By John Rasmussen
Every morning when the sun begins to rise, a collective biomass of plankton, more populated than all the species on earth combined, rise with it. This is the single largest migration in the natural world – a daily event comprised of an unfathomable number of individuals worldwide who serve as the basis of all aquatic food chains.
While fishing during the day, you may have noticed clutter on your flasher within the top few feet of the water column. These are giant plumes of plankton so dense they’ve left a signature on your electronics. Likewise, you may have noticed a similar clutter within the bottom half of the water column during the evening. These too are pods of plankton which have settled near the lake bottom for the night.
There are two types of plankton; Phytoplankton, which is plant-like in nature as they absorb sunlight and nutrients to grow; And zooplankton, which are animalistic in that they actively feed upon other living and decaying life forms.
Phytoplankton are comprised mostly of single-celled plants. Much like their cousins who remain rooted in soil, they too must reach for sunlight. Every morning at sunrise phytoplankton slowly ascends the water column where they will inhabit the uppermost layer until nightfall. This movement is known as Diel Verticle Migration and propagated by the sun. The light allows them to produce oxygen which in turn makes them more buoyant.
Following close behind and feeding on this phytoplankton are zooplankton which is mostly multicellular and can propel themselves through the water on their own accord. They feed on phytoplankton, bacteria, and decaying debris present in lake water. Copepods and water fleas are the largest of the zooplankton growing up to 5 mm long and because of their size, a favorite food of bluegill during mid-winter. Even when consumed in high numbers, however, these tiny creatures simply sustain the bluegill through the long cold winters of the north. Only when the ice begins to thaw will new, larger food sources be introduced, and only then will the bluegill be able to continue to grow in size.
Things like dragonfly larva, crayfish, leeches, and fish fry all become available in great abundance during warmer water months. However, as deep winter sets in, bluegills are forced to settle for much smaller sources of food. They have focused their eyes on tiny varieties of larval insects like midge fly larva, tiny annelids, and casemakers but most of all on the spectacular abundance of zooplankton that swims among them. To find these small shrimp-like crustaceans’ bluegills use the powerful lens of their eye. These lenses are so powerful in fact, they can easily be rendered useless under intense light. Therefore, bluegill are best suited to prey upon these mid-winter foods under lowlight when their sensitive eyes can readily focus on these small creatures without being strained.
If you ask the average angler, they’ll tell you bluegills are a daytime feeder – but this is not entirely true. During the mid-winter period, the largest of these fish often hunker down by day only becoming active when zooplankton descends. The largest bluegills in the lake will patiently wait until first light or dusk to actively hunt these creatures. The reasons for this are threefold…
Firstly, it is difficult for them to reach these swarms of plankton by day. Directly under a frozen ice sheet where water temperatures hover around freezing, cold-blooded bluegill would slip into a lethargic state making it hard for them to efficiently hunt. The bottom layer of a lake maintains a balmy 39 degrees all winter long, a much more suitable temperature.
Secondly, the sensitive, microscope-like nature of the bluegill’s eye will not allow them to effectively hunt these microorganisms when gathered below the ice. The bright white backdrop of the ice sheet and an environment glowing with natural light camouflages this clear bodied prey and blinds the bluegill’s sensitive eyes with a piercing light. If you encounter bluegills under the ice it is due to a lack of oxygen in the lake.
Lastly, the largest of the bluegill’s refusal to expel precious energy by day is based on necessity. In mid-winter, it doesn’t pay for large, heavy-bodied bluegill to actively search out prey throughout the day if that prey is so small it can’t make up for the calories expended in doing so. Smaller, more desperate bluegills may be found feeding throughout the water column by day, but the larger specimens have learned to conserve their energy wisely.
During the early and late ice periods, bluegills will be more active as many additional food sources can be found but in mid-winter, the larger bluegills have gone into somewhat of a hibernation. Not until plumes of plankton begin to rain down upon their stubby snouts, will they begin to frenzy once again.
What To Use
We’ve learned that bluegills feed on very small creatures during mid-winter months and are unwilling to exert very much energy in pursuit of them. In the coldest winter months, bluegills have become accustomed to inhaling their prey with ease. Getting them to bite a jig at all can be an enormous frustration. For these reasons, we strongly recommend using a tiny, #16(3mm) or #14(4mm) tungsten jig. Jeff’s Jigs and Flies offer jigs with some of the most lifelike zooplankton characteristics available. Companies like Kender’s Outdoors also make great jigs in these tiny sizes. Because these companies use tungsten steel to make their jigs, they drop at the same speed a much larger lead jig would fall allowing you to quickly get them down to frenzied bluegills despite the jigs tiny size. Tip them with two spikes or a wax worm for the best results.
Using a 1 to 3-pound test is a must as it will hang straighter, sink faster, move less water, and be less visible. The most important thing to remember when using these light lines is to have a reel equipped with a smooth drag system and to have it set right. Reels can often freeze up causing the drag to fail. We recommend using reels designed with an ice-resistant carbon fiber drag system. Companies like Okuma and Pflueger offer some great ice reels built with carbon fiber drag systems for under a hundred dollars.
This being said, the most important component in any ice fisherman’s arsenal is a quality, sensitive rod. When it comes to these light biting bull bluegills, nothing beats the Bullwhip by Tuned Up Custom Rods. This rod wields a strong yet highly sensitive tip making it extremely easy to detect even the softest of light bites without the need for a spring bobber. The high-vis tip quickly transitions into a powerful backbone allowing for instantaneous hook sets. There are many knockoffs of this nearly decade-old rod but they can’t compare to its strength and quality. For just over a hundred dollars, you can’t go wrong with a Bullwhip.