Action

Modify fishing trap/pot configuration

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

Study locations

Key messages

 COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

  • Survival (1 study): One replicated, controlled study in the Bothnian Sea found that survival of small herring escaped from a pontoon fish trap through a size-sorting grid was similar to trap-caught herring that did not pass through a grid.

BEHAVIOUR (0 STUDIES)

OTHER (22 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

  1. A replicated, controlled study in 1992–1993 of five areas in a shallow estuary in the Kattegat, Denmark (Dieperink & Rasmussen 1997) found that modifications made to eel pound nets (fine-mesh, passive fish traps) reduced the capture of unwanted young brown trout Salmo trutta and, for one of two methods, salmon Salmo salar and rainbow trout Oncorhynchus mykiss, compared to nets fished without the modifications. The first of two modifications, submerging the pot net (the last enclosure in the net before the fyke net – akin to a codend), reduced catches of all species: by 91% for brown trout; 86% for salmon; and 75% for rainbow trout. The second, raising the guard net (located at the entrance to the pound net) to the surface using floats reduced numbers of brown trout (raised: 5–25 fish, not raised: 14–60 fish) but not salmon (raised: 6–18 fish, not raised: 13–15 fish) or rainbow trout (raised: 2–4 fish, not raised: 1–2 fish). In addition, catches of legal-sized individuals of the target eel Anguilla anguilla were similar for both comparisons. Pound net fishing was done in April/May 1992 and 1993 at five locations in the Randers Fjord estuary (22 km2), eastern Jutland, in 2–4 m depth. Every one or two days, pound nets were changed from a standard configuration to a modified one, either with a surface floating guard net or with submerged pot net, and vice versa. For the submerged nets, three different depths were fished: 55, 75 and 100 cm below sea level. The daily catch in each pound net was recorded as the number of each species from both the pot and fyke net sections within a 24 h period.

    Study and other actions tested
  2. A replicated, randomised, controlled study in 1994 of an area of shallow seabed in the Atlantic Ocean off Delaware, USA (Shepherd et al. 2002) found that fish traps modified with escape vents reduced the unwanted catch of undersized black sea bass Centropristis striata compared to traps without escape vents. Across all escape vent sizes, catch rates of bass (all sizes) were lower in traps with vents than without (with: 2–11 bass/trap, without: 10–14 bass/trap) and the average bass size was greater (with: 27 cm: without: 25 cm). The proportion of undersized (<24 cm) bass in traps with vents was reduced by 72–95% compared to without, and the reduction increased with increasing vent size (2.9 cm: 288 bass, 3.2 cm: 80 bass, 3.5 cm: 59, 3.8 cm: 48 bass, no vent: 1,037 bass). Data were collected from 893 trap deployments (18–27 m) during nine trips between May-November 1994. Traps were deployed along lines (strings) of 25 traps in blocks of five trap designs, four with escape vents of different sizes (2.3 cm, 3.2 cm, 3.5 cm and 3.8 cm) and one standard trap without vents. Four strings of 25 traps were set/trip and traps were randomly positioned within a block. Strings were set 5 miles apart and left for 12–32 days before retrieval.

    Study and other actions tested
  3. A replicated, controlled study in 1999–2000 of three fished areas of seabed in the Tasman Sea off New South Wales, Australia (Stewart & Ferrell 2003) found that bottom traps modified with back panels of different and larger mesh type improved the size selectivity of the majority of fish species, compared to the standard commercial trap. For five of 10 species, the estimated size at which fish had a 50% chance of escape (selection size) was greater for modified traps than standard traps (modified: 21–35 cm, standard: 15–25 cm). For four species, the selection size in modified traps was 17–24 cm, whereas all individuals were predicted to be retained in standard traps (see paper for size ranges – reported as length frequency curves). All sizes of one species were retained in both modified and standard traps. See original paper for individual data by species. Data were collected on chartered commercial vessels commercial fishing grounds in three locations during March–October 1999. Deployments were made of three different fish traps, identical (all covered with 37 mm hexagonal wire mesh) except for their back panels: a modified back panel of 50 mm × 75 mm welded mesh (122 trap lifts), a standard back panel of 50 mm hexagonal wire mesh (129 trap lifts), and a smaller 37 mm hexagonal wire mesh to retain and sample all sizes (104 trap lifts). Traps were baited and left on the seabed for 24–72 hours. Fish lengths from the nose to the end of the backbone (fork length) were measured.

