Fish community structure is characterized in the U.S. Geological Survey's National Water-Quality Assessment Program as part of an integrated physical, chemical, and biological assessment of the Nation's water quality. The objective of the National Water-Quality Assessment characterization of fish community structure is to relate fish community characteristics to physical, chemical, and other biological factors to assess water-quality conditions. To accomplish this, fish community structure is described at sites representing selected environmental settings. In addition, spatial and temporal patterns in fish community structure are examined at local, regional, and national levels.
A representative sample of the fish community is collected by sampling a stream reach using two complementary methods. The primary collection method is electrofishing using backpack, towed, or boat-operated electrofishing gear; seining is a secondary technique. Other secondary techniques may be substituted after careful consideration of sampling efficiency and consultation with local fish ecologists. Before fish sampling is conducted, careful consideration must be given to collecting permits; protecting endangered, threatened, and special-concern species; and coordinating sampling efforts with other fish ecologists. After the sample is collected, individual fish are identified to species by ichthyologists. Length and weight measurements are taken, and the presence of external anomalies are recorded.
The U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program is designed to assess status of and trends in the Nation's water quality and to develop an understanding of the major factors that affect observed water-quality conditions an d trends (Hirsch and others, 1988; Leahy and others, 1990). This is accomplished by collecting physical, chemical, and biological data at sites that represent major natural and human factors (for example, ecoregion, land use, stream size, hydrology, and geology) that are thought to control water quality in the river basin. These data are used to provide an integrated assessment of water quality within selected environmental settings, assess trends in water quality, and investigate the influence of major natural and human factors on water quality.