Gillnetting: Difference between revisions

[[File:Eilif Peterssen-Laksefiskeren (1889).jpg|thumb|upright=1.25|right|Oil painting of gillnetting, ''The salmon fisher'', by [[Eilif Peterssen]].]]

[[File:Gillnet illustration.PNG|thumb|300px|right|[[National Oceanic and Atmospheric Administration]] illustration of a gillnet.]]

'''Gillnetting''' is a [[fishing]] method that uses gillnets: vertical panels of netting that hang from a line with regularly spaced floaters that hold the line on the surface of the water. The floats are sometimes called "corks" and the line with corks is generally referred to as a "cork line." The line along the bottom of the panels is generally weighted. Traditionally this line has been weighted with lead and may be referred to as "lead line." A gillnet is normally set in a straight line. Gillnets can be characterized by mesh size, as well as colour and type of filament from which they are made. Fish may be caught by gillnets in three ways:

Most often fish arehave gilledgills. A fish swims into a net and passes only part way through the mesh. When it struggles to free itself, the twine slips behind the gill cover and prevents escape.<ref>{{cite book|last1=Murphy|first1=B.|last2=Willis|first2=D.|date=1996|url= http://www.afsbooks.org/x55029xm|title=Fisheries Techniques|edition=2nd|url-status=dead|archive-url=https://web.archive.org/web/20130221024307/http://afsbooks.org/x55029xm|archive-date=2013-02-21|location=Bethesda, MD|publisher=American Fisheries Society}}</ref>

[[File:BC Bow Picker Mahalo Kai (Commercial Salmon Gillnetter).jpg|alt=image of a commercial salmon bow picker, Mahalo Kai; drum holding net is located in the bow of the boat. The cabin is in the rear.|thumb|Contemporary Canadian commercial salmon bowpicker on trailer. Gillnet is evident on the metal drum in the bow of the boat.]]

Gillnets existed in ancient times, as archaeological evidence from the Middle East demonstrates.<ref>Nun, Mendel (1989). ''The Sea of Galilee and Its Fishermen in the New Testament,'' pp. 28-4428–44. Kibbutz Ein Gev, Kinnereth Sailing Co.</ref> In North America, Native American fishermen used cedar canoes and natural fibre nets, e.g., made with nettles or the inner bark of cedar.<ref>Stewart, Hilary (1977). ''Indian Fishing: Early Methods on the Northwest Coast,'' p.79 in 1st paperback edition, 1982. Seattle, University of Washington Press.</ref> They would attach stones to the bottom of the nets as weights, and pieces of wood to the top, to use as floats. This allowed the net to suspend straight up and down in the water. Each net would be suspended either from shore or between two boats. Native fishers in the Pacific Northwest, Canada, and Alaska still commonly use gillnets in their fisheries for [[salmon]] and [[Rainbow trout|steelhead]].

Both drift gillnets and setnets have long been used by cultures around the world. There is evidence of fisheries exploitation, including gillnetting, going far back in Japanese history, with many specific details available from the [[Edo period]] (1603–1868).<ref>Ruddle, Kenneth and Akimich, Tomoya. "Sea Tenure in Japan and the Southwestern Ryukyus," in Cordell, John, Ed. (1989), ''A Sea of Small Boats'', pp. 337-370337–370. Cambridge, Mass., Cultural Survival, Inc.</ref> Fisheries in the [[Shetland]] Islands, which were settled by [[Norsemen]] during the [[Viking Age]], share cultural and technological similarities with Norwegian fisheries, including gillnet fisheries for herring.<ref>Goodlad, C.A. (1970). ''Shetland Fishing Saga'', pp. 59-6059–60. The Shetland Times, Ltd.</ref> Many of the Norwegian immigrant fishermen who came to fish in the great Columbia River salmon fishery during the second half of the 19th century did so because they had experience in the gillnet fishery for cod in the waters surrounding the [[Lofoten]] Islands of northern [[Norway]].<ref>Martin, Irene (1994). ''Legacy and Testament: The Story of the Columbia River Gillnetter'', p. 38. Pullman, Washington State University Press.</ref> Gillnets were used as part of the seasonal round by [[Sweden|Swedish]] fishermen as well.<ref>Lofgen, Ovar. "Marine Ecotypes in Preindustrial Sweden: A Comparative Discussion of Swedish Peasant Fishermen," in Andersen, Raoul, Ed. (1979), ''North Atlantic Maritime Cultures'', pp. 83-10983–109. The Hague, Mouton.</ref> Welsh and English fishermen gillnetted for Atlantic salmon in the rivers of [[Wales]] and [[England]] in [[coracle]]s, using hand-made nets, for at least several centuries.<ref>Jenkins, J. Geraint (1974). ''Nets and Coracles'', p. 68. London, David and Charles.</ref> These are but a few of the examples of historic gillnet fisheries around the world.

