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

Erik H Meesters,Magda J N Bergman,Finbarr O'Neill

doi:10.1093/icesjms/fsz250

Erik H Meesters, Magda J N Bergman + Show 1 more

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https://doi.org/10.1093/icesjms/fsz250

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Abstract

Abstract 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.

Highlights

In the southern North Sea, bottom trawls have been used for centuries until the tickler chain beam trawl became the dominant flatfish gear in the 1960s
Similar percentages of mortality were measured in some infauna in the trawl path (Rees and Eleftheriou, 1989; Bergman and Hup, 1992), while Bergman and van Santbrink (2000) reported 7–39% annual mortality among longer-lived benthic populations in the Dutch sector
We tested the impact of two alternative trawl types on 13 megafaunal species

Summary

Introduction

In the southern North Sea, bottom trawls have been used for centuries until the tickler chain beam trawl became the dominant flatfish gear in the 1960s. Graham (1955) reported damaged nontarget invertebrate specimens in trawl nets, and Groenewold and Fonds (2000) quantified this fraction as up to 60% of caught phyla. Graham (1955) reported damaged nontarget invertebrate specimens in trawl nets, and Groenewold and Fonds (2000) quantified this fraction as up to 60% of caught phyla. Similar percentages of mortality were measured in some infauna in the trawl path (Rees and Eleftheriou, 1989; Bergman and Hup, 1992), while Bergman and van Santbrink (2000) reported 7–39% annual mortality among longer-lived benthic populations in the Dutch sector. Latter authors stated that most of the casualties did not die while trapped in the net but in the trawl path due to physical damage or successive predation. Bivalve length was negatively correlated with trawling frequency (van Kooten et al, 2015). Declines in suspension feeders (de Juan et al, 2007), epifauna (Buhl-Mortensen et al, 2016), annual faunal production (Hermsen et al, 2003), biomass, species richness, species diversity, and habitat complexity (Collie et al, 1997; Thrush and Dayton, 2002; Reiss et al, 2009) have likewise been attributed to trawling

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