Action

Use circle hooks instead of J-hooks

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

Study locations

Key messages

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (3 STUDIES)

  • Survival (3 studies): Two studies (including one replicated, controlled, paired study) off the coast of Hawaii and in the north-east Atlantic Ocean found that survival of loggerhead and leatherback turtles and leatherback and hard-shell sea turtles caught by circle hooks or J-hooks was similar. One review of studies in five pelagic longline fisheries found that fewer sea turtles died when circle hooks were used compared to J-hooks in four of five fisheries.
  • Condition (3 studies): Two replicated, controlled studies in the Mediterranean Sea and south-western Atlantic Ocean found that fewer immature loggerhead turtles and loggerhead turtles swallowed circle hooks compared to J-hooks. One before-and-after study off the coast of Hawaii found that a lower percentage of loggerhead and leatherback turtles were deeply hooked by circle hooks compared to J-hooks.

BEHAVIOUR (0 STUDIES)

OTHER (11 STUDIES)

  • Unwanted catch (11 studies): Seven of 10 studies (including six replicated, controlled studies) in the Pacific, Atlantic, Atlantic and North Pacific and Mediterranean and one review of studies in five pelagic longline fisheries found that circle hooks or circle hooks and tuna hooks caught fewer sea turtles than J-hooks, or that non-offset G-style circle hooks caught fewer leatherback and hard-shell sea turtles that offset J-Hooks. One of these studies also found that circle hooks caught slightly larger loggerhead turtles than J-hooks, and one also found that offset Gt-style circle hooks caught a similar number of leatherback and hard-shell sea turtles compared to offset J-hooks. One study found that circle hooks caught a similar number of leatherback, green and olive ridley turtles compared to J-hooks. One study found that fish-baited circle hooks caught fewer loggerhead and leatherback turtles than squid-baited J-hooks. The review found mixed effects of using circle hooks compared to J-hooks on unwanted catch of sea turtles depending on the fishery. The other study found mixed effects of using circle hooks or J-hooks in combination with squid or fish bait on the number of loggerhead and leatherback turtles that were caught.

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 2002 in pelagic waters in the north-western Atlantic Ocean (Watson et al. 2005) found that using 18/0 circle hooks with squid Illex spp. or mackerel Scomber scombrus bait instead of J-hooks reduced unwanted catch of sea turtles in a tuna and swordfish Xiphias gladius longline fishery. Mackerel-baited circle hooks reduced loggerhead Caretta caretta catch by 90% (0.04 turtles/1,000 hooks), squid-baited circle hooks by 86% (0.05 turtles/1,000 hooks), and mackerel-baited J-hooks by 71% (0.13 turtles/1,000 hooks) compared to when squid-baited J-hooks were used (0.5 turtles/1,000 hooks). Mackerel-baited circle hooks reduced leatherback turtle Dermochelys coriacea catch by 65% (0.15 turtles/1,000 hooks), squid-baited circle hooks by 57% (0.21 turtles/1,000 hooks), mackerel-baited J-hooks by 66% (0.15 turtles/1,000 hooks) compared to squid-baited J-hooks (0.50 turtles/1,000 hooks). Most (55 of 80) loggerheads caught swallowed J-hooks, while few swallowed circle hooks (3 of 11, results were not statistically tested). No leatherback turtles swallowed either hook type. Five hook/bait combinations were trialled: 0° offset 18/0 circle hooks with 150–300 g squid bait; 10° offset 18/0 circle hooks with squid bait; 20°–25° offset 9/0 J-hooks with 200–500 g mackerel bait; 10° offset 18/0 circle hooks with mackerel bait; and 20°–25° offset 9/0 J-hooks with squid bait (standard in the fishery). Thirteen vessels made 489 deployments, fishing a total of 427,382 hooks (71,000 hooks/bait for each of the four new combinations and 142,000 hooks for the standard combination). On-board observers collected catch data.

