Bottom trawling
Bottom trawling is
.Trawling is done by a trawler, which can be a small open boat with only 30 hp (22 kW) or a large factory trawler with 10,000 hp (7,500 kW). Bottom trawling can be carried out by one trawler or by two trawlers fishing cooperatively (pair trawling).
Global catch from bottom trawling has been estimated at over 30 million tonnes per year, an amount larger than any other fishing method. International attempts to limit bottom trawling have been ineffective.
History
An early reference to fishery conservation measures comes from a complaint about a form of trawling dating from the 14th century, during the reign of
of so small a mesh, no manner of fish, however small, entering within it can pass out and is compelled to remain therein and be taken...by means of which instrument the fishermen aforesaid take so great abundance of small fish aforesaid, that they know not what to do with them, but feed and fatten the pigs with them, to the great damage of the whole commons of the kingdom, and the destruction of the fisheries in like places, for which they pray remedy.[7][8]
Another source describes the wondyrchoum as:
three fathom long and ten men's feet wide, and that it had a beam ten feet long, at the end of which were two frames formed like a colerake, that a leaded rope weighted with a great many stones was fixed on the lower part of the net between the two frames, and that another rope was fixed with nails on the upper part of the beam, so that the fish entering the space between the beam and the lower net were caught. The net had maskes of the length and breadth of two men's thumbs[9]
The response from the Crown was to "let Commission be made by qualified persons to inquire and certify on the truth of this allegation, and thereon let right be done in the Court of Chancery". Thus, already back in the Middle Ages, basic arguments about three of the most sensitive current issues surrounding trawling - the effect of trawling on the wider environment, the use of small mesh size, and of industrial fishing for animal feed - were already being raised.
Until the late 18th century sailing vessels were only capable of towing small trawls. However, in the closing years of that century a type of vessel emerged that was capable of towing a large trawl, in deeper waters. The development of this type of craft, the sailing trawler, is credited to the fishermen of Brixham in Devon. The new method proved to be far more efficient than traditional long-lining. At first its use was confined to the western half of the English Channel, but as the Brixham men extended their range to the North Sea and Irish Sea it became the norm there too.
By the end of the 19th century there were more than 3,000 sailing trawlers in commission in UK waters and the practice had spread to neighbouring European countries. Despite the availability of steam, trawling under sail continued to be economically efficient, and sailing trawlers continued to be built until the middle of the 1920s. Some were still operating in UK waters until the outbreak of World War II, and in Scandinavia and the Faroe Islands until the 1950s.
English commissions in the 19th century determined that there should be no limitation on trawling. They believed that bottom trawling, like tilling of land, actually increased production. As evidence, they noted that a second trawler would often follow a first trawler, and that the second trawler would often harvest even more fish than the first. The reason for this peculiarity is that the destruction caused by the first trawl resulted in many dead and dying organisms, which temporarily attracted a large number of additional species to feed on this moribund mass.
Bottom trawling does not only have a long tradition in European waters. It was also recognized in 1704 during the Edo era in Japan as a common fishing method. A slightly different approach was developed where the "Utase Ami" or "trawled bottom net" was deployed from a sideways sailing boat.[10]
Bottom trawling has been widely implicated in the population collapse of a variety of fish species, locally and worldwide, including orange roughy, barndoor skate, shark, and many others.[11]
Fishing gear
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The design requirements of a bottom trawl are relatively simple, a mechanism for keeping the mouth of the net open in horizontal and vertical dimensions, a "body" of net which guides fish inwards, and a "cod-end" of a suitable mesh size, where the fish are collected. The size and design of net used is determined by the species being targeted, the engine power and design of the fishing vessel and locally enforced regulations.
Beam trawling
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A beam trawl
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A detail
The simplest method of bottom trawling, the mouth of the net is held open by a solid metal beam, attached to two "shoes", which are solid metal plates, welded to the ends of the beam, which slide over and disturb the seabed. This method is mainly used on smaller vessels, fishing for flatfish or prawns, relatively close inshore.
Otter trawling
Otter trawling derives its name from the large rectangular otter boards which are used to keep the mouth of the trawl net open. Otter boards are made of timber or steel and are positioned in such a way that the hydrodynamic forces, acting on them when the net is towed along the seabed, push them outwards and prevent the mouth of the net from closing. They also act like a
The net is held open vertically on an otter trawl by floats and/or kites attached to the "headline" (the rope which runs along the upper mouth of the net), and weighted "bobbins" attached to the "foot rope" (the rope which runs along the lower mouth of the net). These bobbins vary in their design depending on the roughness of the sea bed which is being fished, varying from small rubber discs for very smooth, sandy ground, to large metal balls, up to 0.5 metres (1.6 ft) in diameter, for very rough ground. These bobbins can also be designed to lift the net off the seabed when they hit an obstacle. These are known as "rock-hopper" gear.
