Action

Use a different hook type

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

Study locations

Key messages

  • Twenty-five studies examined the effect of using a different hook type on marine fish populations. Nine studies were in the Atlantic Ocean (Portugal, South Africa, USA, Brazil, Portugal, Iceland), six studies were in Pacific Ocean (New Zealand, Japan, Costa Rica, Hawaii, Fiji) and two studies were in the Mediterranean Sea (Spain, Italy). One study was in each of the Barents Sea (Norway), the Denmark Strait (Greenland), the Coral Sea (Australia) and the Strait of Gibraltar (Spain/Morocco). Four studies were reviews (worldwide, Atlantic and Pacific Oceans).

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (10 STUDIES)

BEHAVIOUR (0 STUDIES)

OTHER (23 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 study in 1994–1995 in an area of sandy seabed in the Atlantic Ocean, off south-west Portugal (Erzini et al. 1996) reported that using a larger hook did not typically reduce catches of small, unwanted fish, but overall catch rates were reduced compared to smaller hooks. Data were not tested for statistical significance. Overall, the average length of fish caught (34 fish species/groups and one octopus species) was larger for bigger hook sizes (largest hook: 30 cm; intermediate: 29 cm; smallest: 29 cm), but no increase in average size was found for most species, and all hooks caught a wide range of species (see original paper for species individual data). There were small increases however for four of the seven most abundant fish species in catches. Average catch weights were lowest for the largest hook size (largest hook: 77 kg, intermediate: 110 kg, smallest: 107 kg). A total of 45 longlines were deployed from March 1994 to March 1995 in water depths of 13–20 m. Hooks tested were a type commonly used by local small-scale fishers: round bent, flattened sea hooks (Mustad type) in three sizes: 11 (largest), 13 (intermediate, most widely used) and 15 (smallest) (see paper for hook dimensions). Individual longlines with 200–300 hooks of each size (39,900 total hooks) baited with razor clam were deployed for 2–4 h at a time. Catches were separated by hook type and species, weighed and fish total length measured.

    Study and other actions tested
  2. A replicated study in 1985 in coastal waters in the Atlantic Ocean off Western Cape, South Africa (Punt et al. 1996) reported that changing hook type (size) resulted in different lengths of hottentot Pachymetopon blochii caught, and size range generally increased with larger hooks. No statistical tests were carried out. The average length of hottentot caught was 260 mm (range: 177–369 mm) with the widest hook used (18.3 mm), 258 mm (range: 160-385 mm) with a 14.4 mm hook, 251 mm (range: 160-351 mm) with a 10.7 mm wide hook, and 231 mm (range: 160-350 mm) with a 7.0 mm wide hook. Experimental line fishing for hottentot was done by 12 anglers over two days in September 1985 using four sizes of Mustad-type hooks (18.3, 14.4, 10.7 and 7.0 mm). Fishing gear was configured to match the traditional line fishery of the region and was undertaken from three dinghies in a marine reserve five nautical miles off the Western Cape. Equal periods of fishing were carried out with each hook size (31 hours of fishing effort/angler). All fish captured were counted and fish length measured at sea.

    Study and other actions tested
  3. A replicated, controlled study in 1995–1996 of two pelagic areas in the Barents Sea, off north Norway (Huse & Soldal 2000) found that a modified hook design (plastic bodies attached) on pelagic longlines caught fewer undersized haddock Melanogrammus aeglefinus, but also reduced the total catch compared to standard hooks. In two of two trials of hooks with inedible plastic bodies attached, the proportions of haddock below legal size (44 cm) were lower than for hooks without plastic bodies (with: 12–31%, without: 15–34%), but overall haddock catch rates were also reduced (with: 43–68 fish/100 hooks, without: 52–77 fish/100 hooks). In one trial of unbaited hooks modified with nylon bristles, catch rates were lower compared to baited hooks without bristles (with: 3 fish/100 hooks, without: 74 fish/100 hooks), and so low that no further trials were done. Trials were carried out in July 1995 and June/July 1996 by two commercial longliners (see paper for full fishing specifications). Modified hooks had either inedible plastic bodies or coloured nylon bristles attached to the hook shank. Hooks were tested on longline fleets of lengths of 50 modified hooks alternated with 50 standard hooks. For trials with plastic bodies, a total of 4,845 modified hooks and 5,000 standard hooks were fished. In the nylon bristle trial, a total of 786 modified and 15,323 standard hooks were fished. Numbers and lengths of captured haddock were recorded.

