Trawling
Trawling is the term used to describe fishing with nets that are pulled ( towed ) behind a ship . Trawls are the most important fishing gear used in deep-sea fishing today .
Trawls
A trawl net is a net that is towed by one or more trawlers and is used to catch schooling fish or bottom fish . There are two main types of trawls used today:
- the pelagic trawl or swim trawl
- and the bottom trawl or trawl.
General information on construction
A trawl is a net that is pulled through the water by one or more ships. It is reminiscent of a horizontal sack that narrows towards the back. It has a very wide opening. This is created in the vertical direction by skillfully adding weights on the lower side and floating bodies on the upper side and in the horizontal direction mostly by otter boards that open the net with the help of the incoming water.
The mesh size of the net is tailored to the type of fish to be caught. However, the meshes are always larger at the opening than at the end of the net, the so-called " codend ".
Pelagic trawls
Pelagic trawls are designed to catch fish species that live in the open water, for example all round fish such as redfish , cod , saithe and also mackerel , herring , sprats , anchovies and, to a lesser extent, sardines .
A pelagic trawl is funnel-shaped and ends in a pocket, the codend , in which the fish are collected. The opening of the net is 50–70 m high and 80–120 m wide, the total length of the net is usually 1500 m. The nets are towed at a speed of 3–4 knots (approx. 5 km / h) in a water depth of 50 to 300 m, sometimes up to 600 m, by one or two trawlers (team fishing). When fishing with pelagic trawls, the fish are usually located using sonar and echo sounders .
Bottom trawls
1: Kurrleine 2: otter boards 3: Jager 4: Stick with stick cock depots 5: Headline stand 6: Lash stand (middle) 7: Basic stand 8: Long antenna 9: Short antenna 10: 1st and 2nd Height scissor board 11: Headline with buoyancy balls 12: Ground rope, weighted with chains 13: Square 14: Belly 15: Hundred mesh piece and tunnel 16: Codline 17: Cod line
Bottom trawls are built to catch bottom fish such as plaice , sole , dab ( flatfish ), and crustaceans such as shrimp that live on the ocean floor. Bottom trawls are used in water depths of 100–1500 m. In the Wadden Sea of the North Sea and on the Baltic Sea coast , fishing cutters use nets on so-called beam trawls .
The bottom trawl is also funnel-shaped and has a catching bag for the fish at the end, but is overall significantly shorter than the pelagic net. On the underside of the net entrance there is a weighted ground rope that is pulled across the sea floor and is intended to scare the fish. Modern bottom trawls also have wooden or steel otter boards that plow a large area of the seabed. Bottom trawling can endanger deep-sea organisms such as the fauna of the deep-sea mountains .
operation area
Trawls are mainly used in the North Atlantic . The leading trawl fishing nations are France, Ireland, Iceland, the Netherlands, England, Denmark and Spain. Among other things, the fish species tuna , perch , herring , mackerel , horse mackerel and anchovies are caught. However, trawls are also used in the North Sea and Baltic Sea to catch North Sea and Baltic Sea prawns ("crabs").
In June 2008, the 15 states of the Oslo-Paris Agreement OSPAR agreed that deep - sea fishing with trawls would be severely restricted in a submarine mountain range of the Mid-Atlantic Ridge called the Alps of the deep sea , and in some areas also prohibited. The resulting protected area is halfway between Iceland and the Azores , is roughly the size of Italy and is therefore one of the largest marine protected areas in the world.
Criticism of trawling
A: Rock bottom with deep sea corals
B: Bare rock bottom without vegetation after fishing with the trawl
This fishing method destroys the seabed and the creatures living on it, including reefs made of cold-water corals , which on the continental margins at depths of more than 200 m in otherwise species-poor regions form important habitats and are "nurseries" for important fish species. It probably also destroys previously unknown and undiscovered animal species and endangers biodiversity . According to a report published in 2020 as part of the Marine Strategy Framework Directive by the European Commission , approximately 43% of Europe's shelf / slope areas and 79% of the territorial seabed are considered physically disturbed, mainly attributed to trawling.