    Study and other actions tested
  4. A replicated, controlled study in 1999–2004 of three sand and mud seabed areas in Vistula Lagoon, Baltic Sea, Poland (Psuty-Lipska & Draganik 2005) found that fyke nets modified with protective sieves (a bycatch reduction device) retained fewer undersized and unwanted individuals of four of four commercial fish species compared to conventional fyke nets without protective sieves. In catches with sieves, the length frequencies of the four most important commercial fish species differed to catches without sieves, with fewer fish of smaller sizes (data presented graphically) and higher average lengths (bream Abramis brama: 29 vs 20 cm, pikeperch Sander lucioperca: 26 vs 16 cm, roach Rutilus rutilus: 18 vs 15 cm, perch Perca fluviatilis: 18 vs 14 cm). Incidental fish catch was sampled at three sites in the brackish Vistula Lagoon (838 km2) from commercial fyke net catches targeting European eel Anguilla Anguilla. In May 2004, the fyke nets sampled (12 deployments) were fitted with selective sieves with openings of 20 × 65 mm to allow fish escape. In May 1999 standard fyke net deployments (22) were sampled (see paper for gear specifications). Captured fish were sorted by species, weighed, and their lengths measured.

    Study and other actions tested
  5. A replicated, paired, controlled study in 1999–2000 in a shallow sandy estuary in the Atlantic Ocean, Brazil (Vianna & D’Incao 2006) found that fitting size-sorting escape grids to stationary shrimp net traps (stow nets) did not reduce the unwanted catch of white croaker Micropogonias furnieri compared to standard shrimp traps without a grid. For grid bar spacings of 25, 30 and 35 mm, unwanted catch of white croaker was not significantly different between nets (with grid: 16–39 fish, without grid: 28 fish). In addition, there was no significant difference in catches of target pink shrimp Farfantepenaeus paulensis between nets with and without grids (all bar spacings; with: 1,783–2,128 shrimps, without: 2,110 shrimps). Trials were done in the Patos Lagoon in late-1999–February 2000. Three commercial shrimp nets were fitted with a circular metal grid with one of three bar spacings (25, 30 or 35 mm) and one standard net was left without a grid. The nets were positioned randomly, and the grids changed between nets. Ten samples were taken, with each net fishing at the same time. Nets were set in the evening and retrieved at the end of the night. All catch was weighed, and fish were counted and identified.

    Study and other actions tested
  6. A replicated study in 2002–2004 in an area of seabed in St Francis Bay in the Indian Ocean, off South Africa (Gray et al. 2007) found that modifying fish traps by increasing the mesh size of the escape panel had no effect on the size-selectivity of commercial target panga Pterogymnus laniarius. The average height of panga in catches was similar between all three relative mesh sizes of the trap escape panels (large: 97 mm, medium: 95 mm, small: 95 mm). In addition, the effect of mesh size on catch species composition, including non-target fish, was not reported, however, it differed with depth and substrate type (see paper for data). Data were collected from 59 trap deployments between September 2002 and July 2004. Three pairs of traps were used during most deployments, each fitted with a different mesh size of escape panel: two large (50 ×100 mm mesh), two medium (50mm × 75mm mesh) and two small (50 × 50 mm mesh). Traps were deployed randomly in depths of 20–99 m and for 2–8 hours. Fish in catches were identified and counted. The sizes of panga, including body height, were recorded.

