Rainbow Trout Oncorhynchus mykiss in the Austrian Alps - a Long-Term Data Series of a Self-Sustaining Population

Rainbow trout (Oncorhynchus mykiss) was introduced to Austria in 1885. Despite decades of intensive stocking the first natural recruits were found in 1974. Today, self-sustaining populations are found in most bioregions of Austria. YOY abundances classify calcareous regions to be the areas of the highest reproductive success. In this study we present long-term monitoring data of a 4^th order Austrian Alpine river, draining from a limestone region.

Rainbow trout were stocked into the Ois River until 1996. Since then the stock relies on a self-sustaining population occurring in sympatry with brown trout (Salmo trutta) and grayling (Thymallus thymallus). Apart from fluctuations, brown trout dominate (65 %) over rainbow trout (30 %) and grayling (5 %) in the average percental distribution of the 18 years’ time series. For rainbow trout as for brown trout the relative proportion of recruits to adult fish varies among years; compared to brown trout the total biomass of rainbows shows less fluctuation in the respective time period. Along with a lower average maximum age the yearly growth rate of rainbows was proven to be higher than that of brown trouts.