Catches, age and growth of the roach Rutilus rutilus (Cyprinidae) in the Middle Ob river basin (within the Tomsk region)

Abstract

The data on the catch, age composition and growth of the roach Rutilus rutilus L. in commercial herd in the Middle Ob basin (in the Tomsk region) are presented. It is shown that the catches of the roach in the middle of the 20th century were 2098 tons per year. In the second half of the 1960s, they fell sharply by more than two times. It was caused by a decrease in the areas of effective spawning due to the reduction of runoff in the Ob during spring floods as a result of the regulation of the level regime by the dam of the Novosibirsk hydroelectric power station. After that, the catch of roach remained at about 1013 tons per year until the beginning of economic reforms in the country, when the catch of this species became unprofitable, as a result of which catches decreased to an average of 436 tons per year. Currently, the basis of commercial catches is made up of roach with a commercial length of 140 to 210 mm and a weight of 50 to 150 g at the age of 2+...5+. It is noted, compared with the 1970–1980s, there is a shift in the age series towards an increase in the value of older age groups, which may indicate underutilization of the stock of the roach. The statistically significant positive relationship between catches of roach and the average duration of flooding of the floodplain in the years of the occurrence of generations that form the basis of catches was revealed. Prolonged floods also provide better conditions for fish feeding (a statistically significant positive relationship between the mass of fish of the same age and the duration of flooding of the floodplain is shown). Thus, the hydrological regime in the spring has a decisive influence on the state of the stocks of roach in the Middle Ob.