Estimated intensity needed for sampling flatfish assemblages in reference areas of tidal mud flats systems may be disproportionately costly and deleterious

Beam trawl surveys were carried out in a tidal stream system of the German Wadden Sea on two to three successive days of comparable weather conditions in three summers. The variability in time and space detected for plaice (P leuronectes platessa), flounder (Platichthys flesus), dab (Limanda limanda) , sole (Solea solea) and lemon sole (Microstomus kitt) was considerable eve n for species with a very high abundance. Other flatfish species such as tu rbot (Scophthalmus maximus) and brill (Scophthalmus rhombus) occurred only occasionally in the catches. Sampling effort calculated to detect a 50 or 2 0% difference between the surveys caused by immigration, emigration or mort ality appears to be disproportionate. It is argued that such a major sampli ng effort of reference areas in tidal mud flat systems is likely to influen ce the results, to harm the environment, and to be very expensive. (C) 2001 Elsevier Science B.V. All rights reserved.