    Study and other actions tested
  7. A replicated, controlled study in 2006 in a lagoon channel in Alfacs Bay in the Mediterranean Sea, Spain (Lopez & Gisbert 2009) found that eel Anguilla anguilla traps with a modified entrance typically reduced the catches of unwanted fish compared to unmodified conventional traps. Overall, the proportion of unwanted fish (all species) was lower in modified traps (63%) than in conventional traps (37%). For individual species, the proportions of young thinlip mullet Liza ramada and golden grey mullet Liza aurata were also lower in modified traps (thinlip: 4%, grey: 21%) than in conventional traps (thinlip: 96%, grey: 79%). Catches of unwanted common goby Pomatoschistus microps, sand smelt Atherina boyeri, Spanish toothcarp Aphanius iberus and juvenile Senegalese sole Solea senegalensis were also lower in modified than conventional traps (data reported as statistical model results). Catches of unwanted black-striped pipefish Syngnathus abaster, sea bass Dicentrarchus labrax and juvenile gilthead seabream Sparus aurata were similar in each trap design (data reported as statistical model results). In addition, proportions of commercial target eel catches were not significantly different between modified (63%) and conventional (37%) trap designs. Modified and conventional traps were deployed on opposite sides of a channel in 23 trials. All traps were a trapezoid frame covered with small mesh (2 mm) and with a funnel entrance. Modified traps had a rigid square-meshed cylinder at the end of the entrance funnel to prevent unwanted species entering the trap.

    Study and other actions tested
  8. A replicated study in 2004 in an area of seabed in the Adriatic Sea, Italy (Morello et al. 2009) found that trap (creel) type did not typically affect the catch of non-commercially targeted fish species, however compared to bottom trawl gear, creels did not catch high proportions of immature fish of commercial species. Overall, the percentage of creels containing non-target species (fish and invertebrates other than Norway lobster Nephrops norvegicus) was similar between Scottish (14%) and Croatian (6%) creels, but for both designs it was lower than for the Italian creel design (52%). However, only two of the 11 catch species were fish, and these were caught in Scottish creels only (<1 fish/creel). By comparison (but not tested statistically) 30 of the 55 species caught in bottom trawl deployments for lobster were fish, including a large proportion of immature individuals of commercial and other species (see paper for data). Data were collected from deployments of three different creel designs and a traditional commercial bottom trawl (11 hauls) in the western Pomo pit in August 2004 (see original paper for gear specifications). Traps were soaked for 24 h at depths of 210–235 m. On each of two deployments, two fleets were shot, one with 81 Scottish creels and the other with 40 Croatian and 20 Italian creels interspersed. Two further deployments were made of Scottish creels only. Trawl hauls were 1 h.

    Study and other actions tested
  9. A before-and-after study in 2000–2008 in a fished area of seabed in the Southern Ocean off South Australia (Linnane et al. 2011) reported that catches of unwanted blue-throat wrasse Notolabrus tetricus and leatherjacket Meuschenia spp. were lower after the introduction of escape gaps to lobster traps. Data were not statistically tested. In 2000 and 2001, unwanted catches of wrasse were 0.12 and 0.09 wrasse/pot respectively, while catches of leatherjacket were 0.28 and 0.36 leatherjacket/pot. In 2003 after escape gaps in lobster pots had been introduced, wrasse catches were 0.05 wrasse/pot and remained between 0.05–0.06 wrasse/pot in the period until 2008. Leatherjacket catches were 0.13 leatherjacket/pot in 2003 and remained below 0.22 leatherjacket/pot until 2008. Escape gaps also reduced catches of undersized commercial target rock lobster Jasus edwardsii by 64%. In 2003, two escape gaps (minimum 5.7 cm height x 28 cm width) were made mandatory at each end of lobster pots in the Northern Zone rock lobster fishery in the Great Australian Bight. Catch rates of undersized lobster and unwanted fish species for the period 2000–2008 were obtained from a voluntary logbook programme established in 2000.

