Effect of Tunnel Wash Water on Survival, Growth and Migration of Atlantic Salmon (Salmo salar) and Brown Trout (Salmo Salar) in River Årungselva

Tunnel wash water is frequently released to the river Årungselva through a sedimentation pond.\nThis tunnel wash water may cause harm to the fish through intrinsic and extrinsic toxic effects.\nA reduction in growth have previously been observed for 0+ brown trout at downstream\nlocations of the sedimentation pond, where fish located below outlet point of the sedimentation\npond had a 21 % lower length than fish located above the sedimentation pond. As no reduction\nin growth were observed prior to the establishment of the sedimentation pond, the author\nsuggested that the reduced growth could be due to the toxic effect from the tunnel wash water.\nSince migration and density was not accounted for, it remains enigmatic whether the observed\ndifference was solely due to the suggested toxic effect.\nThe aim of this study was to estimate differences in survival, growth and migration of Atlantic\nsalmon (Salmo salar) and brown trout (Salmo trutta) caught above and below the outlet point\nof the Vassum sedimentation pond in Årungselva.\nThe study was conducted using capture-mark-recapture methodology in combination with\nPassive Integrated Transponders (PIT) telemetry with two antennas. This set-up allowed for\nestimation of survival, individual growth and migration.\nIn total, 520 individuals were caught by electric fishing. Out of these, 253 individuals were PITtagged\nfrom which 75 were resighted at least once during the November 2014-October 2015\nstudy period. The results show a lower size-adjusted survival in both species for individuals\ncaught below the outlet point compared to those caught above the outlet point. Further, a lower\nlength-at age among 0+ parr of brown trout and 1+ parr of Atlantic salmon, as well as lower\nlength at first-winter for Atlantic salmon parr, were observed for below-individuals compared\nto above-individuals.\nThe reduced survival and growth rate observed in this study occur despite the fact that fish\ndensity is lower at below-sites of the outlet point of the sedimentation pond. Water chemistry\nvariables generally did not vary between above and below sites, apart from chloride, sulphate\nand uranium that all attained higher below-values. However, other physiochemical variables\nthat vary between above and below outlet point sites may influence growth and survival. In\nconclusion, fish at below-sites of the outlet point may experience a higher exposure to pollution\ndue to the release of tunnel wash water based on these results.