Establish long-term fishery closures

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • Five studies examined the effects of establishing long-term fishery closures in an area on marine fish populations. One study was in each of the Norwegian Sea (Norway), the North Sea (UK), the Gulf of Maine (USA), the Bismark Sea (Papua New Guinea) and the Kattegat (Sweden/Denmark).



  • Condition (2 studies): One replicated, before-and-after study in the Norwegian Sea found that in the five years after the long-term closure of a commercial coastal fishery, the weights of young salmon returning to rivers were higher than before, and weights of older salmon were similar or lower. One site comparison study in the Gulf of Maine found that there were smaller, but similar condition monkfish inside an area closed year-round to groundfish fishing for six to seven years than an area open to all fishing.
  • Abundance (4 studies): Two site comparison studies in the Gulf of Maine and Bismark Sea found a higher abundance of only one of seven fish species and lower abundance of monkfish in areas closed to groundfish (bottom-dwelling) fisheries for six to eight years, compared to open areas. One of two replicated, before-and-after studies (one controlled) in the Norwegian Sea and North Sea found that there were more young salmon and similar numbers of older salmon returning to rivers than before, in the five years after the long-term closure of a commercial coastal fishery. The other study found that lesser sandeel biomass and density peaked but there was no overall increase in the three years after a long-term fishery closure compared to before.


  • Behaviour change (1 study): One site comparison study in the Bismark Sea found that in an area closed to customary fishing for eight years, six of seven fish species had a lower flight response distance compared to an area open to customary fishing, making them more vulnerable to capture with spear guns.


  • Reduction of unwanted catch (1 study): One replicated, before-and-after study in the Kattegat found that a combination of long-term fishery closures and areas limited to specific gears reduced unwanted catch of cod compared to before.
  • Reduction of fishing effort (1 study): One replicated, controlled, before-and-after study in the North Sea found that long-term closure of a commercial fishery reduced overall fishing effort for lesser sandeel.
  • Commercial catch abundance (1 study): One replicated, controlled, before-and-after study in the North Sea found that annual sandeel catch rates were varied after the indefinite closure of the commercial fishery in an area.

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

  1.  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 long-term ban on a coastal drift net fishery for Atlantic salmon Salmo salar, there were increases in the catch abundance and weights of young (one-sea winter) salmon 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 fish, before: 80–1,200 fish) and numbers of older, multi-sea-winter salmon were similar (after: 50–3,200 fish, before: 50–3,200 fish). Average weight of grilse increased in all four rivers (after: 1,714–2,340 g, 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 g) 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 were taken from Norwegian Official Statistics.

    Study and other actions tested
  2.  A replicated, controlled, before-and-after study in 1997–2003 of a seabed area in the North Sea, Scotland, UK (Greenstreet et al. 2006) found that in the three years after long-term closure of a commercial fishery for lesser sandeel Ammodytes marinus there was a peak but no overall increase in the biomass and density of sandeel, overall fishing effort was reduced and catch rates varied. The annual biomass of the two youngest groups of sandeel (young of the year and 1+ year) peaked during the closure (2000–2003) compared to the previous three years, but no overall statistical difference was found between periods (after: 0–233,000 t, before: 0–50,000 t). Similarly, sandeel density peaked in the first year after closure (after: 7–48 fish/m2, before: 4–42 m2), but was not statistically different. Fishing effort was reduced each year during the closure (after: 25–50 d, before: 80–280 d) but estimates of catch rates varied (after: 50–190 t/day, 55–130 t/day). In 2000, the sandeel fishery off south-east Scotland was closed indefinitely in response to concerns that seabird colonies were declining from lack of fish prey. Sandeel biomass estimates were derived from acoustic (six transects) and bottom trawl surveys (19 deployments) from a commercial vessel between May–July 1998–2003. Density data were collected from 137–195 grab deployments done each year, and fishing effort and catch data were derived from official fisheries statistics for the Danish commercial sandeel fishery.

