i have an intermediate line and a floating line, can I add a few split shot to the leader instead of buying a fast sinking line?
Yes I suppose so.. I do do put that on the leader above the fly when I do a certain kind of river nymphing. It mimics the action of a hatching caddis fly when used up stream and swung round in front of you and drawn to the surface.
It won't get you deep enough though for mackeral a lot of times. Okay if they are right on the surface but if they are deeper and you don't see surface action. You are limited.
A fish finder if you are on a boat is the easy way to locate them if they are any depth down, or if you don't have one another good way to find them is to feather with a normal boat rod setup. Mark the line were you contact them. That gives you an idea were the fish are and the depth. Or try boatcasting with an uptide type rod and featheres. Chuck it out and retreive it. Do it again and count to 5 then retrieve and so on in an arc. You will soon locate them if they are there. Or just good old fashioned spinning, doing the same thing. Once you locate fish It may be too deep for fly fishing. The line won't get down no matter what hi speed sinking line you put on.
Watch for bird activity, any fry that are being harried near the surface soon attract the Gulls. Sometimes you will see the fry jumping before the birds get wise. An intermediate or slow sink lines will work well in that situation. I would still get hold of a fast sink WF line though or use a shooting head fast sinker that will get to the fish's depth even quicker.
Fly fishing for mackeral from the shore is a bit more of a challenge. I have never got that one down with any guaranteed success. That's a real opportunists game. Just being there at the right time at the right venue with fish close enough is very difficult to get. Spinning lets you cover water quickly and at various depths/distances that the fly rod won't.