Rainbow Trout Abundance Research Articles

Relationship between Phytoplankton Volume and Rainbow Trout—Daphnia pulexInteractions after Phosphorus Inactivation, Medical Lake, Washington

ABSTRACT Fisheries and limnological investigations in post-restoration Medical Lake, Washington, suggest that establishing a successful rainbow trout Oncorhynchus mykiss fishery depends on the maintenance of a healthy Daphnia pulex population and that phytoplankton volume is related to interactions between rainbow trout and D. puluex. As rainbow trout abundance increases, D. pulex standing crop decreases. This change results in an increase in phytoplankton standing crop. Multiple regression analyses on eight years of data was used to determine the statistical relationship between rainbow trout—D. pulex interactions, total phosphorus levels, and phytoplankton volume. Seasonal variation in phytoplankton volume correlated more closely to rainbow trout—D. pulex interactions than did monthly variations in algal biomass. Accounting for the lag in response time between the independent variables and phytoplankton volume improved the percentage of explained variance. The results indicate that the variance in seaso...

Factors related to the distribution and abundance of brown and rainbow trout in New Zealand clear‐water rivers

Abstract Brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) populations at 157 riverine sites throughout New Zealand were divided into groups based on species, size, and abundance. The groups were examined to determine significant differences in hydrological, water quality, water temperature, biological, in‐stream habitat, and catchment variables between groups. A discriminant model was developed with nine environmental factors which correctly classified 72% of a subset of 65 sites. Fish species distribution was related to climatic (water temperature), geographical, and hydrological factors, whereas fish abundance was determined by factors relating to flow variability, river gradient, in‐stream habitat, and the presence of lakes in the catchment.

Response of Wild Rainbow (Salmo gairdneri) and Cutthroat Trout (S. clarki) to Stocked Rainbow Trout in Fertile and infertile Streams

Wild rainbow trout (Salmo gairdneri) and cutthroat trout (S. clarki) were unaffected by stocking of catchable-size rainbow trout in two Idaho streams, except at the highest stocking rates, and even then the effects were limited. In the infertile stream, stocking 50 or 150 trout per section (doubling or tripling the density) did not reduce the abundance of wild cutthroat trout. Wild trout abundance declined at a faster rate in an unreplicated section stocked with 500 trout than in unstocked sections. In the fertile stream, stocking 50 or 100 hatchery trout in sections containing 26–120 similar-sized wild trout did not increase the dispersion or reduce the abundance, growth, or survival rates of wild rainbow trout. When we stocked 400 trout (100 on four dates) in sections containing 32–53 tagged wild trout of similar size, the summer mortality rate of wild trout was higher in stocked than in unstocked sections; the other parameters were not significantly different.

Seasonal changes in abundance of brown trout (Salmo trutta) and rainbow trout (S. gairdnerii) assessed by drift diving in the Rangitikei River, New Zealand

Abstract Numbers and approximate sizes of brown trout (Salmo trutta L.) and rainbow trout (S. gairdnerii Richardson) were estimated by snorkel divers at 6 sites in the middle reaches of the Rangitikei River, North Island, New Zealand, over 14 months. The results showed that different species and sizes of trout varied in abundance with time. The species of fingerling trout (6–12 cm FL) could not be identified because of their small size and shoaling behaviour. Rainbow trout abundance varied seasonally and was greatest in January and April (between 18 and 60 fish per kilometre) when fish between 23 and 38 cm FL were the most abundant size class. Brown trout abundance showed much less variation with time (between 5 and 36 fish per kilometre at most sites). Also in contrast to rainbow trout, the majority of brown trout were > 38 cm FL, and in June, when the greatest density was observed (56 fish per kilometre), 70 redds were seen at the same site. Two sites were dived within a 48 h period to test the variabil...

Two-Year Cycles of Abundance of Age-0 Rainbow Trout in Lake Superior Tributaries

Abstract Two-year cycles of abundance of age-0 rainbow trout (Salmo gairdneri) occurred in two of five Michigan streams where annual population estimates were made in 1967–1974. The cause(s) was not determined, but the cycles could not be related to density of juvenile salmonids, abundance of spawners, meteorological conditions, or abiotic stream characteristics.