Watch the slack, tip up, tip up, now strip, tip up, and lift – set, set… Ok now re-cast.
Managing slack line is crucial to many things fly fishing. Setting the hook, is one of the most important times this comes into play. Fly fishing for trout with flies is not like bait fishing; especially nymph fishing. You are not going to feel a bunch of taps on your line like when a trout gobbles a worm. In fact you are not going to feel it all.
This is why we use objects or marks on our leader – to provide visual representation for what’s going on down below. The point is trout hit and spit the fly so quickly that you get but a mirco-second chance to connect. By the way that’s one of the reasons I do this, because catching fish with worms became too easy; I was looking for new challenges. Never mind that I was eight when this occurred.
Regarding the hook set. If you have too much slack in your line you decrease your chances drastically. For example, if I have five feet of slack in my line, I will need to eliminate it before the hook has a chance to penetrate. Five feet requires me to hold my line at a fixed length and lift the rod approximately five feet, strip five feet of line in, or both. Think about it. So there is a balance between a drag-free drift and too much slack for setting the hook. Of course, there are a ton of exceptions and this is only a generalization but a good one to know and understand.
Manage your slack to catch more fish.