Reproductive Behaviors Related to Life History Forms in Male Masu Salmon,<i>Oncorhynchus masou</i>Breboort, in Lake Toya, Japan

Abstract

ABSTRACT We observed the spawning behaviors of male masu salmon (Oncorhynchus masou) to examine whether the life history forms of males were related to the reproductive tactics. Standard males (mean ± SD = 43.0 ± 7.1 cm), which migrate into the lake and return to the natal creek for spawning, fought with other males to become the dominant male in the reproductive group. The male that became dominant in the reproductive group intensively attacked males of a similar sue and defended an area around a spawning female against other males. Puerile males (22.3 ± 6.3 cm), which grow in the lake and mature while retaining parr marks, attempted to gain a higher hierarchical position in the subordinate group, while being attacked frequently by the dominant male. Precocious males (mature male parr, 11.5 ± 3.3 cm), which mature without migrating to the lake, had a tendency to occupy positions near the females and attempted to use sneaking mating tactics. These males were not attacked by the dominant male. This indicates that the different life history forms of males are associated with different reproductive tactics.