Accuracy of Assessing the Abundance of Fish Generations under Conditions of Incomplete Initial Information

© 2020, Pleiades Publishing, Ltd. Abstract: The accuracy of estimating the relative abundance of generations of fish species under conditions of incomplete initial information is analyzed. Using the example of bream from the Kuibyshev Reservoir, it is shown that, if the information on the age structure is lost for 1 to 8 years, the error in estimating the abundance of generations averages from 5 to 15%. This makes it possible to apply this modification of the method of loss from fishing to estimate the abundance of fish generations in the current conditions. This method of estimating the number of generations may be useful in the analysis not only of fish, but also of other aquatic organisms

The impact of herbivorous fish introduction on the formation of fish communities in water bodies (based on the Khauzkhan Reservoir, Turkmenistan)

The dynamics of the structure of fish species complex in the community of the Khauzkhan Reservoir (Turkmenistan) has been analyzed from the time when it was filled in 1966 to 1990. In order to quantify the observed changes in the fish population, the indices of diversity and dominance and the dynamic phase portrait method have been used and the structural changes have been visualized. Changes in the dominant complex of species and the dynamics of the relative abundance in the catches of fish groups belonging to different faunal complexes and ecological groups have been also considered. A relation between the changes in the structure of fish species complex in the community under study and the changes in the ecosystem of the reservoir has been found. It has been shown that the introduction of herbivorous fish from the first years of the reservoir filling has resulted in a new stage in the formation of its ichthyofauna, which is known as the stage of acclimatization, and in the extension of the formation process. Currently, the fish population of the Khauzkhan Reservoir is at the 4th stage of formation – the stage of an increase in the anthropogenic impact

New approach to assessing the state of fish stocks on the example of bream

© 2020 Publishing House "O- Kratkoe". All rights reserved. This paper substantiates a new approach to the protection of fish resources, based on the transition from the concept of a calculated forecast of catches and quotas to a multilevel system for assessing the status of fish populations under conditions of slow flow. The main levels of the fish population monitoring system are considered. A new approach based an analysis of monitoring results of the main structural and functional population characteristics of fish, on data on the dynamics of the population size and its generations, changes in the age structure, growth rate, abundance of individuals with morphological anomalies. A new approach was tested on the example of a model species of bream (Abramis brama L.) in the Kuibyshev reservoir as a common inhabitant of different morpho-hydrological properties of reservoirs in Europe, belonging to the LC group according to the IUCN classification. An array of new scientific data has been obtained. Based on the calculation of natural mortality by approximating the population curve, taking into account the age composition of catches, it is shown that with a stable replenishment of the fishing herd, when high- and small-numbered generations enter the fishery, depending on the spawning conditions, bream stocks are not expected to be undermined. The results of the study can be used as a basis for assessing the state of fish populations, developing measures for the rational development of their reserves in conditions of unstable hydrological regime of reservoirs and weakening of control over fishing in the protection of fish resources