Aquatic entomology is one of the most important aspects of fly fishing that both lake and stream anglers will be exposed to and learn from. This is a huge subject that one could literally study throughout their entire angling life. However, it is essential that we are at least able to identify those insects that are important trout food and that we also have a basic understanding of the insect’s life cycle and habitat preferences. An integral part of the aquatic entomology subject is recognizing how the various insect life stages move through the water and then applying that information to the way in which we present and/or retrieve our flies.
In streams, much of the aquatic insect life are able to utilize the current to move or drift them as they complete emergence cycles or simply move from one type of habitat to another. In lakes, the larval, nymphal and pupal stages of insects must propel themselves to locate food, avoid predators or reach the surface in order to emerge into the adult form. One of the ways fish recognize prey items is by the unique swimming or movement actions displayed by the food source. Let’s take a closer look at how the various life stages of the important aquatic insect orders move. Keep in mind that these are staple food sources for trout and other fish species found throughout the stillwater world.
Damselflies and dragonflies of the Order Odonata are active swimmers while in the nymphal stage. Damselfly nymphs utilize a 3 lobed set of caudal lamellae or abdominal gills to propel them in a fairly slow, sinusoidal or snake-like motion through the water. They will swim for 3 to 8 inches; pause for up to a couple of seconds then resume moving. Fully developed nymphs swim more continuously as they urgently search out emergent plant stems to crawl up onto and complete the transformation to the adult stage. Dragonfly nymphs swim by venting water through the tip of their abdomen. This action gives the nymph a short, 3 to 5 inch quick burst of speed. Nymphs can sustain several of these fast movements in succession prior to taking a brief rest. In most situations dragonfly nymphs are happy to be crawling along the vegetation or lake bottom in search of food and usually only employ the “jet propulsion” swimming system to avoid predators.
Caddisflies (Order Trichoptera) undergo a complete metamorphosis or life cycle. Most species inhabiting stillwaters belong to the case maker group. These larvae live within a case which is built from bits of vegetation, particles of sand or other debris. Larvae move by using their 3 pairs of legs to crawl and pull their case slowly along the lake bottom and amongst the aquatic vegetation. Their cases leave telltale tracks in the marl or mud flats that cover shoal areas of the lake. Caddis pupa develop within the larval case. The fully developed pupae break out of theirlarval cases and swim quickly to the surface of the lake. Their ascent is aided by an elongated and feathered hind pair of legs which act as oars to quickly move them through the water. Pupae are often swimming up through 20 feet of water and are thus extremely vulnerable to predation by fish. The adult emerges from the pupal stage as soon as the pupa breaks the surface film. The actual pupal swimming action consists of relatively fast 3 to 6 inch long movements followed by brief pauses.
Mayflies (Order Ephemeroptera) are another common inhabitant of productive stillwaters. Most lake dwelling species are good swimmers that are capable of fairly quick but short bursts of speed. Developing nymphs seek food and cover amongst the vegetation growing up from the shallow shoal areas of the lake. When mature, the nymphs will swim to the surface to emerge into the dun or non-reproductive adult stage. The mature nymphs typically swim on a 20 to 30 degree angle to the surface of the lake. They swim in a sinusoidal motion in moderately fast 2 to 4 inch bursts. The nymphs will rest or pause regularly during their ascent. Once at the surface, a split forms along the back of the nymphal shuck to allow the adult form to emerge.
Midges of the Order Diptera are unquestionably the most diverse group of insects inhabiting fresh water. A typical small productive lake in western North America could be host to literally a hundred different species. Midges or chironomids also undergo a complete metamorphosis or life cycle. Larval and pupal stages are poor swimmers but both require an ability to move in order to complete their respective life stages. Most stillwater midge larvae live in the benthic or bottom substrate of the water body. In many instances the larvae construct simple “mud tubes” in which they peer out from to feed on detritus. Larvae do leave their tubes in search of more ideal habitat and in other instances can be swept out of their tubes by strong currents formed during a turnover event or a rapid fluctuation of water levels. In either case the movement of the larvae is restricted to an ineffective wiggling motion. Midge pupa typically develop within the larval tube. Fully developed pupa exit the larval tube and ascend vertically to the surface of the lake. The pupa do not actually swim but wiggle and squirm up through the water. Their ascent is aided by gases trapped beneath the pupal shuck. Often, movement is rather rapid during the last couple of feet before reaching the surface. It is not uncommon for pupa to ascend through 40 feet of water making it a very slow and vulnerable emergence process.
Overall, the movement of these aquatic insects is slow or at best they can move at a moderate speed for a very short distance. Some, like midges only rise or elevate through the water column. It can be hard for many anglers to slow their retrieves down and then maintain the slower pace long enough to effectively retrieve the entire length of a cast.
