Fishing vessels were decommissioned from the late 1980's onwards, and their licences were sold to Spanish owners, amongst others, with the British skipper signing on to the crew so that the licence could be validated.
Inshore vessels, often going for shellfish, sprats or mackerel were arbitrarily decommissioned by size and length overall. This gave rise to some boats just over the prescribed dimensions having parts of their bows or sterns hacked off just so that the owner/skipper could carry on earning a living.
Nets and gear were also closely monitored for mesh sizes etc, and any landings would be inspected by Fisheries officials. This gave rise to large catches being thrown away because they were over quota. Trawled mackerel were generally rejected, although catches taken on hooks and feathers were OK.
I know, I was there. I couldn't restore my boat to trawling because she fell outside the size restrictions, so I went lining instead.
It was hardly a well thought out or organised policy. One trawler owner said he was going to have some signs made up so that he could hang them on his trawl doors warning any fish under quota restrictions to swim off somewhere else so that he wouldn't have to throw them away if they got into his nets.