Fish Foraging Efficiency Calculator

It’s easy for anglers to think that if there is a fish there, there will be a good bite, but being there and feeding are two different things. Just because a trout is sitting in a seam for an hour doesn’t mean it’s eating. It could be burning more energy trying to stay put than it’s getting from the occasional piece of food cruising past.

Net energy gain often decide the difference between frustration and a productive day. It means was the prey worth the chase or just there.

The Fish Energy Balance

First thing: What’s the prey like? A tiny midge has almost no energy per unit, so it only make sense for a fish to feed if it can capture many units. On the other hand, a larger crayfish provides a dense package of energy, but its harder shell increase handling time, slowing the overall intake rate. This calculator on the page will do that math for you, just enter an estimate of both the prey mass and density, saving you from guessing which factor dominates the equation.

Big prey is fast; small prey is voluminous. Regardless of size of the meal, efficiency drops when handling time lingers.

The cost of doing business increases as the water temperature increase. In cold water, the fish are metabolically slow and can affords to be more choosy and even forage for less than prime meals. Why expend calories pursuing something tiny and hard to see when you have such low baseline energy costs? As the water warms, metabolic cost increases. Perhaps there is no reason to chase those tiny insects anymore because the calories burned while chasing them does not match the calories gained from the meal. That’s why peak efficiency tends to occur within a very tight band of temperatures. The fish just can’t justify the cost of eating outside this range.

Habitat structure and visibility determine where you’ll have your best strike percentage: In clear water, a fish sees farther. It also has more visual distractions and may spook shy prey. So it’s easier for a bass to sit off an edge (see ref table) then a walleye crusing a lane of coverless, light-dappled water.

In turbid water, a fish is forced to react to vibration and closeness. That makes for ambush opportunities versus cruising. Current-breaking cover such as vegetation or rock cuts down on the swimmer’s energy expenditure and gives him time to rest between meal.

Bait choice is half the equation; position is the other half. There’s also a hidden factor of competition pressure. When one fish has a feeding lane, he picks off the best stuff and ignores the rest. Throw a school of competitors into that equation and quality of prey decreases for each individual. Their intake rate remains high, but the energy density of each item diminish. That swings the balance back toward quantity versus quality.

This happens frequently during spawning runs as fish must eat anything they can get their gills around just to maintain pace with the crowd.

Take these numbers with a grain of salt. They’re not gospel (nature isn’t perfect), after all, and we will never build an exact model that includes every detail of a changing environment. It’s simply to get a feel for why a location was productive yesterday and not today. You should of used it more often. Did the current pick up? Was the holding cost affected? Did water clarity change and effectively shrink strike zone? If you eliminate variables one at a time, you can identify which disrupted the equation.

So there’s your equation, ultimately it’s a budget on foraging efficiency. The fish has only so much he can invest before he begins to lose ground in terms of his search, movement and handling. If the intake outweighs the cost, we see aggressive, visible feeding activity. If the cost outweighs the intake, the fish become quiet. It waits. It sits.

This understanding of the tradeoff will help you begin to find where the energy balance naturaly tips in the fish’s favor, and that’s what leads to consistent catches.