Monitoring capture stressors and behavioural responses in herring and mackerel during capture and release from purse seines to infer stress/welfare status /

Commercial purse seine fisheries off the coast of Norway target massive schools of herring and mackerel and surround them with nets. In the event of unwanted catch or too large of a school, fished a slipped through creating an opening in the net for fish to swim out of. This practice should be harmless but has shown to negatively impact fish welfare. The welfare status of fish during the capture and slipping process must be better understood to minimize negative impacts and post-release mortality in slipped fish. Through this first look at the entire process, very high crowding, a sign of poor welfare, was found at the discharge opening along with an increase in crowding over time and a link between increasing crowding levels and dropping oxygen levels. These findings agree with other research in this field and provide an understanding of what is happening over the course of the whole process. Suggestions to improve welfare during this process include stricter regulation around discharge opening size, training for crews in proper slipping methodology and development of tools to give feedback to fisherman of real-time welfare status of fish.Master of Science in Marine Biological Resources (IMBRSea)Commercial purse seine fisheries off the coast of Norway target massive schools of herring and mackerel and surround them with nets. In the event of unwanted catch or too large of a school, fished a slipped through creating an opening in the net for fish to swim out of. This practice should be harmless but has shown to negatively impact fish welfare. The welfare status of fish during the capture and slipping process must be better understood to minimize negative impacts and post-release mortality in slipped fish. Through this first look at the entire process, very high crowding, a sign of poor welfare, was found at the discharge opening along with an increase in crowding over time and a link between increasing crowding levels and dropping oxygen levels. These findings agree with other research in this field and provide an understanding of what is happening over the course of the whole process. Suggestions to improve welfare during this process include stricter regulation around discharge opening size, training for crews in proper slipping methodology and development of tools to give feedback to fisherman of real-time welfare status of fish