Mate and sperm competition during multiple-male spawnings of Atlantic salmon

The influence of sperm competition and individual mating behaviour in an externally fertilizing species of fish, the Atlantic salmon (Salmo salar), is estimated from video observations of multiple-male spawnings and subsequent paternity analyses. One male dominated the paternity during polygamous spawnings, fathering more than 80% of the progeny in a single nest. Behavioural analyses of the spawnings showed that the first-mating male had sperm precedence in 6 out of 10 cases. In three of the other spawnings, sperm limitation likely influenced individual success, as the first-mating male had participated in a large number of spawnings. In the final, nearly simultaneous spawning, male size was more important than the 0.6-s difference in spawning times. Thus, male fertilization success can be influenced by a variety of factors, including sperm precedence, male size, and spawning history.