Another point of criticism of trawling is the high proportion of bycatch (80–90%) that results from the use of trawls. This includes young fish as well as other (fish) species and cetaceas ( whales and dolphins ) that drown in the nets. With new nets and selective fishing , fishermen could largely avoid unwanted bycatch.
One disadvantage of trawling is the reduced quality of the catch. While with other fishing methods, for example longlines , the fish come fresh out of the water, in the trawls they die in the water under the pressure of the other fish in the net and are then dragged dead through the water.
In 2004 a petition against bottom trawling, signed by 1,100 scientists, was published.
At the end of 2006, eleven nations had bottom trawl fishing fleets, with Spain having the most vessels with this equipment. The attempt to reach an agreement at the United Nations in 2006 on a ban was torpedoed in particular by Iceland .
In 2011 the campaign network Avaaz.org called for an action against the basic networks . The occasion was a meeting of UN decision-makers on September 15, 2011. Many fishery biologists are calling for an end to deep-sea fishing because, in their opinion, industrial fishing methods are destroying the largest ecosystem in the oceans. This call is supported by the Deep Sea Conservation Coalition .
In July 2016, the European Union agreed in Regulation (EU) 2016/2336 on a ban on ground trawls for European trawlers in deep-sea regions of the Atlantic and, in principle, in the waters of the European Union. They may only be used up to a depth of 800 meters.
See also
Web links
- Fishing techniques. (No longer available online.) In: fischmarkt-bremerhaven.de. 2001, archived from the original on March 4, 2001 (representation of different fishing gear [network types]).
- Pair trawling animation ( Memento from August 6, 2012 in the Internet Archive ). In: greenpeace.org.uk (English; animated representation of a pelagic trawl)
Individual evidence
- ↑ Pelagic otter nets - fishing gear - fish stocks. In: fischbestaende.thuenen.de. Retrieved October 17, 2018 .
- ↑ The Low German word Steert ( Dutch staart ) means tail and tail and etymologically corresponds to the now uncommon Upper and Central German word Sterz .
- ^ Stephan Lutter: Charlie Gibbs: The Alps of the deep sea. WWF, August 14, 2015, accessed September 27, 2015 .
- ^ J Murray Roberts, Stephen D Cairns: Cold-water corals in a changing ocean . In: Current Opinion in Environmental Sustainability . April 2014, doi : 10.1016 / j.cosust.2014.01.004 .
- ^ Andreas Heitkamp: Cold water corals - "Great Barrier Reef" of the north . In: Nadja Podbregar, Dieter Lohmann (ed.): In focus: Marine worlds (= natural sciences in focus ). Springer, 2014, ISBN 978-3-642-37719-8 , pp. 93-102 , doi : 10.1007 / 978-3-642-37720-4_8 .
- ^ New Scientist . No. 2410, p. 6.
- ^ European Commission: Report from the Commission to the European Parliament and the Council on the implementation of the Marine Strategy Framework Directive (Directive 2008/56 / EC) . COM (2020) 259 final. Brussels 25 June 2020 ( online ).
- ↑ Saving our oceans. Declaration of the campaign network AVAAZ. In: avaaz.org, September 16, 2011, accessed September 9, 2019.
- ↑ Science: Fisheries biologists warn against deep-sea fishing. In: focus.de, September 13, 2011, accessed on September 9, 2019 ("Content provided by dpa. It is not checked or edited by the FOCUS online editorial team.").
- ↑ Fishing destroys the life in the deep sea. Industrial fishing methods destroy the largest ecosystem in the ocean. In: scinexx - Das Wissensmagazin , September 9, 2011, accessed on September 9, 2019 (Marine Policy / dapd, September 9, 2011 - NPO).
- ^ Scientists call for end to deep-sea fishing. In: Washington Post . August 30, 2011.
- ^ The Problem. Depletion of Deep Sea Species ( Memento from August 6, 2012 in the Internet Archive ). In: savethehighseas.org. The Deep Sea Conservation Coalition, 2011, accessed September 9, 2019.
- ↑ A better future for the EU deep sea. European Commission, June 30, 2016, accessed June 7, 2019 .