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  4. A replicated, controlled study in 1999 in an area of seabed in the Hauraki Gulf, Pacific Ocean, off New Zealand (Willis & Millar 2001) found that hooks modified with additional wire appendages reduced the amount of discarded snapper Pagrus auratus caught by the gut (associated with post-release mortality), compared to standard hooks in a longline fishery. Overall snapper catch rates were reduced with modified hooks relative to the standard hook (20 mm appendage: 22% less, 40 mm appendage: 33% less). Relative to catches with a standard hook, the relative likelihood of under-sized (<26 cm) snapper being captured by the gut was reduced with both types of modified hook (20 mm appendage: 78% less, 40 mm appendage: 96% less), and decreased with increasing length of hook appendage. Thirteen longline deployments were made from a fishing vessel in January and 12 in June 1999. Each longline had 1,350 hooks, with equal numbers of standard hooks, and two types of hooks modified with wire appendages (20- and 40-mm length). Lines were deployed for one hour. Arrow squid Notodarus sloanii, pilchard Sardinops neopilchardus and blue mackerel Scomber australasicus were used as bait. All catch was counted and fish length measured, and location of hook was recorded.

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  5. A replicated, controlled study in 1997 of deep water in the Denmark Strait off the east coast of Greenland (Woll et al. 2001) found that circle hooks (three types) did not reduce the catch of unwanted roughhead grenadier Macrourus berglax compared to standard hooks in a longline fishery. Overall, the percentage of hooks that caught unwanted grenadier was similar for both hook types (circle hooks: 13%, standard: 14%). However, between the three circle hook types, one caught fewer (11%) compared to the two other types (14–15%). In addition, catch rates of the target commercial species Greenland halibut Reinhardtius hippoglossoides were higher for the same one of three circular hooks compared to the standard hook (circle - blue: 435, standard 281 kg/1,000 hook), and the other two circle hooks were similar (344–368 kg/1,000 hook). Twenty-nine longlines with 1,560 hooks each were deployed from a fishing vessel between July–August 1997. Equal numbers of three types of circle hook and one type of standard hook baited with squid were tested (see original paper for hook specifications). Lines were recovered after 5–14 hours. All fish catch was counted and weighed.

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  6. A replicated, randomized study in 2003 in pelagic waters in Onslow Bay in the Atlantic Ocean, North Carolina, USA (Bacheler & Buckel 2004) found that catch rates of small groupers Serranidae spp., non-target fish species and sharks varied with hook design (circle or J), and larger hooks caught fewer non-target fish species overall, but more undersized grouper and sharks compared to other hook types, during commercial angling for grouper. Overall catch rates of 24 non-target fish species were lowest with the two largest hook types (12: 3 fish/day, 9: 4 fish/day) than the smallest two (7 and 5: 9 fish/day). Catch rates of sharks increased with increasing hook size and were lowest at the smallest hook size (1 shark/day) than the other hook sizes/types (2–3 sharks/day). Catches of small individuals (<50.8 cm) of six targeted grouper species were higher for the largest J-shaped hook (1 grouper/day) than any of the other three hook types (<1 fish/day), however the authors note that this may be due to the small sample sizewhile there were no differences for large groupers across all hook types (6–8 fish/day). In addition, the incidence of gut-hooked fish (higher odds of post-release mortality) was lower for non-target species with the two largest hooks compared to the smallest, and for groupers was lower with the circle hook compared to the three J-shaped hooks (data reported as statistical results). Twenty fishing trips were carried out 20–60 miles offshore from May–August 2003 (12–42 m depth). Four rods were used simultaneously, each with one of four randomly allocated hook sizes/types (5/0, 7/0, 9/0 J hooks or a 12/0 circle hook), baited with frozen fish. All fish landed were identified, counted and fish length measured, and the hook location recorded.