    Study and other actions tested
  2. A before-and-after study in 1994–2006 in pelagic waters off the coast of Hawaii, USA (Gilman et al. 2007) found that fish-baited circle hooks reduced unwanted catch of sea turtles compared to squid-baited J-hooks in a swordfish Xiphias gladius longline fishery. Capture rates of leatherback Dermochelys coriacea reduced by 83% (0.006 turtles/1,000 hooks) and loggerhead Caretta caretta turtles by 90% (0.012 turtles/1,000 hooks) when fish-baited circle hooks were used compared to squid-baited J-hooks (leatherback: 0.03 turtles/1,000 hooks, loggerhead: 0.13 turtles/1,000 hooks). Mortality rates were similar whether circle (35 of 35 turtles survived) or J-hooks (180 of 182 survived) were used. Fewer turtles were deeply hooked when circle hooks were used (leatherback: 0%, hard-shell: 22%) compared to J-hooks (10%, 60%). Target swordfish catch increased by 16% after circle hooks were introduced, but tuna (Scombridae spp.), mahi mahi Coryphaena spp., opah Lampris spp. and wahoo Acanthocybium solandri catch reduced by 34–50% (see paper for details). Catch data from the US National Marine Fisheries Service observer programme were compared from before and after regulations were introduced requiring the use of 10° offset 18/0 circle hooks with fish bait in a pelagic swordfish longline fishery. Prior to the regulations, 9/0 J-hooks with squid bait were used. ‘Before’ data used was from 1994–2002 (120 observed trips of 1,631 sets with 1,282,748 J hooks deployed) and ‘after’ data was from 2004–2006 (164 observed trips of 2,631 sets with 2,150,674 hooks deployed).

    Study and other actions tested
  3. A review of studies in 2000–2004 in five pelagic longline fisheries in the western North Atlantic, Azores, Gulf of Mexico and Ecuador (Read 2007) found that using circle hooks instead of traditional J-hooks reduced overall unwanted catch in three of five fisheries and mortality rates of sea turtles in four of the fisheries. Unwanted catch reduced significantly in two of five fisheries and in one of four years in a third fishery. Sea turtle mortality rates reduced significantly in four of five fisheries. Switching to circle hooks from J-hooks was considered economically viable in three of five fisheries, not viable in a fourth (as target catch was reduced significantly) and the impact was unknown in the fifth. The fisheries were for tuna Thunnus spp. and mahi mahi Coryphaena hippurus. Experiments comparing use of circle hooks (offset and non-offset of different sizes, see original paper) with traditional J-hooks were carried out in 2000–2004 on longline vessels (1–136 vessels/fishery, 48–489 deployments/fishery with 20,570–578,050 hook deployments/fishery).

    Study and other actions tested
  4. A replicated, controlled study in 2005–2007 in pelagic waters in the Mediterranean Sea, Italy and Tunisia (Piovano et al. 2009) found that circle hooks caught fewer immature loggerhead turtles Caretta caretta than J-hooks in a shallow-set swordfish Xiphias gladius longline fishery. Unwanted catch of immature sea turtles was lower when circle hooks (0.4 individuals/1,000 hooks) were used compared to J-hooks (1.4). Five of 20 turtles swallowed J-hooks, compared to none of six turtles caught with circle hooks (results were not statistically tested). Catch rates of commercially targeted swordfish were similar between hook types (circle: 13 individuals/1,000 hooks, J: 15). Catch rates of 10° offset 16/0 circle hooks (2.7 cm gape width) were compared with traditional 20° offset size 2 J-hooks (2.6 cm gape width). Seven experimental trips were conducted using a single commercial fishing boat, totalling 30 fishing sets in July–October 2005–2007. Circle and J-hooks were alternated along the mainline (30,000 total hooks, 50% of each type).

    Study and other actions tested
  5. A replicated, controlled study in 2004–2008 in pelagic waters in the south-western Atlantic Ocean in Brazil (Sales et al. 2010) found that using circle hooks reduced unwanted catch of sea turtles compared to J-hooks in a longline fishery. Unwanted catch of loggerhead Caretta caretta and leatherback Dermochelys coriacea were reduced when circle hooks were used (loggerhead: 0.8 turtles/1,000 hooks, leatherback: 0.7) compared to J-hooks (loggerhead: 1.9, leatherback: 1.6). Fewer loggerhead turtles swallowed hooks when circle hooks were used (6%) compared to J-hooks (25%). However, on average, circle hooks caught larger loggerheads (61 cm average carapace length) than J-hooks (58 cm). Catch rates of most target fish species was increased when circle hooks were used, with the exception of swordfish Xiphius gladius (see paper for details). Catch rates of 10° offset 18/0 circle hooks (2.8–2.2 cm gape width) were compared to traditional 9/0 0° offset J-hooks (2.9 cm gape width). Twenty-seven trips totalling 229 fishing trips were undertaken. A total of 145,828 baited hooks were tested by alternating hooks along sections of the mainline.