The strip and hand twist are two basic retrieves that all stillwater fly fishers should be comfortable using with the various food sources being imitated. The strip retrieve is as simple as it sounds and it is the basic retrieve for almost all fly fishing situations. The rod hand lightly pinches the fly line between the thumb and index (first) finger while the retrieve hand uses the same two fingers to pull or strip in a set amount of fly line. It takes a lot of practice to conduct a 4 inch slow strip retrieve cast after cast for several hours but if that is how the damselfly nymphs are swimming then it is best to go with the flow. Without patience and practice, those 4 inch strips soon become 8 then 12 inch pulls!
How slow is slow? For instance, to imitate a slow 2 inch strip retrieve count up to 2 seconds while the 2 inches is being retrieved. A fast 4 inch retrieve would count between 1 and 1.5 seconds per strip. Caddis pupa probably swims the fastest of these aquatic insect food sources. A fast 6 inch strip retrieve should take approx. 2 seconds to complete.
The hand twist is the other basic retrieve that should be mastered by all stillwater fly fishers. This is a busy retrieve, meaning that it requires more hand movement while at the same time helps to slow down the retrieve. The other advantage of this technique is that the angler has more control over the retrieve as the retrieve hand is always in contact with the fly line. The rod and retrieve hand start off in the same positions as the strip retrieve. The fly line is pulled down by the thumb and index finger of the retrieve hand while at the same time rotating the retrieve hand wrist outward thus leaving an open palm. The fly line is then hooked around the bay finger of the retrieve hand and then brought back to the thumb and index finger. This completes a full hand twist. As the maneuver is repeated coils of line will collect in the palm of the retrieve hand. It is best to release the fly line after 2 or 3 coils have accumulated. The hand twist is certainly the preferred retrieve to use when imitating the midge pupa either rising up through the water column or very slowly moving the pupal pattern horizontally through the water. In these instances a complete hand twist could take upwards of 8 seconds to complete.
The strip and hand twist retrieves will allow the angler to match the movement of these essential stillwater food sources. It can also be beneficial to impart a bit of irregular movement to your fly as it is being retrieved. In other words, try adding several very short, quick one inch strips in succession during any normal strip or hand twist retrieve. I routinely mix in 3 or 4 of these quick strip tactics into any stillwater retrieve. Sometimes this off tempo movement is enough to commit an otherwise slightly sceptical trout into taking the fly.
Wind drifting from an anchored boat is also an effective technique to present flies being fished with floating fly lines. It is used most commonly with mayfly nymphs, damselfly nymphs, caddis pupa and midge pupa. Although technically not a retrieve, wind drifting takes advantage of gentle wind conditions to naturally move the sunk fly in a subtle undulating motion horizontally through the water column. A cast is made sideways or perpendicular to the direction of the wind. A large arching bow develops in the fly line as the waves carry it downwind. The length of the leader and weighted versus un-weighted flies determine where in the water column the fly will travel. Make sure the rod is secure when using this tactic!!
It takes practice in order to get comfortable with these retrieves. While on the water watch for the real insects and note their swimming and movement patterns. That will be the best check as to how realistic your retrieves are being conducted.
For many western stillwaters, early to mid-summer is the time of the year that larger species of chironomids emerge. These pupae which are often in excess of 5/8 th’s of an inch in length regularly emerge from deeper water, sometimes as much as 40 feet in depth. These deep water emergences provide an abundant and safe food source for trout. It is also quite common for trout to feed on both larvae and pupae very close to the lake bottom. Such was the case last year when fishing one of my favourite Kamloops area lakes. A quick look at the waters edge revealed a major windrow of large pupal shucks, a very good sign of things to come. Once the boat was in the water we started slowly covering the lake in search of emerging and adult chironomids while at the same time monitoring my depth sounder. We soon observed pupa suspended in the surface film and adult chironomids sitting on the water that was 29 feet in depth. Almost immediately, fish markings, and some very large ones, began to appear on the sounder screen. There was not a continuous parade of fish crossing the sounder screen but enough to know that they were there and worth spending some time trying to catch them. The sounder also indicated the trout were consistently between 3 and 5 feet of the lake bottom. We chose to fish with strike indicators which would allow pupal patterns to be suspended at the depths the fish were appearing on the sounder. Needless to say, it was not a pretty site trying to cast out a 25 foot long leader plus indicator. However, a very open casting loop and slow casting stroke achieved the necessary results. A slight breeze provided just the right amount of movement to the flies as they slowly moved through the suspended fish. This technique worked well enough that day to fool three rainbows between 5 and 11 pounds.
A good understanding of the chironomid life cycle and appropriate fishing techniques used in conjunction with a properly set up depth sounder were the keys to such a successful day on the water. Depth sounders or fish finders are very sophisticated electronics that can be a valuable aid for the angler in a multitude of fishing situations.
