They look at what bass eat to determine the health, not only of an individual fish but all the bass that live in the same body of water. Their focus is on how many baby bass grow to adults, how fast they grow and how healthy they are as they grow, and their mortality. "If they aren't getting big fast enough," says Odenkirk, "we might be able to help them out by providing more food."
Biologists help bass eat better by stocking forage fish, such as shad, herring or alewives in a lake that doesn't have enough food to help bass grow big. Most of the time, however, bass do pretty well on their own.
Odenkirk says what he finds in bass stomachs is limited only to what foods are available and what they can fit in their mouths. Insects, crayfish, frogs, lizards, snakes, other fish, and even baby birds end up on the dinner menu. Bass even will eat each other. The name of the game is survival, and if a bass has to eat another one in order to live, he won't think twice about it.
Bass also choose their food, based on their size. The bigger the bass, the bigger the meal. Largemouth in California, for example, often eat rainbow trout 10 to 12 inches long. On the other hand, however, stomachs of big largemouth bass also have been found to reveal they were crammed full of tiny grass shrimp...proof that bass will eat whatever is easy to catch.
If available, threadfin shad probably are the favorite food of largemouth bass. Why? Because shad are soft-rayed fish, which means their fins aren't as spiny as, say, a bluegill's. Soft-rayed fish are easier to swallow.
But threadfin and other shad don't live in every lake or pond. In fact, they need water with plankton in order to survive. Plankton are tiny plants that suspend or float in the water. How can you tell if your lake has plankton? Look at the water color. Lakes with a green or light brown tint probably have plankton, but clear lakes don't. If your favorite bass lake doesn't have any threadfin shad, don't worry. There probably are bluegill, crappie, minnows, and other fish.
Odenkirk says insects are a vital food source to young bass. Without little bugs, baby bass can't grow into big fish. Most healthy lakes, ponds and rivers have an abundance of aquatic insects, or insects that live under the water. He also points out that largemouth bass switch from a diet of mostly insects to a diet of fish and other larger prey when they reach about 8 inches.
One thing bass don't eat is plant matter. Although aquatic plant life frequently is found in bass stomachs, fish experts think it ends up in bass' mouths when they are feeding. They don't eat it on purpose.
"Bass suck in their prey, and their prey often live in and around aquatic vegetation," explains Odenkirk. "When they grab a shad or bluegill, they don't want to open their mouths to get rid of the plant matter, so they just swallow everything. Bass don't need nutrition from plant matter the way we do."
Odenkirk says he often finds hooks and pieces of fishing lures in bass stomachs. In some cases, the fish will pass those items that don't digest. Other objects, like hooks, disintegrate in the stomach, thanks to the strong acid that helps digest food.
"Figuring out exactly why bass eat what they eat is still a mystery," notes Odenkirk, who studies smallmouth bass in several rivers in Virginia and has seen many big fish with madtoms, a small member of the catfish family, in their stomachs. "I have no idea why a smallmouth would eat a madtom, which has three sharp, barbed fins, when it has so many other options. The rivers I work are loaded with shiners, sunfish and other forage fish that aren't as spiny as madtoms."
Biologists think bass (and other fish) will choose one type of food over another because it provides them with the vitamins and minerals they need to grow.
The good news is that you don't have to match real fish and other creatures perfectly the next time you go fishing. Look in any professional bass angler's tacklebox, and you'll see an assortment of lures that don't look like anything in nature. Spinnerbaits, buzzbaits, and a variety of wild-looking soft-plastic lures all catch bass. Largemouth, smallmouth and spotted bass are as curious as any other animal and will take a close look at something that seems out of place.
However, while you might pick up an object with your hand to take a closer look, a bass would grab it with its mouth, chomp on it a few times and decide if it's something worth eating. In other words, just because your favorite lure doesn't look like a real creature doesn't mean it won't work. Sometimes, bass will eat anything.
And, occasionally, other things eat bass. Little bass, especially, have a pretty tough time. Many are just another source of food for larger bass and other fish, and all kinds of other predators eat largemouth and smallmouth bass. Odenkirk says a baby bass has about a 10 percent chance of growing into an adult. That is, nine out of 10 little largemouth never make it to their third or fourth birthday. The bigger the bass, the better its chances of survival, but those that do survive can still get eaten.
Plenty of big predators love the taste of fish, including turtles, alligators, herons, otters, and, of course, people. Although many anglers practice catch-and-release, sometimes people keep a few for dinner. There's nothing wrong with that. Fisheries biologists set size and harvest limits to allow anglers to keep bass while still maintaining a healthy and abundant fishery.
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