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  7. A replicated, controlled study in 2003–2004 in an area of pelagic water in the Atlantic Ocean and the Gulf of Mexico (Kerstetter & Graves 2006) found that changing conventional J-shaped hooks to circle hooks did not typically reduce the catches or mortality of non-target fish species in a longline fishery, but deep-hooking (associated with post-release mortality) was reduced. Across both surveys, catch rates of one of seven non-target fish species were lower on circle hooks than J hooks (see original paper for species individual data). The percentage mortality was lower on circle hooks than J hooks for only one of the 10 most commonly caught non-target species in both 2003 (circle: 7%, J hook: 30%) and 2004 (circle: 26%, J hook: 58%). However, the occurrence of deep-hooking was lower on circle hooks than J hooks for four of five species (data reported as statistical model results). Data were collected on a commercial pelagic longline vessel in the tuna Thunnus spp. and/or swordfish Xiphias gladius fisheries during two surveys: July-September 2003 (39 longline sets, using squid Ilex sp. as bait) and January-April 2004 (46 sets, mixed squid/mackerel Scomber scombrus bait). One circle hook type (size 16/0) and one J-shaped hook type (size 9/0) were set alternately on longline sections (30,600 hooks). See original paper for gear specifications.

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  8. A replicated, controlled study in 2005 in an area of coastal, pelagic water in the western North Pacific, off Japan (Yokota et al. 2006) found that changing hook type and size to a circle hook from a standard hook did not reduce the unwanted catches, or capture mortality, of blue shark Prionace glauca in a longline fishery. Across both vessels, average blue shark catch rates were similar with larger hook sizes and different shape compared to the standard (largest: 36–94, intermediate: 38–95, standard: 41–82 sharks/1,000 hooks). Similarly, the proportion of dead individuals did not differ between hook types (data reported as statistical results). Data were collected on two research vessels from 52 fishing deployments between May–September 2005. A total of 900 hooks were used/longline deployment on one vessel and 960 hooks/longline for the other (all baited with Japanese common squid Todarodes pacificus). Blocks of 20 hooks of each of two test hook types (5.2 and 4.3 size circle hooks) and a standard Japanese hook type (3.8 size tuna hook) were fished in a repeating pattern on the longline. During hauling the species, number and condition of fish caught were recorded.

    Study and other actions tested
  9. A replicated, controlled study in 2005 of four shallow coral reef areas in the Coral Sea, eastern Australia (Mapleston et al. 2008) found that changing hook size, but not hook type, reduced catch rates of non-target and target fish species, and there were reductions in hooking injuries with different hooks, compared to conventional J-type hooks used in a commercial line fishery. Across all fish species (five targeted and three non-targeted), catch rates were lower with large sized hooks (2.2 fish/0.5 h) than small (2.9 fish/0.5 h), and there were no differences between hook designs (offset circle: 2.5, non-offset circle: 2.8, J hook: 2.3 fish/0.5 h). Individually, catch rates of two species were lower using large hooks, and catch rate of one species was lower with both circle hook types than J-hooks (see original paper for species individual data). For all eight species combined, the percentage of fish caught with hooking injuries was reduced with non-offset circle hooks (non-offset circle: 3.7%, offset circle: 6.9%, J hook: 7.8%) and small hook sizes (small: 3.9%, large: 9.0%). Fishing trials took place on four research vessels (25 fishing sessions) during January–October 2005 within the Great Barrier Reef off the coast of Queensland (9–50 m depths). A total of six hooks were tested each session: size 4/0 and 8/0 J hooks, 5/0 and 8/0 offset (by 12°) circle hooks, and 5/0 and 8/0 non-offset circle hooks. Fishers were randomly assigned a hook-type at the start of a session and each hook was fished for 30 minutes in a sequential order, baited with pilchard. Captured fish were identified, counted and recorded as injured or uninjured.

