Measuring and assessing the physical impact of beam trawling

Jochen Depestele, Ana Ivanovic, Koen Degrendele, Moosa Esmaeili, Hans Polet, Mark Roche, Keith Summerbell, Lorna R. Teal, Bart Vanelslander, Finbarr G. O'Neill

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

Beam trawling causes physical disruption of the seabed through contact of the gear components with the sediment and the resuspension of sediment into the water column in the turbulent wake of the gear. To be able to measure and quantify these impacts is important so that gears of reduced impact can be developed. Herewe assess the physical impact of both a conventional 4 mtickler-chain beam trawl and a “Delmeco” electric pulse beam trawl. We measure the changes in seabed bathymetry following the passage of these gears using a Kongsberg EM2040 multi-beam echosounder and use a LISST 100X particle size analyser to measure the concentration and particle size distribution of the sediment mobilized into the water column. We also estimate the penetration of the gears into the seabed using numerical models for the mechanical interaction
between gears and seabed. Our results indicate that the seabed bathymetry changes between 1 and 2 cm and that it is further increased by higher trawling frequencies. Furthermore, our results suggest that the alteration following the passage of the conventional trawl is greater than that following the pulse trawl passage. There was no difference in the quantity of sediment mobilized in the wake of these two gears; however, the numerical model introduced in this study predicted that the tickler-chain trawl penetrates the seabed more deeply than the pulse gear. Hence, greater alteration to the seabed bathymetry by the tickler-chain beam trawling is likely to be a result of its greater penetration. The complimentary insights of the different techniques highlight the advantage of investigating multiple effects such as sediment penetration and resuspension
simultaneously and using both field trials and numerical modelling approaches.
Original languageEnglish
Pages (from-to)i15-i26
Number of pages12
JournalICES Journal of Marine Science
Volume73
Issue numberSuppl. 1
Early online date6 Apr 2015
DOIs
Publication statusPublished - 20 Jan 2016

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trawling
bathymetry
penetration
sediment
sediments
water column
particle size
resuspension
measuring
particle size distribution
field experimentation
water
trawl nets
modeling

Keywords

  • bottom impact
  • multibeam echosounder
  • numerical modelling
  • penetration depth
  • seabed morphology
  • sediment resuspension
  • soft sediments

Cite this

Measuring and assessing the physical impact of beam trawling. / Depestele, Jochen; Ivanovic, Ana; Degrendele, Koen; Esmaeili, Moosa; Polet, Hans; Roche, Mark; Summerbell, Keith; Teal, Lorna R.; Vanelslander, Bart; O'Neill, Finbarr G.

In: ICES Journal of Marine Science, Vol. 73, No. Suppl. 1, 20.01.2016, p. i15-i26.

Research output: Contribution to journalArticle

Depestele, J, Ivanovic, A, Degrendele, K, Esmaeili, M, Polet, H, Roche, M, Summerbell, K, Teal, LR, Vanelslander, B & O'Neill, FG 2016, 'Measuring and assessing the physical impact of beam trawling', ICES Journal of Marine Science, vol. 73, no. Suppl. 1, pp. i15-i26. https://doi.org/10.1093/icesjms/fsv056
Depestele J, Ivanovic A, Degrendele K, Esmaeili M, Polet H, Roche M et al. Measuring and assessing the physical impact of beam trawling. ICES Journal of Marine Science. 2016 Jan 20;73(Suppl. 1):i15-i26. https://doi.org/10.1093/icesjms/fsv056
Depestele, Jochen ; Ivanovic, Ana ; Degrendele, Koen ; Esmaeili, Moosa ; Polet, Hans ; Roche, Mark ; Summerbell, Keith ; Teal, Lorna R. ; Vanelslander, Bart ; O'Neill, Finbarr G. / Measuring and assessing the physical impact of beam trawling. In: ICES Journal of Marine Science. 2016 ; Vol. 73, No. Suppl. 1. pp. i15-i26.
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N1 - Acknowledgements This study was carried out within the EU FP 7 project BENTHIS (grant no. 312088). Our thanks go to VLIZ, the fishers of SCH18, and crew members of RV ISIS and RV Simon Stevin, and Hans Hillewaert for diligently providing logistic support. We are grateful for useful input by Adriaan Rijnsdorp, Antonello Sala´ among others, which was facilitated by the opportunity to present preliminary outcomes of our study at the ICES Symposium “Effects of fishing on benthic fauna, habitat and ecosystem function”.

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N2 - Beam trawling causes physical disruption of the seabed through contact of the gear components with the sediment and the resuspension of sediment into the water column in the turbulent wake of the gear. To be able to measure and quantify these impacts is important so that gears of reduced impact can be developed. Herewe assess the physical impact of both a conventional 4 mtickler-chain beam trawl and a “Delmeco” electric pulse beam trawl. We measure the changes in seabed bathymetry following the passage of these gears using a Kongsberg EM2040 multi-beam echosounder and use a LISST 100X particle size analyser to measure the concentration and particle size distribution of the sediment mobilized into the water column. We also estimate the penetration of the gears into the seabed using numerical models for the mechanical interactionbetween gears and seabed. Our results indicate that the seabed bathymetry changes between 1 and 2 cm and that it is further increased by higher trawling frequencies. Furthermore, our results suggest that the alteration following the passage of the conventional trawl is greater than that following the pulse trawl passage. There was no difference in the quantity of sediment mobilized in the wake of these two gears; however, the numerical model introduced in this study predicted that the tickler-chain trawl penetrates the seabed more deeply than the pulse gear. Hence, greater alteration to the seabed bathymetry by the tickler-chain beam trawling is likely to be a result of its greater penetration. The complimentary insights of the different techniques highlight the advantage of investigating multiple effects such as sediment penetration and resuspensionsimultaneously and using both field trials and numerical modelling approaches.

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