Predicting a Trout's Feeding Habits

Rich trout streams have a steady, constant food supply. At the height of the richness scale are spring creeks, which differ little throughout the world. The Le Tort in Pennsylvania, Armstrong's in Montana, and the Test in England have virtually the same food supply as spring creeks in Argentina and New Zealand. Twelve months a year the fish feed on midge pupae, small Blue-Winged Olive nymphs, scuds, and sow bugs. I grew up fishing a small spring creek in upstate New York, and the fly box I used when fishing this stream has served me well on spring creeks elsewhere. Although, if I fish a spring creek in midsummer, I add a couple of ant and beetle patterns, for the most part I can use the same half-dozen patterns in November or April.

A "collector" on the lower Henry's Fork in Idaho, similar to those on the Missouri.

Medium-rich streams like the Beaverkill, the Madison, or the Battenkill lack the constant water temperature and water level of spring creeks, but they still offer trout an almost endless buffet. The difference is that the kind of food changes throughout the season, and a nymph that trout climb all over in late April may be ignored in July. If I planned to fish a medium-rich trout stream like the Deschutes in Oregon, a river that I've never seen but hope to someday, I would not have the same confidence in the contents of my fly box, and I'd have to read up on the river, hire a guide, or stop in to a local fly shop before I chose my flies.

Relatively infertile streams offer a small and inconsistent food supply. Think of the upland brooks or mountain streams you have fished â?? the bouldery kind common in New Hampshire, North Carolina, Vermont, Montana, or California. Or imagine one of those boggy, tea-colored streams punctuated with beaver ponds that run through the lowlands of Maine, Michigan, and Wisconsin. Infertile streams are usually smaller â?? larger rivers run through wider valleys and pick up nutrients from rich bottomland sediments. If a larger river runs through rocky canyons, however, it too may offer a sparse food supply. Examples would be the Gallatin in Montana, the Ausable in the Adirondacks, or the Penobscot in Maine. It can be argued that the Ausable or the Gallatin offers good hatches for the fisherman, but the day-to-day food supply, the stuff that puts inches around a trout's waist, is not as abundant as in rivers that flow through more fertile valleys.

The bad news is that you'll have trouble predicting what kinds of food are prevalent in an unfamiliar infertile stream. The good news is you probably won't have to. Further good news is that the flies you can get away with will be larger. Trout in infertile rivers don't have the luxury of being selective, because they don't see enough of anyone insect to get picky about which one they choose. Either they eat every piece of food that looks remotely edible or they starve. In most infertile rivers the quantity of aquatic insect larvae available to the fish by midsummer is insignificant, and they depend on terrestrial insects that fall into the water for a great part of their food. Since they never see many of the same kind of aquatic insects, and the terrestrials they feed on are a stew of all shapes, sizes, and colors (and we've seen in the last chapter that, all else being equal, trout prefer to eat the largest morsel of food available), all you have to do is turn over a few rocks or shake the bushes and decide what is the largest edible insect they are likely to recognize.

In more fertile rivers you have to pay greater attention to what's on the menu. The trout are used to seeing multiple foods at any given time, and although they are not usually selective to a given species of insect, most of their food falls into specific parameters of size, shape, and color. If you go outside of that realm, you won't draw as many strikes. Here the largest available food item might be rare enough that trout don't recognize it. In the Battenkill, for example, most of the nymphs are small, skinny, and brownish olive-dull. If you turn over enough rocks, though, you'll sometimes find a couple of those giant black stoneflies that trout go crazy over in the Rocky Mountains. I have tried size 6 stonefly nymphs in the Battenkill year after year, with never even a touch. Not only do the trout not eat them, I bet if I could look underwater I'd see them bolting for cover when that ugly nymph rolls into the neighborhood.

One of the most important clues you can get from eyeballing the richness of a river is a sense of how the trout are distributed. I've found that in richer rivers, smaller flies are more effective. I'm not exactly sure why. Perhaps it's because smaller insect life is more abundant, and the fish are more likely to take a fly that's similar to what they're eating, while the fish in an infertile stream grab almost anything that looks edible. On the Beaverkill in mid­June, blind-fishing during the middle of the day when hatches were sparse, I once had to go down to a size 18 caddis to catch trout even in the riffles. Big Wulffs, variants, and other attractor flies didn't even draw splashy refusals. I decided to explore a nearby tributary, which by the look of the water was nowhere near as rich as the Beaverkill. Tired of straining to see the tiny caddis, I put on a size 10 Ausable Wulff, more to enjoy watching the fly bouncing on the riffles than anything else. You know the rest of the story. In every pool there were a couple of trout eager to take the bushy fly as soon as it hit the water. This was less than a hundred yards from trout that wouldn't even look at a fly larger than a 16. Since that day I've noticed that on rich streams like the Bighorn or the Battenkill, I seldom do well blind-fishing with a fly larger than size 16 (except for streamers and during grasshopper time). On small streams or on rivers like the Ausable or the Gallatin, for between-hatch periods I can get away with size 10 or 12 nymphs and dries â?? although during hatches of smaller flies I still use the tiny stuff.

One of the most important clues you can get from eyeballing the richness of a river is a sense of how the trout are distributed. When you don't have the benefit of rising fish to tell you where they are, knowing where they should be saves you from fishing over unproductive water. There is nothing more frustrating than blind­fishing a piece of water, wondering if there are any trout at all underneath your fly. When I fish a stream I have never seen before and start to doubt the presence of trout anywhere near my fly, my confidence erodes and I lose concentration. As a result I can get sloppy about what I'm doing. If you know that feeling too, read on for a confidence booster.

