Search

Baumkurrennetze werden bauartbedingt sehr nahe am Meeresboden geschleppt. Um das Durchscheuern der Unterblätter dieser Netze am Meeresboden zu verringern, werden dort häufig Matten aus Kardeelen von Polyethylenseilen angebracht. Diese Tauwerks-Kardeele sind als 'Dolly Ropes' bekannt. Ein großer Teil des Dolly Rope-Materials wird nach kürzester Zeit auf See freigesetzt. Daraus ergeben sich folgende Probleme: • ökologisches Problem, u.a. durch Eintrag von Kunststoff in das Ökosystem und in die Nahrungskette • ästhetisches Problem, z.B. für den Tourismus an der Nordsee • Problem für die Fischerei und Schifffahrt, z.B. durch Einschneiden der Fasern in Motorwellen und Fischereigerät • mögliches rechtliches Problem durch Verstoß gegen das MARPOL Übereinkommen 1, dass jegliches Einbringen von Kunststoff ins Meer verbietet • mögliche/wahrscheinliche Verschlechterung der Größenselektion der Schleppnetze durch Verschließen der Maschen und dadurch eine Erhöhung der unerwünschten Beifänge Ziel des Projektes 'DRopS' war es, Netzmodifikationen zu entwickeln und zu testen, die den Kontakt des Netzes mit dem Meeresboden verringern bzw. verhindern und somit die Nutzung von Dolly Ropes als Scheuerschutz überflüssig machen. Im Rahmen des Projektes lag der Schwerpunkt zunächst auf der Nordseegarnelenfischerei, wobei die gefundenen Lösungen möglichst auch auf andere Fischereien übertragbar sein sollten. Aus einer Analyse der möglichen verschiedenen Ursachen für das Scheuern des Netzes am Meeresgrund (Abbildung 1; links) ergeben sich mehrere Lösungsansätze (Abbildung 1; rechts). Basierend auf diesen Ansätzen, wurden verschiedene Fanggerätmodifikationen diskutiert, ggf. (weiter-)entwickelt und getestet (Tabelle 1). Diese Fanggerätemodifikationen und die Ergebnisse werden ausführlich in Kapitel 3 beschrieben. [...] Beam trawls are towed very close to the seabed due to their design. To reduce chafing of the lower panels of these nets on the seabed, mats of polyethylene rope cardels are often placed there. These ropes are known as 'dolly ropes'. A large part of the dolly rope material is released after a short time at sea. This results in the following problems: • ecological problem, e.g. due to plastic entering the ecosystem and the food chain • aesthetic problem, e.g. for tourism at the North Sea • problem for fisheries and shipping, e.g. due to fibres cutting into motor shafts and fishing gear • possible legal problem due to violation of MARPOL Convention 1, which prohibits any dumping of plastic in the sea • possible/probable deterioration of the size selection of the trawl nets by closing the meshes, thus an increase of unwanted by-catch The aim of the project "DRopS" was to develop and test net modifications that reduce or prevent the contact of the net with the seabed and thus make the use of dolly ropes as chafing protection unnecessary. The initial focus of the project was on the North Sea shrimp fishery, and the solutions found should be transferable to other fisheries if possible. From an analysis of the possible different causes of net chafing on the seabed (Figure 1; left), several approaches to solutions emerged (Figure 1; right). Based on these approaches, different gear modifications were discussed, possibly (further) developed and tested (Table 1). These gear modifications and the results are described in detail in chapter 3. [...]