Body of the trawl
The body of the trawl is funnel-like, wide at its "mouth" and narrowing towards the cod end, and usually is fitted with wings of netting on both sides of the mouth. It is long enough to assure adequate flow of water and prevent fish from escaping the net, after having been caught. It is made of diamond-meshed netting, the size of the meshes decreasing from the front of the net towards the codend. Into the body, fish and turtle escape devices can be fitted. These can be simple structures like "square mesh panels", which are easier for smaller fish to pass through, or more complicated devices, such as bycatch grills.
Cod end
The cod end is the trailing end of the net where fish are finally "caught". The size of mesh in the cod end is a determinant of the size of fish which the net catches. Consequently, regulation of mesh size is a common way of managing
Environmental damage
Trawling gear produces acute impacts on biota and the physical substratum of the seafloor by disrupting the sediment column structure, overturning boulders, re-suspending sediments and imprinting deep scars on muddy bottoms.[12] Also, the repetitive passage of trawling gear over the same areas creates long-lasting, cumulative impacts that modify the cohesiveness and texture of sediments. It can be asserted nowadays that due to its recurrence, mobility and wide geographical extent, industrial trawling has become a major force driving seafloor change and affecting not only its physical integrity on short spatial scales but also imprinting measurable modifications to the geomorphology of entire continental margins.[13]
Bottom fishing has operated for over a century on heavily fished grounds such as the
Resuspension and biogeochemistry
Bottom trawling stirs up the sediment at the bottom of the sea. The
Bottom trawling can both resuspend and bury biologically recyclable organic material, changing the flow of nutrients and carbon through the food web and thereby alter geomorphological landscapes.
Phosphorus is often found in high concentration in soft shallow sediments.[21] Resuspending nutrient solids like these can introduce oxygen demand into the water column, and result in oxygen deficient dead zones.[22] Even in areas where the bottom sediments are ancient, bottom trawling, by reintroducing the sediment into the water column, can create
Multiple large-scale reviews on bottom trawling have noted that there is a great need for further studies that properly examine the effects of nutrient and toxin remobilization as well as carbon cycling,[26][27] in order to better estimate greenhouse gas emissions and hence the impact on climate change.[28]
Deep sea damage
The
Carbon release
An estimated 370 million tonnes a year of carbon dioxide stored in seafloor sediment is released by bottom-trawling fishing.[32] Most carbon released into the sea enters the atmosphere within a decade.[33] Banning bottom trawling in marine protected areas has been suggested.[34]
Current restrictions
Today, some countries regulate bottom trawling within their jurisdictions:[35]
- The
- The Council of the European Union in 2004 applied "a precautionary approach" and closed the sensitive Darwin Mounds off Scotland to bottom trawling.
- In 2005, the United Nations Food and Agriculture Organization's General Fisheries Commission for the Mediterranean (GFCM) banned bottom trawling below 1000 meters (3,281 ft) and, in January 2006, completely closed ecologically sensitive areas off Italy, Cyprus, and Egypt to all bottom trawling.
- Norway first recognized in 1999 that trawling had caused significant damage to its cold-water lophelia corals. Norway has since established a program to determine the location of cold-water corals within its exclusive economic zone (EEZ) so as to quickly close those areas to bottom trawling.
- Marine Protected Area(MPA) in 2004.
- Tasmanian Seamounts Marine Reserve to prohibit bottom trawling in the south Tasman Sea. Australia also prohibits bottom trawling in the Great Australian Bight Marine Park off South Australia near Ceduna. In 2004, Australia established the world's largest marine protected area in the Great Barrier Reef Marine Park, where fishing and other extractive activities are prohibited.
- Palau has banned all bottom trawling within its jurisdiction and by any Palauan or Palauan corporation anywhere in the world.[40]
- The President of Kiribati, Anote Tong, announced in early 2006 the formation of the world's first deep-sea marine reserve area. This measure – the Phoenix Islands Protected Area – created the world's third-largest marine protected area and may protect deep sea corals, fish, and seamounts from bottom trawling.[41] However, the actual boundaries of this reserve and what harvest limitations may occur therein have not been detailed. Moreover, Kiribati currently[when?] has only one patrol boat to monitor this proposed region.
