It may not be apparent to the casual observer, or even to the novice fly fisherman, but beneath the stark beauty of a tumbling trout stream there lives a complex, thriving community of life. This community of microscopic organisms, aquatic insects, and fishes, is quite intricate. Each form of life, from the tiniest to the largest, is interlinked and dependent upon the other for survival. Scientists call these communities ecosystems, food chains, or food webs.
Aquatic insects, which include subsurface forms of the mayflies, caddis flies, stone flies, and midges, are the primary converters in turning microscopic food into bite size food for higher forms of life such as the trout. There are many orders of aquatic insects, and many families, genera, and species within each order. In their underwater state all these insects are called nymphs or larvae. The characteristic of these forms are discussed in the following:
If a trout stream is health, the most significant aquatic insect group will be the prolific mayflies of the insect order Ephemeroptera. Also significant, but presenting fewer feeding opportunities for the dependent trout, are the caddis flies (order Trichoptera ). The stone flies (order Plecopter) and the but on some streams certain species provide heavy periodic feeding: thus they are important to fly fishermen. There are other insect order, such as odonata (dragon flies and damselflies) and Hemiptera and Coleoptera (bugs and beetles), that can also be of major importance on streams with specialized habitats. But for the most part these would be exceptions to the norm on typical mountain streams or river, and we will limit our discussion to the first four orders named.
MAYFLIES (EPHEMEROPTERA)
Mayflies and trout have almost identical requirements for nutrients, water temperature, oxygen, and stream bottom habitat. With few exceptions a stream unfit for mayflies is usually unfit for trout. There are species within the orders of the insects that can tolerate pollution to the extent where oxygen is reduced considerably or is nonexistent. But such waters are not real trout waters, and so they will not be included here.
In thousands of seine test on hundreds of rivers during the past decade, we have found that the mayfly represents the bulk of the trout's diet. Mayflies exist in every conceivable stream habitat that is not severely polluted or completely smothered by silt. There have been recent claims that mayflies do not tolerate pollution as do insects of other orders, be we have not found this to be the case in our research, at least not on legitimate trout waters. On the contrary, in many cases we've found that where mild domestic pollutions was introduced to highly oxygenated, acidic streams in the form of nutrients, they may fly population has actually increased. Few trout river have taken the human abuse that has been given such famous domesticated rivers as the Beaverkill, the main Ausable (below Ausable Forks, New York), and the Au Sable (Michigan) to name a few. Over the last decades these rivers have been altered through logging, road building, and domestic development, yet today records show many similar examples. The point is that mayfly communities are surprisingly resilient and can with stand most changes in their environment short of lethal industrial pollution or wholesale domestic development.
On the same track, however, we have found that siltation, as a result of poor farming practice and overgrazing is the biggest threat to the survival of the mayfly and other oxygen loving insects such as caddis flies and stone flies. The clearing of land to the banks of a stream results in devastating siltation, which covers up the crevices in the streambed, eliminating the microscopic food farms and apartment complexes where the nymphs and larvae feed and live. The cementing of rocky crevices on the stream bottom changes the entire ecosystem. The elimination of trees and brush not only causes band erosion but also makes the stream heat up to intolerable temperatures, which reduces the vital oxygen supply so necessary to both insects and trout.
Mayflies can be classified in six extremely important families so far as the angler is concerned. (This deviation from the current technical mayfly classifications should prove more efficient and easier to use for the fly fisher, especially at streamside.) The nymphs of these families can be classified into four basic types: crawlers, clingers, swimmers, and burrowers. Each type is equipped with specific body characteristics and appendages, enabling it to survive in its required habitat. The crawlers are variable in size and appearance and generally inhabit stretches of medium current, although they may also be found in fast and slow water types; they consist of the prolific Ephemerellidae family, the feeble legged Leptophlebiidae family, and the tiny mayflies of the Caenidae family. The clingers are the swift water Heptageniidae family. The enormous Baetidae family is made up of quick swimmers, while the burrowing types are of the family Ephemeridae. The mayflies that fall within these basic nymph types, including all related genera and species, are treated comprehensively in our book Hatches, which also includes the evolution, biology, and identification keys of the mayflies. What follows here is a brief summary of the stages of the mayfly and its vulnerability to the trout in each stage.
When the mayfly eggs hatch on the stream bottom, the tiny nymphs (1/2 mm in length) feed on algae, diatoms, and detritus in the protective crevices of rocks. As the nymphs feed, they out row each of the nymphal skins and molt, many times, before they are mature enough to emerge as winged insects.
Contrary to the belief of many fly fishermen, during the nymphal stage (which constitutes 99 percent of its life span_ the mayfly is practically inaccessible to the trout, except during emergence. Only when they leave their hideouts during emergence or, a few days or hours prior to emergence sites, are the mayflies readily available to trout. Over the years, our research records and autopsies reveal the most trout seldom feed selectively on subsurface forms of specific insect species unless the species is active and ready to emerge, even though the streams may be teeming with nymphs or larvae.
When emergence is near, the mayfly nymph's wing pads become much darker and its body becomes more buoyant as the stomach is filled with air. The winged state of the insect within begins to push, stretch, and enlarge against its outer chitinous skeleton, commonly referred to as the nymphal shuck. The nymphs stop feeding now, and their only interest is in migrating to advantageous emergence positions.
As the nymphs move to these emergence sites, their now buoyant bodies frequently cause them to lose their footing, and they float dangerously up from the protection of the bottom. Sensing their vulnerability, they swim and wiggle desperately downward to regain their hold on the safe bottom. Many are gobbled up by the trout. The trout's selectivity at this time affords a good opportunity for the angler who chooses the proper nymph pattern and presents it correctly.
When the hatching hour arrives, the thorax begins to split. The nymphs leave the security of the stream's bottom for the last time and ascend toward the surface. This activity results in advantageous feeding opportunities for the trout, which become very selective as the size, color, shape, and behavior of the naturals.
Some duns successfully pop through the water and into the atmosphere, using the surface tension as an aid in evacuating their nymphal shucks. Some evacuate their shucks under water. During these periods the trout seldom take the surface duns, preferring the more vulnerable submerged duns or emerges, which have yet to unfold their wings from their thoracic humps.
According to the air temperature or the clumsiness of the individual species, the duns may linger on the surface for long periods of time, setting up even more opportunities for the trout. When they finally become airborne they settle in the foliage, where they hide under leaves or on branches. Here they shed their skins for the last time and transform into the brilliant, glossy winged insects called imagoes or spinners.
Shortly after the final molt the males mass in swarms over the riffles. The females flit into the undulating swarms intermittently, securing mates. Once paired they leave the swarm to copulate. Eggs fertilized, the females deposit their eggs to the water in various methods. Some jettison them en masse, dipping their posteriors into the water, while other (such as the large Ephermera burrower_ lie prone on the surface, quivering as they extrude their eggs. Others crawl beneath the surface of the water to deposit their eggs on the bottom. Their mission accomplished, both males and females fall to the surface in incredible numbers, spent, completing their cycle. All the trout need to do is feed on them effortlessly from a convenient lie.
By; Caucci and Nastasi
www.seattlegrapevine.com/user/zz_troutski/groups
