Fig 1.
Schematic drawing of the tickler chain beam trawl (left) and the pulse trawl (right).
For each gear the front (top) and bottom (middle) view of the beam or wing is shown as well the rigging of the tickler chains and ground rope, or electrode arrays and ground rope. Bottom contacting gear components are the shoes, tickler chains and ground rope of the tickler chain beam trawl, and the nose, ground rope and electrode arrays of the pulse trawl.
Table 1.
Estimated hydrodynamic drag (Hd in 103 N.m-1) of different types of beam trawls used in the flatfish fisheries in the North Sea [40].
Fig 2.
Histogram of the mean towing speed of small (< = 221 kW) and large vessels (>221 kW) using a tickler chain or pulse trawl.
Towing speeds were estimated from the VMS recorded speed of PLH.
Table 2.
Mean towing speed of pulse licence holders when fishing with the traditional tickler chain beam trawl or pulse trawl.
Fig 3.
Changes in fishing effort (fishing hours) and landings of sole and plaice of the Dutch beam-trawl fleet (ALL) and the subset of PLH fishing with a tickler chain or pulse trawl (PLH) and fishing with a pulse trawl (PLH-pulse).
Plaice landings also include landings with the twin otter trawl. Solid lines refer to the total fishing area. Dashed lines refer to the SFA.
Fig 4.
Spatial distribution of trawling intensity (annual swept area ratio, SAR) of the total Dutch beam-trawl fleet before (TBB 2009–2010) and after (Pulse 2016–2017 and TBB 2016–2017) the transition to pulse fishing.
Pulse fishing is restricted to the SFA south of the demarcation line at 55oN and 56oN.
Fig 5.
Changes in the area swept, the surface of the sea floor which is trawled at least once per year (footprint) and the number of 1x1 minute grid cells with trawling activities recorded for the total Dutch beam-trawl fleet (ALL) and for the subset of pulse license holders fishing with a tickler chain trawl or a pulse trawl (PLH) or with a pulse trawl (PLH-pulse).
Solid lines refer to the total fishing area. Dashed lines refer to the SFA.
Table 3.
Percentage fishing effort (swept area) of the Dutch beam-trawl fleet and percentage surface area by Eunis habitat in the SFA.
Fig 6.
Time trends in the impact indicators of the total Dutch beam-trawl fleet (ALL) and for the subset of pulse license holders fishing with a tickler chain trawl or pulse trawl (PLH) or with a pulse trawl (PLH-pulse).
Solid lines refer to the total fishing area. Dashed lines refer to the SFA.
Table 4.
Ratio of the impact of the total Dutch beam-trawl fleet and the subset of pulse license holders in 2009 before and in 2017 after the transition to pulse trawling in the total fishing area and the SFA.
Fig 7.
Time trends in the amount of sediments mobilised by the Dutch beam-trawl fisheries (ALL: thick black), the subset of pulse license holders fishing with a tickler chain trawl or pulse trawl (PLH: thin black) or fishing with a pulse trawl (PLH-pulse: red).
Solid lines refer to the total fishing area. Dashed lines refer to the SFA.