“Matching the hatch” is a phrase often kicked around in the fishing world, especially among trout-fishing enthusiasts. The expression comes from the fly-fisherman’s attempts to imitate natural insects with artificial imitations in order to fool fish. Since trout can key in on certain menu items when they are available – and will often ignore all others – getting familiar with the bugs that are present in a stream at the moment you’re fishing can bring you one step closer to your goal of catching.
Cold-water streams are loaded with trout food in various stages of their life cycles, and you don’t need a PhD in entomology to figure out what most of them are. Simple tools and techniques can reveal this underwater world and help anglers get around trout lockjaw. Basic streamside sampling can help cut down guesswork and give you a short list of viable offerings to try to replicate.
It is no secret that trout do the majority of their feeding subsurface; most literature agrees that it constitutes about 90% of their diet. To take advantage of this, many fly anglers use techniques to mimic aquatic insects in their larvae, pupae, or nymph stages. If you have ever seen flashes beaming from your favorite riffle, that could be a sign of trout rolling in and out of their lanes to feed on nymphs tumbling downstream. If you have ever noticed small boils just under the water’s surface, that could be an indication of trout taking emerging pupae or nymphs. A quick stream sample can fill you in on exactly what these trout are gorging on.
It is a good idea to conduct a stream sample before you start fishing. Doing so keeps you from whipping the water with an imitation that the trout aren’t interested in. An excellent sample area to start with is one that is shallow and well oxygenated, with a gravel bottom. Different aquatic insects prefer different water and substrate types, but riffles, or the heads of runs, usually have plenty of trout food for collecting.
The simplest form of streamside sampling is done by picking up and looking at submerged rocks. Choose cobblestone-sized rocks that are easy to lift. Under close inspection, you will find that most rocks have a number of insects crawling or clinging to their underside. Take one of the insects and examine it in the palm of your hand. Right off the bat, even if you don’t know what type of insect it is, you can see its size, color and profile. Already you have a starting point, as long as you have a decent match in your fly box. Do this for each different insect found on the rock. Keep in mind that just because one type of bug is predominant in the sample, it doesn’t exactly mean that’s what the trout are keyed in on – it may take some trial and error. After examination, let the little buggers go and replace the rocks as you found them.
A more thorough stream sample can be taken by a method called seining. A seine net is an effective and inexpensive tool that won’t take up too much room in your vest or chest pack. They can be purchased at your local fly shop for usually around $20. An angler’s landing net can be used as a substitute, as long as the mesh holes have small enough diameters to not allow tiny insects to pass through during sampling. A handy person can even craft their own seine net at home by cutting a flexible window screen to size and attaching two wooden dowels. The one I use, a Wind River Handi-Seine, is made from pliable screen material that rolls up nicely for storage. On either end are sleeves from which extend wooden handles. In the middle of the dark net is a painted white circle, which serves as a visual aid while identifying your sample. The whole package weighs only two ounces.
For a good seining location, walk upstream from where you plan to fish, so as not to spook any feeding trout. If alone, stand in a shallow, rocky riffle facing downstream. Place your seine net snug to the stream bottom. Using your feet, shuffle the rocks and gravel upstream of your net. The shuffling motion will dislodge aquatic insects from the rocks and the flow of the water should guide them into your net. If you’re with a partner, stand just downstream holding the net and have them kick up your sample. After a few seconds of this, take the seine net to the stream bank and begin scanning for food items.
A more direct way of finding out what trout are feeding on is to use a stomach pump. If done properly, this can be a harmless way of inspecting a trout’s stomach contents. However, if done incorrectly, this sampling method can hurt fish, so practicing first on trout coming home for dinner is recommended. For catch-and-release anglers, try practicing on recently stocked trout rather than a wild or holdover specimen. It may take a bit of practice getting used to, but once mastered, a stomach pump is a worthy streamside companion. While a single seine sample can reveal dozens of food options, a stomach pump can cut out some guessing by showing exactly what trout are eating. And like a seine net, a stomach pump can be purchased cheaply from your local fly shop and can fit nicely in your vest or chest pack.
The first step in stomach pumping is to successfully land a trout with a net. After doing so, keep the fish submerged in the net while readying the pump. Next, stick the long end of the pump under the water’s surface and lightly squeeze the bulb to allow some water in. Then gently glide the tube into the trout’s throat. In one fluid motion, compress the bulb and let it fill back up. This step should shoot water into the trout’s throat and suck it back in, along with any contents. Next, carefully remove the tube and revive the fish before releasing it. After that, discharge the stomach contents into the palm of your hand. Some of the food may be partially digested, but under close inspection, it can usually be determined what the trout has been snacking on.
While learning what food options are available to trout can certainly give you a leg up, it does not guarantee them in your net. Even if you figure out what trout are fixated on, you still have to present your offering in a natural manner. Most anglers will admit that presentation most always trumps imitation. In some situations there is so much food to be had that your imitation is a needle in a haystack. A slight modification to your pattern, like adding flash or a hot spot – a brightly colored bead or thread – can be all the difference in triggering a strike.
There is a dizzying array of aquatic insects that can be collected while sampling. The amount and type of insects will vary throughout the calendar year and from stream to stream too. There is an impressive amount of information written about aquatic insects and the imitations used to mimic them. One that I prefer to all others because of its geographic relevancy is Thomas Ames, Jr.’s Hatch Guide for New England Streams. A point-and-shoot camera with a good macro setting can be used to capture images of your samples, which can be brought back to your fly-tying desk or to your local fly shop. Samples can also be preserved in glass vials to study them further. Grain alcohol can be used as a preservative, or a product like Wind River Bug Balmer, which has special ingredients to maintain the true colors of most aquatic insects.
There are certain times when trout in a feeding frenzy will eat almost anything you throw at them. Then there are also situations where trout are obviously gorging on something, yet you can’t buy a hit. Those are the instances where stream sampling can make the difference between a “skunk” and a successful trip. Plain and simple, brushing up on your entomology and taking stream samples can help make you a better trout fisherman and fly tier. The next time you are on the stream, take a few minutes to see what’s on the menu.