What is tail-nipping?
Tail-nipping is the name given to the phenomenon whereby trout are perceived to be nipping at the tail of the fly, rather than engulfing the whole thing. This is assumed by the tell-tale plucks on the line and an inability to hook the fish. It tends to affect long marabou lures most of all and can be seriously frustrating.
Why do trout tail-nip?
First of all, tail-nipping is really just an assumption. Unless you're fishing crystal clear water and can genuinely see that the trout are only nipping the tail of the fly, something else might actually be happening.
Sometimes trout chase so fast that they're able to swallow and spit out a fly way faster than you're able to feel it, and that subtle sensation is often misjudged as tail-nipping. You see this a lot when fishing crystal clear stillwaters.
However, there are also times when trout are just a bit more cautious and simply nip at the tail, rather than taking the whole fly into their mouth.
Basically, something is either causing the trout to not smash the fly confidently, or it's causing the fish to eat it and then immediately spit it out. You need to make adjustments to figure it out.
Is it a bad sign?
While it's frustrating, I'd much rather experience tail-nipping than get no bites at all. Something about your fly or retrieve is getting the fish to bite. All you need to do is get them to bite with a bit more gusto to give you enough time to hook them.
What methods can I try to reduce tail-nipping?
Make the tail shorter
This is often one of the first techniques people try. It will either stop the bites coming altogether (often it's the sinuous movements of the trailing marabou which is attracting the fish) or it will increase the solidity of bites and your hook up rate.
Mix up your retrieve
Instead of stripping back your lure with the same kind of retrieve all day, mix things up. Add some pauses, figure of eight for a while, and throw in some long gentle draws. The change of speed is often enough to change the behaviour of the trout enough for it to swallow the fly.
Stop when you get a nip
When you get another nip, stop your retrieve. The fly will drop back down to the lake bed and the fish has got two options - ignore it and swim off, or have an easy lunch. It takes some guts to do this, but it can work better than continuing the retrieve in many cases. They'll often smash it on the drop.
Speed up your retrieve
If the other options don't work, the last resort is to increase your retrieve speed. You might need to swop to an intermediate or slow sinking line to keep your flies at the same depth, but if you strip back much faster, or even use a roly-poly retrieve, the fish will get less thinking time as the fly whizzes past.