The Forage Connection

The path to a man's heart runs through his stomach, and the same goes for gamefish. To catch a predator, you must first understand its prey.

Savvy anglers know their quarry. They factor its preferred habitat, daily and seasonal movement patterns, and other behavioral quirks into their fishing strategies. This is a great start, but there’s more to the story, because gamefish only hang around the neighborhood if there’s a meal to be had. Which is why successful anglers don’t just study up on their favorite fish, they learn the ins-and-outs of its food supply as well.

Most gamefish—large- and smallmouth bass, crappies, catfish, walleyes, pike, muskies, stripers and white bass, to name a few—feed primarily on fi sh. In scientific terms, they are piscivores. We exploit their dietary preferences by either baiting up with live fish, or tying on one of countless imitations. But we really can’t fully tap the forage factor until we learn as much as possible about the habits of baitfish in our favorite fisheries.

Forage Fundamentals
The list of important forage species is a long one, numbering well into the hundreds, and mastering the biology of such a diverse forage base is a daunting task. On the plus side, only a few species may be primary forage in any single body of water. But we still face complicating factors such as seasonal and life-cycle changes in fish behavior and habitat. Fortunately, you can simplify the process by learning the basics of prey selection and understanding a simple system for categorizing forage fi sh. Every body of water is different, and there is no substitute for knowledge gained from time on the water. But these building blocks are a starting point for milking the most fish out of every trip, whether you’re plying familiar waters or exploring new territory.

Predator/Prey 101
Piscivores eat other fish. But not any fish will do. To earn a spot on the menu, a baitfish must be detectable, and catchable with reasonable effort. It must also be small enough to swallow. And, since prey is engulfed and swallowed head-first, a combination of the predator’s mouth width—what biologists call “gape”—along with the body depth of the prey, are key elements in determining the maximum size of prey that can be eaten.

A few forage species, such as sunfish, have relatively deep bodies, but most others are rather slender. Neither biologists nor anglers routinely measure a predator’s gape or baitfish’s body depth, so let me translate this to length. As a rule of thumb, a predator can swallow deep-bodied prey up to one-fourth of its own length, or slenderbodied prey up to one-third of its length. Forage fish, even if abundant, are of little value and probably unattractive to predators if they’re too big to eat.

That’s not to say an ambitious bass or pike won’t choke on a big baitfish, or one of its own cousins, once in awhile, but for the most part, these length limits are good guidelines to what a predator may be looking for in a meal. Beyond the basics of size, availability and ease of capture comes the concept of “search image.” Here’s how it works: Predators are opportunists—normally eating anything they can catch and swallow. But they often key on specific forage species, and when such search-image bites heat up, you better be mimicking the chosen prey—in terms of appearance, location and behavior—or you’re in for a long day on the water.

For example, when walleyes are feeding on smelt, they often abandon any bottomoriented foraging forays in favor of openwater raids on suspended baitfish. It happens with other species as well. Smallmouth bass expert Dick Garlock has fished the St. Lawrence River for more than 70 years. During that time, he’s witnessed the bronzeback bite bounce from a shallow-water affair, driven by bass busting native minnows, to a suspended pattern once rainbow smelt become abundant, to a deep-water bottom bite centered on exotic round gobies.

I’ve long been fascinated by the process of how predators quickly sift through the multi-faceted factors of size, shape, color and movement to select their prey. Some characteristic, or perhaps the combination of a few factors, trips the trigger. Biologists call this magic “something” a releasing stimulus. And whether you realize it or not, when you start changing lures to get a bite, you are searching for the right releasing stimulus.

I fish hard jerkbaits a lot for bass. If I’m getting bit, but the hits are short or the fish are coming unbuttoned, a small change—color, size, brand—often, if I guess right, results in solid hookups. Something made the bass get serious about crushing a bait that swims within its range.

Umbrella rigs, with their multiple attractors, for example, might work so well because of a releasing stimulus. Small swimbaits catch bass, but small shad don’t swim alone. At times a group of “plastic shad” may better approximate either a search image or a releasing stimulus, enough to make the bass commit. You might wonder how reaction strikes fit into all of this.

After all, if you can throw an artificial lure at the fish that’s so overwhelmingly provocative they can’t resist smashing it, why bother with trying to decipher biology, search images or a releasing stimulus? Here’s my take: The notion of triggering virtually involuntary bites has drawn a lot of attention in the last few years, and I think there’s something to it. But predators have finely tuned senses, and they know what a real meal looks, sounds and smells like. The reaction bite may be a response to sudden, unexpected opportunity to feed, but the lure still has to have the right releasing stimulus. So, when you’re targeting fish-eating predator, that ties back to baitfish biology.

Detecting Prey
Fish have the same five senses we do—sight, hearing, touch, smell and taste—plus a sixth sense, the lateral line system. Feeding relies on multiple senses. Vision is key for detecting prey at long range for most gamefish in clear water. Taste and smell enable the detection of chemical cues, which probably are important for accepting or rejecting potential prey, and help predators find stationary prey. But forage fish are typically not stationary, and chemical cues transmit too slowly to be useful for finding and catching mobile prey.

