I’ve spent a lot of time thinking about this topic, and working hard on my casting skills to test a theory: casting matters. All of the great names in fly fishing credit casting. Presentation is much more technical than most fly fishers realize, and if you like to fish dry flies, it’s critical to your success. Presentation matters in wet fly, streamer and nymphing as well, but a drag free drift of a dry fly is what will be the focus of this post.
A brief discussion of trout vision: more detail in a later post, but start by understanding that trout live in a moving, watery world that provides a visual “window” on the air breathing world. That’s above the surface. This window is available to us as well! Simple exercise, next time you are in a swimming pool, submerge and look up. What you will observe will be a clear view of the world above the surface, the window size dependent on how deep you are in the pool. If you look up from just under the surface (and we presume the surface is reasonably smooth) the closer you are to the surface the smaller the window, the deeper the larger the window. There’s also the issue of refraction: you see more than just the light/images directly above the window, but that discussion can wait as well. For now it’s just important to understand that the trout can see items (natural insects and your fly!) with great clarity as they drift through the window (we’re talking about moving water, but the pool analogy will do for now).
Presuming you’ve made a good cast and your fly is in line with the feeding lane occupied by the trout you are pursuing, the fish has a very clear look at the fly, yours or a natural. Whether the trout is lying near the surface or in four feet of water, it has only moments, dictated by the speed of the current, to assess the item of interest and act to either try to eat it or ignore it. To lengthen this decision making opportunity the trout will use their pectoral and pelvic fins turned against the current to drift backward, extending the time the item is seen in the window.
What does trout vision have to do with casting skill? A lot!! Most dry fly fisherman rely on mending their line to extent the drag free drift. The problem is that even a very careful water mend is likely to move the fly, just a twitch, but enough to alert the trout that the object is not a natural, and the highly sensitive instincts for survival will put the trout off. Maybe not permanently, but at least for that moment. Lets say that your drag free drift is traveling for twelve to eighteen inches. Certainly reasonable and in many cases enough for the trout to react and take your fly. But what if you could extend your drag free drift for three to four FEET! A fish could back up in the current and examine the fly much longer. How does casting manage that? With the aerial mend.
The casting technique for aerial mends is not difficult, but it does require some practice. In its simplest form, the aerial mend is a hard stop of your forward cast, and adding line and rod movement so that two things happen: 1. Your fly continues on towards your target, and; 2. you feed line into the cast that you move left or right to create more slackline (called a reach cast) in response to the current challenges that exist between you and the line of drift to the fish you are paying attention to. You can also add a wiggle (interestingly enough called the wiggle cast) to give slack line in a run with multiple speed currents between you and the fish. The best videos I've seen on YouTube on aerial mends are by Carl McNeil <https://www.youtube.com/watch?v=14njsZy47qg>. Better yet, seek a good instructor to learn these casts and then practice, practice, practice! So, it’s not only tight lines.
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