Escape Volume 1

Guest Blogger: Joe Dellaria, Always Looking to Learn from the Rivers

I don’t know about you, but I prefer to catch big trout.

Not that I always do, but that is my mindset every time I hit the river. I keep a log to track what I catch big fish on and where. Over the years, a surprising theme has emerged; where I catch them is more important than what I catch them on. The bigger surprise is that many of the fish came in water less than 18” deep. In fact, several of the larger fish were in less than 10” of water!

This runs counter to my “fishing intuition.” So, I started thinking about why this might be true. It took several years and the following observations to “connect the dots” and realize that “escape volume” is an important concept for your fishing strategy.

Key Observations: The following observations were made over 3-4 years

  • Situation 1: I was fishing a streamer through a big pool. About halfway in I realized a nice trout was chasing the fly. It kept nipping at the fly but would not commit to taking it. I was getting pretty frustrated until my fly hit the steep sand bar just in front of where I was standing. Faster than I could say, “Look at that,” the trout inhaled the fly and the fight was on. It turned out to be a 15” beauty. While it was not a monster for those who fish out west, for this particular stream it was a trophy! Pretty Cool!
  • Situation 2: There was a pool I fished all season long. It just had that “fishy” look. It had to have a big fish in it but nothing showed repeatedly. Finally, I decided to be on the river before dawn. I put on a #4 beadhead wooly bugger and made my first cast. It was still dark enough that I could not see where the fly landed. I started retrieving after I heard the fly “plop” into the water. It only took a couple of strips before the fish took. I thought I had snagged the bottom and raised my rod to try to shake it free. Before I could shake the rod, the snag bolted upstream. This was my first truly big trout. Being inexperienced I kept increasing pressure on the fly reel spool figuring I could turn the fish. It only took a couple of second before I heard a snap like a 22 rifle being shot. The line went limp. Crap, I hate when that happens. The fish just broke a 2x tippet! I walked over to where the fish had taken the fly and the water was just barely over my ankles in depth. It might have been 8” deep – certainly not much more than that.
  • Situation 3: There is a massive hole way downstream from my usual parking spot. The locals call it the “Blue Hole” as the water is so deep it has a bluish tinge. I worked my way past the hole and went four more holes downstream to let the “Blue Hole” settle before I tried my hand at fishing it. As I worked my way back, I found a really nice run that was 3-4 feet deep that flowed into a pocket created by boulders at the end of the run. Working the fly down the run, I saw it come into view. To my amazement, a large trout was chasing the fly but not taking it. I kept stripping and wiggling the fly trying to induce the fish into a take. No dice, he just kept chasing. The fly reached the end and started to turn in the rock pocket. Once again in a lightning quick lunge, the fish attacked the fly and the fight was on. A fat 18” brown eventually came to net.

All three of these incidents share at least two common themes: 1) A larger than average fish was hooked, and 2) all three fish took the fly when it was presented in a very small space. This led me to conclude that big fish often strike most aggressively when they have reduced the available volume for their prey to escape. I like to call this a reduced “escape volume.”

I will explain this in more detail shortly, but first I have to say I am pretty sure I read about this concept back when I was a teenager. Try as I might, I cannot find where I saw this. So if you know where it has appeared before, please share that with me.

With that said, this is a concept that helps me prepare and be particularly focused when I see these opportunities present themselves. Here’s an easy way to see the concept. If you were playing tag with one other person, it would be much easier to tag the person in a 10 x10 foot square than in a 100 x 100 foot square. Bigger fish up their odds of feeding successfully by choosing feeding positions that reduce the size of the playing field.

Below is a figure that illustrates the concept in three dimensions:

Figure: Illustrating “Escape Volume”
Figure: Illustrating “Escape Volume”

You can see the forage fish in the upper drawing has much more space to escape. It has 27 cubic feet of “escape volume.” While the one in the lower drawing has only one cubic foot of “escape volume.” The minnow in the upper drawing is likely to escape; the one in the lower drawing should say its prayers, as it is likely to be eaten. As the escape volume decreases, the feeding success of the trout increases.

Now if we look back at the three situations at the beginning of the article, we can see how the trout reduced the escape volume before striking in each instance:

  • Situation 1: The trout reduced the escape volume by at least half by trapping the minnow against the sand bar. The fish did not strike until the fly hit the sand bar.
  • Situation 2: The trout was in about eight inches of water. A minnow would have fewer escape routes than if it were in 3 feet of water. The trout smashed the fly.
  • Situation 3: The trout waited to strike until the fly was “trapped” in a tight turn.

Understanding the “escape volume” concept helps me discover new spots where big fish are likely to feed. One such spot is just amazing. It is in the tailout of one of the deepest pools in my favorite river. There is one little pocket up tight against a rock wall. It is almost guaranteed to hold a 15-inch or bigger trout. If I get to it before sun up or just at sun goes down, the fish is likely to be approaching 20 or more inches. It is a dastardly cast. You have to get the fly under an overhanging tree and past a small rock pile standing in front of the spot. The rock pile is about 6-8 inches high above the water. If I snag my fly on the tree or rocks, I always break off the fly, as I am fairly certain there will be a nice trout there. The anticipation is almost unbearable when you make the cast, as the fish is holding in a two to three foot slot. You never know where it will be exactly. Most of the time I can see the wake as the trout lounges for the fly. If you get the fish on it is wild. A large trout in shallow water can be amazing. I land the fish about half the time, as they know exactly where the sharpest rocks are. It’s disappointing when they get off, but it is okay as the adrenaline rush lasts for quite a while.

