Sampling estuarine fish and invertebrates with a beam trawl provides a different picture of populations and assemblages than multi-mesh gillnets

Although many studies have compared different methods of sampling fish fauna, few have examined differences between active and passive gears over large spatial and temporal scales, which may lead to misleading conclusions about their suitability as sampling tools. Using data from two years of sampling in five estuaries of New South Wales (Australia), we illustrate differences in assemblages and size structures of populations of fish and invertebrates sampled with a beam trawl and multi-mesh gillnets. Multivariate analyses revealed that each method gave a different picture of assemblages of fauna. In general, the beam trawl was more effective than the gillnets in sampling penaeid prawns and several small species of fish. By comparison, the gillnets caught a wide size-range of several fishes of commercial and recreational importance, many of which were mostly absent in catches from the trawl. In some cases, however, differences in assemblages and size-structures of populations between methods depended on the particular estuary or period of time in which sampling was done. These findings not only reinforce the need for pilot studies in identifying suitable sampling gears, but also demonstrate that careful attention must be paid to ensure such studies are replicated over appropriate spatial and temporal scales. Moreover, while sampling with both the trawl and gillnets provided the most comprehensive picture of populations and assemblages, we highlight that the suitability of either sampling method depends on the specific objectives of a study and the particular species (or assemblages of species) of interest.