Is it legal?

[Wildfisher]

To kill salmon or sea trout you catch in the sea whilst fishing for other species?

[Laxdale]

You can if you want, but you cannot retain it. Leave it dead on the beach or throw it off the boat.

[burnie]

This seems to say no to keeping a Salmon
Salmon in Coastal Waters
The Conservation of Salmon (Scotland) Regulations 2016 introduced legislation to protect declining salmon stocks by, amongst other things, prohibiting the retention of salmon caught in coastal waters. Compensation was paid to those active coastal fishermen who have been unable to fish for salmon due to the prohibition, for a 3 year period from 2016 to 2018 inclusive, while further research was undertaken to assess the long term position.  The Scottish Government paid £567,806.43 per annum in these three years. The list of recipients can be found online.

Following the assessment of the research done, and of the status of salmon stocks for 2019, the Scottish Government has determined that the prohibition on retaining salmon caught in coastal nets should remain in place.