    Study and other actions tested
  10. A replicated study in 2010 in nine inshore areas in the Bothnian Sea, Sweden (Lundin et al. 2011) reported that herring Clupea harengus pontoon traps modified with two rigid size-sorting grids allowed the escape of high proportions of undersized herring. Data were not statistically tested. Across all trials, between 68–565 kg of the total weight of herring entering the traps (400–1,200 kg) was estimated to have escaped through the grids. By number, this was a reduction in catch of 17–76% (2,420–17,008 fish). The proportion of undersized herring removed from the catches (selection efficiency) was 54–72% across all trials. In addition, higher proportions of herring escaped through grids with 15 mm bar spacing (59–76%) than 14 mm grid bar spacing (17–25%). Data were collected from six deployments (17–120 h soak times) of a herring pontoon trap in May/July 2010. The trap was a single-walled cylindrical fish chamber (6 × 3 m) with small (24 mm) mesh to retain all sizes of herring. At each end of the chamber, a grid consisting of a 300 mm wide ring with 2 mm diameter stainless steel rods fitted vertically inside was fitted. The rods were placed at either 14 mm or 15 mm bar spacing (three deployments of each bar spacing). Underwater cameras monitored numbers of herring escaping through the selection grids. Full trap specifications are given in the original paper.

    Study and other actions tested
  11. A replicated, randomized, paired, controlled study in 2009–2010 in shallow coastal waters of the Bay of Hanö in the Baltic Sea, Sweden (Ovegård et al. 2011) found that floating traps (pots) modified with square mesh escape windows allowed the escape of high proportions of undersized Atlantic cod Gadus morhua, and size-selectivity increased with increasing window mesh size. Pots with square mesh escape windows allowed the escape of over 90% of cod under the minimum landing size of 38 cm (data presented graphically). The length at which cod had a 50% chance of escaping increased with increasing mesh size of the escape window (40 mm: 32 cm, 45 mm: 38 cm, 50 mm: 40 cm). Data were collected in April 2009–January 2010 from a commercial fishing vessel. A total of 54 paired deployments were done of four pots with identical escape window mesh size (three different sizes: 40 mm, 45 mm and 50 mm), and four without windows, set randomly along a line (string). All pots were baited with Baltic herring Clupea harengus and soak-time was 1–14 days. See original paper for full gear specifications.

    Study and other actions tested
  12. A replicated, controlled study in 2003–2004 of seabed and near seabed in the Atlantic Ocean off the Canary Islands, Spain (Arrasate-López et al. 2012) reported that semi-floating shrimp traps caught less unwanted fish catch (non-commercially targeted or discarded) catch than traditional bottom traps, and the difference decreased with depth. Data were not statistically tested. At 100–400 m depths, semi-floating traps caught 18 unwanted species of fish at catch rates between <0.1–858.9 g/trap/day, and bottom traps caught eight species at <0.1–24.9 g/trap/day. Between 401–800 m depth, semi-floating traps caught eight unwanted fish species (<0.1–2,241.0 g/trap/day) while bottom traps caught four species (0.4–140.6 g/trap/day). At the deepest depths (801–1,130 m), semi-floating traps caught five unwanted fish species (<0.1–186.4 g/trap/day) and four were caught in bottom traps (0.5–41.9 g/trap/day). At all but the deepest depths, conger eels Conger conger accounted for a large proportion of the unwanted catch in bottom traps and in semi-floating traps at the intermediate depths (see paper for species individual data). Target shrimp Plesionika spp. catches between floating and bottom traps varied with species and depth (see paper for data). Four research surveys were done around the Canary Islands in 2003–2004 at depths of 100–1,300 m. Two types of traps were used to target shrimp: semi-floating traps of plastic mesh (20 ×15 mm) covering a conical cylinder (56 × 57 cm), and bottom traps made of wire mesh (19 × 19 mm) and an iron rectangular frame (100 × 100 × 50 cm). Semi-floated traps were set in groups of 75 traps, 15 m apart and 2 m above the seabed (total 1,971). Bottom traps were deployed in lines of 10 traps, 50 m apart (total 487). All traps were deployed in daylight hours and baited with mackerel Scomber colias.

