Browsing by Subject "Brown trout"

Agnico Eagle Ltd. gold mine in Kittilä, Northern Finland has released treated process and dry-ing waters into River Loukinen since December 2020. The effects of incoming mine discharge waters to brown trout behavior and movements in the river were studied for the first time in 2021. The monitoring was repeated in 2023 according to the terms of the environmental permit. The results of the 2023 study were used in this master’s thesis for determining whether the mine discharge waters affect brown trout behavior by causing avoidance of the area, migration hindrance, or changes in movement activity in the vicinity of the discharge pipe. Electrical con-ductivity (EC) was used as an indicator of the water quality changes caused by the discharge water. Twenty brown trout equipped with external transmitters were released at the site of the discharge water pipe in River Loukinen. Fish movements were tracked for 49 days in August - October 2023 with 11 stationary receivers and occasional location of individual fish with a hand-held receiver while boating in the river. Observation of bypasses and fish movement activity were specifically targeted within the discharge area by mounting several receivers in the vicinity of the pipe. Water quality of the river was monitored above and below the discharge pipe, to determine the level of impact of the discharge waters on river water and its possible effects on fish behavior. The river area below the discharge pipe seemed to be favorable habitat for brown trout with moderate flow rate and heterogenous bottom. Several individuals spent long periods below the discharge pipe regardless of the continuous EC impact of the discharge waters. Many of the monitored brown trout moved widely in the river and even to the main river (11 km downstream) yet returning to the vicinity of the discharge pipe. The results indicate no evident disadvantage or altered behavior of brown trout even under the direct influence of mine discharge waters. However, there was some indication of lower movement activity during periods of higher or increasing EC and decreasing river flow, but this is most likely due to the observed strong negative correlation between flow and EC. Increasing river flow is generally known to enhance fish movement. Even if the EC measurements downstream of the discharge pipe were higher than the natural EC of the river, studied brown trout seemed to behave in a species-typical way considering the habitat preferences and seasonal variations, and the mine discharge waters showed no clear impact on fish movements.