Sergestes similis is the most abundant pelagic shrimp in modified subarctic waters off Oregon and the northeastern Pacific Ocean. Off Oregon, its distribution changes with season and distance from shore. Largest numbers were caught in waters over the continental slope in 6‐ft midwater trawls and 1‐m plankton nets. Smallest catches were over the shelf and greater than 65 nm (120 km) offshore. Largest nearshore catches were made during winter, largest offshore catches during summer.Observations on the size of eggs in ovaries, the percentage of females with mature eggs, and the catches of young shrimp all indicated that spawning of the S. similis population is prolonged through most of the year. Young shrimp were not uniformly abundant, however, suggesting pulses of spawning in winter and spring.Growth rates and age structure estimates from length‐frequency histograms implied that the population is largely comprised of animals of age‐group 0. Individuals mature sexually after about one year when they attain a carapace length of 11 mm. Large individuals over 12 mm are rare and may die after spawning.