Age-0 Rainbow Trout Oncorhynchus Mykiss Research Articles

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

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.

Estimating Abundances of Age-0 Rainbow Trout by Mark–Recapture in a Medium-Sized River

Abstract We developed and evaluated a sampling methodology to obtain mark–recapture data to estimate abundances of age-0 rainbow trout Oncorhynchus mykiss in 70–125-m-wide reaches of the Henrys Fork of the Snake River, Idaho. Sampling by electrofishing was concentrated in sample areas that were 100 m long and extended from bank to bank; these areas were electrofished 3–5 times within periods of 3–17 d. Adjacent 50-m-long areas upstream and downstream were sampled to quantify movements out of the 100-m sample areas. We evaluated assumptions—closed population and equal catchability—using the field data, and we used simulation to identify the most appropriate abundance estimator for sparse data. Both closed and open population abundance estimators were evaluated. Most trout (84%) were recaptured in the area where they were marked, but about 10% had moved downstream and about 6% were recaptured upstream. Multistrata model analyses confirmed that apparent mortality rates, and hence movement rates, were low. Th...

Spatial and Temporal Variation in Risk to Piscivory of Age-0 Rainbow Trout: Patterns and Population Level Consequences

Abstract We used tethering to measure spatial and temporal patterns of relative risk of predation to age-0 rainbow trout Oncorhynchus mykiss over 2 years in five lakes that varied widely in the abundance of piscivorous rainbow trout. During the day, the most risky habitats were just above the thermocline near the substrate and in open water at the same depth. Risk was intermediate at the surface in the littoral zone and at the surface over the intersection of the thermocline and the lake bottom. The least risky habitat was at the surface in the open water. The intensity and spatial pattern of relative predation risk changed at dusk. The most risky habitat was still at the thermocline–lake bottom intersection, but it was more than twice as risky as during the day. At dusk, relative predation risk increased in the littoral zone and at the surface above the thermocline–lake bottom intersection. The open-water habitats, both at the surface and at the thermocline, had a low relative predation risk. Age-0 and o...

Failure of Submersed Macrophytes to Provide Cover for Rainbow Trout throughout Their First Winter in the Henrys Fork of the Snake River, Idaho

Abstract Submersed aquatic plants that are abundant in some stream reaches have a potential to provide winter concealment cover for juvenile salmonids. We monitored an index of macrophyte abundance in a portion of the Henrys Fork of the Snake River during two winters that differed in severity and assessed the densities of age-0 rainbow trout Oncorhynchus mykiss associated with the macrophytes. The macrophyte index averaged 84–87%, in November 1989 and 1992, and an average of 10–13 fish/100 m2 were concealed there. In 1990, macrophyte cover declined to 59% in January and 46% in early February; fish density declined by about one-third by January and dropped to nearly zero in February. In 1992–1993, the macrophyte index declined to an average of 39% following anchor ice formation in December and to 32% in January. Fish density in December was reduced to about half of the November density and to about 1 fish/100 m2 in January. Movement of marked fish in 1989–1990 was predominantly from macrophytes into cobble...