Partial migration in a landlocked brown trout population

摘要: Population densities of landlocked lake-migratory brown trout Salmo trutta were estimated in two distinct lotic sections, separated by a lentic segment, the Greana River, Sweden, and individual growth habitat use monitored for 835 tagged from September 1998 to June 2000. Residency dominated upstream section where density 0+ 1+ year was low rate high. In contrast, >90% that migrated lake originated downstream section, high low. For ≥2+ individuals, similar between stream but higher than section. Lake-migrants had rates non-migrants (residents) during autumn both years. From May, migrants increased their body mass >35%, whereas <5%. Approximately 70% moved <10 m <2% sections. indicating might function as barrier juveniles. Differences migratory behaviour, indicate environmental factors influence decision migrate. It cannot be excluded, however, observed differences are genetically programmed, selected migration costs favour behaviour residency upstream.