Use a different bait type

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

Study locations

Key messages





  • Reduction of unwanted catch (10 studies): Six of eight replicated studies (three controlled and one randomized) in the Norwegian/Barents Seas, Barents Sea, Denmark Strait, North Atlantic Ocean, Mediterranean Sea and the South Pacific Ocean, found that using a different bait type (including size, species and manufacture method) reduced the unwanted catches of undersized haddock (although in one case in only two of six comparisons), Atlantic cod and other unwanted or non-target fish catch, but unwanted catches of torsk and ling were similar, compared to standard or other bait types. Two other studies found no reduction in unwanted catches of pelagic stingray and overall unwanted fish with different bait types. Two systematic global reviews found that using different bait types did not affect the number of unwanted sharks and rays caught.
  • Improved size-selectivity of fishing gear (1 study): One replicated study in the Denmark Strait found that using a different bait species increased the size-selectivity of commercially targeted Greenland halibut.

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 1990–1991 in two pelagic areas in the Norwegian/Barents Seas, off Norway (Løkkeborg & Bjordal 1995) found that bait on pelagic longlines that had been made to appear larger caught fewer small and undersized haddock Melanogrammus aeglefinus than bait of a standard, smaller size, but catches were similar for torsk Brosme brosme and ling Molva molva. When bait appeared larger, fewer small and undersized (<46 cm) haddock were caught (26 fish) than with standard sized bait (45 fish). However, catches of larger, legal sized (>46 cm) haddock were similar for each bait type (large: 67, standard: 74 fish). Total catch of torsk was similar between bait types, across all sizes (large: 173, standard: 160 fish) (no ling data presented.) In addition, the mean size of fish caught on experimental and standard baits was similar for torsk (54 vs 54 cm) and ling (91 vs 95 cm). Trials were carried out in November 1990 (western Norway, 120–370 m depth), and in July 1991 (northern Norway, 373–415 m depth). Experimental bait was made from a piece of plastic attached to the shank of a circle hook around which the bait was wrapped, giving it a larger appearance. Hooks were baited with mackerel (Scombridae) in western Norway, and mackerel and squid (Cephalopoda) in northern Norway. Hooks were left for 4–14 h in western Norway and 11–12 h in northern Norway. Detailed gear specifications are given in the original paper.

    Study and other actions tested
  2. A replicated, controlled study in 1996 of two coastal pelagic areas in the Barents Sea, off north Norway (Huse & Soldal 2000) found that longline catches of undersized haddock Melanogrammus aeglefinus were lower in two of six comparisons of four different bait types with normal bait. In one trial, the proportion of haddock below the legal size (44 cm) was lower on restructured sandeel Ammodytes spp. bait (5%) and large mackerel Scomber scombrus bait (9%) compared to normal mackerel bait (16%), but similar on restructured mackerel bait (17%) or large restructured mackerel bait (14%). Overall catch rates were similar on all five bait types (51–76 fish/100 hooks). In another trial, restructured baits of sandeel and mackerel caught similar proportions of haddock below the legal size (44 cm) as normal mackerel bait (restructured: 17–19%, normal: 18%) and catch rates were also similar (restructured: 57–76 fish/100 hooks, normal: 74 fish/100 hooks). Two trials were carried out in June/July 1996 by two commercial longliners fishing in two areas using different hooks/rigging configurations (see paper for specifications). Four bait types and sizes (twice the normal size) were tested against a standard bait of 2 cm-thick slices of mackerel. Restructured baits were based on minced fish and algal binding agent. Baits were tested on longline fleets consisting of groups of 50 hooks with test baits (400–4,566 hooks) alternated with groups of 50 hooks with standard baits (7,250–15,323 hooks). Numbers and lengths of haddock captured were recorded.

    Study and other actions tested
  3. A replicated study in 1999 in a coastal gulf in the South Pacific Ocean off New Zealand (Willis & Millar 2001) found that using different types of bait in a longline fishery did not alter the incidence of hooking injury (related to higher post-release mortality) in unwanted undersized snapper Pagrus auratus. Proportional catches of undersized snapper hooked by the lip were similar for each bait type (squid Notodarus sloanii: 0.02, pilchard Sardinops neopilchardus: 0.02, mackerel Scomber australasicus: 0.02), and undersized snapper caught by the gut (squid: 0.016, pilchard: 0.011, mackerel: 0.015). In addition, the proportion of all sizes of snapper hooked by the gut was similar (squid: 0.2, pilchard: 0.1, mackerel: 0.1). Data were collected onboard a fishing vessel in the Hauraki Gulf in 1999, from 13 (January) and 12 (June) longline deployments. Each longline had 1,350 hooks, baited with equal numbers of the three bait types. Lines were left in the sea for one hour. Arrow squid, pilchard and blue mackerel were used as bait. All catch was counted and measured. Location of hook (lip or gut) was recorded.

