Importance of Small Streams
Zero, first and second order streams account for most of the total stream miles within any watershed and cumulatively provide much more habitat for aquatic organisms than large rivers. Small streams are also highly productive systems, owing to their relationships with adjacent upland habitats. These areas of high productivity are often used for spawning and nursery habitat by fish that normally inhabit larger waterways as adults. Even intermittent and very small perennial streams play an important role in transporting invertebrates, detritus, and other organic matter that fuel downstream food webs.
One study in Alaska estimated that fishless headwater streams export enough invertebrates downstream to feed 100 to 2000 young-of-the-year salmonids per kilometer of salmonid habitat (Wipfli & Gregovich, 2002. Freshwater Biology (2002) 47:957-969). In another study, of Sagehen Creek in California , researchers estimated that 39 to 47 percent of rainbow trout in the population spawn in an intermittent tributary that flows for less than half the year (Erman & Hawthorne, 1976, Trans. Am. Fish. Soc. 105:675-681).
Small streams provide important summer habitat for cold-water fish that move up into headwater streams to escape unfavorably warm conditions in ponds and rivers. Headwater streams also provide a significant amount of woody debris input to mountainous stream systems.
In addition to providing critical habitat for fish, small streams support many animals that do not occur in larger streams and rivers. These include species of stream salamanders and crayfish, and probably countless other invertebrate species. Many rare species of crayfish are confined to a very limited number of small streams.