Bottom otter trawls with cut back upper panels were tested in the fischeries on Baltic Sea flounder and North Sea plaice to reduce cod by-catch. In a first series of experiments on board the fishing research cutter “Clupea” the cod-bycatch was reduced by 63 %. The catch of flounder was by 92 % higher in the cut back trawl. The same trawl with the same experimental set-up achieved aboard the fisching research vessel “Solea” on the other hand a reduction in cod-bycatch by 69 %. The catch of flounder was 23,3 % lesser in the topless trawl, which was in contrast to the “Clupea” trials. In the second series of experiments with the same cut back trawl the splits were shortened to reduce the net opening height from 0,9 m to 0,6 m previously. The cod-bycatch was reduced by 86 % and the catch of flounder was 81 % higher in comparison to the complete trawl. A prototype made of stronger net material but based on the cutting and rigging design of the tested cut back trawl with the shortened splits was tested with commercial twin trawlers. The cod-bycatch was reduced by 82,2 %, the catch of plaice by 43,3 % and the catch of dab by 44,6 % in the comparison to the commercial used trawl TV280. The flounder catch was in the topless trawl 10 % higher. In the North Sea in the comparison to a bottom trawl TV300 the cod by-catch was reduced by 89,8 %, but the catch of plaice and dab were 54 % and 58,7 % lesser. In the next step was a prototype of a normally in the North Sea plaice fisheries used trawl tested with a cut back of 2 m only. The cod catch was reduced by 16,9 % but the plaice catch, however , by 22,3 %.KurzfassungSchleppnetze mit verkürzten Oberblättern wurden in der Fischerei auf Ostseeflunder und Nordseescholle zur Verringerung des Dorschbeifanges erprobt. In einer ersten Versuchsserie mit dem Forschungskutter „Clupea“ wurde der Dorschbeifang um 63 % reduziert. Die Fänge der Zielart Flunder waren im reduzierten Schleppnetz dagegen um 92 % höher. Das gleiche Schleppnetz mit gleichem Versuchsaufbau erzielte auf dem Fischereiforschungsschiff „Solea“ dagegen eine Reduktion des Dorschbeifanges um 69 %, wobei im Gegensatz zu den „Clupea“-Versuchen der Flunderfang um 23,3 % im reduzierten Netz geringer war. In der zweiten Versuchsserie wurden die Netzstander am reduzierten Schleppnetz verkürzt, um die Netzöffnungshöhe zu verringern.Dadurch wurde der Dorschbeifang in Versuchen mit dem Forschungskutter „Clupea“ um 86 % verringert und die Flunderfänge waren im reduzierten Schleppnetz 81 % höher.Basierend auf dem Zuschnitt des erprobten Schleppnetzes, jedoch aus stärkerem Netzmaterial gefertigt, wurde ein Prototyp auf kommerziellen Doppelnetz-Kuttern erprobt. In der Ostsee wurde in diesen Versuchen der Dorschbeifang um 82,2 %, der Schollenfang um 43,3 % und der Klieschenfang um 44,6 % mit dem im Oberblatt verkürztem Schleppnetz im Vergleich zum Kutterschleppnetz TV280 reduziert. Der Flunderfang war im reduzierten Schleppnetz 10 % höher. Auf der Nordsee wurde mit diesem Versuchsnetz im Vergleich zu einem TV 300 der Kabeljaubeifang um 89,8 % verringert, die Schollenfänge waren jedoch 54 % geringer und die Klieschenfänge 58,7 % geringer als im Vergleichsnetz. In einer weiteren Variante wurde ein in der Nordseeschollenfischerei verwendetes Grundschleppnetz mit 2 m geringfügig im Oberblatt zurückgeschnitten und mit dem Prototyp auf einem Doppelnetz-Heckschlepper verglichen. Der Kabeljaubeifang wurde dadurch um 16,9 % der Schollenfang aber um 22,3 % verringert Johann Heinrich von Thünen-Institute, Federal Research Institute of Rural Areas, Forestry and Fisheries began publishing the Informationen aus der Fischereiforschung - Information on Fishery Research in 2010

Trials with the “topless” version (with reduced upper panel) of the bottom trawl resulted in a 63 % reduction of cod bycatch in numbers, compared to the complete trawl. Flounder catches increased by 120 % on average. Further modification of the net opening height to optimize the trawl performance are underway. Johann Heinrich von Thünen-Institute, Federal Research Institute for Rural Areas, Forestry and Fisheries began publishing the Informationen aus der Fischereiforschung - Information Fishery research in 2010. Johann Heinrich von Thünen-Institut, Institut für Ostseefischerei, AG Fischereitechnik

Mathematical modelling shows that the projection area of the trawl twine influencing its hydrodynamic resistance can be reduced by approx. 30 % through increasing the mesh size of the trawl wings and the conical parts of the trawls, in combi-nation with the use of thinner twine. The interrelation between fuel consumption and projection area of the trawl twine as well as the influence of the enlarged meshes of the wings and first panels on the catch composition can only be measured by trials on fishing boats. Johann Heinrich von Thünen-Institute, Federal Research Institute for Rural Areas, Forestry and Fisheries began publishing the Informationen aus der Fischereiforschung - Information on Fishery Research in 2010. Johann Heinrich von Thünen-Institut, Institut für Ostseefischerei

In 2004 the fish processing company Euro-Baltic Fischverarbeitungs GmbH Mukran, went into operation on the Isle of Rügen at the Baltic coast of Germany. About 20 % of the herring landed there is discharged from the cutters into the processing plant by pipes, driven by pumps, in case that the landed volume exceeds 10 t fresh weight. In such case the herring is transported in water suspension by means of a pressure-vacuum suction pump system into containers and further transported via conveyer belt to a flowscale. During this process most of the water runs off. It is however unknown how much water remains with the fish and is eventually weighted as fish. To estimate this proportion the mixture of water and fish was stored in special transport containers, which allow the measurement of the run-off. As a result the study shows that on average 2 % of weight measured by the tape scale is water. Along with this factors were determined which influence the variability of the proportion of water. Johann Heinrich von Thünen-Institute, Federal Research Institute for Rural Areas, Forestry and Fisheries began publishing the Informationen aus der Fischereiforschung - Information Fishery Research in 2010. Johann Heinrich von Thünen-Institut, Institut für Ostseefischerei, Landesforschungsanstalt für Landwirtschaft und Fischerei Mecklenburg-Vorpommern, Institut für Fischerei, Euro-Baltic Fischverarbeitungs GmbH