Gillnetting was an early fishing technology in colonial America,{{vague|reason="Colonial America" is not a [[proper name]] of any region. (But "colonial America" is ambiguous among (at least) the New World, the 13 Colonies, and North America north of the [[Rio Grande]]|date=February 2018}} used for example, in fisheries for Atlantic salmon and shad.<ref>Netboy, Anthony (1973) ''The Salmon: Their Fight for Survival,'' pp. 181-182181–182. Boston, Houghton Mifflin.</ref> Immigrant fishermen from northern Europe and the Mediterranean brought a number of different adaptations of the technology from their respective homelands with them to the rapidly expanding salmon fisheries of the Columbia River from the 1860s onward.<ref>Martin, 1994, p. 44.</ref> The boats used by these fisherman were typically around {{convert|25|ft|m|0}} long and powered by oars. Many of these boats also had small sails and were called "row-sail" boats. At the beginning of the 1900s, steam powered ships would haul these smaller boats to their fishing grounds and retrieve them at the end of each day. However, at that time [[gasoline|gas]] powered boats were beginning to make their appearance, and by the 1930s, the row-sail boat had virtually disappeared, except in Bristol Bay, Alaska, where motors were prohibited in the gillnet fishery by territorial law until 1951.<ref>Andrews, Ralph W. and Larsen, A.K. (1959). ''Fish and Ships'', p. 108. Seattle, Superior Publishing Co.</ref>

The Columbia River Basin is currently under a management agreement that spans from 2008 to December 31, 2017.<ref>{{cite web|publisher=NOAA Fisheries West Coast Region|title=Environmental Impact Statement for Programmatic Review of Harvest Actions for Salmon and Steelhead in the Columbia Basin related to U.S. v. Oregon :: NOAA Fisheries West Coast Region |url=http://www.westcoast.fisheries.noaa.gov/fisheries/salmon_steelhead/united_states_v_oregon_DEIS.html|website=www.westcoast.fisheries.noaa.gov|access-date=30 November 2017|language=en-us}}</ref> This management agreement looks to gather information on fish harvesting through means including gillnets.<ref>{{cite web|title=2008-20172008–2017 United States v. Oregon Management Agreement May 2008|url=https://www.fws.gov/pacific/fisheries/hatcheryreview/Reports/snakeriver/SR--079.revised.2008-17USvOR_Mngmt_Agrmt.pdf|website=U.S. Fish and Wildlife Service|access-date=30 November 2017}}</ref> The parties involved will convene again to decide on further action after the current agreement ends.

[[ImageFile:Gillnet selectivity.png|thumb|upright=1.25|Selectivity properties of a gillnet on a hypothetical population]]

Gillnets are a series of panels of meshes with a weighted "foot rope" along the bottom, and a ''headline'', to which floats are attached. By altering the ratio of floats to weights, buoyancy changes,<ref>Martin 1994, pp. 52-5752–57.</ref> and the net can therefore be set to fish at any depth in the water column. In commercial fisheries, the meshes of a gillnet are uniform in size and shape. Fish smaller than the mesh of the net pass through unhindered, while those too large to push their heads through the meshes as far as their gills are not retained. This gives gillnets the ability to target a specific size of fish, unlike other net gears such as [[trawling|trawls]], in which smaller fish pass through the meshes and all larger fish are captured in the net{{ref|Pawson}}.

Commercial gillnet fisheries are still an important method of harvesting [[salmon]] in Alaska, British Columbia, Washington, and Oregon. In the lower [[Columbia River]], non-Indian commercial salmon fisheries for spring Chinook have developed methods of selectively harvesting adipose fin clipped hatchery salmon using small mesh gillnets known as [[tangle net]]s or tooth nets. Non-adipose fin clipped fish (primarily natural origin salmon) must be released.<ref>http{{Cite web |date=20 January 2012 |title=2012 Joint Staff Report: Stock Status and Fisheries for Spring Chinook, Summer Chinook, Sockeye, Steelhead, and Other Species, and Miscellaneous Regulations |url=https://wdfw.wa.gov/sites/default/files/publications/01353/wdfw01353.pdf |access-date=3 November 2023 |website=[[Washington Department of Fish & Wildlife]]}}</ref> Fishery management agencies estimate a relatively low release [[Fish mortality|mortality rate]] on salmon and [[Rainbow trout|steelhead]] released from these small mesh gillnets.

