| dc.description.abstract | To evaluate the recent efforts to better the conditions for migrating Atlantic salmon (Salmo salar) seeking spawning areas in the upper reaches of Skienselva River watershed. 75 salmon were tagged between 24. June and 15. July 2021. And tracked regularly throughout the season using radio telemetry. Improving the fishway at the hydropower plant Skotfoss, has proven worthwhile, as the proportion of salmon successfully crossing this manmade obstacle, has significantly increased from 16 percent of tagged salmon in 2020 (n=60), to 52 percent in 2021 (n=69). But despite the improvements, salmon are still significantly delayed during their initial steady upstream migration by 29.5 days (Min=2 days, Max=92 days, SD ± 22.2 days). After the ascend, 20 salmon (41%) showed varying degree of motivation to enter their eventual spawning system and spent mean 24 days holding in other systems. Sauar held the largest proportion of these undecisive salmon (n= 15). These 15 salmon either spawned in Heddøla R. (n=7) or Bøelva R. (=8) spending a mean 23 days before continuing their migration, time spend in Sauar R. seems influenced by how fast salmon cross Skotfoss. All salmon were present in their spawning tributaries within the first week of October, the factors driving this motivation to migrate further and why salmon spent so much time in Sauar R. is undisclosed. Salmon in Heddøla R. and Bøelva R. are estimated to spawn in October as their positions are significantly more aggregated compared to November where salmon seem to segregate and leave the spawning areas, seeking a suitable holding spot for overwintering. Only one salmon is observed to initiate the downstream migration towards marine habitat, the rest are believed to overwinter in suitable areas within their rivers or migrate to the larger lacustrine areas like Heddalsvatnet L. or Norsjø L. 6 salmon was present in Sauar R. during the high-resolution tracking period to study the external factors affecting spawning behavior, in the period from 12. October to 12. December 2021. 4 of the 6 salmon present in Sauar R. either expulsed their tag or succumb to a mortal fate in late September or early October. Data from this period is based on observations on external driving factors from two individuals (nobservations =142). We found that the two Active salmon moved less as temperatures fell (rho=-0.357, P-value < 0.0001) and moved less as discharge increased (rho= -0.223, P-value = 0.002). Depth was influenced by both temperature (rho=-0.672 P value < 0.001) and discharge (rho= 0.249 P-value < 0.002). Light intensity didn’t significantly influence behavior nor were there any significant differences in behavior between day and night (Light/No Light), however a visual pattern is indicating a diurnal pattern throughout the period. Unconsciously tracking on four dead fish or expulsed transmitters, provided an estimated error of the tracking method used, to be (Min = 0.74, Max = 67.23, Median = 7.48, IQR = 6.99, SD ± 7.29 meters nobservations = 302). | |