Many salmonid species show spectacular spawning behavior, and because the often spawn in shallow water they are easy to observe from land. Often the dorsal fi n or even part of their back break the water surface and often many individuals spawn simultaneously at the same site. Most salmon and trout species show spectacular reproductive behavior, which may include intense fighting between males for access to females, intersexual interactions, vigorous bed-cutting by the females and defense of their nests against other females (e.g., Jones 1959). The mating system of salmonid species have been characterized as one in which the females compete for territories (spawning sites) and males compete for access to females (Schroder 1982; Gross 1985; Sargent et al. 1986; Fleming and Gross 1989; cf. Petersson and Järvi 1997). Other studies, however, have pointed out that salmonid males may establish spawning territories around females and/or high quality nest sites (Mathisen 1962; Hanson and Smith 1967; Hartman 1969; Jonsson and Hindar 1982; Heggberget et al. 1988; Foote 1990). A female salmon may gain in fi tness by spawning with the most dominant males; in the long run her progeny may benefi t genetically, providing that the male characteristics that confer a high dominance rank have some genetic basis

1 Department of Aquatic Resources, Institute of Freshwater Research, Swedish University of Agricultural Sciences, Stångholmsvägen 2, SE-17893 Drottningholm, Sweden.