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  10. A systematic review study in 2009 of hook effects on non-target billfish species Istiophoridae spp. in pelagic commercial and recreational fisheries in the Atlantic and Pacific Oceans (Serafy et al. 2009) found that reductions in billfish mortality, but not catch rates, using circle hooks were found for four species compared to J hooks. No differences in catch rates (fish/1,000 hooks) between circle and J-shaped hooks were found in nine comparisons for the four species (white marlin Tetrapturas albidus, blue marlin Makaira nigricans and striped marlin Tetrapturus audax, and sailfish Istiophorus platypterus) in seven of seven studies. Three comparisons found reduced billfish mortality rates using circle hooks in three of seven studies, for: white marlin (circle: 0–48%, J-hook: 35–60%), blue marlin (circle: 53%, J-hook: 70%) and sailfish (circle: 33%, J-hook: 73%). However, seven other comparisons across five studies found no differences in mortality between hook types for each of the four billfish species. In addition, five of seven comparisons in five of six studies reported lower deep-hooking rates (associated with higher mortality) with circle hooks for white and striped marlin and sailfish, and two studies found no effect for white marlin. A quantitative review of hook effects (circle vs J hooks) on billfishes was conducted by searches of published and grey literature via library and electronic database records, as well as communications with agencies and individuals conducted by the author. Eleven studies reported species-specific hook data from commercial pelagic longline fisheries and recreational rod-and-reel fisheries.

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  11. A replicated study in 2004–2005 of rocky seabed in the Mediterranean Sea, off Majorca, Spain (Cerdà et al. 2010) found that larger hook sizes in a recreational fishery reduced overall catch numbers of fish, but maintained yields (weights), and size-selectivity was improved. Average catch rates by number were lowest at the largest hook size (5.7 fish/angler/30 min) compared to the smallest (8.6 fish/angler/30 min), and the three intermediate sizes were similar to each other (6.1–7.5 fish/angler/30 min). However, there were no differences in the overall yield (average catch weight) between all five hook sizes (212–240 g/angler/30 min). The length at 50% selectivity of four common fish species occurring in similar size frequencies differed between hook types and, although the size of the differences varied between species, increased with increasing hook size (largest: 9.2–14.6 cm, smallest: 7–10.1 cm). From March 2004 to August 2005, a total of 33 angling trips were conducted at 10–35 m depths. Angling trips were 30 min long and were fished using J-hooks of one of five hook sizes, from size H4 (the largest) large to size H8 (the smallest, see original paper for hook dimensions). Fish captured were counted and fish length measured.

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  12. A replicated study in 2000–2005 on rocky seabed in the Strait of Gibraltar, Spain (Czerwinski et al. 2010) found that larger hooks improved the size-selectivity of black spot seabream Pagellus bogaraveo compared to smaller hooks in a longline fishery, but depended on size structure of the population being fished. Across both trials, the average length of seabream caught, and the subsequent estimates of size-selectivity, differed between all four hook sizes (except in the second trial for two hooks of similar dimensions, sizes 9.5 and 10), and increased with increasing hook size (data reported as graphical analyses). In addition, seabream length frequencies and selectivity estimates differed between trials as the result of differences in the size structures of the populations encountered. Two experimental fishing trials using four sizes of circular hook were done on a commercial vessel in the Strait of Gibraltar from November 2000 to July 2005. Trial one tested three hook sizes (9, 10, 11, largest to smallest) on 50 longline sets (3,500 hooks of each size). Trial two tested a size 9.5 hook with sizes 9 and 10 during 106 sets (7,420 hooks each size). See original paper for hook dimensions. All hooks were baited with sardine Sardina pilchardus and fishing was done at depths up to 850 m over rocky seabed.

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  13. A replicated, controlled study in 2004–2006 in pelagic waters in the Gulf of Papagayo, Pacific Ocean, Costa Rica (Swimmer et al. 2010) found that using a different circle hook type (offset) in a longline fishery targeting dolphinfish Coryphaena hippurus did not reduce the incidental capture of pelagic stingray Pteroplatytrygon violacea or silky shark Carcharinus falciformis, compared to conventional non-offset circle hooks. Incidental catch was similar with offset and non-offset hooks for stingray (6.1 vs 4.7 ind/line) and silky shark (1.8 vs 2.5 ind/line). Eleven species of bony fish were also caught incidentally, for which catches were higher on offset hooks compared to non-offset hooks for seven species, lower for two and similar for two (see original paper for species individual data, not tested statistically). Data were collected from fishing trips between November and March 2004–2006, deploying longlines with offset (by 10°) and non-offset circle hook types (size 14/0) set alternately along 7 m lines attached to the main monofilament fishing line. All trips used Humboldt squid Dosidcus gigas as bait to target dolphinfish. Lines were deployed in the morning and soaked for 12 hours. All species caught/hook type were recorded. Data from 33,876 hooks across six trips were included in the analysis.