One of the biggest challenges to successfully fishing stillwaters is understanding its underwater structure. To many anglers, a lake appears as a deep featureless bowl. Knowing the “lay of the land” is fundamental in determining where and how to fish a lake. Littoral or shoal areas, drop-offs and deepwater zones of a lake correspond to the riffle, run and pool zones of a typical stream or river. Each of these 3 habitat types offer potential fish and fish food habitat at various times of the stillwater or stream season. Fish finders or depth sounders can accurately point out the key geographic features of a lake basin. This becomes particularly important when fishing murky or algal stained waters as shoals and drop-offs cannot be seen with the naked eye. Key physical features such as the depth and extent of shoals, transition zone of drop-offs, weed beds, sunken islands and even the texture of the lake bottom can all be viewed on the screen of a depth sounder. As their name implies, fish finders can also identify the presence of fish, mark their exact depth and give an indication of relative size or body mass. These units will also mark the extent of algal blooms and the depth where thermoclines become established. Thermoclines are narrow bands of water which are formed when an upper warmer layer of water meets a cooler layer of water. Thermoclines will often act as a barrier to mixing and can therefore affect the distribution of oxygen and the vertical migration patterns of zooplankton.
HOW FISH/DEPTH FINDERS WORK
Fish finders or depth sounders operate using the principals of sonar (SOund, NAvigation and Ranging) which was developed during World War II to track submarines. Sonar uses sound waves to determine the presence and location of underwater objects. A transmitter, transducer, receiver and a display panel make up a sonar unit. Basically, an electrical signal is sent from the transmitter to a transducer which converts the signal to a sound wave and sends it through the water. When the sound wave strikes an object the signal is rebounded or echoed back to the transducer. The transducer then converts the echo to an electronic signal which the receiver sends to a display or viewing screen. The time taken to send a signal and receive a return echo is used to determine the depth of the object. The transmitter sends many signals per second which results in the continuous recording of the bottom image of the lake. Other objects like fish, downed trees or weed beds will also send back signals and show up on the display screen. There are a number of variables that affect the amount and quality of information obtained from a fish finder. High frequency sonar signals (greater than 150kHz) have increased resolution but travel shorter distances in the water. Lower frequency signals have less signal resolution but can travel or receive impulses from a greater distance. The design of the transducer is also important in the effectiveness of a fish finder. The transducer emits a sound wave in a cone shaped beam. Wide cone angles produce a greater view of what is under your boat but at the expense of depth capability. Narrow cone angles such as those less than 15 degrees are more suited for salt water or deeper applications. As an example, a 90 degree transducer cone sending a signal through 25 feet of water will provide a 50 foot wide diameter area of coverage on the lake bottom. Numerous fish finder manufacturers offer models designed with multiple beam transducers in order to achieve the wide cone angles used for more specialized fishing situations.
There are also fish finders designed with side scan or horizontally directed transducers. Some manufacturers offer a side scan transducer as an option thus allowing one to switch back and forth between the two transducers. This feature has good application to stillwater situations because again much of the fishing effort is in shallow water.
There are also compact hand held sounder units available that provide a digital display of the depth. These flashlight sized units are perfect for packing into hike-in lakes or flying into remote fishing camps that may not be set up with more sophisticated fish finders.
SELECTING THE RIGHT FISH FINDER FOR STILLWATERS
Most fish finders are designed for use in a hard hulled crafts such as fibreglass, wooden or aluminum boats. Transducers are designed for both permanent and portable installations. They can be mounted permanently to the inside hull of a boat or to the outside of the transom, fitted to an electric motor or temporarily attached to the transom of a boat with a rubber suction cup support. After market accessories including portable transducer brackets for boats and pontoon boats and float tube fish finder mounts are also available for most of the popular brands of fish finders. The key features to consider are frequency of the signal being sent and received and the transducer cone angle. Cone angles of between 50 and 150 degrees are ideal for stillwaters because the majority of the angling effort is done in water less than 30 feet deep.
INTERPRETING THE FISH FINDER
Present day fish finders are considerably more advanced than those available even 10 years ago. Many manufacturers offer the latest “side imaging” feature that definitely has applicability to trout lakes. As with most modern day electronics, the new depth sounders do a lot more than just tell you the depth. That means one must read and understand the operating manual to fully take advantage of it’s capabilities. A key function found on most fish finders is the sensitivity control. This regulates the ability of the unit to detect objects and create an echo signal. Sensitivity is affected by such things as water clarity, algal blooms and interference from other electronic devices. One of the best ways to learn about your sounder is to play with it on a clear water lake where trout or other fish can be seen swimming under or around your craft. These conditions will illustrate just how fine adjustments can be made in order to filter out the size of sonar markings such as small fish or suspended debris.
Fish finders can be a very useful aid to the stillwater angler. They can be invaluable when learning the underwater structure of a new lake and thus identifying the preferred habitat of trout or other game fish. A properly calibrated unit with the appropriately sized transducer can indicate the location and size of fish plus identify the depth to which algal blooms extend and outline the formation or absence of thermoclines. This “electronic” information can then supplement one’s understanding of prevailing food sources, emergence timing and fishing tactics.