Cease or prohibit mobile midwater (pelagic) fishing gears

Overall effectiveness category Awaiting assessment
Number of studies: 1
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Effectiveness

not assessed
Certainty

not assessed
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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.

Study locations

Key messages

One study examined the effects of ceasing or prohibiting fishing with towed (mobile) midwater fishing gears on marine fish populations. The study was in the Norwegian Sea (Norway).

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Condition (1 study): One replicated, before-and-after study in the Norwegian Sea found that in the five years after drift netting was prohibited in an area, the weights of young salmon returning to rivers were higher than before, and weights of older salmon were similar or lower.
Abundance (1 study): One replicated, before-and-after study in the Norwegian Sea found that in the five years after the use of drift nets was prohibited, there were more young salmon returning to rivers than before, and similar numbers of older multi-returning salmon.

BEHAVIOUR (0 STUDIES)

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

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 paper
Jensen 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.

Please cite as:

Taylor, N., Clarke, L.J., Alliji, K., Barrett, C., McIntyre, R., Smith, R.K., and Sutherland, W.J. (2021) Marine Fish Conservation: Global Evidence for the Effects of Selected Interventions. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

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This Action forms part of the Action Synopsis:

Marine Fish Conservation

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