Features of fishery and indices of reproduction for pink salmon Oncorhynchus gorbuscha of Iturup Island (Kuril Islands)

Abstract

Annual data on the 1976–2019 year-classes of pink salmon from Iturup Island are presented, as their number on spawning grounds, abundance of wild and hatchery juveniles migrating downstream, and returns of adult fish after the marine period of life. On average, 1.48 . 106 spawners entered annually the rivers of Iturup Island in these years and 237 . 106 fry juveniles rolled down (the downstream migration index was 165 juveniles per conventional producer), plus 133 . 106 juveniles from salmon hatcheries. After fattening in the sea, the annual returns were 16.56 . 106 ind., on average, so the marine survival index was 4.70 %. This is the highest value of the return for the Sakhalin-Kuril region, relative to the area of spawning grounds and to the number of spawners. The year-classes of odd years dominated until the middle 1990s, then the year-classes of even years became more numerous. Biological parameters of fish (body length and weight, fecundity) fluctuated from year to year both for odd and even year-classes, though these parameters averaged for a long period of observation had no difference between the odd and even year-classes, as well as the indices of reproduction efficiency.