    Study and other actions tested
  4. A replicated study in 1997 in an area of seabed in the Denmark Strait off the east coast of Greenland (Woll et al. 2001) found that baiting hooks in a longline fishery with grenadier (Macrouridae) reduced the catch of unwanted (non-target) fish, and increased the size-selectivity of the target Greenland halibut Reinhardtius hippoglossoides, compared to squid bait (Cephalopoda). The proportion of the total number of hooks with unwanted non-target fish (consisting mostly of roughhead grenadier Macrourus berglax) on them was lower for grenadier bait (1%) than for squid bait (21%). For the target halibut, catch rates were 34% more using grenadier bait. However, the average size of halibut caught were larger (grenadier: 82 cm, squid: 72 cm). Data were collected from deployments of five longline sets (750–1,080 m depth, 5–14 h), by a fishing vessel between July-August 1997. Each set had 1,560 standard hooks, baited alternately with squid or grenadier (species not reported). All halibut and unwanted fish caught were counted, and their lengths recorded.

    Study and other actions tested
  5. A replicated, controlled study in 2003–2005 in an area of seabed on the Georges Bank in the North Atlantic Ocean, USA (Ford et al. 2008) found that using a fabricated bait instead of a natural bait reduced the amount of unwanted cod Gadus morhua in a bottom longline fishery for haddock Melanogrammus aeglefinus. Overall, the average weight of cod/haddock caught was lowest with the fabricated bait (<0.01 kg cod/kg haddock); and herring bait caught less cod (0.01–0.03 kg cod/kg haddock) than squid bait (0.02–0.07 kg cod/kg haddock). Data were obtained from records of 147 longline trips (621 deployments, 78 or 92 m depth) conducted by commercial fishers from October 2003–June 2005, under special permits to fish in an area closed to groundfish fishing since 1994. Three bait types were tested: three fabricated baits combined for analysis (‘Norbait’ based on herring, mackerel or both), squid and herring (species not reported).

    Study and other actions tested
  6. A replicated, randomized study in 2007 of an area in the Gulf of Maine, USA (Pol et al. 2008) found that using a manufactured instead of a natural bait reduced the amount of unwanted Atlantic cod Gadus morhua caught in a longline fishery for haddock Melanogrammus aeglefinus. Total catches of cod were lower with manufactured bait (172 kg) than with natural herring Clupeus harengus (461 kg) or clams Mercenaria mercenaria (640 kg). The amount of unwanted cod/targeted haddock was also lower using manufactured bait (0.4) than herring (1.1) or clams (0.8). Legal-sized haddock catch was not statistically different between the manufactured bait (309 kg), herring (257 kg) or clam baits (640 kg). Catches of seven other non-target fish species were mainly caught with herring bait rather than the manufactured bait or clams (not statistically tested). In April-May 2007, eight experimental fishing trips were carried out in Massachusetts Bay. During each trip, a longline set was deployed in three areas, each with six sections (250 hooks). One of three bait types was alternated every two sections: commercially manufactured bait (‘Norbait’, mainly Atlantic mackerel Scomber scombrus), herring and clams. Bait order was randomized and each string was set at 60 m. Hooks were 11/0 circle hooks 41 mm long and 2 mm in diameter. See original study for full details of the bait used.

    Study and other actions tested
  7. A replicated study in 2005–2007 in pelagic waters in the Mediterranean Sea, Italy (Piovano et al. 2010) found that changing the size of the bait on pelagic longlines did not reduce the unwanted catches of pelagic stingray Pteroplatytrygon violacea. Neither the size of bait size (small or large), or the absence of light attractors, had a significant influence on the number of stingrays captured (data reported as statistical results). However, average catch rates were lowest with circle hooks (1 stingray/1,000 hooks) compared to J shaped hooks, and larger J hooks had lower catches than smaller J hooks (large: 3–6, small: 6–8 stingray/1,000 hooks). A total of 97 experimental fishing sets (86,116 hooks) were done between June-October from 2005–2007 in the Strait of Sicily, on nine commercial vessels targeting mainly swordfish Xiphias gladius. Small baits were round sardinella Sardinella aurita and horse mackerel Trachurus trachurus (26 sets), and the large bait was mackerel (Scombridae) (71 sets). Hooks were J shaped (two small, one large) alternated with circle hooks (one size). Light attractors (battery operated and chemical light sticks) were deployed on 72 sets.

