Cease or prohibit mobile midwater (pelagic) fishing gears
Overall effectiveness category Awaiting assessment
Number of studies: 1
Background information and definitions
Mobile midwater (pelagic) fishing gears are nets deployed in the water column above the seabed, typically used to catch pelagic fish species such as herrings Clupeidae, tunas Thunnus spp. and salmon Salmonidae. They include midwater trawls and semi-mobile gears such as purse seines, ring nets and pelagic drift nets. Mobile pelagic gears are generally considered less damaging to seabed habitats than towed bottom fishing gears as they do not purposefully contact the seabed and thus the impact is reduced. However, they are still capable of catching large numbers of fish of both target and non-target species, and accidental contact with seabed features may still occur. Ceasing or prohibiting fishing with mobile pelagic fishing gears may reduce overall fishing effort and fishing mortality in an area, and subsequently reduce the effects on fish populations.
Supporting evidence from individual studies
A replicated, before-and-after study in 1980–1994 of four Norwegian rivers draining to the Norwegian Sea (Jensen et al. 1999) found that in the five years following a ban on drift netting in a coastal fishery, there were increases in the catch abundance and weights of young (one-sea winter) Atlantic salmon Salmo salar returning to rivers, but fewer changes for multi-sea-winter salmon. In three of four rivers, overall numbers of grilse (young salmon returning from the sea to fresh water for the first time) were higher in the five years after the ban (after: 500–4,000, before: 80–1,200) and numbers of older, multi-sea-winter salmon were similar (after: 50–3,200 before: 50–3,200). Average weight of grilse increased in all four rivers (after: 1,714–2,340g, before: 1,558–1,996 g), whereas two-sea-winter salmon weights decreased in two (after: 5,769–6,211 g, before: 6,500–6,988) and there were no changes for three-sea-winter salmon (after: 9,075–10,764 g, before: 8,938–10,752 g). In addition, effects of the ban on salmon populations returning to four Russian rivers (outside of the ban area) were found for three rivers draining to the Barents Sea, but not for one draining to the White Sea (see paper for data). A total ban on sea fishing for salmon using drift nets was introduced in Norway in 1989, while other methods such as bag and bend nets continued. Data on catches of salmon (mainly rod and line) for four Norwegian rivers (Repparfjord, Alta, Namsen, Stryn) from 1980–1994 was taken from Norwegian Official Statistics.Study and other actions tested
Referenced paperJensen A.J., Zubchenko A.V., Heggberget T.G., Hvidsten N.A., Johnsen B.O., Kuzmin O., Loesnko A.A., Lund R.A., Martynov V.G., Nꬱsje T.F., Sharov A.F. & Økland F. (1999) Cessation of the Norwegian drift net fishery: changes observed in Norwegian and Russian populations of Atlantic salmon. ICES Journal of Marine Science, 56, 84-95