    Study and other actions tested
  6. A replicated, paired, controlled study in 2006–2007 in pelagic waters in the western equatorial Atlantic Ocean off the coast of Brazil (Pacheo et al. 2011) found that using circle instead of J-hooks in a longline fishery did not reduce unwanted catch of leatherback turtles Dermochelys coriacea, green turtles Chelonia mydas or olive ridley turtles Lepidochelys olivacea. Numbers of sea turtles caught with circle hooks (leatherback: 1.4 turtles/1,000 hooks, green: 1.4, olive ridley: 2.5) was statistically similar to J-hooks (3.1, 1.7, 1.9). Catch rates of commercially-targeted bigeye tuna Thunnus obesus increased when circle hooks were used (23 fish/1,000 hooks) compared to J-hooks (17 fish/1,000 hooks). Catch rates of commercially-targeted sailfish Istiophorus platypterus reduced when circle hooks were used (0.6 fish/1,000 hooks) compared to J hooks (4.4 fish/1,000 hooks). Catch rates of all other commercially-targeted species were similar between hook types (see paper for details). On six fishing trips, three commercial pelagic longline fishing vessels (24.6–26.9 m long) using similar gear carried out 81 deployments targeting swordfish Xiphias gladius and bigeye tuna Thunnus obseus (11–15 deployments/trip) in August 2006–January 2007. Circle hooks (size 18/0, 0◦ offset) and traditional J-style hooks (size 9/0, 10◦ offset) were alternated along the mainline (50,170 hooks in total, divided equally between circle and J-hooks). Hooks were baited with squid Illex sp. and lit with battery-run light attractants. Lines were deployed overnight.

    Study and other actions tested
  7. A replicated, controlled study in 2004–2010 in Ecuadorean, Panamanian and Costa Rican fisheries in the eastern Pacific Ocean (Andraka et al. 2013) found that unwanted catch of sea turtles was reduced when circle hooks were used instead of J-hooks in five artisanal surface longline fisheries. Unwanted catch of sea turtles was reduced when circle hooks were used compared to J-hooks in mahi mahi Coryphaena hippurus fisheries in Ecuador (circle: 1.3–1.6 turtles/1,000 hooks, J: 2.0–2.2) and Costa Rica (circle: 2.3, J: 2.9) and in combined tuna Thunnus albacares, billfish (Istiophoridae and Xiphiidae) and shark fisheries in Ecuador (circle: 0.6, J: 1.3), Costa Rica (circle: 0.4–1.5, J: 1.3–1.5) and Panama (circle: 0.9, J: 2.0). The effect on target fish species was mixed; in three comparisons circle hooks increased catch, in three they reduced catch and in one there was no difference (see original paper for details). A voluntary program to test use of circle hooks instead of traditional J-hooks began in the Eastern Pacific Ocean in 2004. Unwanted catch of sea turtles was compared between circle hooks (sizes: 14/0–18/0) and traditional J-hooks (J-style or tuna) in mahi mahi fisheries (Ecuador: 2 fisheries; Costa Rica: 1 fishery) and combined tuna, billfish and shark fisheries (Ecuador: 1 fishery; Panama: 1 fishery; Costa Rica: 2 fisheries). Hook sizes, baits, vessels and longline materials varied between fisheries (see original paper). Hook types were placed alternately along the long lines. A total of 3,126 longline deployments were made (328,523 total J-hooks; 401,839 total circle hooks).

    Study and other actions tested
  8. A controlled study in 2008–2012 in pelagic waters in the Southern Atlantic (Santos et al. 2013) found that using circle hooks reduced unwanted catch of loggerhead Caretta caretta and leatherback Dermochelys coriacea turtles compared to using J-hooks when using squid Illex spp. instead of fish Scomber spp. bait. When squid was used as bait, the catch of all turtles was lower when using non-offset circle hooks (0.7 turtles/1,000 hooks) and offset circle hooks (0.6 turtles/1,000 hooks) compared to J-hooks (1.7 turtles/1,000 hooks). Total turtle catch was similar when mackerel bait was used (non-offset circle: 0.2 turtles/1,000 hooks; offset circle: 0.2 turtles/1,000 hooks; J-hook: 0.3 turtles/1,000 hooks). This pattern was observed for both leatherback and loggerhead turtles (see original paper for details). Overall turtle survival was higher when offset circle hooks were used (49 of 59, 83% of individuals alive) compared to non-offset circle hooks (38 of 72, 53% of individuals alive) or J-hooks (99 of 155, 64% of individuals alive). This pattern was observed for loggerhead turtles, but leatherback turtle survival was similar between hook types (see original paper for details). Three hook types baited with either squid or mackerel were used alternately on a commercial longline fishing vessel: traditional J-hook (size: 9/0) and two circle hooks (a non-offset and a 10ᵒ offset, both sized: 17/0; 148,800 total hooks/type). In total 310 longline deployments (1,440 hooks/deployment; 446,400 total hooks, lines set to 20–50 m depths) were carried out overnight in October 2008–February 2012. One bait type was used in each deployment. Turtle catch was monitored by onboard observers.

