A previous survey reported that swimming crabs Portunus trituberculatus (Miers, 1976) in the East China Sea may have a low risk of sperm limitation under the current nonselective fishing practices. In this study, the possible mechanism of avoiding sperm limitation was investigated in a mating season (from July to November 2007) from a male perspective. Males reached 50% gonadal maturity at a carapace length of 99.4 mm and the reproductive measures (vas deferens weights, sperm number, and sperm concentration retained in the vasa deferentia) did not differ significantly throughout the mating season. As shown for other decapods, the quantity of seminal material in the vasa deferentia increased significantly with male size, without a concomitant change in sperm concentration. The proportion of stored sperm transferred at a single mating was calculated, and the results showed that males exhibited low sperm transfer at each mating, regardless of size. These findings indicate that the current fishery practices for P. trituberculatus may have little impact on the quantity of sperm stored by males throughout the mating season. This would guarantee that males of all sizes retain the capacity to mate throughout the breeding season, and, moreover, provide sufficient sperm to fertilize eggs spawned by their mates and reduce the risk of sperm limitation under the current fishing practices in the East China Sea.