We know that simple-brained animals like trout can’t deal with a lot of information at once, so while they are hunting they probably can’t think of much else. This isn’t selectivity but tunnel vision.
Prey abundance influences the degree to which a predator can afford to be specialised because it affects the search time involved for each item eaten. Rich food supplies favour specialised or what we call “selective foraging. We could think of this as a prey ‘band width’.
Diets are broad band(long search time), when prey are scarce but narrow band (short search time).when a prey type is abundant.
Some implications for anglers are;
-They do not actually ‘select’ the specific prey, but simply get in a feeding ‘groove’ that lasts as long as the supply of that specific food form is present in abundance.
-During periods of sustained abundance – like a hatch –which can last for hours, days or even weeks, the trout become fixed in a predatory groove. A sustained sequence of successful encounters with a specific food item that establishes the groove. The trout are not deciding or actively “choosing” which prey to eat. If there is not enough of a particular prey to establish a groove, they remain ‘generalist’.
Trout are not essentially selective predators. Trout are classified as generalist predators by nature. This is the reason the so-called general patterns like the Royal Wulff, the Hare’s ear and the Adams are such good flies, everywhere trout swim. Its also why a few of those old patterns have remained in our fly boxes for over a century.
-If the hatch is patchy or of short duration the trout will be not be keyed to any particular prey.
-On waters where long sustained hatches of a specific insect are rare, irregular or non-existent, the trout are most certainly not selective and it is a mistake to expect them to be.
-On days when the food available is varied, the generalised attractor type of trout fly is probably the best bet. In fact, the less specific your fly is the better. A good generalist fly contains one or more ‘triggers’ in its design, and is similar in size to the most common prey items in the trout’s environment. A set of good generalist flies in a range of sizes will serve you well wherever you fish for trout.
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Bob Wyatt is a photographer, recognised author and painter, Certified Fly Casting Instructor and fly angler. He has published two highly regarded books on fly fishing.
What Trout Want: The Educated Trout and Other Myths and Trout Hunting: The Pursuit of Happiness. Both available on Amazon
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I believe it’s Lefty that is credited with saying “There’s more bullshit in fly fishing than in a Texas cattle yard” (excuse the French) A phrase that is no more apt than when citing the 'Fluoro vs Mono' discussion.