Estimation of the water content of herring landings caused by pressure-vacuum double tank pumps and using of multi purpose transport containers About 80 % of herring that is landed in the fish processing company Euro-Baltic Fischverarbeitungs GmbH Mukran, on the Isle of Rügen at the Baltic coast is transported from the cutter into the processing plant by pumping. For this purpose 700 l-Euro-size polyethylene tubs (containers) are filled with herring by means of a pressure-vacuum pump-systems during the unloading of the cutter. To be able to pump the fish from the hold on board it is kept floating in water (transport water). At the end of the pumping/transporting process the fish ends in a dewatering box before reaching the tub, where the transport water is separated from the fish. Then, the not completely dewatered fish is slipped into the transport containers. The amount of transport water reaching the containers depends on the type of PV-equipment and on the amount of transport water in the fish holds of the different cutters. Methodologically the mixture of fish and water must be weighed together. For the experiments specially designed transport container were used which allow the measurement of the run-off of the water to be quantified and thus to measure the proportion of water remaining with the fish. Based on 30 experiments it could be shown that on average 6 % of remaining weight of the mixture is water. Furthermore, factors were detected which influence the variability of the proportion of water. Johann Heinrich von Thünen-Institute, Federal Research Institute for Rural Areas, Forestry and Fisheries began publishing the Informationen aus der Fischereiforschung = Information on Fishery Research in 2010.

A primary objective of the Common Fishery Policy of the European Union is the reduction of discards and unwanted by-catches in the fishery. In principle this could be achieved if the catching methods were optimised for this. Still high numbers of undersized flatfish are caught in the bottom trawls. Although EU regulations make the use of the BACOMA codend mandatory in the Baltic Sea cod areable to escape through square mesh escape window of the BACOMA net the whereas flatfish still remain in the cod-end. Gear experiments have been carried out with the aim to better separate cod from the flatfish fraction already when entering the rear belly, making use of the natural behaviour of the fish, i. e. the preferred swimming distance from the bottom of the net in the funnel. As cod have a natural tendency to keep a relativly great distance from the bottom, flatfish tend to stay close to it. It was attempted to separate both fractions by splitting the funnel into an upper and lower part with a horizontal panel. This wastested for two different nets, a cod trawl to separate cod from flatfish, and an eel-trawl to separate cod and flatfish from eel. Cod and flatfish separation is best at a panel distance of 50 cm from the bottom. Thus, 74 % of the cod were found in the upper panel, whereas 75 % of the flounder were in the lower section. A separation of eel from cod was however not possible, since eel tend to rise to the upper part of the net, together with cod. Johann Heinrich von Thünen-Institute, Federal Research Institute for Rural Areas, Forestry and Fisheries began publishing the Informationen aus der Fischereiforschung = Information on Fishery Research in 2010.

With respect to future environmental impact assessment different bottom trawls are presently investigated for their suitability for sampling the fish fauna in potential windpark areas asses. For this purpose the international Baltic Sea Trawl, the Box trawl, two different small beam trawls and small eel fykes were compared on a research cutter in June 2002. The best catchability with the highest abundance of demersal fish species and widest length distribution was obtained with the Box trawl. During another cruise in December 2002 the Box trawl was again compared with the Windpark trawl. As a result the Box trawl performed best, with regard to the overall catchability. However the Windpark Trawl is easier to handle under the conditions onboard small fishing cutters. Johann Heinrich von Thünen-Institute, Federal Research Institute for Rural Areas, Forestry and Fisheries began publishing the Informationen aus der Fischereiforschung = Information on Fishery Research in 2010.

A great number of offshore wind energy generators are planned to be erected in the Baltic Sea in the near future. The question arises which impact these constructions may have on the living environment, of which fish are the most prominent candidates. Before these questions are tackled, however, tests need to be done to find out which bottom trawl is the most appropriate one to investigate possible effects. For this purpose four different trawls have been compared. As a result a number of key parameters for the design of an appropriate bottom otter trawl are given. Johann Heinrich von Thünen-Institute, Federal Research Institute for Rural Areas, Forestry and Fisheries began publishing the Informationen aus der Fischereiforschung = Information on Fishery Research in 2010.

Im Institut für Ostseefischerei (IOR) werden zur Untersuchung der Überlebensfähigkeit von Discards und zur Zwischenhälterung von Laichdorschen mobile Fischhaltungsräume benötigt. In Pontonrahmen eingehängte Netzkäfige sind dafür erfahrungsgemäß eine einfache Lösung. Diese Hälterungseinrichtungen haben den Vorteil, daß sie bedarfsweise in ausgewählten Wasserreservoirs eingesetzt werden können. Sie sind als schwimmende Einheiten von Pegelschwankungen unabhängig und bei Aufrechterhaltung derHälterungsfunktion flexibel im Standort. Aufgrund des häufigen Einsatzwechsels ergab sich im IOR die Notwendigkeit, eine leicht montierbare und transportable Netzkäfigeinheit zu konstruieren. Johann Heinrich von Thünen-Institute, Federal Research Institute for Rural Areas, Forestry and Fisheries began publishing the Informationen aus der Fischereiforschung = Information on Fishery research in 2010.

Johann Heinrich von Thünen-Institut, Federal Research Institute for Rural Areas, Forestry and Fisheries began publishing the Informationen aus der Fischereiforschung = Information on Fishery research in 2010