Marine News from the Great Lakes

Getting’ Down with Summer

Published: Friday, August 15, 2014



clientuploads/news/August 2014/GettingDownWithSummer.JPGDuring the warmest days of the fishing season, Great Lakes’ water temperatures reflect the conditions in the atmosphere above. Of course, that’s the case year-round, but at no time do water temperatures affect fish behavior more than when they peak each July and August.


Actually, that should read “behave less,” for many of our favorite cold-blooded gamefish species shut down to a degree when their fluid surroundings assume bathtub temps. Warmer water holds less of the life-giving oxygen that fish need, and by staying somewhat lethargic, the fish require less food for fuel—read that food—and the oxygen it requires to pursue it.


The fish also often go deep this time of year to find the coldest water possible. But the fish can only plummet to a certain point before hitting the wall called the “thermocline,” a depth below which temperatures dramatically plummet and oddly enough, oxygen is suddenly scarce and most fish cannot survive. During the dog days of summer, the thermocline may set up as shallow as six feet or as deep as sixty; each water body is different and the line between oxygen rich and barren may fluctuate by the day, hour, or area of the lake. And it is a lake or reservoir phenomenon–although deep, slow moving rivers have been known to display a thermocline.


Relegated to remaining above the thermocline, this time of the year fish tend to stack-up and suspend at particular depths where they find just the right combination of temperature, oxygen, and food. These comfort zones can be extremely specific, and added to the lethargic ways of many of the game fish—which are not inclined to move very far out of their way to investigate, let alone eat, an offering—it can make it difficult for an angler to induce a strike.


This is when controlled-depth fishing devices come into their own as invaluable tools for anglers. While there are many fishing accessories that can be used to control the depth of a presentation, none perform the act as precisely as downriggers.  


In its simplest form, a downrigger consists of an arm or “boom” with a pulley at one end and the other fitted to a spool of cable. It can be threaded through the pulley and cranked to raise and lower a weight into the water from where it is mounted on the back or side of a slow-moving boat.


That weight, usually made of lead weighing from a pound to twelve or more, is fitted with a release clip that is snapped onto the to the fishing line, which the weight pulls down to a specific depth and holds, as it trails the bait or lure behind. One or more additional lines, called stackers, can be held with clip releases set on the cable above the weight to present baits at various depths. The near-vertical presentation is dictated by the weight of the ball and the forward speed of the boat–the heavier and slower the more vertical the weight hangs.

What a downrigger allows the angler to do is present baits at a precise depth–and keep them there. When a fish finder or trusted fishing buddy tells you that the trout are suspended at 23 feet, with a downrigger you can drop your baits to run at exactly 23 feet, putting them into the feeding range of the fish.      


That precision is key this time of the year when many of our most popular game fish species suspend at the coolest oxygen-rich water they can find, which is often just over the thermocline. By noting on your fish finder the depth level of the thermocline–which most modern sonars can discern and display as a visible line or shadow–you can drop your baits to troll just over that level and into the maws of the fish that lurk there.


Downriggers come from small, portable, manual models that actually fit into an oarlock to sophisticated powered rigs capable of trailing devices that measure speed and water temperature at the ball. There are even video cameras, that you see on many Great Lakes charter boats, that transmit live images to display screens monitored by anglers on the boat above. In between are simple manual downrigger models that can be temporarily fitted to mounts attached to the transom, gunwale, or rails of trailerable-size boats and used only when conditions dictate – which across much of the Great Lakes is right about now!

tags: Fishing

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