Escalation of an asymmetric contest: mortality resulting from mate competition in Atlantic salmon, Salmo salar

Male anadromous Atlantic salmon, Salmo salar, fatally injured mature male parr during spawning. The wound consisted of three parallel cuts which exposed musculature on one side of the parr either directly below or immediately posterior to the base of the dorsal fin. The spacing of the cuts matched the spacing of the anadromous male's lingual and mandibular teeth. The wounding of parr in this manner is consistent with the observation of larger males vigorously shaking smaller males between their jaws. Mortality resulting from anadromous male aggression contributes to the low survival of mature male parr. Given the high mortality associated with parr maturation, if male parr must compete with anadromous males and other parr at all spawning sites, parr may be willing to risk escalated contests during mate competition with anadromous males to fertilize eggs.