Comparative stream residence of juvenile brown and rainbow trout in a small lake inlet tributary, Scotts Creek, New Zealand

Abstract

Species composition, population changes, and emigration of 0+ lake trout in Scotts Creek, an inlet tributary of Lake Alexandrina, were studied. Trout populations were dominated by late emerging 0+ rainbow trout Salmo gairdneri. Rainbow trout juvenile migration consisted primarily of newly emerged nocturnally migrant fry, whereas that of brown trout S. trutta was mostly of fish which had undergone a period of stream residence. Pattern of initial downstream migration of early migrants was consistent with a passive dispersal mechanism. Although rainbow trout dominated the 0+ salmonid populations, brown trout made greater proportional use of the stream for rearing. This situation arose from differences in patterns of emigration between the species, particularly that of newly emerged fry, with rainbow trout showing a much greater tendency to emigrate upon emergence. The significance of migratory strategies and interspecific competition in relation to lotic vs lentic rearing of brown and rainbow trout is discussed. -Author