Zooplankton Rules Ice Fishing!

Modern ice fishing pioneer Dave Genz “put it all together” with his theory on the role that tiny marine animals play in governing the daily activity levels, and locational tendencies, of all species of fish. Understand this and you understand much of the big picture.

By Mark Strand

On the one hand, panfish are predators.
Granted, they don’t prey on particularly worthy adversaries; bluegills and crappies can take down zooplankton without a struggle. Perch only have to inhale with moderate gusto to extract a burrowing insect from its burrow.
But on the bigger hand, panfish are also potential prey.
Can you imagine what it’s like to be exactly what pike, walleyes and bass are looking for?
On the one hand, panfish profit from taking advantage of the natural rhythms of each daily cycle. When their food sources are active and available, they, too, activate, motivate, get out there and eat.
On the other hand, to avoid being eaten, they try to make themselves scarce when bigger predators are on patrol.
There are natural collision courses, such as the onset of rapidly rising or falling light levels, when walleyes hammer perch because the ‘eyes have a major vision advantage. But by and large, panfish follow a daily plan that includes moving and feeding at prime times, then laying low during the bulk of the brighter daytime hours.
This daily cycle means everything to you as an ice angler.

Prime-time Fish are Active
On most days, on most waters, there are two distinct prime times: sunrise and sunset. These periods of rapidly changing light levels appear to be the cause of ‘vertical migration’ of zooplankton. These teeny-tiny animals make a variety of movements, but the dominant one is upward at dusk (eventually to, or near, the surface) and downward near dawn.
When the water fills with this microscopic life, that triggers increased activity in everything from burrowing insects to fish of all sizes. It’s nature’s rush hour. Even at the risk of being eaten by a pike or other predator, panfish move in active pursuit of calories.
This is the time when you can sit tight on a good spot and catch a lot of fish in a few minutes.
Dave Genz has a plausible theory that guides our overall approach.
“When the zooplankton begin moving upward around sunset,” he says, “they’re concentrated within a few feet of the bottom. Because they’re so thick (in one depth zone), bluegills and other panfish species can feed efficiently by just opening their mouths and swimming.”
After darkness falls and zooplankton continue to rise toward the surface, they’re not as concentrated, ‘stringing out’ like traffic on a rural highway. At this point, Genz thinks, black crappies can still feed efficiently on them, having relatively larger mouths than sunfish, but extremely fine gill rakers suitable for the purpose.
“That explains why you catch crappies through the night sometimes,” says Dave, “but the bluegills quit when it gets dark.”

It’s All About the Zooplankton
Study the scientific literature and you’ll see that zooplankton migration is a complex subject full of variables. But in most ‘ice-fishing lakes’ there seems to be this classic pattern of most zooplankton remaining deep in the water column during the day (when light levels are high), either on bottom or suspended at a level where they are hard to see. Then, as sunset approaches, massive swarms (sometimes called patches) of zooplankton rise toward the surface, where they feed on phytoplankton (tiny plants) at night.
Then, when light levels increase as sunrise approaches, zooplankton reverse the migration and move back into deeper water.
On most days, in most bodies of water, these zooplankton migrations are the cause of fish movements and relative activity levels.

Daytime Fish: Typically Less Active
Bring on the brighter daylight hours and most panfish become a quite different creature.
Now, rather than moving in pursuit of food, they are hiding, to avoid becoming food for vision-guided predators.
There are three classic daytime panfish hiding places:

• In the weeds
• Depressions (deeper holes) in bays or on large flats
• Suspended over open water, at a depth where they become hard for predators to see

Panfish are not active at this time, on most days. They are not looking for food, but they will ‘sample’ your bait, if it looks natural to them.
If you mainly pursue panfish, this is the time when you must remain on the move, drill lots of holes, and keep looking until you locate fish. This is also the time when attention to detail in presentation is critical.

Beware the Exceptions
Every time you try to say anything about fishing, you think of exceptions. There are exceptions to any general rule, but this zooplankton-panfish connection will lead you to fish, and help you understand what it takes to catch them, on most days.
Keep an eye out for rapidly-changing light levels in the middle of the day, because that can trigger early zooplankton movements and bring on prime time activity patterns in panfish and bigger predators. For example, if a day starts out bright and sunny but heavy cloud cover rolls in after lunch, suspect that the fish might go on a feeding binge.

