The RCC assumes that aquatic insects will adjust in their abundance, distribution, and position in the river to best utilize all of the organic matter. Fluctuations in the abundance of different groups can also be expected with the season (increases in shredders following large inputs of leaves in the fall, or increased numbers of scrapers following algae blooms in the spring and late summer).
We will also generally see a shift in the type of organic matter as one moves from 1st order streams down the river into higher order reaches. Imagine if me if you will a small mountain creek originating below a glacier or a winter snow pack in the Rocky Mountains. This first order stream is shallow, narrow enough that you can step across, and is winding itself through a forest dominated by lodge pole pines. Be it in the Rockies, the Smokies, or the Cascades, the organic matter in first order stream is going to be dominated by leaves, needles, and other large pieces of terrestrial organic matter. There will also be limited small pieces of organic matter washing into the stream as well as plant and algae growth in the stream. The insect community in these reaches is going to be predominately made up of Shredders and Collectors. Interestingly, we see an almost constant proportion of predators throughout the river though the species composition shifts.
As we move into mid-order reaches the stream is beginning to get wider, deeper, while the slope is getting smaller. We are still receiving some large organic material in the form of leaves and wood from the land, but are also seeing an increase in aquatic plants and algae. There is a marked increase of fine organic particle washing in from upstream. It is in mid-order streams that you will find the greatest diversity, number, and abundance of invertebrates. In this reach collectors make up the majority of the species and biomass, with grazers accounting for the second largest group. You may also find local concentrations of shredders where tributaries or flooding bring in quantities of unprocessed leaves and wood.
As we finally move to the higher order reaches (the Platte, Rogue, Illinois, Snake, and Mississippi rivers) the rivers increase in width, depth, and temperature, while the slope is greatly reduced. There may be trees and grass along the shores, but the organic matter they contribute to the system is minute compared to that grown in the system. Put your head under the water for a minute and picture the bottom of the river. You will see sand, silt, and organic muck bottom with a few cobbles (softball sized stones) or submerged logs. Minute plankton are the main food source in this stretch of the river and the invertebrate community again shifts to exploit it. These reaches are inhabited almost exclusively by Collector-Gathers and Collector-Filters (assorted true fly larva, chromonids, some caddis larva, and a few mayfly nymphs).
Using the RCC to Pick Your Pattern:
It’s time to take the RCC down to your river and help you pull the right patterns out of your fly box. You don’t need a hatch to be going off to pick a pattern that is likely to produce.
The RCC tells you which feeding types and families of invertebrate inhabit each stream order and therefore which invertebrates the fish are feeding on.
Whether you’re on a new stream or are fishing an old favorite, take a minute to look around. What order stream are you on? What is growing on the banks and in the water? Put your hand in the water and feel around – is it fine sediment, gravel, cobbles or boulders? How clear is the water (increased clarity will promote plant and algae growth in the stream)? What season is it (Did the system just receive a large influx of leaves during the fall or a spring flood?)? Finally, are there any tributaries in the vicinity where you are fishing that would be a source of larger organic matter?
Match your pattern to the prominent food type in the stream.
If you are in a reach receiving quantities of large, course organic material, tying on a caddis larva or a stonefly nymph would be a good bet. If you are in a reach with a soft sediment bottom and full of fine organic matter, prospect the pools and eddies with a chromonid, larva, or worm pattern. Are you in a mid-order stream with a boulder-cobble substrate covered with a fine film of algae (you might not see it but it is there!), drop your mayfly patterns.
I hope this will help you hook more fish and enhance you time on the water. Take some time to read your riv, and leave the sweet corn on the shelf.
Vannote R.L., Minshall G.W., Cummins K.W., Sedell J.R. & Cushing C.E. 1980. The river continuum concept. Canadian Journal of Fisheries and Aquatic Sciences, 37: 130–137.
Special acknowledgement and thanks to Professor Stan Gregory from Oregon State University from whom I borrowed some graphics.
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