Reproductive Characteristics of Pike Esox lucius (Esocidae) in the Kama Reservoir (Perm Krai)

The pike Esox lucius (L., 1758) is an apex predator important for commercial and recreational fisheries in Eurasia and North America, and aspects of its reproductive biology remain, for the most part, unstudied. Based on materials collected in 2016–2023, we have studied the ontogenetic, interannual, and geographic variability of sex–age composition; absolute (AF) and relative (RF) fecundity; gonadosomatic index; and egg diameter of pike in the Kama Reservoir. The spawning requirements were also investigated. Individuals from 3 to 16 years in age were used in the study. The results showed the high importance of the plant substrate for spawning. In years with an early spring, pike spawning occurred extremely late, at 14–19°C, only after the water level had risen, providing adults access to the spawning substrate. The AF of pike in the Kama reservoir corresponds to fish from the southern part of the range of this species. In terms of RF, pike in the Kama reservoir occupy an intermediate position between the northern and southern populations. In contrast to AF, which constantly increases with age, the RF and GSI (gonadosomatic index) of pike in the Kama Reservoir increase in fish up to 8 years of age. In older individuals, a decrease in these indices were observed. The results of the studies may indicate that the most favorable conditions for pike habitat are formed in the central part of the reservoir, which is characterized by the largest area of shallow habitats, as is evidenced by the maximum values of AF and RF, as well as the reduced mortality of males. At the same time, under conditions of negative climatic anomaly, despite large linear growths, pike from the central part of the reservoir were characterized by a lower condition factor, as well as GSI, AF, and RF, which may be determined by a greater amplitude of water temperature fluctuations in shallow habitats under adverse weather conditions.