10 minute read
Trout Myths Trout Have a Blind Spot Directly Behind Them
from TROUT - Fall 2023
BY TOM ROSENBAUER
Much been written about trout in the last 500 years that while not exactly wrong, is often penned by an angler who fishes one watershed and doesn’t realize that fish in different parts of the country and world don’t follow those rules. I can think of a couple examples.
One is Art Flick’s Streamside Guide to Naturals and Their Imitations —a delightful and helpful book I memorized as a kid and took as gospel, but soon found out that either the hatches he wrote about didn’t exist in my local streams, or the local insects didn’t behave like the ones he wrote about. Flick did all his research on the Schoharie and its tributary the West Kill and hardly even drove over the mountain to fish the Esopus or the Beaverkill. And then there was an author from Colorado back in the 1980s who wrote an entire book about a method he developed to fish emerging caddis pupae by yanking his special fly very rapidly to the surface. The problem is that the species of caddis in his local rivers is not widespread, and observations by angler/entomologists like the late Gary LaFontaine and Thomas Ames proved that most caddis pupae tentatively rise to the surface.
I love it when someone busts these myths with science, or with decades of observation of trout in a wide variety of habitats. Not all of them are myths, some are just bits and pieces of facts that get contorted into whatever theory the author is trying to shoehorn them into.
A good example is that “Trout have a blind spot directly behind them so you can creep right up to them if you approach from behind.” Theoretically true but realistically impossible. Most anglers have figured it out over years of trial and error, but propagating this semi-truth to novice anglers may lead to frustration.
Most authors who have really studied the vision of trout, Like Jason Randall in Trout Sense, Goddard and Clarke in The Trout and the Fly, and Gordon Byrnes in a 1990 article in Fly Fisherman magazine entitled “How Trout See” get it right when they say this rear blind spot has little significance. Still the myth persists. And I honestly couldn’t criticize people who said you could sneak right up to a trout from directly behind it until I proved it to myself.
I once spent an entire season trying to determine how close I could get to trout if I approached them from their “blind spot.” If you look at those neat charts in books you’ll see straight lines extending back behind the head of a trout at either an acute angle or a rectangle slightly larger than the width of a trout’s body. It doesn’t appear to allow for much of a blind spot, so I decided to see how close I could get to feeding fish. I did this in small streams in Vermont, on Catskill tailwaters, on the Henry’s Fork in Idaho, and in Wyoming spring creeks. Although trout vision and response to predators should be consistent, I didn’t want to introduce any regional bias into my observations.
The trout I tried to approach were either hovering below the surface or in shallow water because I needed to be able to see the reaction of the fish. Even though trout are restricted to what they can see of the outside world because of the circular window above them due to the refractive properties of water, the shallower they are in the water column the narrower the window. All the trout I approached had a relatively narrow window but could still see something of the outside world. I also tried to eliminate places where pushing waves ahead of me would alert the fish. I used rocks or logs to break my waves, or approached fish in the tails of pools where the riffled water below would block any pulses.
I didn’t crouch down because if there was truly a blind spot behind a fish I did not want to introduce another variable by hiding below their window to the outside world. I avoided casting to these fish because the movement of my fly line and rod hand may have extended beyond the supposed blind spot because I always cast a bit sidearm. All these places were in smooth water because the broken surface of a riffle allows you to get closer to fish, but in broken water it’s tough to see their reaction and I wanted to observe their response to my approach.
One fish was in a small Vermont meadow stream and was rising periodically but always just a tip of the head punctuated by a sip. It never moved off to one side or the other to eat. I got directly downstream of the fish and was careful not to make waves and crept upstream at a painfully slow pace. The fish kept rising until I got about 15 feet from it. It stopped rising, sunk lower in the water column, and I could see its body tremble which always reminds me of a sprinter in the starting blocks because I know when I see that the fish is about to bolt for its refuge. And it did, into the deeper pool up above.
Some trout I distinctly remember were three large rainbows on the Henry’s Fork in the shallow water at the head of the Millionaire’s Pool, all feeding subsurface together. With careful wading I was able to get within 20 feet of them. I was satisfied and was not going to pass up a chance at one of these fish so I knotted on a size 18 PMD nymph. Just as I was about to cast, one of the fish decided to chase something downstream and as it wheeled around to face me, I was suddenly pinned in its binocular vision. He knew something was up because there wasn’t an object there a few minutes ago, and even though I didn’t move a muscle he bolted down in the deep water below, taking his two friends with him. I find rainbows are like that. They are more likely to make a downstream-facing rise than other species, and they also cruise more often than browns or cutthroats so you never know when a fish could be heading back to the beginning of his racetrack cruising cycle, pointed directly downstream.
I think there is one main reason I couldn’t get close to those feeding trout. Even if trout have a wider blind spot than the placement of their eyes would indicate, a feeding trout does not stare directly ahead. As it feeds it moves from side to side to inspect drifting food.
Another situation I faced was with a large cutthroat taking small olive mayflies in a Wyoming spring creek. I tried to stay directly downstream, and even locked my hands behind my back to try to thin my profile and prevent excess movement. The fish kept rising pointed straight upstream and I was able to get within 14 feet of it when it noticed something especially tasty two feet to the left of its normal feeding lane and made a splashier rise that it had been exhibiting. I’ve watched trout enough to suspect that when they make a splashy rise that’s out of character, it’s usually because as they are moving for a fly they spot you. And what appears to be a rise is them making a quick detour to the nearest logjam. Sure enough, when I looked back to his feeding station it was empty.
I think there is one main reason I couldn’t get close to those feeding trout. Even if trout have a wider blind spot than the placement of their eyes would indicate, a feeding trout does not stare directly ahead. As it feeds it moves from side to side to inspect drifting food. When it does that, the area directly behind it gets more exposure from its peripheral vision. Trout have a cone of binocular vision around 30 degrees in front of them where they have acute vision and substantial depth of field, but a much wider range of peripheral vision to the side because their eyes are located on each side of the head. You move to cast and they’re going to blow your cover.
There are always mitigating factors that let you get almost within a rod length of a trout that could make you believe they do have a blind spot. Trout feeding heavily on a hatch can get so preoccupied with food they can be tough to frighten. Riffled water hides our approach by distorting their view of the outside world. And low light, especially when combined with a heavy hatch and a riffled surface makes you think you could step on a trout before it was disturbed. And you’ll find that heavily pressured trout will let anglers get a lot closer because they’ve learned that if they spook every time someone wades up to them, they’ll starve. But those circumstances have nothing to do with a blind spot and everything to do with their preoccupation and bold behavior. In situations like this, you can even get very close to a trout even when approaching from directly upstream.
I feel that we can still get closer to trout by approaching them from behind. Their vision is not as acute behind them, and I would imagine that at the extreme range at the rear end of their peripheral vision you’d have to be making a lot of quick movements. It’s hard to cast properly without making quick movements. Keep false casting to a bare minimum and wear muted colors—or try to stay in the shade—and you’ll be able to get closer to trout where you can make a more accurate cast with less drag. But don’t rely on that blind spot you hear about. Assume they can always see you if you can see them.
I find rainbows are like that. They are more likely to make a downstream-facing rise than other species, and they also cruise more often than browns or cutthroats so you never know when a fish could be heading back to the beginning of his racetrack cruising cycle, pointed directly downstream.
