Utvärdering av rörelsemönster hos öring (Salmo trutta) utifrån otolitmikrokemi

Sammanfattning: The classic view of trout (Salmo trutta) life history is that trout begins its life in freshwater, migrates to the ocean after about 1-4 years and then returns to freshwater to spawn. As trout fry have been caught at the mouth of the River Emån, near the Baltic Sea, researchers have speculated that some trout emigrate during their first year of life. The purpose of this study was to describe the variation in the length of time trout reside in freshwater before they migrate to the ocean for the first time. Another purpose was to investigate whether it was possible to discern where and how long the fish spent in freshwater and saltwater during different parts of their lives. Between 2007 and 2009, 23 adult trout were captured in the River Emån in southeastern Sweden. From each fish, a microchemical analysis of the sagitta otolith was conducted. The analysis focused on measuring the ratio of strontium:calcium from the center of the otolith to its outer edge at 6μm intervals. Based on this analysis, I found that 26% of the trout in the population emigrated to sea before they had reached the age of one. The largest proportion (48%) of trout emigrated between 1 to 2 years of age. The results of my study indicated that there was a significant correlation between age and the number of times that the fish remained in freshwater. I also analyzed the ratio of zinc:calcium and manganese:calcium. The analysis of zinc showed annual fluctuations, including a high value during the fish's first year and a seasonal pattern, with higher values of Zn:Ca in spring and summer. My results also showed some variation of the trace element manganese, half of the fish showed a peak in their first year. The results of this study indicate that by analyzing the concentrations of trace elements in otoliths one can describe individual variation in brown trout movement patterns and life history.