Basin Visual Estimation Technique (BVET) and Representative Reach Approaches to Wadeable Stream Surveys: Methodological Limitations and Future Directions
Basin Visual Estimation Techniques (BVET) are used to estimate abundance for fish populations in small streams. With BVET, independent samples are drawn from natural habitat units in the stream rather than sampling "representative reaches." This sampling protocol provides an alternative to traditional reach-level surveys, which are criticized for their lack of accuracy in estimating abundance at larger scales. BVET methodologies have been adopted and used by numerous government agencies for monitoring stream biota. Many of the assumptions of BVET methods however, cannot be met in streams where they are being implemented because of unsuitable conditions for BVET surveys. Lack of bed control structures, variability in flow regimes, and lack of consistency among observers create difficulties in assessing habitat using BVET methods. BVET methods also are used to assess assemblage structure in streams although that was not the application for which they were originally designed. Representative reach approaches also have problems, as they often do not accurately reflect conditions present throughout the stream. We review various studies in which BVET and representative reach methodologies were employed and make recommendations for their most appropriate application given a range of study objectives.