A Modified Drop Net for Sampling Fish Communities in Complex Habitats: A Description and Comparison with Other Techniques

Abstract

AbstractA modified drop net (area = 19.3 m2) was constructed to enhance the collection of fish from within complex freshwater habitats. The net was evaluated in three pools located within the Pilbara region of north Western Australia. The net's efficiency was determined by comparison with gillnetting and beach seining; accuracy of the net was investigated using the toxicant rotenone. In terms of efficiency, the modified drop net and beach seine generated similar descriptions of the fish community (relative abundance, species richness, ordination of a species–abundance matrix); panel gill nets collected a diminished subset of the community. Efficiency of the drop net remained relatively constant among pools, whereas the seine became increasingly easy to use as habitat complexity decreased. In terms of accuracy, the drop net produced estimates of total fish abundance similar to those obtained by use of rotenone and adequately depicted site‐related differences in fish community structure (multivariate ordination in space). The drop net and rotenone collected similar numbers of species, but the drop net missed some species that were present in very low abundance. The drop net also underestimated the abundance of one benthic species. We recommend use of the drop net when studying ephemeral pools where habitat complexity changes through time or when precise estimates of density are required. Beach seining, which has minimal gear requirements, is recommended for situations in which only a general description of the community (species–abundance matrix) or species richness information is required. When the drop net is used, gill nets should also be used to collect large size‐classes that are in low abundance.