- Venezuela was the first country to ban industrial trawling in its territorial waters and EEZ in 2009.[42][43]
- Hong Kong passed legislation banning trawling on 18 May 2011 in an effort to restore the territory's devastated fish stocks and marine ecosystem. The ban came into effect on 31 December 2012. The government paid HK$1.72 billion to affected trawlers in a buyout scheme. Persons who contravene the ban can be fined or imprisoned under the Fisheries Protection Ordinance (Cap 171).[44][45]
Lack of regulation
Beyond national jurisdictions, most bottom trawling is unregulated either because there is no
The North East Atlantic Fisheries Commission (NEAFC) also recently closed four seamounts and part of the mid-Atlantic Ridge from all fishing, including bottom trawling, for three years. This still leaves most of international waters completely without bottom trawl regulation.
As of May 2007 the area managed under the South Pacific Regional Fisheries Management Organisation (SPRFMO) has gained a new level of protection. All countries fishing in the region (accounting for about 25 percent of the global ocean) agreed to exclude bottom trawling on high seas areas where vulnerable ecosystems are likely or known to occur until a specific impact assessment is undertaken and precautionary measures have been implemented. Observers will also be required on all high seas bottom trawlers to ensure enforcement of the regulations.
Failed United Nations ban
In 2006, New Zealand Fisheries Minister Jim Anderton promised to support a global ban on bottom trawling if there was sufficient support to make that a practical option. Bottom trawling has been banned in a third of New Zealand's waters (although a large percentage of these areas were not viable for bottom trawling in the first place) [38]
See also
- Environmental impact of fishing
- Deep Sea Conservation Coalition (DSCC)
- Demersal fish – Fish that live and feed on or near the bottom of seas or lakes
- Mincarlo – 1961 fishing trawler , a historic sidewinder trawler
- Fishing dredge
References
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- ^ "Fishing and Farming Methods from the Seafood Watch Program at the Monterey Bay Aquarium". www.seafoodwatch.org. Retrieved 2018-08-23.
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- ISSN 0362-4331. Retrieved 2021-03-18.
- ^ "Bottom trawling releases as much carbon as air travel, landmark study finds". The Guardian. 2021-03-17. Retrieved 2021-03-20.
- S2CID 134879666.
- ^ March, Page 33
- ^ Collins, J.W. (1887). "The Beam Trawl Fishery of Great Britain with Notes on Beam-Trawling in Other European Countries" (PDF). Bulletin of the United States Fish Commission. p. 292. Retrieved 17 March 2017.
100 MegaByte PDF
- ^ Davis, F (1958) An Account of the Fishing Gear of England and Wales. 4th edition, HMSO.
- ^ Nakamoura E, Ourakami T (1900) Histoire de l’industrie de la pêche maritime etfluviale ouJapon. (Translated from the Japanese into French). Bureau des produits maritimes etfleuviauxdu ministère d’agriculture et commerce, Tokyo
- ^ Roberts, Callum (2007). The Unnatural History of the Sea, Island Press, p. 238
- ^ Urbina, Ian (July 28, 2015). "A Renegade Trawler, Hunted for 10,000 Miles by Vigilantes". The New York Times. Retrieved November 20, 2020.
- ^ a b Oberle et al. (2018), “Submarine Geomorphology: Bottom Trawling and other Fishing Activities”, Book: Submarine Geomorphology Chapter 25, Springer, doi: 10.1007/978-3-319-57852
- ^ "Beam trawling on the North Sea". Greenpeace. Archived from the original on 2008-12-10. Retrieved 2009-01-12.
- International Union for the Conservation of Nature and Natural Resources17 November 2004.
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- ^ "In Brief: Deep-sea Trawling Has "Devastating" Impact, Study Finds". National Geographic Society. 2014-05-19. Archived from the original on September 20, 2020.
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- ISBN 9780080437514.
- ^ US Department of Commerce, National Oceanic and Atmospheric Administration. "What is a dead zone?". oceanservice.noaa.gov. Retrieved 16 October 2020.
- ^ Giannakourou, A., Orlova, T.Y., Assimakopoulou, G., Pagou, K. (2005) Dinoflagellate cysts in recent marine sediments from Thermaikos Gulf, Greece. Continental Shelf Research 25, 2585-2596.
- ^ Weaver, Dallas E (2007) Remote Impacts of Bottom Trawling Archived 2009-04-10 at the Wayback Machine.
- hdl:10261/244111.
- ^ NRC (2002) (National Research Council) Effects of trawling and dredging on seafloor habitat. National Academies Press, Washington, DC
- ^ ICES (2006) International Council for the Exploration of the Sea (ICES): report of the WorkingGroup on Ecosystem Effects of Fishing Activities. ACE 05:1 179
- ISSN 2212-0416.
