January 27, 2014
Most pike waters offer considerable diversity, from the aquatic equivalent of lush rainforests to hostile deserts; yet, unlike our world — where landforms and features are relatively static — the environment in which most pike live is dynamic. The layout often changes dramatically from one season or calendar period to the next. A portion of the lake that was pike paradise in summer often won't attract any fish during winter.
"Pike in the winter are poorly understood," says Dr. John Casselman, a former Senior Research Scientist with the Ontario Ministry of Natural Resources, and a world-renowned pike specialist. "I've always said that we know less about what they do in the winter than any other time of the year. What pike do in the winter is much more impressive than what they do in the summer."
According to Casselman, our pike fishing success throughout the year, especially in the winter, is influenced by three environmental factors — water temperature, the amount of dissolved oxygen water holds, and the quantity of light streaming through it. These parameters affect the growth and survival of the fish, he says, and determine where we're likely to find them. These factors also play a role in determining their mood.
Growth, Activity and Water Temperature
"Although the growth optimum for pike is 66°F to 70°F," Casselman explains, "they grow well in water temperatures ranging from 50°F to 73°F. That's why we call them mesothermal or coolwater fish. They thrive in temperate environments where the water is highly transparent, where there is an abundance of vegetative cover, and where the development of the vegetation-openwater interface is high."
You won't find many places in the winter where the water temperature is near optimal for pike — least of all, in prime pike country where most lakes, rivers, and reservoirs have at least a foot or two of ice and snow blanketing the surface. But knowing that water temperature affects a pike's growth and activity remains important. While the fish increase in size much more slowly in the winter (only 3.9 percent of their maximum), unlike many other species, they continue growing. That means they're feeding, even though the icy water temperature may reduce their overall level of physical activity.
The amount of light entering the water column also has an effect on pike activity. Casselman: "We see maximum growth in their natural environment during periods of the year when the amount of daylight is greatest. Long day-length periods stimulate growth, undoubtedly functioning through the endocrine system and possibly through thyroxin and growth hormone."
Viewed another way, since pike feed by sight when days are long, as they typically are in the late spring and early summer, the fish consume more food more often, eating everything from suckers and perch to leeches and mayflies. Associated with extended dinner hours, not surprisingly, is a corresponding increase in swimming activity.
So, one would assume that in the dead of winter, when the photoperiod is typically short, the fish would feed little. But that is not the case, as many pike anglers who have enjoyed excellent ice fishing are aware.
"The science community can't fully explain some of the winter results," Casselman observes. "It is not known, for instance, why in some experiments where the day length was extremely short, and where it mimicked winter-illumination levels, the pike did not exhibit a marked decrease in their growth rate."
Could it be that in winter, while the quantity of daylight may be much reduced, the quality of it, after having passed through a foot or more of ice and snow, may be close to ideal?
"From angling studies conducted during the open-water period, we know that pike feed more actively on cloudy, overcast days than on bright, sunny days," Casselman says. "On days when light intensity is high, they feed more actively during evening and to a lesser extent morning twilight, and when light intensity is low."
Indeed, Casselman says that typical light levels under the ice in winter may closely approximate prime light conditions during the open-water season. It's also why winter pike anglers often enjoy success on sunny winter days, when the same conditions during the open-water season would shut pike down. As Casselman explains it, "The intensity of illumination in the laboratory that causes pike to be most active (300 to 700 lux) is more similar to the illumination just under the ice at midday in January (400 to 800 lux) than it is to summer midday intensities."
Casselman says angler success is most directly related to the amount of oxygen in the water. If the level falls below approximately 2 parts per million, the fish cease feeding.
"Any decrease in oxygen concentration effects a decrease in growth rate," he says. "The critical oxygen concentration is 0.84 parts per million. This lethal oxygen concentration is frequently encountered at low temperatures in association with winterkill, which occurs in lakes where oxygen is depleted under the ice cover in late winter."
Still, Casselman emphasizes, pike are extremely tolerant of low winter-oxygen levels. In shallow, weedy lakes where oxygen is greatly reduced during the winter as a result of plant decomposition, the fish readily survive oxygen concentrations as low as 3 parts per million.
While the pike may not die at these extremely low levels, their overall activity level and their feeding patterns are essentially nonexistent. Stressed for oxygen, the sluggish pike clearly have more urgent needs than finding dinner.
Casselman says that the ability of pike to withstand critically low winter-oxygen levels is likely a genetic characteristic inherited from the survivors of previous winterkill events. This fact explains why some pike may perish in one lake where winterkill is uncommon, yet survive in a shallower, weedier lake where this phenomenon is the rule, rather than the exception.
Casselman points out that the environmental factors just discussed, not an empty stomach, are what trigger pike to become active. In the laboratory, when water temperature, light levels, and oxygen conditions become prime, pike activity is spontaneous and totally independent of foraging.
He also says that deteriorating environmental conditions can cause pike to become active, which in the process increases angling success. He discovered, for instance, that the catch-rates during January and February were often high because the oxygen levels in the shallow, weedy bays and coves were often depressed, the fish moving to areas of the lake where higher levels were present.
In fact, pike have an astonishing ability to locate areas of a lake, river, or reservoir richer in oxygen in the winter, leaving behind much poorer-quality digs. The fish are so attuned environmentally that they can follow a positive oxygen gradient, much like a hound on the trail of an escaping fox.
Indeed, every supreme winter pike location I've ever known has an oxygen-rich creek, stream, or river flowing into it. An example of one of my favorite spots is a major bay adjacent to the basin of a large lake, where In-Fisherman Editor In Chief Doug Stange and I set up one recent winter to film a segment for In-Fisherman television. The first pike that Doug hauled onto the ice and then carefully released was an imposing 22-pound fish. The second fish minutes later was an only slightly smaller 20-pounder.
The 75-acre bay is chockful of lush cabbage weeds in the open-water period. But these die and decompose over the winter, sucking oxygen from the water. They smell like mothballs, if you fish too close to the edge and snag one of last year's stalks. The pike slide out of the shallow bay and set up on the first lead-in rocky point that defines the transition between the oxygen-rich, warmer, deep-lake basin, and the oxygen-poor, cold and weedy flat. Pike may even ride out on, and relate to, the tongue of river water that runs through the center of the bay.
But not all winter pike movements are horizontal like this. In shallow lakes where the big, toothy predators and their prey can't escape to more oxygen-rich portions of the lake, the fish suspend directly under the ice where the last vestiges of oxygen remain. These vertical movements typically occur in February, as oxygen becomes depleted from bottom portions of the water column.
"The pike literally suspend on a 45-degree angle," Casselman says, "with their mouths sucking in the last inch or less of water at the ice interface that still contains a trace of oxygen. I've watched as they've used their fins to fan the water around their heads to create a current of water. The current directs more water through their gills, but it also creates a dome under the ice. And the pike literally poke their noses through the surface into that pocket."
*Gord Pyzer, Kenora, Ontario, was for more than 20 years an Ontario resource manager. Today, he's an In-Fisherman magazine field editor who has written numerous award-winning articles for our publications and has appeared along with In-Fisherman editors on television.