Gillnetting

Mesh size, twine strength, as well as net length and depth are all closely regulated to reduce bycatch of non-target species.

Native fishers in the Pacific Northwest, Canada, and Alaska still commonly use gillnets in their fisheries for salmon and steelhead.

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).

[8] Welsh and English fishermen gillnetted for Atlantic salmon in the rivers of Wales and England in coracles, using hand-made nets, for at least several centuries.

Gillnetting was an early fishing technology in colonial America,[vague] used for example, in fisheries for Atlantic salmon and shad.

[10] 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.

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.

It also served to make the industry much more competitive, as the fisherman were forced to invest more in boats and equipment to stay current with developing technology.

The introduction of fine synthetic fibres such as nylon in the construction of fishing gear during the 1960s marked an expansion in the commercial use of gillnets.

Some researchers have found gill-nets still catching fish and crustaceans over a year after loss[1], while others have found lost nets destroyed by wave action within one month[2] or overgrown with seaweeds, increasing their visibility and reducing their catching potential to such an extent that they became a microhabitat used by small fish.

[3] This type of net was heavily used by many Japanese, South Korean, and Taiwanese fishing fleets on the high seas in the 1980s to target tunas.

[15] United Nations General Assembly Resolution 46/215[16] called for the cessation of all "large-scale pelagic drift-net fishing" in international waters by the end of 1992.

Oregon voters had the chance to decide on whether gillnetting will continue in the Columbia River in November 2012 by voting on Measure 81.

[22] There have been proposed regulations to shut down drift gillnet fisheries whose by-catch numbers (which include dolphins, sea turtles and other marine life) were too high.

[26] The bill's focus is to ban the use of large-scale nets while supporting the use of alternative methods of fishing to decrease the maximum amount of bycatch.

[26] 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,[27] and the net can therefore be set to fish at any depth in the water column.

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 nets or tooth nets.

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.

Recent WDF&W reports suggest that purse seine is the most productive method with having highest catch per unit effort (CPUE), but has little information on the effectiveness of selectively harvesting hatchery-reared salmon.

[33] More conclusive research has been conducted jointly between the Confederated Tribes of the Colville Reservation and Bonneville Power Administration on a 10-year study on selective harvest methods of hatchery origin salmon in the Upper Columbia River by purse seine and tangle net.

Researchers commented that the use of recovery boxes and shortened periods between checking the nets would have likely decreased mortality rates.

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.

By adjusting the design these nets can fish in surface layers, in mid water or at the bottom, targeting pelagic, demersal or benthic species.

[38] This bottom-set gear has two parts: The combined nets are maintained more or less vertically in the usual way by floats on the floatline and weights on the groundline.

However, the issue of concern with this type of net is the bycatch of species that are not targeted, such as marine mammals, seabirds and to a minor extent turtles.

Tangle nets as adapted to the mark-selective fishery for spring Chinook salmon on the lower Columbia River have a standard mesh size of 4+1⁄4 inches (11 cm).

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.