A spectrum of reproductive strategies can manifest within the same species to help improve reproductive advantage when faced under the pressure of sexual competition, known as alternate reproductive tactics (ARTs). Chinook salmon are external fertilizing species that exhibit the sneak-guard strategy of ARTs. The larger hooknose males dominate for optimal mating position, while jack males rely on the sneak tactic to achieve fertilization in relation to their smaller body size. During copulation, a single female’s egg may be fertilized by more than one male. Therefore the threat of sperm competition is increased as the ejaculate from multiple males can interact during this time. As jack males establish a position further away from the female’s egg during fertilization attempts, it is proposed that jacks should invest more in spermatozoa quality. Although poorly understood, previous studies have suggested that differences in spermatozoa quality may play a critical role in sperm competition. Considering that the seminal plasma strongly regulates spermatozoa quality and other processes critical for fertilization success, we employed label free quantitative mass spectrometry utilizing ion mobility separation coupled to cross-species bioinformatics to examine the seminal plasma proteome of Chinook salmon.