Finding Winter Fish
It’s one thing to be ‘book smart’ about winter fish locational tendencies.
It’s another thing to go find them, on your own, on an iced-over lake.
Let’s take what we know about the typical behavior patterns of sunfish, crappies and perch, and apply it on the ice. In many cases, the bigger predators, especially pike, will not be far from the panfish species.
If you followed Genz and his fellow members of the Ice Team, you might be surprised to see that they don’t catch fish at every spot they try. But you would be impressed with the effort level, as they continue to look until they find what they came for.

Good Daytime Panfish Spots
When panfish are hiding from predators, look for them…
* In the weeds or other available cover.
If a lake has abundant weeds, and they grow down to about 8 feet or more, chances are many fish will use the weeds. (Especially at early and late ice.) Best weeds are green, upright and healthy. In some iced-over lakes, some weeds actually grow if sunlight penetrates. But, even when weeds are brown and yucky, fish will still use them, especially if they remain upright. In the middle of the day, key on thick clumps of weeds close to outside edges.

• In depressions and other holes.
  If you know that panfish typically inhabit a certain large bay, for example, and you can find a couple places where it dips even a few feet deeper, those “depressions” as Genz calls them, can be the key daytime spots.
  Some of today’s ultra detailed contour maps will show you these depressions and holes. If the detailed map can be displayed on a GPS unit, you can go right to the spot and start drilling holes. But, absent such help the best thing to do is run parallel ‘transects’ in your boat before ice forms. Mark the location of key spots by taking shore markings or saving them as waypoints on a GPS.
• In deeper water.
  As we already noted, many panfish use the relative security of water depth to hide from predators during bright daylight hours. The fish simply hold in a depth “where they’re hard to see,” notes Genz, who has long suspected this connection. If a lake does not have much in the way of weeds or other shallow-water cover, panfish will use ‘the cover of relative darkness’ in this way to escape predators.
• Specifically, sticky-bottom areas.

It was Genz who got onto the magic of what he called sticky-bottom areas.
In places where the bottom composition is neither rock hard nor too ‘mushy,’ burrowing insects make their home. In the days before the Vexilar, “we used to use those lead weight depthfinders you clamp on your hook,” remembers Genz, “to find the bottom and set your bobber. I noticed that in a lot of places where we caught big panfish, when you dropped that weight to the bottom it would stick when you tried to pull it out. Your rod tip bent, and you had to pull to get it free.”
Sticky-bottom zones are often on ledges and slopes leading to humps, depressions, and other structural features. Nowadays, members of Team True Blue find them with a Vexilar: when the Gain control is set sufficiently high to easily show your bait, you will not see a ‘second echo’ of the bottom signal. (Details are in the owner’s manual and instructional DVD that come with every Vexilar.)
Sticky-bottom areas in middle depths have bonanza potential. “That’s the frontier in ice fishing,” says Genz. “When you find those fish, they’re often the biggest ones in the lake, and they’re usually not pressured. You can have those spots to yourself.”
(Lindy makes Techni-Glo and Go-Fer-It clip-on weight depthfinders, that let you manually probe for the rod-tugging resistance of sticky bottoms.)

Good Prime Time Spots
Even if you get on a good bite in the middle of the day, chances are it will die away come prime time. The fish are more active at prime time– and precisely because of that, not likely to remain in their daytime haunts.
At prime time, key on edges!
If midday fish were in thick weeds, look along the edges of the weeds.
If daytime panfish were tight to the bottom in a depression, look for them to move up on the shallower flats and cruise for food at prime time.
If daytime panfish were on the flat sections of a sticky bottom area, look for them to move up on the side slopes at prime time, as burrowing insects poke out of their holes to feed on rising zooplankton. “Along those ledges,” says Genz, “the fish don’t have to stand on their heads to scoop things off the bottom.”

Seasonal Movements, too
If the ice remains for more than about a month or so, many fish will show seasonal tendencies. “This is another thing ice fishermen need to remember,” says Genz. “Fish will start out shallow at first ice, move to the middle of the lake at midwinter, and then move back shallow at late ice. It’s similar to what they do in the summer.”
Genz cautions that this does not rule out the potential for deep water fish at first and last ice, or shallow fish at midwinter. But it helps you start looking.

Water Clarity Means Everything
How deep is deep? How deep do the weeds grow? How deep do panfish go when ‘hiding’ from predators? It all comes back to how clear the water is. Generally speaking, the clearer the water, the deeper the weeds grow, and the deeper the fish go.