you should fish the drowes then. prawn/shrimp only gets a good amount of fish when march comes in for some reason, just when the water warms up a wee bit more. i suppose with a rise in water temp they will be more active and therefore aggressive to a shrimp! thats only my wee theory and maybe not fact.
another place where you can fish prawn is on parts of the moy and blackwater. have a look at these rivers for march/april and you will be in with a chance.
by the way, as you are only new to salmon fishing, keep trying different methods as you could find out that you like to fish say, spinner or worm better than prawn. or maybe even fly if you had a notion to start it. either way, just keep your options open and dont restrict yourself to just one method, it may not always suit