    Study and other actions tested
  13. A replicated study in 2010 of mud and sand seabed in two estuaries in the Solitary Islands Marine Park in the Tasman Sea, Australia (Butcher et al. 2012) found that the number of unwanted fish caught in traps in a mud crab Scylla serrata fishery was lower in three of four trap designs. Across six days of fishing, unwanted fish catches (consisting mainly of yellowfin bream Acanthopagrus australis) in hoop nets (3 fish), rectangular pots (9 fish) and wire pots (5 fish) were lower than in round pots (287 fish). In addition, all trap designs retained similar sizes of commercial target mud crabs (8–19 cm). Between February and June 2010, five traps of each of four designs were deployed for three, six or 24 hours across six days of fishing. Designs were: steel-framed hoop traps (0.75 m diameter × 0.65 m, 150 mm mesh), rectangular collapsible plastic pots (0.88 × 0.55 × 0.20 m) with “V” shaped entrances, rectangular wire pots (0.90 × 0.60 × 0.30 m) with 50 x 0.75 mm wire mesh and two funnel entrances, and round, collapsible plastic pots (0.90 m diameter × 0.27 m) with four funnel entrances. All traps complied with existing regulations and were baited with sea mullet Mugil cephalus in a 10 × 10 mm mesh bag, and deployed 50–100 m apart.

    Study and other actions tested
  14. A replicated, controlled study in 2010 in an inshore area of the Bothnian Sea, Sweden (Lundin et al. 2012) found that survival rates of trap-caught small Baltic herring Clupea harengus membras that had passed through a size-sorting escape grid were similar to trap-caught herring that had not passed through a grid. The mortality of herring that had passed through the escape grid was 3–13% compared to 7–45% for herring caught without a grid. When the effects of water temperature variations during the trials were considered, no significant difference in mortality rates between traps was found. Herring were sampled in a herring trap (pontoon trap) in six alternate trials in July-September 2010: three using a stainless steel sorting grid with 14 mm bar spacing and three with no grid. Small herring were caught in the trap by passing through a sorting grid mounted at the entrance of the fish chamber. The trap was then closed and the herring retained in situ for seven days. As control fish, herring of all sizes were trapped without passing through any grid. Numbers of herring enclosed varied between 172 and 2,170. For each trial, herring survival rates after the seven days were assessed.

    Study and other actions tested
  15. A replicated, randomized, controlled study in 2010 in two areas of seabed in the Strait of Georgia, in the Pacific Ocean, British Columbia, Canada (Favaro et al. 2013) found that two of five modified designs of traps commercially targeting spot prawns Pandalus platyceros caught fewer unwanted fish and protected rockfish Sebastes spp. compared to a conventional unmodified trap. Overall, unwanted fish catches were 69% and 68% lower in the five and seven-ring tunnel-equipped traps than the conventional traps respectively, but unwanted fish catch rates in the three other modified trap designs were similar to the conventional trap (data presented graphically – see original paper). Only six rockfish were caught overall: none in tunnel-equipped traps, one in the 6.4 cm entrance trap, two in the 7.0 cm entrance trap and three in the unmodified trap. In addition, average rockfish body weight and length were lower in traps with a five-ring tunnel and both five and seven-ring tunnel entrances respectively, compared to other designs (data reported as statistical model results). In addition, all modified traps caught fewer and generally smaller commercial target prawns than conventional traps (data reported as statistical model results). Traps were randomly ordered in groups of 10 along single weighted lines at 50–120 m depths. All traps were truncated cone designs with 3.8 cm mesh. Conventional traps (7.6 cm single-ring entrances) were compared to five modified designs with either a reduced diameter entrance (7.0 cm or 6.4 cm), or a tunnel-design 7.6 cm entrance of four, five or seven rings (see original paper for gear specifications).

    Study and other actions tested
  16. A replicated, controlled study in 2012 at two coral reef sites in the Indian Ocean, Kenya (Gomes et al. 2014) found that traditional traps with added escape gaps reduced the catches of unwanted fish compared to unmodified traps. Across both sites, biomass of non-commercial reef fish catch was lower in modified traps (40–210 g/trap) compared to unmodified traps (242–328 g/trap). At one site, commercial catch was similar between the trap designs (502–827 g/trap) and at the other site commercial catch was greater using the modified trap (1,376 g/trap) compared to the unmodified design (1,032 g/trap). Data were collected at a fish landing site between January-April 2012, from trap catches by fishers from two areas of the Mpunguti Marine National Reserve (10 km2, established 1978). Fish catch weights were sampled from 77 catches using modified traditional traps (two 3 × 30 cm escape gaps) and 161 catches using unmodified traditional traps (161 samples).