    Study and other actions tested
  9. A replicated, controlled paired study in 2008–2011 in pelagic waters in the north-east Atlantic Ocean (Coelho et al. 2015) found that changing to non-offset circle hooks from offset J-hooks in a longline swordfish Xiphias gladius fishery reduced unwanted catch of sea turtles. Unwanted sea turtle catch was reduced with non-offset G-style circle hooks (leatherback turtles Dermochelys coriacea: 0.34–0.50 turtles/1,000 hooks; hard-shell turtles (Cheloniidae spp.): 0.07–0.14), but not offset Gt-style circle hooks (leatherback turtles: 0.73–0.78 turtles/1,000 hooks; hard-shell turtles: 0.07–0.19), compared to traditional offset J-hooks (leatherback turtles: 0.94–0.99 turtles/1,000 hooks; hard-shell turtles: 0.16–0.35). Mortality and hooking location of leatherback turtles was similar between hook types (see paper for details). In August 2008–December 2011, a commercial vessel carried out 202 overnight longline fishing deployments (lines: 55 nm long with 5 branchlines, deployed 20–50 m deep, lit by green lights). Whole squid (Illex spp.) or mackerel (Scomber spp.) were used as bait (one type of bait/line deployment). Three hook styles: 10° offset J-hooks traditionally used in the fishery; non-offset G-style circle hooks; and 10° offset Gt-style circle hooks were alternated every 70–80 hooks along the line in a randomized start order (254,520 total hooks deployed with 42,420 of each hook/bait combination). Unwanted catch was counted and released.

    Study and other actions tested
  10. A replicated study in 2004–2011 in pelagic waters in the Eastern Pacific Ocean (Parga et al. 2015) found that using circle hooks or tuna hooks instead of traditional J-hooks reduced the likelihood of olive ridley turtles Lepidochelys olivacea swallowing hooks in an artisanal surface longline fishery. All results were reported as odds ratios, see original paper for details. Both circle and tuna hooks were less likely, and circle hooks least likely to be swallowed overall, by olive ridley turtles compared to J-hooks. In 2004–2011 incidental sea turtle catch rates of circle hooks (sizes 12/0–18/0), tuna hooks and traditional J-hooks (see original paper for hook specifications) were compared by placing hooks in alternative sequence along longlines (3.5 million total hooks used in 8,996 line deployments). Bait used was classed as squid (Dosidicus gigas, Illex sp. and Loligo sp.) or fish (Opisthonema spp., Scomber japonicus, Auxis spp. and Sardinops sagax) and only deployments using one type of bait were included in analysis (4,838 of 8,996 line deployments). Information on hooking location and entanglement of sea turtles was recorded (1,823 total olive ridley turtles).

    Study and other actions tested
  11. A replicated, before-and-after study in 1992–2015 in pelagic longline fisheries in the Atlantic and North Pacific (Swimmer et al. 2017) found that using circle hooks on longlines resulted in less leatherback Dermochelys coriacea and loggerhead Caretta caretta bycatch compared to when J-hooks were used. The chance of catching turtles on longlines was lower in the Atlantic when circle hooks were used (leatherback: 0–6% chance with fish bait (species not provided), 9% with squid bait (species not provided); loggerhead: 0–5% with fish bait, 11% with squid bait) compared to J-hooks (leatherback: 13% with fish bait, 20% with squid bait; loggerhead: 9% with fish bait, 18% with squid bait). The same was true in the Pacific (leatherback - circle hook: <1% vs. J-hook: 1%; loggerhead: circle hook: 1% with fish, 2% with squid vs. J-hook: 5% with fish, 13% with squid). Following the introduction of regulations on bait and hooks, overall bycatch was reduced in both the Atlantic (leatherback: 40% reduction; loggerhead: 61% reduction) and Pacific (leatherback: 84% reduction; loggerhead 95% reduction). Fisheries were closed in 2001 and re-opened with regulations regarding bait (fish or squid) and hook type (circle or J-hooks) (see paper for details). Pelagic Observer Program data from before (1992–2001) and after (2004–2015) regulations was used to determine the number of turtles caught/1,000 hooks.

    Study and other actions tested
Please cite as:

Sainsbury K.A., Morgan W.H., Watson M., Rotem G., Bouskila A., Smith R.K. & Sutherland W.J. (2021) Reptile Conservation: Global Evidence for the Effects of Interventions for reptiles. Conservation Evidence Series Synopsis. University of Cambridge, Cambridge, UK.

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