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Float Tube Fishing in Ireland

Having a really great time fishing from the world's best floating fishing platform

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.

Where do brown trout in a large lake live? Is there a particular feature or terrain they like?
Individual brown trout use specific locations near cover (referred to as home sites) as resting locations during the day, and at night they move various distances, travel to and from a feeding place, and generally return to the same home site the next morning.
Some fish use multiple home sites, and the average separation between multiple home sites for those fish was over 500 m.

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.

Are rainbows preferences different to browns? Yes. In comparison, rainbow trout select cooler water temperatures and greater depths than brown trout. That's why winter fishing for rainbows is so good comparatively speaking. (If we fished for browns during winter they would take well too, because that is what happens in the US where winter fishing if permitted. They don't all spawn every year, many overwinter in the lake.) Rainbows are more daylight active too. Brown trout are better in slightly warmer water, and when the shallow waters of the lake warm up from the sun as the season progresses browns utilise these areas better. Brown trout tend to be less mobile than rainbow trout and make more use of the shallow littoral zone than rainbows, which is likely due to consuming more varied diet of the browns, whereas the rainbows consume a greater proportion of chironomids. 

Can we learn anything from other lake trout species? Yes. Cutthroat trout preyfish rarely locate in suitable places for hunting during the hours of daylight, so the cutts hunt and feed at night. That this gives them an advantage over the prey fish is shown by the fact that nocturnal foraging by large cutthroat trout accounts for 34–64% of all prey fish consumption. Small size midwater and bottom dwelling fish species the world over tend to have evolved similar shoaling and anti predator behaviours, so browns hunting different forage fish in different countries must still learn the same skills as trout in other countries, because the prey fish behave much the same, and so the predators in different places will come up with the same behavioural answers to hunt successfully.

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.

Are brown trout pelagic or benthic? Free water or bottom structure? Do they prefer open water or cover? Where do they rest when not feeding? The brown trout is adaptable, like people, some specialise in this behaviour, and other specialise in a different behaviour. Some will cruise the surface grazing on insect hatch surface drift, these temporarily develop a noticeably more silvery camouflage colouration while doing this. Early in the season, the previous year's dead decaying weed beds have asellus in quantities, live weed beds have shrimp in quantities, and and most trout will habitually feed on these. Larger brown trout will hunt sticklebacks and coarse fish. Later on insectivorous brown trout, which are the numerical majority, may bottom feed, grazing chara weed for nymph and crustaceans. Some of the trout will specialise in hunting corixa midwater in the 2' - 4' shallows. Gillaroo subtype trout specialise in snails and crustaceans.  The piscivorous trout will remain keyed onto the prey fish, but adjust to suit their new areas on concentration as coarse spawning time arrives.
A large supply of one particular food, like a heavy mayfly hatch will cause groups of trout to switch temporarily to the "easy food", before they revert to their own particular hunting skills.
The importance of wind drift should be appreciated, as the wind will often move all the surface food of a huge lake into a tiny area for a few hours, and the deep food to another. Trout in lakes will be very quick to capitalise on the accumulation. I have written an article on the Dynamic Effects of Wind on Irish Loughs which is specific on this subject.

When at rest brown trout locate in relation to woody debris and bottom structure like rocky broken ground and rough dropoffs, indicating a utilisation of the debris, probably for cover and/or feeding positions. Edge type places where rough bottom meets silty bottom with weeds can be particularly good.

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 daily occurring conditions move brown trout temporarily to other locations ? Wind direction, food distribution, light levels, cover for fish, the time of day or night, a possible thermocline all interact. It seems to me from my sonar that sometimes trout move en-masse into a midwater location for pelagic feeding on underwater hatches of chironomid pupae as they rise towards the surface from the deeps.

How do the trout know where to go? Either a combination of seasonal triggers learned by that lake's sub-specie of trout, or by a smelling of enzymes released by the bloodworm and pupae as they "blow their ballast chambers" to come up. I think odour is more likely, but trout would have to learn that an odour means available food. Stockie browns seem to fail at locating big water mid-water pupae, but wild trout are there feeding long before the surface hatch occurs. If sea bass can smell from substantial distances a peeler crab when the shell cracks and the new shell underneath is exposed to the water, it is highly likely that brown trout and rainbows can smell the equivalent "birth juices" released by a million midge pupae preparing to hatch all at the same time. There is no doubt that they are able to find and move in on subsurface hatches over deep water, however they do it. The (unfortunately now extinct) char shoals were observed by Irish fisheries staff to do it 30 metres down, in 60-90 feet of water in L. Conn , and trout were mixed in those shoals of feeding salmonids. Remember, since this is buzzer pupae, we are not talking piscivorous trout, unless the ferox types go after other smaller pelagic trout and char, which they undoubtedly do.

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.

Daily Movements:
The hourly activity of fish increase dramatically at dusk, continue at a lower level overnight, and then increase again at dawn before declining to near zero during the day. Movements from daylight cover to nocturnal feeding areas, involve greater distances than normal daylight movements. The movements at the feeding area, in the dark, may be short because the trout is where the food is.

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.

