In Norway, scientists found that salmon which had suffered any of the following:
"The purpose of the study was to collect information on angling procedures and the effects of hook and release on Atlantic salmon in the River Alta, northern Norway, covering both grilse and multi-sea-winter salmon in a non-artificial setting with real anglers."
ANGLING HARM CAUSES STRESS AND UNNATURAL BEHAVIOUR
"Behaviour after release seemed to be affected by hook and release. ... Increased playing time, increased number of runs during the angling event, hooking in the throat, bleeding at the hook wound, increased handling time, air exposure and water temperature were factors that affected hooked and released Atlantic salmon negatively, either indicated by a poor condition at release, increased stress levels or unnatural behaviour after release.
INCREASED CHANCE OF DEATH
"All these variables have been shown to increase mortality in other fish species."