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  14. A replicated, controlled study in 2004–2005 of one area of seabed and one mid-water area in the Atlantic Ocean, off Brazil (Afonso et al. 2011) found that using a circle hook type instead of a conventional J-type hook in a longline finfish fishery did not reduce the capture of unwanted sharks and rays (elasmobranchs), but did reduce the capture mortality of some species. For pelagic longlines, incidental catch rates were similar between the circle and conventional J hook for six of 10 shark species (circle: 0.3–1.8, J hook: 0.3–2.1 catch/unit effort), however, they were higher for four (circle: 2.3–6.4, J hook: 0.8–2.6 catch/unit effort). Total fishing mortality rates of three species were lower on circle hooks (22–27%) than J hooks (67–80%) and, although survival was typically higher on circle hooks for the other seven species, they were not statistically different (0–100% on both hook types). For demersal longlines, there were also no differences in catch rates between hook types for eight shark and ray species (circle: 0.2–1.4, J hook: 0.0–1.3 ind/1,000 hooks), and fishing mortality of two shark species was lower on circle hooks (0–23%) than J hooks (50–74%). See original paper for species individual data. Between August 2004 and April 2007 two hook experiments were carried out with pelagic and bottom set longlines. A total of 224 pelagic longline sets (7,800 hooks, moray-eel Gymnothorax spp. bait) were deployed off Recife (8–14 m depth, 1–3 km from the coast) with alternate sets of circle hooks (size 18/0, 0° offset) and conventional J hooks (size 9/0, 10° offset). Twelve demersal longline sets (650 hooks, skipjack tuna Katsuwonus pelamis bait) were deployed off Natal at 40–70 m depths. Hook types (circle and J hooks as before) were alternated in equal numbers for each set.

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  15. A replicated, controlled study in 2005–2006 in an area of pelagic water in the Pacific Ocean around Hawaii, USA (Curran & Bigelow 2011) found that circle hooks typically caught fewer and larger unwanted non-target fish species compared to two conventional hook types used in the longline fishery for bigeye tuna Thunnus obesus, and that fish condition (as a proxy for post-release survival) was higher for some unwanted species. Circle hooks reduced catch rates of 14 of 14 and eight of 14 unwanted species, compared to conventional tuna and J hooks respectively, as well as two of three and three of three non-target but commercially valuable (incidental) species. Circle hooks caught similar numbers of bigeye and incidental yellowfin tuna Thunnus albacares as tuna hooks and similar numbers of bigeye tuna as J hooks (data reported as statistical model results). Fish length varied between hook types for four of seven unwanted species, and two incidental species. Of the unwanted species that showed differences, two species were largest with circle hooks and two with J hooks. Length of target bigeye tuna and incidental yellowfin tuna were similar across hook types (data reported as statistical model results). The condition (as a proxy for survival) of fish captured using circle hooks was higher for three and five unwanted species compared to tuna and J hooks respectively (data reported as statistical model results). Data were collected between June 2005–February 2006 on 16 tuna longline vessels. Vessels alternated a circle hook type (size 18/0) with one of two existing hook types (Japanese tuna hook or J hook, size 9/0) throughout the longline gear. Observers monitored 1,393 sets (1,182 circle vs tuna hooks, 211 circle hooks vs J hooks). See original paper for gear specifications. All fish caught were identified, and fish length and condition recorded.

