Bluegills, Perch, Crappies

Do most fishermen know what panfish are eating under the ice? With bass, pike, and walleyes it’s easy. They eat fish. But panfish forage on so many things throughout the year, often switching from one food source to another several times a day, that determining what they eat can be impossible without a thorough understanding of the lake’s biota.

Even biologists don’t know in most instances. Fewer than one percent of all micro-organisms have been identified and classified worldwide, according to biologists writing for Time. Of the macro-invertebrates, which provide the bulk of a bluegill’s diet, only about 10 percent have been identified. Jeff Zernov of Aqua-Vu underwater camera fame recently brought in a video showing millions of macro-­invertebrates rising from the bottom to dance in front of his underwater lens at sunset. None of us, including our resident biologist, knew what we were seeing.

The good news is that panfish forage lots in winter—which is why they can be caught so readily at times. But what exactly are they eating? With little doubt, panfish are eating zooplankton at some point every winter. Perhaps all day every day. And will that knowledge help you catch them? Only one way to find out.

Teeny Bugs
Zooplankton (microscopic animals) feed primarily on phytoplankton (microscopic plants). This predator-prey relationship of the aquatic food chain takes place virtually everywhere year ‘round. Bluegills, sunfish, perch, crappies, and minnows feed directly on zooplankton, confirmed from observation and by examining stomach contents.

Not only do panfish eat zooplankton, but they thrive upon it. Studies in Michigan suggest that lakes producing big zooplankters tend to produce big bluegills. In most cases, these fish are feeding upon some variant of the common water flea, from the group called Daphnia. Big in this case is 2 to 3 mm long and visible to the naked eye.

Dr. Harold Schramm of the University of Florida has studied the interactions of bluegills with various zooplankters. “Some zooplankters are big enough to see without a microscope,” he says. “They’re suspended in the water, almost neutrally buoyant, making little jerky movements and hopping around in all directions. They use swimming appendages to move both vertically and horizontally, but tend to hop along in one direction long enough to be intercepted quite easily. To be most accurate, you might say that larger bluegills key on larger crustacean zooplankters.”

One way to get big is to eat what’s most abundant in your environment, because it takes less energy to travel between meals. And, perhaps more importantly, it takes less time. In many bodies of water, zooplankters are so prolific that bluegills, perch, and crappies can drift and graze endlessly through winter. It’s like living in a zero-gravity chamber with thousands of M&Ms floating around.

But many bodies of water have far fewer zooplankters to graze upon in winter. In waters that don’t have stable plankton counts, populations crash periodically if predation is too high or sunlight steadily decreases due to mounting snow cover and ice thickness. In those lakes, panfish forage on nematodes, blood worms, and other wormlike critters that live in soft bottoms. They might switch to small minnows, too, or a mixed diet of burrowing nymphs, worms, and grass shrimp.

Hop Like A Flea
Cladocerans—Also known as water fleas, Cladocerans include the genus known as Daphnia. These creatures move by waving their antennae, which are located on relatively strong appendages near the head. Daphnia move by a series of “hops” produced by short, rapid strokes of the antennae. Other Cladocerans, including those of the genus Latona, use single powerful strokes to propel themselves in quick darting motions. All of the Cladocerans are capable of moving both vertically and horizontally.

Cladocerans reproduce in spring at water temperatures in the 40°F range. As the water warms, reproduction accelerates, then levels off. In ponds and hypereutrophic waters, populations wane to the point where few individuals can be found during summer. A secondary “bloom” may occur in fall, but numbers invariably die back in winter, though a few tough specimens always survive the winter.

In large bodies of water, numbers may peak in spring and fall, but populations remain much higher through summer and winter than in ponds and tiny lakes. Large specimens are visible to the naked eye, often reaching 1 mm and sometimes over 3 mm in length. Most Cladocerans are translucent or clear with little pigmentation, though some secrete shells and may appear yellowish, reddish brown, gray, or black.

According to Robert Pennak in Fresh-Water Invertebrates of The United States, “It’s useless to predict or formulate any preconceived notions concerning the seasonal abundance of Cladocerans in a particular lake or pond. Relative abundance and the specific timing of maximum or minimum populations may vary considerably within a single species in the same lake from one year to the next. Predation pressure is being given importance in the seasonal abundance problem.”

