samples are collected at synoptic sites, only one sampling reach is required. Retrospective data can provide information concerning questions addressed by synoptic sites.
The sampling season should occur during low- and stable-flow periods (usually mid-June to early October). Sampling during low- and stable-flow conditions minimizes problems that occur with reduced stream access during higher flows, and maximizes the su itability of wadeable stream sampling methods, which facilitates comparability of data among sites. Choosing a sampling season in which flow variability is low increases the likelihood that samples throughout the study unit can be collected under similar flow conditions and reduces the chance that an unusually high flow would interfere with sampling.
Life history characteristics also must be considered in relation to the sampling season. Many fish species make extensive seasonal migrations. However, studies have shown that fish populations and individual fish tend to remain in the same area during summer low-flows (Funk, 1957; Gerking, 1959; Cairns and Kaesler, 1971). Thus, sampling efficiency tends to be greatest during this time period (Allen and others, 1992).
Fish community sampling considerations must be addressed before sampling takes place and fish community structure is characterized. Data collection is only a part of the process of gaining an understanding of fish community structure. In addition to a nalyses of retrospective data and reconnaissance of candidate sampling locations, consideration must be given to collecting permits; protecting endangered, threatened, or special-concern species; and coordinating sampling efforts with other fish ecologists.
Collecting permits must be obtained prior to sampling, and all project personnel must comply with State laws regarding fish sampling. The collection of fishes is regulated through State-issued collecting permits. State agencies typically require perm it holders to submit a report summarizing data-collection efforts. Sufficient lead time (at least 2 months) must be allowed between the time of permit application and scheduled dates for sampling. The appropriate law enforcement authorities must be cont acted prior to each sampling event, because some of the methods or gear approved in a collecting permit are illegal for use by nonpermit holders.
Endangered, threatened, or special-concern species require careful consideration during sampling. Endangered species are those in danger of extinction throughout all or significant parts of their ranges. Threatened species refers to those taxa that are likely to become endangered in the near future. These definitions were established by the Endangered Species Act of 1973, and aquatic organisms defined as endangered or threatened