Sea Trout or Salmon?

Sea Trout or Salmon? 

Sea Trout, River Maine & Brown Flesk, 2018

So caught this fish today and at first taught it was a Salmon. I admit I was rushing and I did think at the time it was quite small for a Salmon at this time of the year. So when the pics went online it wasn' long before I realised it was a Sea Trout!