Male competition and breeding success in captively reared and wild coho salmon (Oncorhynchus kisutch)

Abstract

In the Pacific Northwest, releasing captively reared adult salmon (Oncorhynchus spp.) for natural spawning is an evolving strategy for the recovery of imperiled populations. However, the ability of captively reared fish to spawn naturally may be compromised by their artificial rearing environments. In this study, wild coho salmon (O. kisutch) males outcompeted captively reared males and controlled access to spawning females in 11 of 14 paired trials in laboratory stream channels. In two cases where satellite males were observed participating in spawning, DNA genotyping results determined that they did not sire any of the progeny. When spawning occurred at night and was not observed, DNA results confirmed behavior-based determinations of dominance made before dark. Dominance was established soon after the males were introduced into a common arena containing a sexually active female. We hypothesize that decisions by subordinate males to avoid direct competition may have minimized conflict. The competitive inferiority of captively reared coho salmon in this and a previous study probably reflects deficiencies in rearing environments, which fail to produce appropriate body coloration and body shape and perhaps alter natural behavioral development.