Comparison of mechanical disturbance in soft sediments due to tickler-chain SumWing trawl versus electro-fitted PulseWing trawl

Jochen Depestele (Corresponding Author), Koen Degrendele, Moosa Esmaeili, Ana Ivanovic, Silke Kröger, Finbarr G. O'Neill, Ruth Parker, Hans Polet, Marc Roche, Lorna R. Teal, Bart Vanelslander, Adriaan D. Rijnsdorp

Research output: Contribution to journalArticle

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Abstract

Ecosystem-based management strategies increasingly require assessments of bottom trawling impacts on benthic habitats at the detailed level of different gear types. Two types of bottom trawls for catching flatfish (tickler-chain SumWing and electrode-fitted PulseWing trawls) were compared by combining several observational and modelling techniques to assess the changes in trawl penetration and associated effects on the seabed texture and sediment sorting. Bathymetrical measurements using a multi-beam echo sounder (MBES) confirmed that the SumWing trawl tracks were consistently and uniformly deepened to 1.5 cm depth in contrast to 0.7 cm following PulseWing trawling. MBES backscatter strength analysis indicated that SumWing trawls (3.11 dB) also flattened seabed roughness significantly more than PulseWing trawls (2.37 dB). Sediment Profile Imagery (SPI) showed that SumWing trawls (mean, standard deviation) homogenised the sediment deeper (3.4 cm, 0.9 cm) and removed more of the oxidised layer than PulseWing trawls (1 cm, 0.8 cm). SPI imagery showed that the reduced PulseWing trawling impacts allowed a faster re-establishment of the oxidised layer and micro-topography in contrast to SumWing trawling. Particle size analysis suggested that SumWing trawls injected finer particles into the deeper sediment layers (~4 cm depth), while PulseWing trawling only caused coarsening of the top layers (winnowing effect). This is in agreement with numerical modelling, which predicted that SumWing trawls would penetrate deeper into the sediment than PulseWing trawls. The total penetration depth (mean, standard deviation) of the SumWing trawls (4.1 cm, 0.9 cm) and PulseWing trawls (1.8 cm, 0.8 cm) was estimated by measuring the depth of the disturbance layer and by modelling the erosion of the surficial sediments due to sediment mobilisation in the wake of the gear (SumWing = 0.7 cm; PulseWing trawl = 0.8 cm). Our study has shown that PulseWing trawls reduced most of the mechanical trawling impacts on the seabed compared to SumWing trawls for this substrate and area characteristics.
Original languageEnglish
Pages (from-to)312-329
Number of pages18
JournalICES Journal of Marine Science
Volume76
Issue number1
Early online date20 Sep 2018
DOIs
Publication statusPublished - 1 Jan 2019

Keywords

  • beam trawl
  • biogeochemistry
  • habitat impacts
  • particle size distribution
  • penetration depth
  • pulse trawl
  • seafloor integrity
  • sediment resuspension
  • Seafloor integrity
  • Pulse trawl
  • Sediment resuspension
  • Penetration depth
  • Biogeochemistry
  • Particle size distribution
  • Habitat impacts
  • Beam trawl

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