Hi Rex - welcome to the forum.
Good to hear that you got into kayak fishing. It's the most exciting way to fish
I never have problems with seals where I fish so wouldn't know how to keep them at bay. Probably best to fish a bit further away from their beach/rocks.
As for bigger fish - what size of fish are we talking about?
I find its easier to bring bigger fish into the yak than small ones. They tend to stay calm once the fight is over. Smaller fish are all over the yak if you're not careful.
The biggest fish I catch are around 1 meter long king fish or 40 - 60 cm long snapper.
I guess salmon and cod are of similar size so should be easy to land them in the yak with either a big net or gaff and then kill them quickly.
If people concentrated on the really important things in life, there'd be a shortage of fishing poles.