spatial and temporal patterns in fish community structure are examined at local, regional, and national levels.
The fish community sampling design incorporates existing data with assessments of the fish community at sites representing selected environmental settings. The type of sample collected to describe fish community structure is a representative sample and requires that geomorphic channel units (pools, riffles, and runs) of the sampled stream section are representative of the geomorphology of the stream and use of multiple sampling methods.
The sampling reach is the section of stream sampled for fish and should include at least two examples each of two different types of geomorphic channel units. Where this is not possible, the length of the sampling reach should include one meander wavelength, based on a distance of 20 times the channel width. In addition, a minimum-maximum sampling reach length of 150 to 300 m (500 m in wide streams) for wadeable streams, and 500 to 1,000 m for nonwadeable streams, is established to provide a minimum sampling reach length necessary to ensure the collection of a representative sample of the fish community and limit sampling reach length to a distance that prevents unnecessary sampling and minimizes crew fatigue (and associated reduction of sampling efficiency). Sampling should take place during low- and stable-flow periods. Prior to sampling, consideration must be given to collecting permits; protecting endangered, threatened, or special-concern species; and coordinating sampling efforts with other fish ecologists.
Each of the methods designed to collect fish is selective for some component of the fish community and varies in its sampling efficiency. Using sampling methods that complement each other takes advantage of differences in selectivity and efficiency among methods.
Electrofishing and seining are the two methods used to obtain a representative sample of the fish community. Backpack electrofishing gear are used in relatively shallow (less than 1 m deep), small (less than 5 m wide) headwater streams. Towed electrofishing gear are used in relatively wide (greater than 5 m) wadeable streams with sufficient access for towed gear. Sampling of wadeable streams using electrofishing gear begins at the downstream boundary of the sampling reach and is conducted in an upstream direction. Two passes are conducted, and all fish are processed immediately following completion of each pass and released downstream of the sampling reach. Electrofishing boats are used to sample nonwadeable streams. Sampling begins at the upstream boundary of the sampling reach proceeding in a downstream direction by maneuvering the boat along one shoreline. A second pass is conducted along the shoreline not sampled during the first pass.
Seining is conducted after electrofishing to complement electrofishing collection efficiency and obtain a representative sample. Three types of seines are used to collect a representative sample: (1) a common sense seine, (2) a bag seine, and (3) a beach seine. Wadeable streams are sampled by seining using the common sense seine, the bag seine, or both. In riffle areas, a common sense seine is used to conduct kick seining. A sample collected by kick seining is taken at every riffle within the sampling reach. The samples from all riffles are combined, and the fish are processed immediately. In wadeable sampling reaches that are relatively free of obstructions, the bag seine is used. Seining downstream