First indications for reduced mortality of non-target invertebrate benthic megafauna after pulse beam trawling

Two alternative stimulation techniques to reduce mortality in benthic megafauna were tested relative to standard tickler chain beam trawling: longitudinal electrodes (pulse trawl) and longitudinal chains. Longitudinal chains caused higher mortality than pulse trawling in 3 species. Standard trawling gave higher mortality in Echinocardium cordatum than pulse trawling. Between longitudinal chain and standard trawling were no significant differences. This trend in decreasing mortality from longitudinal, to standard and then pulse trawling was confirmed by a similar decline in: i) numbers of significant species mortalities per trawl type, ii) average mortalities, i.e. longitudinal chain caused 41% more mortality than standard trawling and pulse trawling 43% less, iii) pre- and post-trawling community dissimilarities. A significant majority of species showed higher mortalities after longitudinal than after standard trawling and, conversely, lower mortalities after pulse trawling. Trawls with longitudinal chains instead of cross tickler chains increase megafaunal impact. On the contrary, pulse trawling can reduce the impact, although average mortality remains substantial (25%) even in impoverished benthic test assemblages in the southern North Sea. Power, generally was low and reference areas, free of (pulse) trawling, and inhabited by more vulnerable taxa will facilitate higher powered studies on the impact of standard and alternative trawling techniques.