ON BIOLOGY OF SOCKEYE SALMON ONCORHYNCHGUS NERKA FROM THE ZHUPANOVA RIVER (EAST KAMCHATKA)

Abstract

Runs and escapements of sockeye salmon to the Zhupanova River have increased since 1985 with the run of 10.63 . 103 ind. instead of 1.45 . 103 ind. in 1960–1984, on average. The increasing was reasoned by change of the pink salmon odd year-classes domination in West Kamchatka to domination of even year-classes after the extremely high escapement in 1983. In 2005–2006, the sockeye salmon stock in the Zhupanova River became even more higher that continues till nowadays (runs of 68.20 . 103 ind. in 2005–2017, on average). This growth corresponds with general increasing of the pacific salmons abundance in the Russian Far East as the result of favorable environmental and feeding conditions in the North Pacific. General biological indices (age, body length and weight, maturity, fecundity) of mature sockeye salmon originated from the Zhupanova River are presented on the data of commercial catches in the sea in 1999–2017. The sockeye salmon population from this river has 11 age groups. The age group 1.3 is the most abundant and associated with the age groups 1.2 and 1.4. Majority of sockeye in the catches from the Zhupanova has the age 1.3 (on average 66.2 % in 1999–2017). Besides, returns of underyearlings with age 0.2, 0.3, and 0.4, and the fish with age 2.2, 2.3, 2.4, 3.2, and 3.3 are detected. The body length and weight are similar for all age groups of sockeye salmon: for males/females the mean length is 57.56/57.70 cm, mean weight is 2.69/2.62 kg. The mean males:females ratio is 44.7 : 55.3. The mean absolute fecundity is 4121 eggs. In opposite of sockeye salmon in some rivers of East Kamchatka, the population of the Zhupanova has no negative year-to-year trend of the body length or weight.