Comparison of gillnet and trawl in diurnal fish community sampling

The fish community in a shallow, eutrophic lake basin in southern Finland was sampled diurnally with gillnets and trawl. The differences in species number, relative abundances and length distributions were considered. The fish density estimations differed notably depending on the gear and diurnal period. The most abundant species in the trawl catch, smelt, was almost totally missing from the gillnet catch. The proportions of perch, roach, white bream and asp were higher in the gillnet catch. Gillnets regularly underestimated the proportion of small (<10 cm) individuals in size distributions. The trawl probably underestimated the density of piscivores. In the two gears, diurnal changes, in both fish catch and species distribution, were considerable. Both trawl and gillnets are needed to get more reliable figure of fish communities in shallow eutrophic lakes.