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  16. A replicated, controlled study in 2006–2007 in an area of pelagic water in the Atlantic Ocean, off Brazil (Pacheco et al. 2011) found that circle hooks caught fewer unwanted rays Myliobatiformes and sailfish Istiophorus platypterus compared to J hooks, and overall similar amounts of other target and non-target fish groups. Overall, circle hooks caught fewer rays (two species, mainly pelagic stingray Pteroplatytrygon violacea) than J hooks (circle: 21, J hook: 161). Catches of unwanted sailfish were also lower on circle hooks (2) than J hooks (10). Overall catches of three other species groups (billfish Istiophoridae, other bony fish and sharks) and total catch composition were similar for each hook type (data reported as statistical model results). The occurrence of deep-hooking injuries (associated with higher post-release mortality) was lower on circle hooks than J hooks for all species groups (data reported as graphical analysis). In addition, target catches of tunas Thunnus spp. were higher on circle (29/1,000 hooks) than J hooks (23/1,000 hooks), but swordfish Xiphias gladius catches were similar. Data were collected during six pelagic longline trips using three vessels in August 2006 and January 2007. A total of 81 longline sets were fished (50,170 hooks) with circle hooks (size 18/0, 0° offset) alternated equally with J hooks (size 9/0, 10° offset) baited with squid Illex sp.

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  17. A replicated, controlled study in 2009 at a fish farm reservoir in the Atlantic Ocean, off southern Portugal (Veiga et al. 2011) found that changing hook size did not affect the short-term post-release mortality of immature individuals of three sea bream Sparidae species, but survival of fish that were deep-hooked with an intermediate sized hook was reduced. Overall post-release mortality rate for the three species combined was low (6%) and ranged from 0% and 3% for the two-banded Diplodus vulgaris and black Spondyliosoma cantharus sea breams, respectively, to 12% for gilt-head sea bream Sparus aurata. Hook size alone did not affect mortality rates. However, deep-hooked fish were 2.6 times more likely to die than shallow-hooked fish, and fish hooked with the intermediate sized hook were deeply hooked more frequently than the smaller and larger hook sizes (data reported as statistical results). A total of 384 fish of the three bream species were captured by six anglers in October 2009 from a fish farm reservoir in the Ria Formosa. Three typically used hook sizes were tested, baited with ragworm Hediste diversicolor (7.5, 7.9 and 10.6 mm barb widths, see original paper for other dimensions). Two randomly selected hook sizes were trialled/fisher. After capture, fish total length and hooking location were recorded by species and fish were tagged. Tagged fish were placed into 1 m3 sea cages and the number of dead fish recorded after 2–3 h.

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  18. A replicated, controlled study in 1994–2010 in an area of pelagic water in the Pacific Ocean off Hawaii, USA (Gilman et al. 2012) found that using circle hooks in a longline tuna Thunnus spp. fishery did not typically reduce the amount of unwanted catch of other fish species compared to conventional J-shaped or tuna hooks. The data were reported as statistical results (response to hook design of standardized catch rates). Catch rates of unwanted shortbill spearfish Tetrapturus angustirostris and striped marlin Tetrapturus audax were lower on sets using the wider circle hooks than sets with the narrower J-style and tuna hooks, but catch rates of unwanted blue shark Prionace glauca and oceanic white tip shark Carcharhinus longimanus and bigeye thresher shark were higher. Swordfish Xiphias gladius and bigeye thresher shark Alopias superciliosus standardised catches were not affected by hook type. In addition, target catches of tuna species Thunnus obesus were higher on sets with circle hooks than J or tuna hooks. Observer data were analysed from the Hawaii longline tuna fishery, collected between March 1994–July 2010. Catch data from nearly 72 million hooks in 34,613 sets from 2,767 trips were included. The predominant hook types used were various designs and sizes of circle hook (6 main types), J hook (2 main types) and tuna hooks (4 main types) See original paper for hook specifications.

