I usually find that my problem isn’t my fly, but rather where (depth, seam, pocket, etc), or how (twitch, dead drift, swim). So most of the time I change flies it is to switch from nymph or dry.
I usually change “something” every 20-30 minutes… amount of split shot, position of strike indicator (assuming I’m fishing the same type and depth of water, otherwise I make an adjustment as soon as I switch holes), or flies. If I’m fishing dries, then I switch after about my 3rd or 4th refusal.
after about 3 passes and no fish in the same area … but that’s 3 passes multiplied by the number of places from your casting position … seams, surface, bottom, weeds, structure, varying retrieves … danged it - I hate to say it - but … depends on the water, weather, fly.
but - like taoski noted - its about every 20 mintues I change something on the line
To minimize the number of changes I spend the first 15 minutes to 1/2 hour of my fishing ritual studying the insect in and around the water. I will do this at different times of the day to best understand what the fish are feeding on. But, there are those times when nothing seems to work and in addition to changing flies frequently, I have to tie on more tippet as well. :x
Its actually the last change I usually make. Assuming you make even a semi-educated guess on what the fish are feeding on…and there is not a huge hatch going off. For me its depth, angle of approach, and presentation. Then I will usually switch sizes. After that its the fly itself.
I agree that presentation is key above just about anything else, but that is subjective too. I tend to stick with the same 5 or six flies no matter what and that has always worked for me. I think many tyers and anglers tend to get a little caught up in having the exact match for species/sub-species and having the most variety of flies in the box. I use the classic, tried and tested flies that may not be as specific in their imitations (i.e humpy, hare’s ear, pheasant tail). If fish aren’t hitting the classics that usually produce on the water, then the presentation and location need to be changed before the fly does.
The middle and lower sections of the Provo river in Utah are a perfect example of this. Hare’s ear, Pheasant tail, bugger, caddis, BWO. You don’t need any other flies all year long. Just change the presentation.
Since everything is kind of new to me I usually start out with a fly pattern I have never tried. If I cannot get anything working then I usually turn to a Hare’s ear or pheasant tail and grind it out. When fishing with dries I usually just bounce around until I find what is working. I still have not fished dries enough to know why a fly is working and others are not. I need to get better at my bugology.
I do the same than GBF.
Regarding the “after how long you change a fly”…well let’s say that I take the chance to change the fly when the trees eat them… I have to tye another one anyway… :roll:
If the fish are rising but NOT to my presentation/fly, it’s obvious to me I have to change something. If, however, there are NO rises at all but the seam etc looks promising I sometimes beat the water to a froth trying to entice a fish to rise to/eat my offering. " Common fishy, eat it, it’s good for you". As you can probably deduce, I do a whole lot more fishin than catchin.
There have been times during a masking hatch that I’ve changed flies after only a minute or two. If I hit the hatch on the head I’ve fished the same fly for hours.