Fishing the River Continuum Concept – The Building Blocks – Part 1 of 2

Despite what I thought as a kid fishing at trout farms outside of Knoxville Tennessee or farm ponds in Nebraska, sweet corn is not a nature staple for most fishes. While some larger game fish will eat other fishes, almost all fish, for at least during some phase of their lives, rely heavily on aquatic invertebrates and zooplankton. My goal in this entry is to help arm you with the knowledge to be able to choose the best fly patterns for your stretch of river based on the season, and the river reaches position within the whole network river. To do this I’ll be breaking down the River Continuum Concept, but first I need to flesh out a few vital bones upon which the RCC is built.

First you need to understand stream order. The smallest creeks that start up in the top of the watershed are considered first order streams. When two first order streams come together they form a second order stream, two second order streams combining forms a 3rd order stream and so on. When a lower order stream flows into a higher order stream, the number of the higher order is retained (ex. When a 2nd order stream flows into a 3rd order stream; the stream below that point will continue to be 3rd order stream).

Secondly, the RCC assumes a knowledge invertebrate (aquatic insects) Functional Feeding Groups – dividing insects into groups based on how they eat. There are 5 function feeding groups - Scrapers, Shredders, Collectors-Gathers, Collector-Filters, and Predators. The prevalence of any group in a given stretch of river depends on the predominant types of food.

The Scrapers (or Grazers) eat the fine layer of algae, bacteria, and microbes that grow on every submerged surface. This group contains snails, scuds, shrimps, some caddis larva, a few stone fly nymphs, and most mayfly nymphs.

The Shredders are the first invertebrates to attack large organic matter in the stream (leaves, grass, aquatic plants, etc.). Whether it is leaves falling into the stream or algae and plants growing within the stream. They take the large pieces and break them down into bite sized bits. This group consists largely of caddis larva, stonefly nymphs, and some beetles.

The Collector-Gathers and Collector-Filters pick up the pieces left over from the shredders, feces, and other small bits of organic matter. This group is made up of some caddis larva, and the majority of the true fly larva and chronomids.

The final group is the predators. The predators include the dragonfly and damselfly nymphs, some mayfly and stonefly nymphs, hellgrammites, and the majority of the aquatic beetles and true bugs. They prey upon zooplankton and other aquatic invertebrates.
Now that we have the skeleton of the RCC we’ll flesh it out tie it into how to read your river and choose the best pattern in the next installment.

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 recognition and thanks to Professor Stan Gregory from Oregon State University from whom I borrowed some graphics.