Optimal Foraging Theory

I have a buddy with whom I have spent some time fishing and a lot of time sharing ideas.  He once said, “Fishing is mostly about understanding fish”.  I liked that quote so much, that I wrote it down when he said it.  Thanks Bruce.  Right now you might want to pull up a chair, because I have a pointy-headed biological theory to discuss with you in this blog post.  I promise this will help you understand fish, and the better you understand them the more and bigger fish you will catch.

When I give fishing seminars I usually make it a point to talk about the relatively small brains of fish.  Those big fish we want to catch are not smart, they do not swim around trying to figure out how to embarrass fishermen and fisherwomen.  The fish are not smart enough to know the difference between a fish hook and a hole in the ground.  However, the fish we pursue are very successful at following their instincts and surviving.  There are a few weeks each year when adult fish are interested in reproduction, but most of the time the fish we are trying to catch are simply following their instincts trying to find enough food to eat and grow and to avoid being eaten themselves.  Predator/prey dynamics drive the entire aquatic ecosystem, and for anglers it is extremely important to understand predator/prey dynamics because we not only have to find the fish, we then have to entice them to bite on our hooks.

Optimal foraging theory is a biological theory that has been applied to a lot of biological systems, and I believe it very much applies to the behavior of the fish we pursue and it can help explain feeding behaviors.  Simply put, optimal foraging theory states that predators will select for prey items that give them the greatest return of energy per the energy they have to expend in capturing that prey.  Predators have to take in more energy than they burn; they either do that or there comes a morning when they wake up dead.

So, that is optimal foraging theory, simple ain’t it?  But what can that theory teach a bunch of anglers?  First of all, I am a believer in “big baits for big fish”.  One reason I believe in big baits for big fish is because optimal foraging theory would predict that to be true.  Predators can obtain more energy by capturing large prey items than they can by running around capturing a bunch of small prey items.  Studies have shown that predators like muskies, walleyes, and largemouth bass will consume prey items up to 40 and even 50% of the predator’s own body length!  Fish may try to eat anything that can fit through the width of their throats.  Think about that for a second; a 28-inch “master angler” walleye may eat prey items as large as 11 inches!  A 40-inch muskie may consume prey items up to 16 inches or more and a 21-inch largemouth may consume prey items up to 8 or 9 inches long!  I am suggesting that those large fish may not only feed on prey items that large, they may actually select for them, prefer them!

Could have eaten a bait even bigger than the one she inhaled!

Now, do not misunderstand optimal foraging theory, I did NOT say that large fish do not eat small prey items.  We all know stories of trophy muskies being caught on crappie minnows and there are plenty of examples of fish growing really large on small prey.  At times smaller prey items may be the “optimal forage” because they are so abundant or so easy for predators to catch.  Nebraska reservoirs are often packed with millions of young-of-the-year (YOY) gizzard shad in the summer and at that time every predator fish in the water may be eating YOY shad because they are so abundant; they are the “optimal forage” at that time.  On the other hand, optimal foraging theory would predict that all things being equal, the big fish we want to catch will select for larger prey items because those prey items are worth more energetically.  Optimal foraging theory would predict that larger fish, having larger energy demands, would likely select for larger prey items.

By the way, right now, autumn, is one of the times when I believe “big baits for big fish” is most true.  As the days get shorter and the water begins to cool, all creatures seem to know that winter is on the way, and winter is the “hard time” for most creatures.  In the fall fish feed heavily because they need the extra energy, extra “fat”, to help them get through the winter.  In addition, many of our species of fish begin developing eggs and milt in the fall, and those gametes or sex products (sorry, I had to throw out another pointy-headed biologist term or two there) will essentially be “on hold” throughout the cold of winter.  Egg and milt development begins in the fall and final maturation takes place next spring just prior to spawning; the development of eggs and milt requires a lot of energy.  Fish need extra energy to develop eggs and milt right now in addition to preparing for the winter.  Fall is an excellent time to fish because the fish are feeding up, and those fish will be likely to select for large prey items if they are available.  In addition the natural prey, especially bait fish, have grown throughout the summer and will be larger in the fall.  “Big baits for big fish” is something to keep in mind especially during the fall.

Optimal foraging theory would also predict that predators take advantage of opportunities when they can easily capture and ingest the most prey/energy.  When capturing prey is less likely to be successful, predators may not feed; they conserve energy.  My best way to illustrate this is to use a terrestrial predator as an example, one you can watch on “NatGeo” or “Animal Planet”.

I love watching shows about the big cats in Africa (by the way, I do not “cheer” or feel sorry for the “poor little prey animals”, I “root” for the predators), and I am sure most have seen what I am talking about.  We all know that when the big cats, for example African lions, get hungry they go on the prowl.

When those cats are on the prowl they are looking for a prey item that will be easy to capture, one that will offer the least risk to themselves.  They are looking for “optimal forage”.  And when they find that particular prey item, they make a kill.

Of course you all know what happens when the lions make a kill; the whole pride shows up and they literally gorge, ingest as much energy as possible.

And then you also knows what happens after the feast. . . . They find a nice shady spot and lay up.

The fact is that most of the time predators are conserving energy!  They wait until the opportunity arises again when they can capture prey with the least amount of effort or they wait until they have to take in more energy (i.e. get hungry).

Here’s the thing:  Those same predator/prey dramas that we can watch on our TVs are occurring below the surface of the waters we fish, everyday, all day long.  The better we can understand those predator/prey dynamics the better we will be able to find and catch fish!  Keep in mind that much of the time fish are not actively feeding, they are conserving energy.  When anglers encounter fish that are not in a “positive feeding mood”, they will be more likely to entice a few fish to bite by slowing down, using more vertical presentations (e.g. live bait rigging, vertical jigging), and using baits and lures that are smaller and more natural.

Every angler knows that actively feeding fish, those in a “positive feeding mood” are always a lot easier to catch.  One strategy to employ on the water may be to cover as much water as possible in an attempt to encounter fish that are actively feeding.  In that case presentations that can be fished fast, presentations that can cover a lot of water, more horizontal presentations (e.g. casting a spinnerbait, trolling crankbaits), presentations with big, bright, loud baits, may work best.

There are no magic baits or lures, nothing works all the time.  Each day on the water an angler is faced with putting together a puzzle; figuring out where the fish are, what they are doing and how they can be caught.  Oftentimes, as soon as one puzzle is completed and some fish are caught, everything changes and the whole process starts over.  That is the challenge of fishing and one reason I never get tired of it.  An understanding of optimal foraging theory can help you figure things out, perhaps help you put a few pieces of that puzzle together.