The main suspect at the moment is global warming - temperature of the Norwegian Sea seems to predict fish numbers. More fish are still in the north of Norway with many fewer the further south you go. It's a possibility that the UK may not see very many. These are Norway's numbers for fish caught - actual numbers are estimated at somewhere under 2 million in 2021I think the jury is out on that one, what I find difficult to understand is why this salmon is doing so well compared to the Atlantic salmon.
Numbers of Pinks caught in Norwegian rivers
Source: Berntsen, NINA
Massive growth there but we didn't see anything like that in the UK
Scotland 2017 139 fish, 2019 20 and 2021 169.