Importance of Movement–Reproduction

During the breeding season animals move to find mates and smaller individuals may have to move to avoid areas dominated by larger, territorial adults. A common strategy among river and stream fishes is to segregate habitats used by adults from those used by juvenile fish. Adult fish typically use habitats in areas of deeper water and more stable hydrology than those in which they spawn. They migrate to spawning areas that have higher productivity or fewer predators such as floodplains and headwater streams. In these areas recently hatched fish can take advantage of decreased predation or higher productivity with the large number of juveniles compensating for the risks inherent in these more variable habitats ( Hall , C.A. 1972. Ecology 53(4):585-604).

The most dramatic examples of breeding movements are the long-range migrations of anadromous fish – species that live much of their adult lives in the ocean, yet return to freshwater streams and rivers to breed. These include various species of salmon, sea-run trout, shad and other herring species, sturgeons, and other fish. The common eel is a catadromous species, living as adults in freshwater and migrating to the ocean to breed.

Adult salmon live in the ocean until the breeding season when they migrate long distances to reach spawning streams. As they become larger, juvenile salmon hatched in these streams make their way downstream to the ocean, where the large marine food base can support much higher growth rates than can be supported in freshwater environments. Other fish species make similar, but less dramatic migrations to reach spawning habitats. Pike and pickerel move into vegetated floodplains to spawn. Many “non-migratory” fish (e.g. some species of trout, suckers, and freshwater minnows) utilize headwater streams as spawning and nursery habitat.

In contrast to fish, many stream salamanders utilize intermittent headwater streams as adults, but deposit their eggs in more perennial areas of the stream. The semi-aquatic adults can readily move up into headwaters to exploit the productivity of these areas. Their less mobile larvae are aquatic and need areas of more reliable, year-round hydrology.