    Study and other actions tested
  3. A site comparison study in 2004–2005 of two areas of mud and gravel seabed in the Gulf of Maine, USA (3) found that year-round closure of an area to fisheries targeting bottom-dwelling fish (groundfish) for six to seven years, resulted in lower abundance and size of monkfish Lophius americanus abundance inside the closure area compared to outside, feeding intensity varied and condition was similar. Overall, monkfish abundance and size were lower inside the closure area than outside (data reported as statistical model results). The abundance of larger monkfish (401–800 mm) was similar inside compared to outside (inside: 0.3–0.8 fish/tow, outside: 0.3–1.2 fish/tow), but was lower for monkfish between 0–400 mm (inside: 0.3–0.8 fish/tow, outside: 1.3–2.7/tow). Stomach fullness of adult monkfish was higher inside (10 g/mm3), than outside (6 g/mm3), but juvenile (<300 mm) stomach fullness was similar (inside: 8 g/mm3, outside: 11 g/mm3). Monkfish condition was similar across protection levels (data reported as statistical model results). In addition, monkfish feeding intensity and condition were generally more strongly affected by habitat type than the closure. In autumn 2004 and spring 2005, a total of 32 otter trawl deployments were conducted at paired sampling sites, rock/cobble edge and mud, inside and outside, of the Western Gulf of Maine Closure Area. The area was closed to groundfish fishing in 1998, initially to reduce fishing mortality of key groundfish species such as cod. Monkfish were counted, lengths measured, weighed and stomach content recorded.

    Study and other actions tested
  4. A site comparison study in 2008 at two reefs in the Bismark Sea, Papua New Guinea (4) found that long-term closure of areas to traditional fisheries (those with customary fishing rights) resulted in greater abundance of only one of seven species compared to fished areas after eight years, and the flight response of six species decreased. Striated surgeonfish Ctenochaetus striatus were more abundant inside closed areas compared to fished areas (closed: 47, open: 25 fish/1,000 m2), but abundances of the other six species (orange-lined triggerfish Balistapus undulatus, Bleeker’s parrotfish Chlorurus bleekeri, daisy parrotfish Chlorurus sordidus, yellowbarred parrotfish Scarus dimidiatus, dusky parrotfish Scarus niger, and humpback red snapper Lutjanus gibbus) were similar (inside: 1–31, outside: 1–14 fish/1,000 m2). In addition, flight response of all but one species (humpback red snapper) inside the closure area was shorter (closed: 131–365 cm, open: 207–551 cm), making them more vulnerable to capture by spear guns (range 1.3 to 3.1 m). Fish were surveyed on reefs off Karkar Island inside and outside one site (0.5 km2) that at the time of the study had been closed to customary fishing (using spear guns and hand lines as primary gear types) for 8 years, with the exception of a 2-week period during which it was opened to fishing for a ceremonial feast (details of when sampling took place were not reported). The community maintains a customary system of reef management where a portion of the reefs is closed for several years when the clan chiefs decide fish are staying out of the range of spear guns. Sampled reefs outside the closure area had not been closed to fishing. At five locations at each site, two, 50 × 5 m belt transects at 2–4 and 6–8 m depths were surveyed by underwater visual census. Fish flight distance was measured by placing weighted markers on a measuring tape at the start position of the fish and the final position after disturbance.

    Study and other actions tested
  5. A replicated, before-and-after study in 1996–2012 of four areas of seabed in the Kattegat, off Sweden/Denmark (Vinther & Eero 2013) found that a combination of closed areas and areas limited to specific gears resulted in a reduction in unwanted catch (likelihood of being caught and retained) on cod Gadus morhua by the Danish bottom fleet compared to before implementation. Across all areas, fishing impact (reported as a function of fish density, fishing effort and gear size selectivity) was reduced for all size groups of cod, by 60% in the period after management measures were introduced (2009–2011) compared to the impact before (2008; see paper for data). In addition, by area, the reduction in fishing impact was largest in areas subject to permanent or partial closures, but a decline in fishing impact was also found in areas outside of closures due to a general change to more selective gears. In contrast, in a seasonally closed area, fishing impact was estimated to have increased in 2009–2010 in relation to 2008 (see paper for data). In 2009, Sweden and Denmark introduced protected areas on historically important cod spawning grounds. The protected zone had four areas in which fishing was either completely forbidden or limited to specific selective gears (Swedish size sorting grid and Danish SELTRA codend with 300 mm mesh size in exit window) throughout part, or all, of the year. Annual changes in fishing impact were estimated by overlaying the spatial and temporal distribution of cod and fishing pressure. Analyses of cod distribution were based on time-series data from six research trawl surveys (between 20–80 stations/year spanning 1996–2012) in the first, third and fourth quarters of a year. Fishing effort data from the Danish fleet in the Kattegat derived from logbooks and satellite-based vessel monitoring systems were analysed for the period 2008–2011.

    Study and other actions tested
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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Marine Fish Conservation

This Action forms part of the Action Synopsis:

Marine Fish Conservation
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