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  19. A systematic review in 2015 of 44 studies assessing the reduction of unwanted catch of sharks and rays (Elasmobranchii) in longline fisheries worldwide (Favaro & Côté 2015) found that using circle hooks or appendage hooks (circle hooks with an additional wire arm to increase its width) did not reduce the overall amount of unwanted sharks and rays caught compared to traditional J hooks, but did catch fewer of one of three individual species. Overall, the catch percentages of sharks and rays caught on circle and appendage hooks were similar to J hooks but catches of pelagic stingray Pteroplatytrygon violacea were reduced by almost 75% on circle hooks. Blue shark Prionace glauca and Galapagos shark Carcharinus galapagensis catches were similar between all hook types (data reported as graphical analysis). The systematic review summarized the effects of various actions to reduce unwanted catch (see original paper for search methods) from 27 publications yielding 44 studies reporting shark and ray catch data. A total of 23 and 17 studies reported effects of using circle hooks and appendage hooks, respectively, relative to control hooks.

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  20. A replicated, controlled study in 2008–2012 in a wide area of pelagic water spanning the Southern Atlantic Ocean (Amorim et al. 2015) found that using two circle hook types instead of a traditional J hook in a commercial longline fishery targeting swordfish Xiphias gladius, reduced the overall discarded catch of bony fish, but not sharks and rays (Elasmobranchii), and the effects varied between species. Average catch rates of total discarded bony fish (five species/groups) were lower on circle hooks than J hooks (circle: 0.8–0.9, J hook: 1.8 ind/1,000 hooks), but this varied between individual species. Catch rates of all shark and ray discards (nine species/groups) did not differ between hook types (circle: 2.3–2.6, J hook: 2.3 ind/1,000 hooks), but there were also differences for individual species (see original paper for species individual data). Data were collected from 310 experimental longline sets, deployed from October 2008 to February 2012. Three different hook types were tested: two circle hooks of identical dimensions, but one with no offset angle and one offset by 10°, and one existing J-style hook used by the Portuguese swordfish pelagic longline fleet (see original paper for gear specifications). A total of 446,400 hooks were fished, baited with mackerel Scomber spp. and squid Illex spp., with hook types alternated in groups of 80 hooks.

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  21. A systematic review in 2016 of 40 studies assessing actions to reduce unwanted catch in pelagic longline fisheries worldwide (Gilman et al. 2016) found that using circle hooks instead of J-style hooks did not typically reduce the number of unwanted sharks and rays (Elasmobranchii) caught, but they did increase survival rate and reduce the incidence of deep-hooking. All data were reported as graphical analyses – see original paper. Catch rates were higher on circle hooks than J hooks for four of five species and lower for one species Survival rates at gear retrieval were higher on circle hooks than J hooks for three of three species. Using wider circle hooks rather than narrow J hooks increased catch rates of five of nine and reduced catch rates of four of nine species, whilst survival rates at gear retrieval were higher for five of six species and lower for one of six. The proportion of deep-hooked individuals (leading to higher fishing mortality) was lower on wider circle hooks than narrow J hooks for six of six species. In addition, wider hooks (of all designs) increased catch rates in one case and decreased them in another, compared to narrow hooks, and increased survival at gear retrieval. 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). All data were reported as ratios of the number of findings with a significant increase or decrease. A meta-analysis was done of 40 studies in global locations on the effects of different hook and bait types on unwanted shark/ray catch rates, survival and deep-hooking injury, in pelagic longline fisheries.

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  22. 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 changing the hook size on longlines improved size selectivity for only two of five commercially targeted fish species, but reduced catch numbers of all species, and was also affected by bait size. Across both areas, hook size affected fish size selectivity only for wolffish Anarhichas lupus and cod Gadus morhua in the northern area, but not haddock Melanogrammus aeglefinus, tusk Brosme brosme or ling Molva molva (data reported as statistical results). The average length of wolffish caught increased by 1.3 cm for each increase in hook size, irrespective of bait size. However, for cod in the northern area, hook size improved size selectivity only when the small bait size was used, and average length increased by 1.4 cm with every increase in hook size. In addition, catch numbers decreased with increasing hook size for all species (data reported graphically). Six fishing trials were conducted on commercial longliners between November 2008 and December 2009 (five trials north of Iceland, one trial in the south) at depths of 50–140 m. Five hook sizes (EZ-Baiter hooks, sizes 10–14) and two sizes (10 and 30g) of Pacific saury Cololabis saira bait were tested (see original paper for dimensions). The two bait types were alternated in 100-hook blocks, each divided into five 20-hook blocks rigged with one of the five hook sizes. A total of 4,800 hooks were set each trip (except one trip of 2,400 hooks). Lines were hauled after one hour and fish species, number and length recorded.

