An empirical test of biases in the rapid visual technique for species-time censuses of reef fish assemblages

For an assemblage of fishes inhabiting a warm temperate, rock reef near San Diego, California (USA), a series of censuses were made based on frequency of occurrence and standard numerical counts. These data were then compared with a parallel study based on the rapid visual technique (RVT) of Jones and Thompson (1978). Because the RVT ranks abundances according to frequency of encounter and disregards variations in the spatial distributions of different species, the method overemphasizes the importance of widespread albeit rare fishes but under-emphasizes patchy although abundant species. The discussion considers the relative merits of the RVT method for characterizing assemblages of fishes on temperate rock reefs and on tropical coral reefs.