Are there seasonal migrations that "clear out" some locations of big trout, and "switch on" other locations?
Seasonal Movements:
Fish tracked for more than 1 year used the same home sites each summer and generally exhibited similar behaviour each year. Acoustic tagging of brown trout indicated that the trout use much of the available lake but do not remain in the extremities of the inlets in summer.
 In winter  - to - spring the trout are widely distributed throughout the lake including the inlets, but in summer were only detected in the main lake and not in the inlets. The acoustic tracking also indicated that trout did not display behaviour that could be interpreted as site affinity. It was concluded that they did not have home ranges, but were nomadic and covered large areas. The tagged trout were often located near the shore (within approximately 200 metres) .
There are reported home range and homing abilities in brown trout, but no such behaviour was observed in these browns. The trout distributions were related to food resources and the fish distributions correlated with areas where there was an abundance of preferred prey, or prey of a large size. Lake Eildon trout are piscivorous, whereas the New Zealand trout were invertebrate feeders. A piscivorous diet may force trout to follow the food source and limit the development of home ranges or territories.
Lake Eildon does not have the extensive weed beds of New Zealand lakes and macroinvertebrate production may be relatively low as a result; this is supported by the low frequency of benthic organisms in the Lake Eildon trout.
The difference between invertebrate feeders and piscivorous browns matters, because Ireland's Midland lakes are very fertile with huge quantities of invertebrate trout food, a trout in L Ennell or Sheelin can grow to 5lbs on a diet of invertebrates, shrimp, louse, crayfish, and mixed flylife. But the Western Loughs have a lower ph, and trout may switch to a fish diet at a lower size. This will increase their tendency to cover a wider area. The invertebrate feeders stay where the food is, the larger fish eaters cover greater distances getting their greater food requirement. Note that where they hunt they likely use local features for ambush.
Do brown trout follow wind drift to greater distances? We don't know for sure. Maybe pelagic specialist brown trout do, but they possibly get to their territorial limit, and go back, leaving what is beyond for their next door neighbours. In fact, on rivers, brown trout of larger size have been proven to have a wider territory than smaller trout in the same area, so this just happens as they grow bigger. Chasing and finding fishy dinners just pushes the trout's territory out further, until it seems to no longer be an area with boundaries at all.
A working guide: the bigger it is in size, the farther it may have come.
Late Season Migration:
As the season progressed the fish were tracked to the southern part of the loch and then up into the spawning streams.
It should be noted all trout don't spawn every winter. Many large ones at least have a strong tendency to spawn every second year only. Del Canty, a fishery biologist, fish breeder, and exceptional catcher of truly big trout told me once he believed that the rare absolutely huge monsters,  would some day be found to be naturally sterile fish, natural triploid if you like, or maybe spawners every 3-4 years only, and this accounts for their even faster growth than other large trout of less monstrous size.

If Large Browns are Active During the hours around daybreak and nightfall, what information is available on night fishing for freshwater predators? Not much unfortunately. Ray Johnson a Utah brown trophy hunter of unusual dedication wrote a book called Big Trout, and he certainly caught more twenty pound browns that anyone else on record, with photos to prove it. He trolled in the dark as a matter of routine relying on small tried and tested areas of water to produce. Johnson believed that the pre-dawn twilight period was vital to catch large brown trout. He would troll through same spot repeatedly, stopping only to move fast from one spot to the next and then troll that small place intensively. Much of his fishing was winter fishing after ice-out which is not permitted in Ireland so the tight locations he exploited may not exist in Ireland during the warmer months as most lake species spread out more during summer. I speculate that what Johnson experienced in shallow water in winter temperatures and winter light levels is exactly what happens in deeper water during the summer months, but deep trolling is not so simple, distant landmarks are less accurate, and not everyone uses GPS. Conclusions about fish behaviour derived from deep fishing tend to be somewhat less precise. Also the prey fish have a different environment and different tactics to evade the trout available to them. The general tendency to hunt prey into a horseshoe, rock/weed cup or reef wall and thus corner them will still be used by the trout because that is a fundamental way all trout hunt food that is not coming on a drift to them. It also explains the tendency why  the same precise rock, or gap between rocks in a huge bay a mile wide produces several big trout over several years. Local knowledge from time observing water is paramount.
Regarding the use of artificial lures at night, it's not the same species but there is some good information on American bass behaviour at night in lakes, that is very helpful as a starting point where conditions are similar to the features found in brown trout lakes. Here is an excellent article on this subject:

Night Bassing Postulates,  by Ralph Manns

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.



The Trout – The Natural History of the Brown Trout, Frost, W. E. & Brown, M. E.
Brown Trout in Ireland, O’Grady, Dr. Martin; Kelly, Myles; O’Reilly, Shane

Linking piscivory to spatial–temporal distributions of pelagic prey fishes with a visual foraging model, M. M. Mazur, D. A. Beauchamp

Brown Trout (Salmo trutta): a technical conservation assessment. [Online]. USDA Forest Service, Rocky Mountain Region, Belica, L. (2007, April 26).

Biology and movement of large brown trout in Lake Eildon, Douglas J (2008) , Fisheries Revenue Allocation Committee Final Report. DPI, Victoria

The Summer Movements of Large Piscivorous Ferox Trout, (Salmo trutta) in Loch Garry, Perthshire, Scotland, Joseph Thorley, Alastair Thorne, Alisdair MacDonald and Alastair Johnstone

Ferox Trout and Arctic Char, Greer, Dr. Ron

Importance of woody debris for stream dwelling brown trout (Salmo trutta L.), Karl Sundbaum

Movement patterns of large brown trout in the mainstream au sable river, Michigan, DIANA James S. ; HUDSON John P. ; CLARK Richard D.

Del Canty’s Bellyboat Bible, Canty, Del
Guide to Fly Fishing Pyramid Lake, Barron, Terry
Big Trout: How and Where to Target Trophies, Taylor, Bernie
Trout From A Boat , Moss, Dennis
Personal conversations with the staff of the Central Fisheries Board, Ireland, Irish Regional Fishery Boards, waterkeepers, commercial fishery owners, and my many angling colleagues too many to mention.

Night Bassing Postulates, Ralph Manns, BFHP Forum, Articles pages for Article #7



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