    Study and other actions tested
  17. A replicated, controlled study in 2011 of a fished area of seabed in the Indian Ocean, Kenya (Condy et al. 2015) found that modified fish trap designs (escape slots of four different sizes) reduced the catches of smaller unwanted fish compared to unmodified traps. Average fish length and weight were greater in the modified traps for three of the four slot widths compared to the unmodified trap (length: 21–26 vs 20 cm/trap; weight: 208–424 vs 178 g/trap). The catch percentages of immature fish were lower in modified traps (19–37%) than unmodified traps (50%). Between September–October 2011, catches from fishing grounds local to Kibuyuni (2–3 km radius) were sampled. Catches in local fishing traps of weaved wood fibre without escape slots were compared with modified traps with escape slots of varying widths (2, 4, 6, 8 cm). Five fishers participated in 12–24 days of experimental fishing with 108 samples analysed/trap design. Traps were set for 24 h and checked daily.

    Study and other actions tested
  18. A replicated, controlled study in 2012 in an inshore area in the Bothnian Sea, Sweden (Lundin et al. 2015) found that a pontoon fish trap modified with a square mesh escape panel fitted in the fish chamber reduced the catches of immature whitefish Coregonus maraena compared to traps without a panel. The proportion of undersized (<30 cm) whitefish in catches was 9% in modified traps and 32% in unmodified traps. A total of 72% of the whitefish <30 cm was estimated to have escaped through the panel that would otherwise have been captured. The number of whitefish caught in the modified trap was lower (488 fish) than the unmodified trap (1,003 fish). Data were collected from 28 deployments (9 m depth) of two pontoon traps fished at the same time 800 m apart between June-August 2012. The fish chamber with and without a 50 × 50 mm square mesh panel were exchanged between traps every two weeks (four replicates). See original paper for trap specifications. Escaping fish were sampled by video cameras attached next to the panel.

    Study and other actions tested
  19. A replicated, controlled study (year not provided) in two coastal brackish sites in the Gulf of Bosnia, Baltic Sea, Sweden (Lundin et al. 2015) found that pontoon traps fitted with a size-sorting escape grid reduced the catches of small fish compared to traps without a grid. The proportion of the total catch of small perch Perca fluviatilis, whitefish Coregonus maraena and roach Rutilus rutilus in traps fitted with a grid (0–55%) was lower than traps fished without a grid (56–90%). In addition, average size of perch, whitefish and roach caught in traps with grids was larger (grid: 28–37 cm, no grid: 22–31 cm). Fish were sampled with two different types of pontoon trap used for perch fishing (see paper for specifications). The traps were located at two sites for a total of 27 fishing periods, in June-August. Each trap was fitted with a 30 x 40 cm size-sorting grid of vertical 2 mm stainless steel bars with 30 mm bar spacing. Grids were covered with fine-meshed netting for nine of the fishing periods to sample catches without a grid. All fish caught in the traps were measured. Sampling year was not reported.

    Study and other actions tested
  20. A replicated, controlled study in 2013 of an area of seabed in the Atlantic Ocean, USA (Rudershausen et al. 2016) found that traps with larger mesh sizes improved the size-selectivity of black sea bass Centropristis striata and reduced the catches of undersized individuals, compared to conventional smaller mesh sizes. The length at which bass had a 50% chance of escape increased with increasing trap mesh size (64 mm mesh: 325 mm, 57 mm mesh: 290 mm, standard 51 mm mesh: 260 mm, standard 38 mm mesh with 51 mm back panel: 245 mm). The average catch rate of bass below the minimum landing size (<279 mm) decreased with increasing mesh size (64 mm mesh: 0 fish/trap, 57 mm mesh: 1 fish/trap, standard 51 mm mesh: 6 fish/trap, standard 38 mm mesh with 51 mm back panel: 9 fish/trap). Data were collected in Onslow Bay (sampling season not reported) from 350 deployments of five different trap types, all of square mesh: 64 mm mesh, 57 mm mesh, 51 mm mesh, 38 mm mesh with a 51 mm back panel, and one small mesh trap (38 mm) to sample all sizes of fish (between 33 and 119 deployments each). Traps were baited and set on the seabed at least 100 m apart for 1–12 hours. All bass were counted, and total length measured.