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  23. A replicated, controlled study in 2011–2014 in an area of pelagic water in the South Pacific Ocean around Fiji (Piovano & Gilman 2017) found that using circle hooks in a longline fishery targeting mainly tunas (Scombridae) and swordfish (Xiphiidae) resulted in fewer incidental captures of sharks (Selachii) and rays (Batoidea), compared to conventional J-shaped hooks alone or a combination of J and circle hooks. Using circle hooks alone caught fewer sharks and rays than using J-shaped hooks or a combination of J and circle hooks, and fishing in July–December resulted in fewer shark and ray captures, compared to fishing in January–March (data reported as statistical model results and odds ratios). In addition, using larger size bait and shorter (<17 m) distances between secondary lines attached to the mainline reduced the incidental capture of rays (data reported as statistical model results and odds ratios). Data from 2,367 gear deployments were obtained from the Fiji Observer Programme for the Fiji longline fishery covering the period January 2011 to December 2014. Data were analysed to assess the effect of different factors on incidental capture of sharks and rays. These included hook type (J-shaped and circle hooks), bait sizes (large and small), distances between the branching lines on the mainline, years and season.

    Study and other actions tested
  24. A replicated, controlled study in 2009–2013 in an area of pelagic water in the Mediterranean Sea, off Sicily, Italy (Piovano & Swimmer 2017) found that hooks attached to the fishing line with rings (‘ringed’ hooks) caught fewer of two of three unwanted species in a longline swordfish Xiphias gladius fishery, compared to hooks attached directly to the line. Ringed hooks caught fewer unwanted sunfish Mola mola (0.04 ind/1,000 hooks) and blue shark Prionace glauca (0.04 ind/1,000 hooks) compared to non-ringed hooks (sunfish: 0.08, blue shark: 0.19 ind/1,000 hooks). However, numbers of unwanted pelagic stingray Pteroplatytrygon violacea were higher on ringed hooks than non-ringed hook (ringed: 0.71, non-ringed: 0.63 ind/1,000 hooks). Target swordfish and bluefin tuna Thunnus thynnus catches were higher on ringed hooks than non-ringed hooks (swordfish: 8.47 vs 6.65, tuna: 0.71 vs 0.47 ind/1,000 hooks). Catches of targeted little tunny Euthynnus alletteratus were similar between hook types (both 0.04 ind/1,000 hooks) but target dolphinfish Coryphaena hippurus catches were lower on ringed hooks (ringed: 0.00, non-ringed: 0.04 ind/1,000 hooks). Fishing trials took place in July–September in 2009–2013 using ringed or non-ringed circle hooks (size 16/0). Hooks were 5 cm long and either attached to the branchline with a ring or directly to the line, with each type set alternately along the mainline. Sixty-five sets of gear were fished from six vessels, totalling 50,800 hooks.

    Study and other actions tested
  25. A systematic review in 2018 of 42 studies of the effects of hook type in pelagic longline fisheries worldwide (Atlantic and Pacific Oceans) (Reinhardt et al. 2018) found that using circle hooks instead of conventional J-style hooks did not reduce catch rates of unwanted sharks (Selachii), and did not typically reduce the mortality of most sharks upon gear retrieval. Data were reported as statistical results – see original paper. There was no difference between hook types in catch rates of seven of 13 species, whilst catch rates of six of 13 unwanted shark species were higher on circle hooks than on J hooks. Mortality upon gear retrieval was lower for three of ten shark species on circle hooks than J hooks, and similar for seven species. Catches of target tuna Thunnus spp., billfishes Istiophoridae and swordfish Xiphiidae were higher on circle hooks than J hooks in five of 13 cases and lower in two cases. The systematic review summarized the effects of using circle hooks in longline fisheries compared to conventional J hooks on catch rates and at-vessel mortality during gear retrieval from 42 studies.

    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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