I am a multi-species fisherman as trout season closes the end of September in the state I fish in most. After a few years, I realized the escape volume explains the annoying habit of northern and sometime bass or muskie to take the lure just before you pull it out of the water. They know that as the target gets closer to the surface of the water the escape volume is shrinking and their odds of feeding successfully increase dramatically. Alternatively, maybe they are taunting me, as they know I will pull the lure out of their mouth in excitement.

In any event, this is a useful concept to help fly anglers recognize new spots where big fish may feed. As I said at the beginning, I like to catch bigger fish. So now I look for smaller “escape volumes” to up my odds!


  1. I think the general idea of what you are observing and calling “escape volume” has some merit, but maybe in a different context. The general term “baitfish” is a bit misleading and although this is a generalization, most forage fish in swift rivers aren’t peacefully swimming around in current waiting to be “chased” by a bigger fish with bigger fish making “calculated decisions” to trap forage in areas with small “escape volumes”. When observing large schools of fry along the edges of a stream, they avoid the swift current because they cannot contend with in. They will escape up or down stream in the calm water but not into the current. Of course the larger the fry and other small forage fish are, the more current they can handle, but once a forage fish (healthy or not) is in current it cannot handle, it is essentially at the mercy of the flow, much like a human trapped in a serious rapid.

    Trout are opportunistic feeders, instinctively knowing where to position themselves in the flow to maximize the food that comes their way and eating anything that looks like food. The fact that they “chase” things is more a result of opportunist instinct, not calculated behavior. Most trout food (aquatic (both nymphs and adults) and terrestrial insects, forage fish) are essentially helpless once in the flow and will travel a path downstream dictated by the current, not the food. The hydrology of the current and river structure determines where food flows and trout align themselves with the “feeding lanes”. As you observed, many such feeding lanes are small and associated with other structure that provide security for the trout. Areas that exhibit “low escape volumes” may indeed be favored over areas with “high escape volumes” because the food funnel is much tighter and concentrates food in much tighter quarters. Thinking about these “tight” feeding lanes by looking for “low escape volume” is interesting approach to identifying the areas where the probability of anglers success will be higher.

    The largest brown I’ve ever landed (27.5”) was hooked in a tight seam that is less than a foot deep, a foot wide and a few feet long. It is surrounded on three sides with extremely shallows riffles. The funnel of food in this seam can be measured in 100s of mayflies/second (MFS). Any forage fish that get sucked into the funnel would be helpless. Yet despite feeding on an endless supply of BWOs, the brown sucked down a #6 bugger like it was desert. Good ideas.

  2. Hi Mike,
    I thought this idea might draw a response from you! Thanks for taking the time to respond.
    In principle, we agree. In the end, trout are opportunistic. They will do whatever leads to the most food with the least effort. It is a simple math problem. A fish must expend less energy getting the food than the energy the food provides if it is to grown and remain healthy.
    Trout feed both near current lines that provide a steady stream of food and in smaller spots with less current. Part of the determining factor of which is most preferable depends on food sources and stream conditions. I think part of the problem is you are fishing on western streams where current is much more of an issue. I have fished only a few western streams – but in each instance standing in anything deeper than knee deep required careful attention to securing a stable position – those who are cavalier often experience a very cold bath. In these conditions, trout primarily feed in opportunistic lies just outside of significant current that carries food to the fish.
    The streams I fish have a fraction of the current you probably experience. In most cases, I can easily wade to the top of my waders with the only concern being whether there is an undetected low spot. In current conditions such as this, low light conditions encourage the fish to move shallower and hold next to cover. Most of my larger fish come from these spots unless there is a prolific hatch of some sort.
    Each of the three instances I described happened. Each trout “shepherded/chased” the forage and did not strike until the “strike volume” shrunk to their clear advantage. In addition, I have watched, with great frustration, as a nice fish missed my fly as it whizzed by in swift current. I call these “swing-and-a-miss strikes.” Low current, low strike volume feeding positions lead to more efficient feeding.
    Your example for your largest trout supports the idea. The particular spot you describe had another large advantage in that the food was funneled into a small area. In my experience, spots like that are “super spots” that often hold large fish all the time. I had one such spot that was good for nearly ten years – several consecutive major run-offs last year ruined the spot. But, in that decade before that, I could almost guarantee a 15-20″ fish if I was the first one through (for my rivers that is an excellent fish).
    I have interviewed numerous people who fish trout at night in my area. When I inquire where they catch their trout, without exception they say at the tail of pools and in dead spots at the head of pools. When I ask how deep they are fishing, it is always less than two feet deep. I have not tried night fishing myself (I can only fish so much) but this rings true to the concept of fish focusing on lower “strike volume” areas for feeding.
    Finally, maybe you are not looking for these spots and are missing some great chances at nailing some larger fish that are there for the taking. You may recall one of my earlier articles described fishing the shallow side of the river early in the morning. This is an excellent example of a reduced “strike volume” feeding spot as well.
    We need to get together and hash this out over a nice spot on a river. Let me know when you are up for that.
    All the best, Joe

    1. Interesting! My experience has proven to me that nice trout often lie close to the bank and often in shallow water!
      I never just walk right up to the water but carefully hang back and cast my fly from about 20 feet from the bank and only a few feet out making as least disturbance as possible! I have hooked numerous nice trout this way!
      Most will walk up almost to the water and cast out 20 feet or more not realizing the trout have already been flushed that were close to the bank and furthermore scared other trout further out during their escape!

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