    Study and other actions tested
  8. A systematic review in 2015 of two relevant studies from 44 that assessed a range of ways to reduce unwanted catch in longline fisheries in global pelagic waters (Favaro & Côté 2015) found that changing bait colour (dyeing it blue) did not reduce the unwanted catches of sharks and rays (Chondrichthyes) compared to traditional bait. Numbers of sharks and rays caught on bait that had been dyed blue were similar to those caught on traditional, non-dyed bait (data reported as graphical analysis). Three global databases were searched, and publications identified that reported the numbers of sharks and rays caught in fishing gears with and without devices to reduce unwanted catch (‘bycatch reduction devices). A meta-analysis was carried out on 44 studies, two of which two contained data on the effects of using different bait types.

    Study and other actions tested
  9. A systematic review in 2016 of 41 studies of pelagic longline fisheries worldwide (Gilman et al. 2016) found that changing bait type (using fish instead of squid), did not typically reduce the number of unwanted sharks and rays (Elasmobranchii) caught, or the incidence of deep-hooking injury associated with higher mortality, and did not increase survival at gear retrieval. Data were reported as graphical analyses (see review). When using fish instead of squid for bait, catch rates of sharks and rays were higher for seven of nine unwanted elasmobranch species, and lower for two species. Fish bait increased the incidence of deep-hooking injury in one of one unwanted species compared to squid bait. In addition, wider circle hooks baited with fish bait caught more of three of four species and fewer of one of four species, compared to narrow hooks (of all designs). The study performed a meta-analysis of 41 studies globally on the effects of different hook and bait types in pelagic longline fisheries on unwanted elasmobranch catch rates, survival and deep-hooking injury (see original paper for full search methods).

    Study and other actions tested
  10. A replicated study in 2008–2009 in six areas of deep water in the North Atlantic Ocean, off Iceland (Ingólfsson et al. 2017) found that increasing the bait size reduced the capture of unwanted small fish compared to using a smaller bait size. The average length of hooked fish was greater with larger bait size than smaller bait for: cod Gadus morhua (large: 55–72 cm, small: 46–70), haddock Melanogrammus aeglefinus (large: 47–53 cm, small: 45–52,), tusk Brosme brosme (large: 47 cm, small: 43 cm), ling Molva molva (large: 65 cm, small: 63 cm) and wolffish Anarhichas lupus (large: 48–64 cm, small: 45 cm). Six fishing trials were conducted from commercial longliners between November 2008 and December 2009 (five trials off the northwest coast of Iceland, one trial off the southwest) at depths of 50–140 m. Large (30 g) and small (10 g) sizes of bait made of Pacific saury Cololabis saira were alternated every 100 hooks (up to 4,800 hooks/set) and gear fished for one hour. Hooked fish were recorded and their lengths measured.

    Study and other actions tested
  11. A replicated study in 2014 of two areas of seabed in the South Pacific Ocean, New Zealand (Major et al. 2017) found that using different bait types in crustacean traps did not reduce the catches of unwanted fish. In the first trial testing mackerel Scomber australasicus and squid Nototodarus sloanii baits, there was no significant difference in the amount of unwanted fish catch between baits (mackerel: 0.6 fish/trap, 0.2 fish/trap). In the second trial, unwanted fish catch again was similar using barracouta Thyrsites atun bait (3.7 fish/trap) compared to squid bait (2.2 fish/trap). Bait species were tested in two trials on grounds fished for New Zealand scampi Metanephrops challengeri. In November/December 2014, a total of 140 traps baited with squid and 139 baited with mackerel were deployed at Chatham Rise. In April 2015 at Cape Palliser, 46 traps baited with squid and 45 with barracoota were deployed. Four types of traps were used, equal numbers baited with each bait species. All traps were deployed on the seabed and left for 18 hours before retrieval. All unwanted catch was identified and counted.

    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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Marine Fish Conservation

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Marine Fish Conservation
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