The lateral line system detects water movement. Most anglers think of it as the line of sensory cells on the sides of the fish’s body. While that’s true, what you’re actually seeing is a line of pores in the scales, or the skin, that opens into a canal containing the sensory cells. Although hard to see and off the radar of most anglers, these canals are also well developed on the fish’s head—exactly where they need to be to detect water movement ahead of the predator.

The lateral line system excels at locating prey at night or in turbid water, but evidence is mounting that the forwardfacing canals are also involved in catching prey in clear water. In experiments with northern pike, biologists found that the predators were less successful at catching baitfish when the sensory cells in the head were blocked, even though the water was clear and the pike could easily see their prey. The take-home message for anglers is plain. Always consider how a lure affects the water around it, because the amount of water displaced, along with lure speed, may be the releasing stimulus needed to make a predator commit.

Habitat Considerations
Like gamefish, forage species have habitat preferences. For simplicity’s sake, we can break them into three categories: cover oriented; open water/bottom dwelling; and open water/suspended. Understanding these groups—and the baitfish that prefer them—can help you select presentations, lure shapes, colors and movement patterns that mimic what a predator is looking for in these habitats.

Cover-Oriented: Weeds, timber and brush are home to many forage species, including a variety of sunfish and minnows. Such cover helps conceal baitfish, but for ultimate protection from predators, they need some type of camouflage. We see this in the dull brown and olive coloration of many minnows, as well as the seemingly bright colors of many sunfish—the gaudiness of which is tempered by vertical bars or other mitigating patterns that break up the fish’s outline amid the shadowy world of plant stems and brush piles.

It’s tempting to target ambush predators like largemouth bass and northern pike along the outside edge of cover, where it’s easiest to present baits and lures, but most cover-loving forage hide somewhere inside it. I fish the edge, but also work the cover. Many times, I’ve zeroed in on the weed edge, but busted burly bass buried inside the greenery.

Open-Water/Bottom-Dwelling: Ranging from cobble and boulders to sand and soft bottom, this habitat is home to suckers, sculpins, round gobies and various minnows. Baitfish colors include dull grays, greens and browns, often with subtle mottled patterns.

These fish hold tight to bottom, often seeking shelter between and under rocks if available, and generally move slowly if at all. Mimic them by dragging lures on bottom or slowly swimming baits just above it, experimenting with intermittent pauses and deflections off cover.

Open-Water/Suspended: Baitfish here “hide” with two-tone camouflage that’s dark (like deep water or the bottom) when seen from above and light (like brightly-lit surface water) when seen from the side or below. Examples include the shad varieties, blueback herring, alewives and tullibees; some, like the open-water emerald shiner, add a transparent twist. Perpetually on the move, often in schools, these fish are best imitated with dark-backed, light-sided swimming lures or flashy, erratically moving baits that resemble a sick or wounded individual surrounded by healthy schoolmates.

Seasonal Factors
Time of year is important for several reasons. Spring signals the return of openwater baitfish to shorelines, rock shoals or creeks for spawning. Predators pick up on this, and so should fishermen. For example, on many southeastern reservoirs, the late-spring shad and blueback herring spawn ushers in epic largemouth bass action. Big-blade spinnerbaits and swimbaits fi shed early in the morning over flats and points draw big bites. A less well-known but equally productive pattern occurs when walleyes fatten up on fall-spawning tullibees.

Brian “Bro” Brosdahl, a veteran northwoods guide and ace competitor on the Cabela’s Masters Walleye Circuit, fishes inside weed points connecting deep water to tullibee spawning flats when he sees these fish working the surface. Changes in habitat are not only related to spawning. In southern reservoirs, shad spend summer in the main lake but move into coves and bays in fall—with bass in hot pursuit. Young yellow perch and bluegills are typically associated with weedbeds, but large perch and bluegills sometimes occupy open water in summer. I’ve caught big northern pike suspended over deep water in the summertime, and many anglers do well trolling everything from spinner rigs to spinnerbaits for off -structure walleyes. These open-water bites for typically cover- and structure-oriented gamefish are related to the seasonal movement of their preferred forage.

While some forage fish change locations in a lateral dimension, others make vertical migrations. Cool-water species such as smelt and tullibees may move shallow in spring and late fall, but warming water and thermal stratification in summer force them into the abyss. When these fish make brief vertical migrations into or above the thermocline to feed, predators follow.

One seasonal shift that’s easy to over- look is the change in forage size. In early summer, when juveniles of many baitfish species are too small to attract the attention of large gamefish, locating (and mimicking) meal-sized prey—even members of species normally off the preferred menu—can be key to success.

On the flip side, fast-growing forage, such as gizzard shad, can quickly grow too large to be eaten by all but the largest predators. As a result, even though gizzard shad are primary forage for a variety of predators in many waters, they’re not the dominant prey throughout the year. Young gizzard shad are the preferred food of walleyes and smallmouth bass in Missouri River reservoirs from spring through midsummer, but in fall, the predators switch to smaller, more easily swallowed forage species.

Hunters know their quarry’s movements and feeding patterns. But gamefish, unlike animals that eat plants, feed on other fish that follow their own patterns. Anglers should think like a predator, but in the end, need to think like its prey, too.

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