Trophy Trout : Finding Big Brown trout in large Loughs: Locations and Migration Patterns

This is a summary of scientific research published, and the proven knowledge to date, not a statement of opinions, or repetition of angling advice "heard somewhere". Some of my angling knowledge is added from diary, from logged results, or direct observations. Norm.

Do big brown trout prefer different locations to smaller trout? What are those preferences? Is there a particular feature or terrain big brown trout like? Yes. Larger brown trout prefer better cover whether that be increased depth (debatable) or rock cover or woody debris or a change in bottom type. The larger browns are usually found near larger concentrations of food than smaller trout, that's why they grew larger! Smaller trout will be driven out of a preferred home by bigger more aggressive browns. The smaller trout find the "best feeding ground", but the large fish will not be in the middle of this place, but instead be adjacent to this. The preferred place of the larger trout will have a "best hunting ground", a wide area within which the larger trout are hunting the smaller fish. So over time the actual specific cast that caught big fish, place, direction of cast (or trolling pass) is likely to catch other big fish on later dates, as they have occupied that specific preferred spot while on a hunting patrol type route. Summary: look over or under deep water by day, and near the surface in shallows by night, often near a feature that goes from shallows to deeps like a river inflow or a rocky reef extending out from shore or island.

Where and when do big browns feed? All research and angling results point to the same answer. The large trout go where their food is concentrated  in a particular place, and preferably when that food is active, making the food species vulnerable to attack. The largest trout are where a natural funnelling topographical feature concentrates quantities of food into a tight area. Find the food, the big trout will visit when their feeding time arrives. It's interesting to note that their activity cycle (during 24 hours) is identical to the activity cycles of Gammarus freshwater shrimp, Asellus water louse, and close to the activity cycle of the nocturnal crayfish, presumably an evolutionary link between predator and prey. The even bigger trout, the very large predator fish, will be following the smaller trout and coarse fish concentrations and turn up in the same places in their role as apex predator.

What depth do the large trout prefer?
Applying the trout's temperature preferences to the temperature and depths in Eildon Lake indicated that in winter, trout habitat extended from the water surface down to about 30 metres. In summer the increased temperature of the warmer surface layers push the preferred temperature water to 15 metres deep and compress suitable conditions for trout to a 10 metre strata between this depth/temperature and the thermocline, the top of the hypolimnion being 25 metres deep.
The presence or absence of a thermocline, and oxygen temperature needs of the trout can interact to create a layer of water in the lake which is preferred by the trout during the hot calmer months. In summer, the area of Eildon's suitable trout habitat was reduced by 71% from the winter habitat and was restricted to the main body of the lake and excluded the shallow inlets.
An average large Irish Lough on an average summer day, has no thermocline due to ongoing wind turnover,  so the trout can go as deep as their food is, 50-70 feet is no problem, but more food is living in the shallows. I would look at depths of 12 - 20 feet during day, and check down to 30 feet. At night I would fish surface level to 8 feet, firstly in depths between 3' and 8', and afterwards check the surface layer of water but over a deeper area.
These depth ranges would cause a lot of lake to be "eligible", but other filters can be used to narrow down the areas that qualify for angling effort, in particular the wind driven currents of the lough.
Wave break the surface film to reduce light levels and provide cover, so when a wave is present I shift angling effort towards the upper end of the depth band, and nearer to the surface.  The waves also increase lake surface area and this increases oxygen intake of low oxygen water, which energises fish in the surface layers, exactly the same way a cooler water does. Bright sun and calm can move them down in the water column, seeking cover and comfort. I personally prefer to fish deep when I believe the fish are deep. There is an alternative and you might not have to actually fish deep, because big brown trout can come up like a polaris missile after a shallow bait presented over deep water. I know of several instances where static Rapala lures have been taken by ferox/predator brown trout while the boat was stopped, and the rod resting on the side with work going on setting up other rods for salmon trolling. The rod resting went crazy and the trout was on. A following fish that hung about in the area after the boat stopped and lures taken in? A lot depends on how much they want it, and the realism/attitude of the static lure.

Do the trout in some locations "go down" while other locations the trout "come up on the take" to give us the false impression of fish stocks moving about?
Yes. Or the trout in one location come on the take while other trout in other locations go down. Due to changing conditions, like eg a passing area of wave within a generally calmer surface, taking zones can move across the lake from place to place, like a giant hand passing over a map of the large lake, and this affects desire of the fish under these passing zones to feed. This is a major lake fishing feature to be aware of.

Telemetry on Scottish Ferox shows that fish eating trout are significantly different in behaviour from insect or mollusc eating brown trout in that their home range is very wide or they don't have one, or it's located upon the food fish shoals which themselves move.
Brown trout, especially big ferox brown trout, are not territorial. The ferox with sonic tags cruise to all parts of the loch, moving a kilometre in a matter of hours. It is possible they used the wandering char shoals current location as their home territory. The telemetry results indicates that during the summer months Loch Garry ferox tend to cruise through the surface waters of the loch undertaking frequent dives. At night the fish become less active and move into shallower water closer to the shore. So the information indicates that ferox dive during the day to prey on arctic char located in deep water, rise up to a preferred temperature or light level after feeding, and become less mobile at night, moving into the margins to hunt shallower prey during the hours of darkness.

