Time-based method for determining fish abundance in fishing rivers

The article touches upon the problem of the rational use of fish stocks in fishing water bodies, which implies using modern accounting methods for fish abundance and fish stocks. To this end, instrumental surveys are carried out. In the fishing rivers of Kazakhstan (the Zhayik and Kigash Rivers) there was previously used the biostatistical method of accounting based on data from fishing statistics. The statistical data have recently become unreliable, since they do not take into account the illegal, unregulated and unreported catch. Instead of the biostatistical method, it has been proposed to use the time-based method which considers the fish that have passed along the river for a certain period of time and extrapolating these data for the entire duration of the fish run. The results of using the method to estimate the abundance of semi-anadromous fish species in the Zhaiyk River in the spring of 2019 are shown. There has been developed the method determining the catchability of a commercial seine on the river by conducting simultaneous fishing with two seines following one after another. For each fish species in the catch, the catch coefficient should be calculated separately. Examples of calculating the abundance, ichthyomass, and commercial stocks of various fish species (roach, sazan, bream, asp, crucian carp, sabrefish, catfish) that entered the river in the spring of 2019 are presented. There is found a difference in the values of the commercial fish stocks determined by the time-based and biostatistical methods, due to the lack of the subjective component of the forecast.