Effects of shrimp-trawling on abundance of benthic macrofauna in Gullmarsfjorden, Sweden

Hypotheses about effects of shrimp-trawling on large benthic macrofauna wer e tested in a manipulative experiment in Gullmarsfjorden, Sweden. The exper iment lasted 1.5 yr and included 3 trawl sites and 3 control sites, each of which was sampled at 4 times before and 4 times after trawling was commenc ed (a total of 480 samples). Gear and intensities were chosen to approximat e those before trawling was prohibited 6 yr before the experiment. The over all trend was that biomass and abundances of animals decreased as a consequ ence of trawling but few taxa differed significantly among treatments. The mean abundance of echinoderms, in particular the brittlestars Amphiura sp., decreased significantly and substantially after 7 to 12 mo of trawling. In general, however, changes in abundances of animals from one time of sampli ng to another, and from before to after trawling started, differed among si tes. General models based on size and feeding strategy did not accurately p redict differences among taxa in sensitivity to disturbances. Differences i n overall impacts between this and previous experiments are discussed in te rms of fishing intensity, natural variability and experimental design.