This is something I've been asked to write about; yes, I do that too sometimes. Although not very often of course and I really wanted to write about the double-handed dildo I've been fluff-chucking about but I'll do that some other time. So that's something to look forward to.
The first thing you should know about fly selection is that it's based around either one of two principles.
Principle no 1: fish eat and our flies should represent either something which looks like what they are currently eating or else something which looks edible. If your artificial flies closely imitate the naturals then they are said to be imitative. If they are pretty scruffy and non-descript they are said to be suggestive.
Principle no 2: fish will not only take flies because they want to eat them, they can also be induced to take a fly through some sort of built-in response mechanism – in a similar way you can trigger a cat to leap at your flyline while practicing your loops, Emma. These flies are generally quite colourful and are best tied while stoned. As a tactic for trout this is best used in moderation since it can spook (scare) the fish when it doesn't work. In the case of salmon in freshwater this is pretty much all you've got since these fish aren't eating.
So let's complete principle no 2. When the fish aren't eating you can sometimes trigger the response by pulling a bright attractor fly in front of them. It's also quite possible to induce a take with an imitative fly (by moving it) but fly section here is usually based around colour. If this was all there was to flyfishing then it would be pretty dull. Carry an orange dob-nobbler in your box by all means but only use it when you want people to think you're a jerk.
Back to feeding fish, because this is what we're most interested in. Here in New Zealand – with regards to fly selection – there are three types of fisheries. There is the backcountry river, there are the lakes and there are lowland waters (which include spring creeks and farmland rivers such as the Mataura).
Fly selection in the backcountry is simple. There's not much aquatic variety here and what there is is either stonefly (large prehistoric-looking aquatic insects which hatch to become hard-winged insects), caddis/sedge (moth like insects but with a water-birth, long antennae and hairy wings as opposed to scaly wings), upwinged/mayfly (quite beautiful insects which look like miniature sailboats when they hatch) and terrestrial (land based) insects such as Cicadae and green beetles.
Anyway all you need is a Royal Wulff.
Fish two flies. A size 10 Royal Wulff / yellow Humpy / Adams as your dry fly and then, below it, a size 10 pheasant tail nymph. Early in the season you may need a larger heavier nymph (size 8). Later in the season a smaller one (size 16). Sometimes during early season a good tactic is to use three flies; Royal Wulff with a pheasant tail nymph tied 4 or 5 feet behind with a #16 nymph trailing 12 inches beyond this. This is for when the fish want the small fly quite deep and the Royal Wulff allows you to time the strike (cos it disappears).
Instead of a pheasant tail you may want a hare and copper – which is more of a tradition here.
For the vast majority of backcountry fishing this is all you'll ever need, which makes life simple. Very occasionally it doesn't work in which case you have to pay close attention to what the fish are doing. If they are feeding then you have to work out on what. Check to see what insects are appearing on the water. You'll have to work this bit out by yourself, making it more satisfying when it happens.
Although you can fish exactly the same methods as for backcountry rivers I don't do this since I believe that there are more effective methods. The fish are eating caddis, midge pupa and freshwater shrimp, I guess, but like in the backcountry, they are quite opportunistic. Fly size and presentation are of greater importance than pattern – unless they are on sedges or green beetle.
I have three methods and flies for each. The first technique is to use a fly which is best fished while pulled/moved. My number one fly for this is a damsel nymph. Quite often fish will follow the fly and only take when you pause the retrieve – so that's important to remember. At night I do exactly the same thing but with a black woolly bugger. Occasionally I'll fish a muddler on the top dropper and a damsel on the point. It's a sort of induced take and a great technique for blind-fishing (fishing the water, in hope - hang on; searching the water).
During the day, especially after the fish have seen a fly or two, the trout will simply not take the damsel. There are two other methods: nymph fished either free-fall or else twitched along the bottom. You must go fairly small for this; say size 14 or 16. A hare and copper is perfect.
The third method is to fish one, two or three dry flies. Low floating dry flies are great. I use Bob's Bits and Shipman's, not that you'll find either of those in NZ. Pretty much any emerger flies will do. Just cast in front of the fish so that the fish gets to find the flies on his own.
Although the fish are generally more selective here I actually use less patterns. The fish often rise to small mayflies (they call everything in New Zealand a mayfly - it's that sort of country) and I'd be happy with any dark CDC emerger on a size 16 or 18 hook (I'm that sort of angler). Occasionally you'll want a size 16 or 18 nymph (I'm thinking lower Mataura here) or a size 14(ish) sedge. But mostly it's size which matters most and for once we're talking small.
So here you go:
Royal Wulff, Humpy, Adams (size 10) and if you have to pick one then choose the Wulff.
Pheasant Tail nymph #10
Hare and Copper #10
Tungsten bead nymph #16, #18
Deer hair sedge #10, #14
Damsel nymph #10
CDC emerger #16
Black woolly bugger.
Ps all fly patterns can be found in the exciting Member's Section.