Life History Forms of Male Masu Salmon (Oncorhynchus masou) in South Primor'e, Russia

In South Primor'e (Russia), mature male masu salmon (Oncorhynchus masou) parr are found at age 0 + to 3 + (9–22 cm). After first maturation, some male parr die, while others survive and mature the following year. Immature males become smolts after one or two winters in rivers and migrate to the sea in spring–early summer. After one winter in the sea, they return as sea-run normal-sized (40–70 cm) males at age R.1 +. Besides mature male parr and normal-sized sea-run males, jacks (28–33 cm) at age R.0 + were found. Such males return to rivers after some months of marine life and do not overwinter in the sea. Some jacks previously spawned as parr, while others did not. All jacks and normal-sized sea-run males die after spawning. Thus, male masu salmon mature as one of four life history forms: (1) male parr, (2) jacks that matured previously as parr, (3) jacks that did not mature previously as parr, and (4) ordinary sea-run males. While mature male parr and sea-run males are ordinary life history forms, both forms of jack are rare.