    Study and other actions tested
  21. A replicated, controlled study 2007 in an area of seabed in the Barents Sea, Norway (Jørgensen et al. 2017) found that modified floating pots (one entrance) did not reduce the amount of undersized commercial target Atlantic cod Gadus morhua compared to conventional pots with two entrances, and increased the amount of non-target haddock Melanogrammus aeglefinus. Catch rates of undersized (<44 cm) cod were similar between one-entrance pots (2 cod/pot) and two-entrance pots (2 cod/pot). Catch rates of haddock (all sizes) were higher in one-entrance pots (1.3 haddock/pot) compared to two-entrance pots (0.6 haddock/pot); the proportions of undersized (<40 cm) haddock being 44% and 69% for one- and two-entrance pots, respectively. In addition, legal-sized (>43 cm) cod catches were higher in one-entrance pots (2 cod/pot) than two-entrance pots (1 cod/pot). In September 2007, a total of 140 floating cod pots (100 × 150 × 120 cm) were set for 24 h in Varangerfjord, Norway. Seventy pots were conventional two-entrance pots (25 x 15 cm entrance) and 70 pots were modified to have one entrance. Pots were set every 50 m along a groundline at 108–150 m depth, and baited with squid Illex sp.

    Study and other actions tested
  22. A replicated, paired, controlled study in 2016 of four seabed sites in the Gulf of St. Lawrence, Canada (Poirier et al. 2018) found that modifying a fyke net reduced the capture of unwanted American eel Anguilla anguilla and winter flounder Pseudopleuronectes americanus compared to unmodified, conventional fyke nets, and the overall number of unwanted species (fish and invertebrates) in catches decreased. Across sites, catch numbers of unwanted eel and flounder (the two main unwanted fish species caught) were lower in modified nets (eel: 3, flounder: 7) than unmodified nets (eel: 37 fish, flounder: 43). The species composition (fish and invertebrates) was different between nets (for fish, flounder and mummichog Fundulus heteroclitus accounted most for the reduced catch in modified nets) and the number of unwanted species was lower in modified nets (modified: 5 species, unmodified: 12 species). In addition, numbers of target catch of green crab Carcinus maenas were reduced in modified nets (modified: 1,791, unmodified: 6,637). Data were collected at four sites in Murray Harbour off Prince Edward Island in July 2016. At each site, a removable ‘bycatch reduction device’ was randomly assigned to one of two conventional fyke nets (used to target green crab) and both nets set 100 m apart for three sets of four consecutive 24 h deployments, the device being switched between nets/set. After each individual 24 h deployment, fyke nets were fished at low tide. The ‘bycatch reduction device’ consisted of a sloped barricade ramp attached to a removable hoop with an entrance slit designed to prevent entry of non-target species (see paper for gear specifications).

    Study and other actions tested
  23. A replicated, controlled study in 2013–2014 in three areas of sandy seabed in the Tasman Sea off the coast of New South Wales, Australia (Richards et al. 2018) found that modified traps fitted with permanent magnets reduced the catches of unwanted sharks and rays (Elasmobranchii), compared to conventional traps with no magnets or traps fitted with non-magnetic material. Catch rates of sharks/rays in traps with magnets were lower (0.2/trap) than traps with no magnets (0.3/trap) and traps with non-magnetic material (0.3/trap). Commercial target snapper Pagrus auratus catches were higher in traps with magnets (1.1 kg/trap) than without magnets (0.8 kg/trap) and 1.0 kg/trap in traps with non-magnetic material. In addition, the presence of sharks/rays in traps reduced commercial target snapper catches by 34% (1.5 vs 2.3 kg/trap). Between December 2013 and August 2014, a total of 1,015 traps of three different designs were set in three areas of sandy seabed at 5–102 m depth. Traps had a wooden frame (180 × 120 × 80 cm) covered in 50 mm wire mesh with a 100 × 60 mm escape panel at the rear. Each trap design had three funnel entrances, either with or without four magnets (75 × 13 × 16 mm) or with four non-magnetic bars (same size as magnetic) attached to each funnel.

    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.

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