Use of female nest characteristics in the sexual behaviour of male sockeyesalmon

On three island beaches in Iliamna Lake, Alaska, large numbers of male sock eye salmon gathered and spawned in artificial excavations that mimicked a f emale's nest immediately prior to spawning, while apparently ignoring the c ontrol site. The number of males attracted was correlated positively with c hanges in the operational sex ratio. In contrast, on the mainland beach exa mined, no reaction to the artificial nests was apparent. The results are di scussed in terms of mate searching behaviour by males, the duration of the spawning period, and associated selection pressures on males to use charact eristics of their environment that provide information on availability of f emales. (C) 1999 The Fisheries Society of the British Isles.