I grew up in Alaska and have strong memories of going to rivers in the late spring/summer for the Pacific salmon, Oncorhynchus spp., runs. These salmon are anadromous – they migrate by the thousands up from the ocean to freshwater rivers to spawn (breed and lay eggs). They’re semelparous, meaning that after they breed, they die. Breeding happens late spring through fall, so I was surprised about the fall spawn of our native Atlantic salmon.
While Atlantic salmon, Salmo salar, are generally anadromous (again, migrating from saltwater to freshwater for reproduction), here in Vermont our salmon are all landlocked, meaning that juveniles remain in freshwater (e.g. Lake Champlain) and return to the sea (source).
Unlike Pacific salmon, they’re iteroparous (meaning they breed multiple times during their life). Though functionally most individual Atlantic salmon are semelparous, dying after just a single reproductive cycle – roughly 90% of the individuals spawning in a year are spawning for the first time. At maturity – around 3 or 4 years old for males, 4 to 5 for females – Atlantic salmon move up into the rivers surrounding their resident lake as early as September to breed. Breeding can occur as late as December.