Chapter 18: Coldwater Streams
Robert E. Gresswell and Bruce Vondracek
Coldwater streams are typically found in headwater areas across North America. These systems tend to have channel slopes of greater than 2%, pool–riffle sequences that promote aeration, and riparian canopies that moderate temperatures. Environmental gradients and processes often produce continuous and predictable changes in habitat from headwaters downstream, and species assemblages (e.g., macroinvertebrates, amphibians, and fish) generally reflect the gradients.
Maximum daily mean water temperature is usually less than 22°C in coldwater streams. Water temperature is maintained by groundwater inputs and (or) weather conditions in high-elevation and temperate areas. Most coldwater streams occur in snowmelt-dominated drainages, but in regions that are more temperate, coldwater streams can occur in rain-dominated systems where groundwater inputs are common.
Productivity and faunal diversity in coldwater streams are low (especially in western North America) compared with warmwater streams. In Yellowstone National Park, for example, there were only 13 native fishes in almost 4,300 km of coldwater streams. At the same time, the proportion of coldwater streams occupied by fishes was great. Only high-elevation coldwater streams isolated above barriers were historically devoid of fish, apparently because they were not invaded following late-Pleistocene glaciation (Smith et al. 2002). Since the latter part of the 19th century, however, salmonids have been introduced into most all of these formerly fishless streams in North America.
Salmonids, cottids, and cyprinids are the dominant fish taxa in coldwater streams, and salmonids support highly-valued recreational fisheries. In fact, coldwater streams in North America attract anglers from around the world who seek opportunity to catch native and nonnative salmonids. In this chapter, abiotic and biotic characteristics of coldwater streams with emphasis on factors that influence fisheries management are discussed. Although historical and current approaches are noted, an emphasis is maintained on emerging management trends, concepts, and approaches. The reader is encouraged to seek detailed information concerning specific topics from preceding chapters in this book and cited literature. We have limited the discussion to potamodromous (migrating only in freshwater) and nonmigratory fishes; Chapter 19 provides information on anadromous (feeding and growing in the ocean or an estuary, but reproducing in freshwater) fishes and tailwater habitats.