Overall, chinook salmon generally spawn at 2-7 years of age (typically 3-5) in fall, depending on the population. A small proportion of males (called jacks) mature after only spending about 6 months or 18 months at sea, and still others mature without having migrated to sea at all. Eggs hatch in about 2-3 months and alevins complete development in another 1-2 months (depending on temperature, hence related to latitude and elevation). Juveniles stay in fresh water for a few days or 1 year (rarely more). Adults die soon after spawning. Several distinct spawning populations may occur in one stream; these may differ in duration of juvenile rearing, size and date of ocean entrance, timing of adult return and spawning, age composition of spawners, fecundity, and egg size (see Nehlsen et al. 1991).