Polyethylene ropes are often mounted on beamtrawls in the North Sea to prevent net damages due to abrasion. The, so called, dolly ropes are wiped off after a short while and get lost at sea.
Only a small part of the plastic waste in the sea is visible to humans as a large part of it remains under the sea surface or far away from the coasts. On the shores of the North Sea, colorful, mostly orange or blue threads, ropes or balls are particularly visible during a boat trip or while walking on the beach.
Although the origin of plastic waste is often difficult to determine, it is likely that a large proportion of these colored plastic fibers originate from bottom trawling. Especially in the beam trawl fisheries directed to sole and North Sea shrimps, the nets are dragged very close to the ground due to the design.
To protect the bottom side of the gear, it is often provided with abrasion protection. Various materials can be attached to the meshes of the gear in order to prevent abrasion of the material on the seabed - especially of the codends.
One of the most common materials used as scuff protection in bottom trawling are the so-called „dolly ropes“. These are Polyethylene ropes (PE ropes), which are cut to size by the fishermen and woven into the net material.
During fishing, the dolly ropes fray very easily and parts of it break off. Within two weeks 10 to 25% of the material has already been torn off. After this time, the remaining cords become tangled or entangled, reduce their flexibility and cause sand and gravel to clog. As a result, the remaining dolly ropes are replaced.
The aim of this project is to develop and test trawl gear modifications that reduce or prevent the contact of the gear with the seabed, thus making the use of dolly ropes as abrasion protection superfluous. Initially we will focus on the shrimp fishery in the North Sea.
1. Change of gear design
The construction of a gear has a decisive influence on the behavior of the gear while fishing and also on how close the gear comes to the seabed. The following modifications are potential candidates:
2. Reduction of the catch of heavy material
The codend is also pulled down by catching heavy organisms (e.g., clams and sea urchins) or heavy material (e.g., stones and sand). Accordingly, one approach is to reduce the amount of these heavy materials - especially as they are unwanted bycatch. Several options are possible, such as:
Which gear modifications can reduce or avoid the contact between the gear material and the seabed?
How practicable are the newly developed modifications on board commercial fishing vessels?
Does the developed gear modification affect the catchability of the gear? It is important to distinguish the effect of the not-use of dolly ropes (e.g. due to changed selectivity) and the effect of the net modification.
How does a modified gear behave in long-term use, or can gear damage be reduced to an acceptable level in the long term?
Is it possible to transfer the solutions, developed within the project, to other fisheries?
1.2018 - 12.2020