a water body with high level of commercial fishery load because it forms more than a half of roach commercial catching in Ukraine. On the contrary, “Dniprovsko-Orilskiy” Natural Reserve was taken as a water body where human impact is minimum. Subsequently, comparing of the basic biological features of the roach from water bodies with different commercial fishery load illustrated the value of the study. It is found that the roach age range in Kremenchuk Reservoir is much higher than in subordinate waters of the Natural Reserve fund. Namely, the roach population in Kremenchuk Reservoir consisted of seventeen age groups while in “Dniprovsko-Orilskiy” Natural Reserve it comprised ten age groups only. However, size-weight features of species under study across the age groups 6+ –10+ in water bodies with the intensive commercial fishery were statistically lower than in protected waters of the Nature Reserve. Namely, length of these age groups in Kremenchuk Reservoir was equal to 24.6–33.5 cm, compared with 25.0–37.0 cm in the National Reserve. Naturally, that weight was equal to 334–957 and 340–1320 g, respectively. In general, this result does not fit into the traditional concept that the fast-growing roach should inhabit the lacustrine biocenosis of the Dnieper reservoirs. In addition, the absence of commercial fishing in waters of “Dniprovsko-Orilskiy” Natural Reserve leads to increase in number of fast-growing individuals in the population that effectively go out of predators pressure. On the other hand, high direct and indirect anthropogenic pressure cause the elimination of fast-growing individuals of the roach from population in Kremenchuk Reservoir that is proved by the curves of growth and the onset of fish-mass culmination. This study indicates that high anthropogenic pressure at present time has reached a degree which cause accumulation of stunted fish in the roach populations in Dnieper reservoirs. This is a notable effect, at least from the regulatory point of view.

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