Finding ciscoes can help you catch more giant walleye, lake trout, pike, bass and muskies this fall. Here’s how

LEARN THE LAKE

The first step is to understand that most of our lakes are split into three separate and distinct zones of water from late spring through autumn. First there’s the warm 25- to 35-foot upper layer of surface water, known as the epilimnion. Then there’s the deep cold basin zone known as the hypolimnion, and separating the two is the eight- to 15-foot belt-like layer called the metalimnion, or thermocline. It functions like an invisible barrier restricting movement between the upper and lower sections. You can’t see it, but if you dive down into it, you will feel it, because the water temperature will plunge at least one degree per foot of descent.

Locating the thermocline is critical, because it’s the zone where ciscoes gravitate and thrive. It’s so profoundly important, in fact, that many biologists refer to it as the “cisco layer.” I like to call it something else—the shooting gallery. That’s because ciscoes bunch up so tightly in the thermocline that predator fish shoot up and down into it to get their favourite food.

Fish are cold-blooded creatures, so the only way they can regulate and control their body temperature is to swim in water that has the ideal temperature for their survival. Walleye, bass, pike and muskies are referred to as warm- or cool-water fish because their preferred temperatures are found within the epilimnion. Lake trout, burbot and whitefish, on the other hand, are cold-water loving species, with their optimal water temperatures typically found in the hypolimnion. Again, ciscoes are sandwiched between those two precincts, with their greatest abundance typically found in water temperatures ranging between 10°C and 14°C.

“Ciscoes dominate the thermocline due to the competing trade-offs between food availability, predation risk and metabolic drivers like temperature and oxygen concentration,” Therrien says. “At the thermocline, zooplankton densities are highest as a result of seston accumulation (carbon debris) that zooplankton feed on between the epilimnion and hypolimnion. Zooplankton is the major component of cisco diets, so it is profitable for them to stay at that depth.”

In terms of predator avoidance, the thermocline is an advantageous habitat for ciscoes to be in, as their major predators have more generalist foraging strategies. “If ciscoes can move away spatially from the other sources of prey, then their predators have to make a choice to pursue them,” Therrien says. “We can hypothesize that not all predators will make that decision, and some will instead forage for other prey away from them.”

The thermocline also has the optimal temperature and oxygen concentration that ciscoes require. “This is important, because to avoid predators, ciscoes need to optimize their metabolic rate, while keeping it low enough to not unnecessarily lose energy,” Therrien says. In short, ciscoes know they have a target on their backs, and that the predators have their crosshairs on them. The trick for anglers is to put that predicament to their advantage.

BONUS TIP: CISCO MANIA

Cisco expert Christian Therrien (above) says predators find the silvery prey fish so delectable that they’ll vacate their preferred warm, shallow comfort zones and venture into much colder, deeper water to find them. Therrien says he’s caught smallmouth bass 40 feet down while trolling for lake trout and northern pike at depths of 90 feet, for example.