Study

Fishing methods to reduce sea turtle mortality associated with pelagic longlines

  • Published source details Watson J.W., Epperly S.P., Shah A.K. & Foster D.G. (2005) Fishing methods to reduce sea turtle mortality associated with pelagic longlines. Canadian Journal of Fisheries and Aquatic Sciences, 62, 965-981.

Actions

This study is summarised as evidence for the following.

Action Category

Use circle hooks instead of J-hooks

Action Link
Reptile Conservation

Use a different bait type: Sea turtles

Action Link
Reptile Conservation
  1. Use circle hooks instead of J-hooks

    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.

    (Summarised by: Maggie Watson, Katie Sainsbury)

  2. Use a different bait type: Sea turtles

    A replicated, controlled study in 2002 in pelagic waters in the north-western Atlantic Ocean (Watson et al. 2005) found that unwanted catch of sea turtles was reduced when using mackerel-baited Scomber scombrus instead of squid-baited Illex spp. J-hooks, and tended to be lower when circle hooks were used in a tuna Thunnus spp. and swordfish Xiphias gladius longline fishery. Unwanted catch of sea turtles was reduced when mackerel-baited J-hooks were used (0.13–0.15 turtles/1,000 hooks) compared to squid-baited J-hooks (0.5 turtles/1,000 hooks). When mackerel-baited circle hooks were used, unwanted catch was 0.04–0.15 turtles/1,000 hooks compared to 0.05–0.21 turtles/1,000 hooks when squid-baited circle hooks were used (results were not statistically tested, see original paper for details including individual species responses). Commercially-targeted swordfish catch increased when mackerel was used (see original paper). Five hook/bait combinations were trialled: (1) 0° offset 18/0 circle hooks with 150–300 g squid bait, (2) 10° offset 18/0 circle hooks with squid bait, (3) 20°–25° offset 9/0 J-hooks with 200–500 g mackerel bait, (4) 10° offset 18/0 circle hooks with mackerel bait and (5) 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 for combinations 1–4 and 142,000 hooks for combination 5). On-board observers collected catch data.

    (Summarised by: Maggie Watson, Katie Sainsbury)

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