During the warmer months when water temperatures rise, trout and salmon generally become less active, but the key to target active fish is to fish deep. Scott Gray explains

Trout and salmon (salmonids) are a cold water fish species which thrive in cool, well oxygenated water, in the warmer months of the year in the deeper lakes and impoundments they often change their behaviour as they are constrained by their physiological requirements. As the surface waters warm salmonids tend to prefer to inhabit the deeper cooler waters at this time of year so they make a vertical migration to depths which provide the right conditions for their survival.

Hooked up down deep to a hard fighting summer salmonoid.

Many of these deep lakes and impoundments undergo a process of ‘stratification’ which is a seasonal process that occurs during the warmer months in which the water column develops a thermocline (which is an area where there is a sharp drop in temperature) and often below this point there is limited oxygen available for salmonids to survive. Sometimes this phenomenon may occur as shallow as 5 metres, but in other waters it may be greater than 20 m. Salmonids are physiologically constrained by the water column and don’t want to spend too much time in the warm surface waters, but alternatively they need plenty of oxygen and can’t survive below the thermocline because of reduced oxygen, so as a result they usually congregate just above the thermocline.
When the fish congregate in this manner they are usually easy to mark up on your sounder and with a large concentration of fish in a narrow vertical zone in the water column once they are located it is easy target them providing you can get a lure down to them! Your sounder is of paramount importance in this situation and can be the difference between catching nothing and successful day out. The fish might not always bite, but at least you know that your lure is in the zone.
Deep trolling is a great technique for searching and catching salmonids in lakes in the summer months. Once you have identified the areas the fish are holding there is a number of ways you can get your lure down and this usually requires using some sort of a rig to present your lure at depth.
These rigs can be designed specifically for this purpose – some examples include down riggers, paravanes, release weight systems, deep diving lures and leadcore lines.
All have “pros” and “cons” and associated costs and your choice will depend on the style of fishing. Here are a few ways you can get your lure down to the fish when they aren’t on the surface.

1. Deep diver lure assist
• Pick a large deep diving lure (a 5m+ lure generally costs around $25)
• Remove both sets of treble hooks
• Run a lure off the back tow point about a metre behind the tow point.
• Works well for depths of around 5 metres maximum
• Effective for bibbed minnows or using soft plastics on a single hook
2. Weighted release clips or Snap Weights
• Cheap and simple (~ $25 for a packet of two).
• Basically consists of a clip, a split ring and a lead sinker.
• Choose weights according to depth, great for depths 2-6m.
• Use trial and error to determine what weight is required.
• Once the fish is hooked wind in the line, then pause and remove the clip then fight the fish with no resistance.

3. Paravanes
• Cheap and effective (<$20).
• Use the adjustable clip on the top of the paravane to control depth.
• Attach the lure directly to the paravane about 1-2m behind the tow point.
• Attaching the lure directly to the paravane may inhibit the way the fish fights.

4. Leadcore line
• Very effective (usually <$35 per spool).
• Coloured hollow braid with a lead core.
• Usually colour incremented every 10 meters.
• Suits baitcaster outfits with good line capacity (you preferably need 5 colours of leadcore on a spool for general use plus some braid backing).
• A great line to get your lure down from 2-10m in depth, depending on your trolling speed.
• Heavier than usual to fish with and requires a good quality level-wind reel to ensure that the leadcore line is spread evenly across the spool.
• Leadcore line is a little different and heavy to use, but is very effective!

5. Downrigging
• Comes in a range of sizes for different situations (you can spend from $200-$700 on a setup)
• Basically a rod and reel style set up to get your lure to depth.
• For the more serious angler
• Variable bomb or weight size depending on depth (bombs cost around $50)
• Great for trolling from 5-40m depth (has depth counter for easy depth measurement)
• More expensive than other conventional methods, but very effective.
• Use in conjunction with a sounder is very important to prevent gear loss and target fish in the strike zone.

There’s no reason you can’t catch big brown trout all year round by fishing deep!

Now that you have selected your preferred method of getting your lure down then you need to decide which lure is the best for the scenario that you intend to fish. Generally if you are using winged lures like Tassie Devils or Cobras then these will swim well at low speeds of 1.5-3km per hour. If you notice you are getting line twist then you are probably going too fast, so it pays to check the action on your rod and always test your lure in the water and check your GPS speed before you set your lures to depth. If you are using bibbed minnows then you can usually afford to run them at slightly faster speeds of 3-4.5km per hour. Like in any situation the size and colour of your lure selection is usually specific to the water you are fishing and the baitfish you are trying to represent. In low light situations I prefer darker lures and on clear days and when fishing in clear water I prefer lighter more natural colours.
While leader diameter is always an important consideration I usually tend to fish a bit heavier at depth than I do in the shallow margins, so it doesn’t hurt to increase the breaking strain of your leader as long as it doesn’t affect the way that your lure swims. When fishing deep I will use 8-15 pound fluorocarbon depending on the terrain that I am fishing.
While trolling for salmonids in summer is not something that anglers usually prefer it is actually a very successful way of targeting trout and salmon and the catch rates I’ve had over recent years have been just as good, if not better than those of the cooler months. It all about finding the fish and taking advantage of their behaviour which makes them congregate in relatively narrow zones in the water column. If you fish too deep or shallow you probably won’t get a strike, but if you find the congregating fish this definitely leaves the odds of a strike stacked in the anglers favour. Give it a try and I bet that once you have found the fish deep in the warmer months you will get instant results!
Scott Gray is located in south-west Victoria, but spends plenty of time chasing fish across Australia and the South Pacific. While he enjoys all forms of fishing you will often find him spinning for big brown trout in the region’s rivers and lakes or stickbaiting for kingfish or tuna along the coast. He has a rich background in fisheries science and education and is currently sponsored by Rapala VMC Australia.