Historical and Current Distribution of the Brown Trout, European Grayling and Volga Nase in Small Rivers in the Republic of Tatarstan

We have studied the historical and current distribution of brown trout, European grayling, and Volga nase in the Republic of Tatarstan. The influence of environmental variables on the current distribution of these fish was assessed using regression methods. The probability of occurrence in small rivers of all three fish species is currently low, ranging from 2.8 to 5.3%. Each of the recorded environmental variables had statistically significant relationships with presence/absence of at least one fish species, but only two variables (elevation and human impact) significantly affected the probability of occurrence of all species in the study.