Australian fish eating brown trout are similarly mobile with no home range: The Lake Eildon brown trout on a fish diet did not display any home range behaviour and were generally found to roam over large areas of the lake. The fish that were tracked the most, used the entire length of the lake including some of the inflowing tributaries. There was no obvious association or affinity of trout locations with any particular lake feature or area. The trout generally moved around and did not stay in any area for long.

Are there daily migrations that "clear out" trout, and move fish to other locations?
Yes for the fish that are willing to move. The smaller fish are more local with smaller territories. they tend to stay put and "go down" when conditions are unfavourable. Take a look here: Large lake Series 2 : Effects of Wind and here Large Lake Series 3: Lough Zones, Fish Migrations & Location for more on this.

What distance from land do the trout prefer?
Research conducted on brown trout in the Great Lakes by telemetry has shown that about 90% of all trout are within a kilometer of the shore. It is a fair working assumption that  60% of all trout are within 400 metres of the shoreline, whether that be the main shore, or the shore of an island.  The trout is a creature of the shallows, and the majority of the other trout are usually oriented to offshore shallows, like sunken islands which may appear only during extreme low water events. The true ferox strain is more liable to travel greater distances from shore than "normal" trout of equal size, as it's piscivorous tendency takes it after pelagic food shoals, and may be found suspended over extreme deeps sometimes but in proximity to the shoals of preyfish, but even ferox will still make for shore and the surface layers after dark descends.

Dave Hawk, a distinguished and apparently deceased TX basser, used to suggest anglers fish windy points in daylight and at dusk, but fish quiet water at night, when bass need to hear and feel with more accuracy to feed successfully.

Many anglers believe bass are willing to move farther from cover at night. See the earlier post suggesting fishing the open water often found in swimming areas. Any sandy open beach with rocks or short grass and crawdads will do, particularly if it's quiet water. As this can be too much like random casting to open water, pick places with bisecting structures. Pick places, for example, where a fence or treeline from the shore to deep water bisects the paths of bass moving along the shore at a constant depth or near the surface.

When the moon is bright, fish lure colors suitable for early dawn and late twilight. White and chartreuse are often as good as black or red under a bright full moon.

Dirty water limits night fishing. Muddy-lake bass need bright sunlight to feed efficiently, so they day feed in very shallow water. And, night, dirty-water angling usually is poor for bass. Fish mainly clear to slightly stained lakes at night.

After dark, shad disperse and are found evenly throughout large areas of the lake (they can't see to school). They may be at all depths above the thermocline, or be concentrated at one depth. A good depth finder will show these scattered shad as clutter. However, a very bright full moon can allow shad schooling, and create fantastic open-water surface bites, by the biggest bass in the lake.

On dark nights, my data show bass shallower and more likely to suspend than on clear nights. I tend to fish only topwater, or near surface areas when it is very dark. When light is bright, in contrast, bass can see about as well underwater as they can during twilight. Any depth and bottom lure good at dawn and dusk is good under the full moon. And crank baits, jigs, and worms work well. Much better than they do in the deep dark.

Vegetation goes stale at night, emitting CO2 and using up O2. After about midnight, bass often leave weedbeds and move into open water adjacent to the beds to have ample oxygen. Try topwaters over deep water, many bass suspend at night. The scattered shad make good silhouettes against the lighter sky and clouds. This is particularly true on power plant lakes, where the lighted generator buildings may outshine the moon.

Forget the words about leaving grass, IF the grass is on a point where current brings in fresh oxygen. IN such spots, the bass love the grass all night.

Much has been said about noise and rattles at night. They work ---sometimes. But, a bass can sense ( hear and feel) very subtle movements. A natural presentation often works better than noise, particularly with C&R experience bass in clear, calm water.

Pre-spawn bass bite very well at night. My best fishing experiences at Fayette County Lake were fishing full moon nights in January, and February (50 pounds+, ten bass, if we'd kept them).

At night, with calm water, the bass hear depth finders, trolling motors, and boat noises with great clarity. If bass in your lake are heavily pressured and C&R experienced, turn off the gear unless you must use it to position your boat. Anchor if possible near honey holes.

Glowing, luminescent lures work sometimes, particularly on dark nights where bass haven't seen them many times before. BUT, a faint glow is better than bright. You want to bass to be able to find your lure against the dark bottom, but not able to see it from afar. You can recharge fluorescent baits with a flashlight, but a old camera flashgun does it better. Just don't use the lure until the glow has subsided. The glow lasts much longer than with a flashlight.

Black, black and blue, and black and red spinnerbaits have worked for me, as have buzzers of the same colors. Any color worm is Okey, as long as it's black and blue or black and chartreuse. the black is visible to fish looking up, but disappears against dark bottoms and vegetation. Bass eyes are however most sensitive to blue/green so blue and chartreuse tails actually give maximum contrast against these same backgrounds. Go two-toned at night, unless you're fishing on top.

I like fishing topwater but the idea of two treble hooks flying through the dark night air after a missed hookset sort of takes some of the fun out of it. So always hold your rod down and to the side away from the bow or stern. A missed strike will send the hook laden bait safely by. Actually this is a good idea even in the day time with any top-water or snagged lure, likely to spring back toward the boat.

Re Lures: chartreuse back/black bellied cranks like the Norman Deep Little N, (use a black magic marker and chartreuse bait) and black/chartreuse or blue tailed plastics. These work better than solid black. For an explanation, look on the BFHP Articles pages for #7: "Night Bassing Postulates.

Copyright for this article is Norman Greene's - reproduction only with permission of the author.