The first time I fished the Missouri River was a lesson in the value of fishing water I would have passed up on other rivers. The Missouri is a productive tailwater, and its currents carry a rich soup of insect life all the time. Paul Roos, who was guiding my wife Margot and me, kept talking about looking for "collectors." At first I couldn't figure out what he was talking about, but Paul has guided on the Missouri for over twenty years, so I kept my eyes open and my mouth shut. When Paul finally pointed out a collector, I realized he meant the slow, barely swirling backwaters along the bank and behind islands in the river, where trout waited to collect flies that had drifted out of the main current. The trout could lie just under the surface without expending much energy because the currents were nearly imperceptible. Paul used the term 'collectors' to describe both the places and the fish, and we soon found ourselves gazing with intense concentration at water we wouldn't have given a second glance on other rivers. The Missouri is so rich fish can thrive on the extra food that peels off from the main current. I suspect that on the Missouri the bigger fish are found in the collectors: their energy expenditure is at a minimum, so they can grow bigger, faster.

Trout in rich rivers are evenly distributed, all over the place, because there is enough food to support them everywhere.There were trout in the main currents as well, but because we were fishing a Trico hatch it was easier to spot the trout in the slow water. There is no reason to think that if we were fishing blind the trout would not have been in the same spots. Trout in rich rivers are evenly distributed, all over the place, because there is enough food to support them everywhere. Even in shallow sloughs with a mud or sand bottom, spots that look more suitable for minnows or frogs, trout can be found. In fact I've noticed that large brown trout in spring creeks seem to prefer these places over the deeper channels. On the other hand, in infertile rivers trout distribution is spotty. They will not be found in backwaters because it might be an hour's wait for a piece of food to drift by, even at the height of a heavy hatch. So trout in rivers that aren't so rich frequent the logical spots, the places that scream for a well-placed cast with an Adams or Hare's Ear nymph. These logical places are the areas protected from the heaviest flow of water, but close enough to the main current so a sideways tip will allow trout to intercept food. At the edge of seams, at the tail of a pool, in front of and behind rocks, and where the head of the pool spills over a shelf-these are all logical places, and we'll talk more about them in the next chapter on stream reading.

Applying Richness to Your Fishing Strategies

This knowledge, then, can help you form a fishing strategy. On rich streams, cover all the water. Never assume that a trout won't be right in front of you, and concentrate on covering the water closest to you with repeated casts, changing flies or techniques often if you aren't getting any strikes. Armstrong's Spring Creek offers about a mile of water on the O'Hair Ranch, and they divide it among up to fifteen fishermen a day. One fifteenth of a mile of water seems like fishing in a closet until you get around a bend where you can't see any other fishermen and you stare at the water. If the trout are rising or it's sunny enough to see into the water, you won't ever want to move, unless you must stretch your legs. I've often wished that someone would tie me to a cattle stile and make me fish twenty feet of water on Armstrong's. I would be a better fisherman for the ordeal, and I would not be wanting for targets.

Trout in infertile rivers (top) will be found in the main flow, while those in rich streams (bottom) will be found throughout the channel, even in near-stagnant sloughs.

If you tied me to one of the hemlocks along Manchester Brook, though, I'd be ready to gnaw through the rope in five minutes. On infertile rivers, pass up much of the water, the stuff that doesn't look fishy. Move faster between spots, then concentrate hard on the best­looking water. You can also move faster on infertile rivers because the fish don't agonize over fly patterns â?? so neither should you. Trout in infertile rivers will move farther for a fly, so unerring casts are not as important here, and if your fly lands within a foot of where you think a trout is lying and floats drag-free (or swings properly if you're fishing a wet or streamer), make a few more casts and move on. I don't want to suggest that you get sloppy, but many times I have seen trout in unproductive streams move five feet for a dry fly. The only time a trout will move this far on a fertile river is when there are large, meaty flies like salmon flies (a huge, size 4 or 6 stonefly that hatches on western rivers) or grasshoppers on the water.

Remember I said I was going to give you some great excuses for getting skunked? Here's one that relates to the richness of a trout stream: In fertile rivers trout appear to feed in spurts, with periods in between when they seem uninterested in any food and can't be tempted with any fly. There are exceptions: although some biologists have observed these slack periods, Bob Bachman's Spruce Creek fish never stopped feeding in the daylight hours when he could see them. Generally speaking, however, there are slack feeding periods in rich streams â?? not only in winter or the early season, when nobody argues with the fact that trout feed for only a couple of hours when the temperature climbs above 50 degrees, but during the height of the season, when water temperatures are perfect and insects are in the drift all day long. In streams that aren't so rich trout feed even at high noon and in late afternoon (times when trout from richer waters most often take a siesta). Because they never get enough food, they are on the alert all the time. As we saw in the last chapter, though, trout learn to anticipate cycles of abundance, and trout in richer streams may be able to kick back for a couple of hours in the afternoon, knowing there will be a spinner fall in the evening.

If I'm fishing a biologically productive river like the Delaware or the Bighorn and I go without a strike for a couple of hours, I don't brood, because I know he trout will switch on later. (This is assuming I have confidence in the fly I've tied on and the way I'm fishing it.) But if I fish over two pools in an infertile river without a strike, I look for another explanation. The fly I've chosen may be so far off that the trout won't look at it or someone may have just fished through the pool and spooked all the fish. I may not be fishing the fly deep enough (often the case in high, cold water), or there may be no trout in these two pools. Another possibility is that I may have spooked the trout with clumsy wading and sloppy casts. In any case, if the situation arises, I either pack up and move, or sit on the bank and make adjustments to my tackle and my approach.

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