Seasonal Survival, Movement, and Habitat Use of Age-0 Rainbow Trout in the Henrys Fork of the Snake River, Idaho

Abstract

We quantified seasonal abundances, apparent survival rates, movements, and habitat use of age-0 rainbow trout Oncorhynchus mykiss in a 25-km reach of the Henrys Fork of the Snake River, Idaho, to determine what factors limit recruitment to the population. Natural production of rainbow trout occurred in each year of the study (1995-1997) and ranged from 158,000 to 306,000 age-0 fish each summer. No significant loss of age-0 rainbow trout occurred between summer and autumn; suitable habitat was present throughout the channel in all reaches and supported large abundances of age-0 rainbow trout through this period. The greatest losses (77-100%) occurred during winter and primarily involved fish from center-channel macrophyte beds. Most river sections, which had only simple bank habitat, did not support any age-0 rainbow trout through the entire winter. Overwinter survival was greatest (18-23%) in Box Canyon, a river section characterized by complex bank habitat, high gradient, and large substrate. Fish that were marked in river sections with simple bank habitat in autumn had moved to sections with complex bank habitat by the following spring. Winter habitat limits rainbow trout recruitment in the Henrys Fork.