Problems that can arise from selective harvesting are smaller reproducing adult fish, as well as the unexpected mortality of the fish which sustain injuries from the gillnet but are not retained in the fishery. Most salmon populations include several [[Age class structure|age classes]], allowing for fish of different ages, and sizes, to reproduce with each other. A recent 2009 study looked at 59 years of catch and escapement data of [[Bristol Bay]] [[sockeye salmon]] to determine age and size at maturity trends attributable to the selectivity of commercial gillnet harvests. The study found that the larger females (>550&nbsp;mm) of all age classes were most susceptible to harvest.<ref name="Kendall, Neala W 2009">Kendall, Neala W, Jeffery J. Hard and Thomas P. Quinn. 2009. Quantifying Six Decades of Fishery Selection for Size and Age at Maturity in Sockeye Salmon. Evolutionary Applications. 523-536523–536.</ref> The study suggests that smaller, younger fish were more likely to successfully traverse the gillnet fishery and reproduce than the larger fish. The study also found that the average length of sockeye harvested from 1946 to 2005 was 8&nbsp;mm larger than the sockeye who escaped the gillnet fishery to spawn, reducing the fecundity of the average female by 5%, or 104 eggs.<ref name="Kendall, Neala W 2009"/> If a salmon enters a gillnet, but manages to escape, it can sustain injuries. These injuries can lead to a lower degree of reproductive success. A study aimed at quantifying mortality of Bristol Bay sockeye salmon due to gillnet-related injuries found that 11–29% of sockeye sustained fishery-related injuries attributable to gillnets, and 51% of those fish were expected to not reproduce.<ref>Baker, Matthew R and Daniel E Schindler. 2009. Unaccounted Mortality in Salmon Fisheries: Non-retention in Gillnets and Effects on Estimates of Spawners. Journal of Applied Ecology (46). 752-761752–761.</ref>

There have also been studies done to see if differing strategies could potentially decrease the estimated 400,000 annual avian by-catch in coastal fisheries. These include three strategies that have a possible reduction in up to 75% of avian by-catch: gear modifications, where visual devices will be placed near the top of the net so birds will be able to see the nets; abundance-based fishery openings, where of birds will determine whether the nets will be set out or not; and time-of-day restrictions, which goes along with abundance- where bird by catch tended to occur at dawn and dusk, where as fish catch occurred mostly at dawn.<ref>{{Cite journal|title=Novel Tools to Reduce Seabird Bycatch in Coastal Gillnet Fisheries|last=Melvin|first=Edward F.|date=December 1999|doi=10.1046/j.1523-1739.1999.98426.x|volume=13|issue = 6|journal=Conservation Biology|pages=1386–1397|s2cid=86638654 }}</ref>

For marine mammal by-catch, field experiments have shown that the use of pingers on nets resulted in significantly lower numbers of by-catch than nets without pingers. After this study was completed by Jay Barlow, it was determined that there would be a 12-fold decrease in [[short-beaked common dolphin]]s caught, a 4-fold decrease in other [[cetacea]]ns and a 3-fold decrease in [[pinniped]]s for nets containing pingers.<ref>{{Cite journal|last=Barlow|first=Jay|date=April 2003|title=Field Experiments Show That Acoustic Pingers Reduce Marine Mammal Bycatch In The California Drift Gill Net Fishery|journal=Marine Mammal Science|volume=19|issue=2|pages=265–283|doi=10.1111/j.1748-7692.2003.tb01108.x|s2cid=26969713 |url=http://digitalcommons.unl.edu/usdeptcommercepub/236}}</ref>

The tangle net, or tooth net, originated in British Columbia, Canada, as a gear specifically developed for selective fisheries.<ref>Petrunia, William Mark (1997). "Tooth Net Fishery. Report on Scientific License 96.149." Jan. 5, 1997.</ref> Tangle nets have smaller mesh sizes than standard gillnets. They are designed to catch fish by their nose or jaw, enabling bycatch to be resuscitated and released unharmed. Tangle nets as adapted to the mark-selective fishery for spring Chinook salmon on the lower Columbia River have a standard mesh size of {{convert|4-+1/4&nbsp;inches (10.8&nbsp;|in|cm.)}}. Short net lengths and soak times are used in an effort to land fish in good condition. Tangle nets are typically used in situations where the release of certain (usually wild) fish unharmed is desirable. In a typical situation calling for the use of a tangle net, for instance, all fish retaining their adipose fins (usually wild) must be returned to the water. Tangle nets are used in conjunction with a live recovery box, which acts as a resuscitation chamber for unmarked fish that appear lethargic or stressed before their release into the water.<ref>{{cite web|url=http://www.salmonforall.org/tanglenet/|website=Salmon For All|title=A Sustainable Fishery|access-date=4 April 2018}}</ref><ref>[[FAO]]: Fishing Gear Types: [http://www.fao.org/fishery/geartype/219/en Gillnets and entangling nets]</ref>

#{{note|Erzini}} Erzini, K. Monteiro, C., Ribeiro, J., Santos, M., Gaspar, M., Montiero, P. & Borges, T. (1997) An experimental study of "ghost-fishing" off the Algarve (southern Portugal). Marine Ecology Progress Series 158:257-265257–265.

#{{note|Hall}} Hall, M.A. (1998) An ecological view of the tuna-dolphin problem: impacts and trade-offs. Reviews in Fish Biology and Fisheries. 8:1-341–34.

#{{note|Kaiser}} Kaiser, M.J, Bullimore, B., Newman, P., Lock, K. & Gilbert, S. (1996) Catches in "ghost-fishing" set nets. Marine Ecology Progress Series. 145:11-1611–16.

* [http://www.seawatch.org/position_papers/gillnet.php Sea Watch | Gillnets] {{Webarchive|url=https://web.archive.org/web/20130624190740/http://www.seawatch.org/position_papers/gillnet.php |date=2013-06-24 }}