Chasing BIG Trout - The Protein Theory

In this very informative article, Inland Fisheries scientist Rodney Walker reveals some innovate British lake fishing methods that just might undo the big fish we all know exist down there in our favourite lakes.

In the past decade or so, fishing techniques for catching trout in Tasmania have evolved dramatically. Along with the technological advancements in equipment both within Australia and overseas, the most notable of these changes is probably the adoption of methods that have been tried and tested in the United Kingdom. Loch style fishing is one technique that has proven highly successful here in Tasmania. This method originated in Scotland and I firmly believe that the United Kingdom has several other hidden methods that will take large bags of large fish down under if given the chance.

On a recent trip to the UK, I worked for the Fisheries department (Environment Agency), and through my work, met many anglers that all had a tale to tell. One of my work companions however, shared with me a fishing technique that has caught countless fish for him and many other anglers through the Loch's and Reservoirs of Scotland and England. So many in fact that the technique used has been prohibited in several waters throughout England.
The technique evolved from "the protein theory". The protein theory simply states that as fish grow larger, they often under-go a dietary change from insects and small aquatic/terrestrial invertebrates, to larger prey items, namely other fish. This piece of information, coupled with the fact that predatory fish can consume a prey item up to one-third of its own body length, has lead to fly fishing methods designed to target these elusive large fish.

The Technique
Fishing using this technique is really straightforward and is best practiced in weather conditions not favourable to most other fly-fishing methods (i.e. winds over 10 knots). This allows any fly fisher to practice their art in all weather conditions and at all times of year.
The most difficult part of this method is learning to fish the various depths until the fish are located. Lead core line will sink at about one foot per second, so by estimating the depth of water your fishing in, allow the line to sink freely to about 8 to 10 foot above the bottom. To do this, cast the line overboard and feed out additional line, while counting the fly down to the required depth. Once the depth is reached, allow the boats drift to work the fly across a chosen stretch of water.  It is best to allow the boat to drift without the aid of a drogue as this will keep the fly off the bottom and give the fly sufficient speed to resemble a small bait item. I find that by fishing over the stern and drifting bow first across any chosen water enables the speed and direction of the boat to be easily controlled. The use of a rudder will allow the boats drift direction to be controlled, however if a rudder is not available you can always use the outboard rudder or the oars (attached to the rollicks by the handles) trailing beside the boat to assist steering.
The depth that the fly is worked at can be varied by adjusting the time allowed for the fly to sink and also by the standard retrieval of the fly. Periodically retrieving the fly throughout a drift will also produce fish and may give you an idea of the water depth that fish are holding/feeding at. Fly size and colour are also important, so try several patterns, sizes and colours in order to achieve the best results.

Suggested Equipment
Windy weather over 10 knots are the conditions to look for, as this technique is best practiced in weather conditions that often turn fly fishermen away. The rough weather provides adequate momentum to the boat, and in turn works the fly to its full potential.

Lead core line and fly rods
These large fish eating predators will usually remain deep in the water column as they feed sporadically and remain in deep water for cover. In order to get a fly down to where these fish reside, a lead line is essential. Ten metres of lead core line attached to two hundred metres of memory free shooting head backing will comfortably fish water depths to 30 feet, however a full lead core line will easily dredge depths to 60 feet. A fly rod of A.F.T.M. weight greater than 9# is essential to fish any lead core lines and heavy rods with A.F.T.M weights over 13# will be required to use a full lead core line. Some saltwater outfits may cater for these weights and purpose built lead-lining rods are easily obtainable on the Internet. I use Steve Parton purpose built rods, namely The Imperator - AFTM 11#-13#, and The Beastmaster AFTM 13#-15# available at The locally produced Blackridge and Driftwood salt water rods should suit as well as the more expensive Sage, Strudwick and Loomis rods. Your local tackle dealer will be able to help source equipment that will plumb the depths.

A Boat With Depth Sounder or Fish Finder
A boat is essential unless fishing deep pockets of fast flowing rivers, where shore casting can cover fish. In most instances this technique will best target lake fish and therefore a boat is required to cover deeper areas of a lake. Being able to steer the boat on a long drift is also very handy. In order to do this a rudder that is either fitted to the boat or adapted from the oars, will allow obstacles to be avoided and any lake features to be tracked.
A depth sounder or fish finder will help find potential deep pockets (i.e. old creek beds etc) and locate fish within these areas. These electronic fishing aids are becoming increasingly more affordable and accurate, and certainly will add to the safety of your vessel.


Depending on the size of fish you want to target, flies can range in size from your standard Matuka's to large fish imitations up to 6 inches and bigger. Remembering that the larger the fly the fewer fish that will be big enough to take it, and obviously therefore the lower the catch rates. The up side is that using a 6 inch fly may only get one take for the day, but you can bet that the fish will be worth taking!

When and Where to use the method
The methods outlined above can be used at anytime throughout the season with great success. I believe however, that these larger trout often feed most vigorously early in the season after spawning, when they're attempting to regain lost body condition. This is also often the time when weather conditions can prevent the more traditional fly-fishing methods being employed

One fact that first convinced me that this method would work effectively in Tasmania comes from Lake Crescent. When this water was at its prime, it contained many trophy fish. These large trout fed almost exclusively on the golden galaxias (Galaxias auratus), a native fish in the Crescent and Sorell impoundments. These galaxias commonly grow to 15 centimetres but can reach lengths of 25 centimetres. Any dedicated fishermen of Lake Crescent (prior to its closing due to carp infestation) would no doubt have noticed the presence of these fish when cleaning their catch. The dominance of G. auratus in the stomach of these fish suggests the diet shift from the abundant insect life within these lakes to the almost exclusive consumption of baitfish.

This method can also be used in water bodies reserved for fly fishing only. It is in these areas where lure and bait fishing has not taken its share of the bottom dwelling fish, that this method may produce the best results. Often in these waters, especially if they are deep (such as Dee Lagoon), the fly-fishing angler only targets the top of the water column and ignores the deeper habitat. It is certain that in many of these areas, the larger protein feeding trout will reside and may never be caught by traditional methods currently employed. After all, these fish have no need to venture into the surface water as plenty of baitfish regularly frequent the depths for cover and protection.

In addition to this, now that there is no longer a closed season on seven of our best performing water bodies (Craigbourne Dam, Great Lake other than canal Bay, Lake Barrington, Lake Burbury, Lake Gordon, Lake King William and Lake Pedder), I believe that this method could become one of the better producing techniques throughout the winter period. During these colder times, all fish, large and small usually remain in deep water and therefore in order to catch them in numbers, we must fish in the deeper water.

I have witnessed this method being used with great success on Grafham Water in the United Kingdom, taking several predatory species such as; perch pike (zander) to 9 pound, northern pike to 25 pound, brown and rainbow trout to 6 pound. I am not suggesting that this technique should be adopted in preference to the more traditional methods already employed on our waters here in Tasmania, but I do think that it is a very useful addition to any fly fisher persons repertoire.

Rod Walker

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