Thursday, February 4, 2010

Opportunistic vs. Selective Feeding

Consider the long held theory that trout feed opportunistically sometimes, and selectively at other times.  The theory goes that when there are few insects of a specific species on the water, the trout will feed opportunistically - they feed on anything that drifts or floats past them.  That is, if they are in the [mood] to feed and there is no hatch, they will feed on whatever is available.

When there is a hatch, it is said that trout feed selectively.  The theory goes that there are many insects of the same species on the water, and therefore, the trout become accustomed to to them and will only feed on them - selectivity being that the trout will forsake all but the abundant (hatching) bug on the water.  They are being "selective".

Who makes up this stuff?

I believe that trout feed opportunistically all the time.  They can't afford to be selective.  How can they? Their number one instinct is survival, so how could they afford to be selective?  Yes, when they are in a feeding mode and a hatch is not taking place, they will feed on anything that passes by them that they sense is food.  And yes, when they are in a feeding mode and an insect is hatching in abundance, they will feed only on the insects that are hatching, and ignore all others.

But it is not selective feeding, it is survival - when an insect is hatching and many of them are available, of course the trout will feed only on them.  It speaks directly to their survival instinct - why take anything else but the bug that is hatching?  They can identify it as food, it's easy to feed on (little energy is needed because the prey is a clear and obvious food item), and identifying anything else is a waste of time.

Trout don't waste time.  They cannot afford to.  When they identify a food source that is abundant (a hatch) they will feed on only that.  It is an opportunity that minimalizes the need to waste any trial and error effort.

I used the term mode, as opposed to mood, to describe the trout's behavior when their bodies tell them they need to feed, intentionally.  One of the problems I think with fly fishing theories is that we tend to anthropomorphize trout behavior. i.e. "trout think".  They do not think, otherwise I might have said "mood" to describe a trout whose biological clock tells it that it needs to eat.  As in, "You know, I'm damn hungry, and there are a load of Pale Morning Duns on the water surface that I am going to sip in like pretzels and beer."

Trout behave, therefore, they cannot be selective.  Selectivity implies that they are making an intellectual choice.

Trout do not think.  They behave, and that behavior has been evolving for eons.

I'm not done with this one.............more to come.

10 comments:

FoulHooked said...

Does selection require cognitive reasoning? I understand what you are trying to say, but just because a trout (to our knowledge) has no capacity for abstract thought does not mean they cannot be selective. Or does it? Or am I missing the point? Let's say a trout takes your fly (i've heard it happens); in order to do so, he has to make 2 "choices" as I see it 1-he has to "choose" to eat rather than not eat and 2-he has to choose to eat your fly in preference to anything else around. Yes, it's stimulus-reaction but it's still selection.

Ed

Matt Grobert said...
This comment has been removed by the author.
Matt Grobert said...

Good points. Trout do choose to eat or not. But are they selective, as in disriminating? Or is it an opportunity, as in a chance, especially one that offers some kind of advantage?

FoulHooked said...

No, I completely agree with you...I was just arguing semantics. Don't you hate it when people do that? Slow Friday at work I guess.

You can parallel the way a trout identifies likely food items with how most people read; we could focus on each individual letter (physical trait) but generally we use context and a few cues to fill in the gaps. The latter is much more efficient, but sometimes leads to mistakes. Thankfully nobody has gutted me for misreading a sentence...yet.

Anonymous said...

WOW man, You guys are deep....

Matt Grobert said...

Dear Anonymous,

If I wanted a shallow comment, I would have gone to my friend Chris "Mr. Chef" and said something random to him.....he's always good for a wise crack!

Midgeman said...

From the standpoint of the trout, selectivity is a matter of instinct. A trout's most basic instinct is survival and in regards to feeding, to feed in the manner that requires the least energy output for the maximum calorie intake. If there is no hatch, but they're seeing a broad range of tidbits drift by, they will generally feed opportunistically. If the food supply becomes more specific, i.e. a hatch comes off; they will feed on the most available phase of that hatch as it progresses. This will generally mean initially pupae or nymph, then emergers, then adult. They will, in nearly all instances, find that cripples make a nice addition to the emerger / adult phase of the hatch. The whole issue of selectivity or educated trout stems from an angler's inability to match the numerous keys that best define the “more bang for the buck theory” when it comes to caloric intake. We as anglers have to have an excuse for failure when we are unable to match wits with a purely instinctive animal, in this case a trout with a brain the size of a pea. We will never fully understand their world and they could not grasp ours, but it's sure fun when the two worlds cross!

Matt Grobert said...

Well said, Midgeman! Although the more bang for the buck (caloric intake) is another big question - why do trout sometimes feed on tiny BWO's, when there are larger, more substantial bugs on the water in good numbers? Do they taste better? Amazing how an animal with such a small brain can make us so humble.......

Midgeman said...

There are some occurrences that, we as humans, just can't fathom or relate too! Maybe it’s a matter of which size insect first attracted their attention and locked in the feeding rhythm. Then again some mysteries can't be solved and had there been trout at my Super Bowl party they might well be finning around discussing why that old dude in the Simms hat ate all the Lays Potato Chips, but didn't touch the Ruffles... I will say this; in fishing a lot of tailwaters out here it's very common to see me fishing a size 18 BWO trailing a size 22 BWO a foot behind. I may now and for ever, refer to this approach as the Lays/Ruffles technique for hatch matching.....

FoulHooked said...

http://turningoversmallstones.blogspot.com/2010/04/fishing-writing-that-incorporates.html