- ^ Report of the Secretary-General (2006) The Impacts of Fishing on Vulnerable Marine Ecosystems. United Nations. Retrieved on 10 August 2008
- ^ Reed JK, Koenig CC, Shepard AN, and Gilmore Jr RG (2007) Long Term Monitoring of a Deep-water Coral Reef: Effects of Bottom Trawling[usurped] Twenty-sixth annual Scientific Diving Symposium. Retrieved on 10 August 2008
- ISSN 0013-0613. Retrieved 2015-09-18.
- ISSN 0261-3077. Retrieved 2024-03-13.
- ISSN 2296-7745.
- ^ "Bottom trawling is huge source of carbon emissions, new study reveals". Environment. 2024-03-13. Retrieved 2024-03-13.
- ^ [1] Archived February 4, 2012, at the Wayback Machine
- ^ Trawl Rockfish Conservation Area (RCA) Boundary Modifications Draft Environmental Assessment September 2013, National Marine Fisheries Service Sustainable Fisheries Division Northwest Region (PDF)
- ^ "West Coast fishery rebounds in a rare conservation 'home run'". Associated Press. December 26, 2019. Retrieved December 27, 2019 – via Los Angeles Times.
- ^ a b "NZ to close 30pc of waters to trawling - National - NZ Herald News". Nzherald.co.nz. 2006-02-14. Retrieved 2013-09-09.
- ^ "New Zealand, world, sport, business & entertainment news on Stuff.co.nz". Archived from the original on 2007-09-30. Retrieved 2006-08-16.
- ^ [2] Archived May 15, 2006, at the Wayback Machine
- ^ "Kiribati creates world's first deep-sea marine reserve - World". smh.com.au. 2006-03-30. Retrieved 2013-09-09.
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- ^ Fischer, Johanne (2010). "Review of the implementation of the international plan of action for the conservation and management of sharks" (PDF). FAO Fisheries and Aquaculture Circular. 1076.
- ^ "Facts About the Trawling Ban in Hong Kong Waters". WWF Hong Kong. Retrieved 27 July 2016.
- ^ "AFCD officers intercept illegal trawler (with photo)". Hong Kong Government. 26 July 2016.
- ^ [3] Archived September 13, 2009, at the Wayback Machine
- ^ [4] Archived June 26, 2006, at the Wayback Machine
- ^ "Earth Negotiations Bulletin - ENB SUMMARY OF THE WORKING GROUP ON MARINE BIODIVERSITY BEYOND AREAS OF NATIONAL JURISDICTION - MONDAY, 20 FEBRUARY 2006". Iisd.ca. Archived from the original on 2012-07-22. Retrieved 2013-09-09.
- ^ "Pacific Leaders Back Bottom Trawling Ban | Scoop News". Scoop.co.nz. Retrieved 2013-09-09.
- ^ "Science/Nature | Ban on 'brutal' fishing blocked". BBC News. 2006-11-24. Retrieved 2013-09-09.
- National Research Council (US) (2002) Effects of Trawling and Dredging on Seafloor Habitats. National Academies Press. ISBN 0-309-08340-0
Further reading
- Benn, Angela R.; Weaver, Philip P.; Billet, David S. M.; Van Den Hove, Sybille; Murdock, Andrew P.; Doneghan, Gemma B.; Le Bas, Tim (2010). "Human Activities on the Deep Seafloor in the North East Atlantic: An Assessment of Spatial Extent". PLOS ONE. 5 (9): e12730. PMID 20856885.
- Martín, Jacobo; Puig, Pere; Palanques, Albert; Ribó, Marta (2014). "Trawling-induced daily sediment resuspension in the flank of a Mediterranean submarine canyon". Deep Sea Research Part II: Topical Studies in Oceanography. 104: 174–183. hdl:10261/80451.
- March, E. J. (1953). Sailing Trawlers: The Story of Deep-Sea Fishing with Long Line and Trawl. Percival Marshal and Company. Reprinted by Charles & David, 1970, Newton Abbot, UK. ISBN 071534711X
External links
- Bottom trawling imagery Annotated satellite images from a number of bottom trawling activities around the world
- Deep Sea Conservation Coalition Campaign for a ban on deep sea bottom trawling
- FAO Gear type fact sheets Gear type fact sheet on various types of bottom trawls
- Oceana: bottom trawling facts
- "Oceans and Coastal Areas". UNEP: System-Wide EarthWatch. Archived from the originalon 2006-10-14. On the role bottom trawling plays in global fisheries
- Bibliography of the Effects of Fishing Gear on the Seabed and Benthic Communities
- Pictures of beam trawlers from the east coast of the UK