Egg stocking is a common method of re-establishing brown trout (Salmo trutta) populations, while the outcomes have been shown to give different results depending on variations in methods and locations. More recently, the dispersal of yearlings has been studied, but research on intraspecific interactions after egg stocking and the optimal number of eggs stocked are less studied. The aim of this study was to increase the understanding of stocking of egg methodology and how competition from older trout affect the resulting density of yearling trout. This was done to contribute to an optimization of growth and survival of trout from egg stockings. The study was based on data on egg stocking numbers and density estimates of young trout from electrofishing surveys in Rotälven, a tributary to Österdalälven, Dalarna County. Egg stocking has taken place from 2018 and onwards with a continuous increase in numbers from 84,000 to 1.35 million eggs per year. Here I studied eleven approximately 1000 m stream sections that had been sampled for surviving yearlings of trout from egg stockings in each section located in the main channel of Rotälven. There was a difference in the density of yearlings on the side of the river where the egg was stocked compared to the opposite side. On the other hand, there was no difference in the density of yearlings in the section where 100,000 eggs were stocked compared to the section where 50 000 were stocked. Furthermore, there was no correlation between the density of yearlings and older fish density in the study sections or in different stream velocities. Furthermore, was there neither any correlation between average length of yearlings nor densities of different ages of trout. These findings could contribute to an optimized stocking of egg through increased understanding of competition between year classes and stocking of egg methodology.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:umu-212530 |
| Date | January 2023 |
| Creators | Rode, David |
| Publisher | Umeå universitet, Institutionen för ekologi, miljö och geovetenskap |
| Source Sets | DiVA Archive at Upsalla University |
| Language | Swedish |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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