Most Cladocerans undergo daily vertical migrations, upward at night and downward with the rising sun. During most of these migrations, water fleas like Daphnia rise and descend between 6 and 30 feet, depending on the clarity and depth of the water. These migrations take place in winter as well as summer. Where bottom is above the thermocline, zooplankters settle into the substrate at the end of their downward migrations and become less active until light begins to diminish.

At ice-up, zooplankters tend to migrate out to the middle of bays and basins, staying under open water or thinner ice away from shore—another reason why panfish often migrate to deep basin areas in winter.

Copepods are another important class of invertebrates for panfish. Almost universally distributed from shallow to deep water throughout freshwater habitats of North America, some species of Copepoda crawl or run along bottom, but most swim with a backward kicking motion. This causes a jerky stop-and-go motion through the water.

Copepods tend to sink, and those that swim retard this process by extending their antennae forward at the end of each stroke. These function as parachutes, which they bend back in line with the body a split second before the next stroke. Copepods are quicker and more elusive than Daphnia.

Copepods may exceed 3 mm in length, but typically max out just under 2 mm. Interestingly, most copepods are dull gray or brown, while others are garishly adorned in bright shades of orange, purple, or red. Brightly colored versions tend to be heavily preyed on by panfish.

Panfish approach these two types of zooplankton differently. When panfish attack and capture a Daphnia, they casually swim up, hesitate in front of their prey, then suck it in. When panfish attack the more evasive copepods, however, they carefully position themselves before aggressively swimming into the prey, trying to overtake it and suck it in before it can scoot away. Success rates for panfish attempting to capture Daphnia are three or four times higher than with copepods.

Amphipods—These scuds and “freshwater shrimp” live in ponds, lakes, rivers, and streams. They tend to cling to bottom or weeds and range in size from about 5 mm to 20 mm. Amphipods are most active at night, and they tend to thrive in cold, dark environments. Specimens have been found 300 meters down in Lake Superior. They tend to skitter on their sides, hence the nickname “sideswimmers.”

They swim by flexing the body, much as true shrimp do, in an undulatory backward fashion. Locomotion occurs in a sort of dart-sink-dart or dart-dart-dart pattern. They can crawl on weed stems, swim freely, or burrow deep enough to hide themselves. Bluegills, and sunnies in particular, love them. One species, considered a zooplankter, roams open water. Amphipods are clear, translucent gray, cream colored, or white.

Ever wonder why we carry so many colors of jigs in our panfish ice boxes? Or why one or two colors seem to catch all the fish? Study these tiny creatures long enough and you’ll find one for every shade in the rainbow.

Daphnia comprise the major zooplankter forage for panfish in northern states, according to Gary Montz, aquatic biologist for the Minnesota DNR. “Copepods are quite prolific, too, though they move much quicker and tend to be more difficult for panfish to corral in winter,” he says. Grass shrimp, scuds, and other amphipods are mostly macroinvertebrates, though one species is considered a zooplankter.

“Some northern lakes support thick populations of amphipods, while others don’t,” Montz says. “Amphipods, Daphnia, copepods, dragonfly nymphs, midges, mayflies, fish larvae, and ­bottom-dwelling nematodes and blood worms probably are the most important items panfish feed upon, but the complete list is long.” (And nobody has one.)

Jigga Witha Wigga
Most of this information is of incidental value unless you know the biota of your lake. How do you evaluate the macroinvertebrate community for type and number? Who knows. State biologists almost never try to determine population densities of these little creatures at the base of the food chain. But they do run across them and, at least from an anecdotal point of view, asking a local biologist about them is as good a place as any to start.

If Daphnia populations are strong, count on their being important to gills, crappies, and perch in winter. Since zooplankters can move move up or down and migrate up as the light fades, down as it increases, vertical jigging techniques are perfect for imitating them. Some of these little bugs can move several times their body length with one stroke or swimming motion. But that still isn’t far by our standards. A hop-pause-hop in the evening or a drop-pause-drop in the morning might be effective for bluegills feeding on zooplankters, but be subtle, especially when you see a fish approach your jig.

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