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Hook locations in sea turtles where and why? Michelle Sims Duke University

Hook locations in sea turtles where and why? Michelle Sims Duke University. Overview. 1) Definitions - hook locations, ports, fisheries. 2) Where are turtles hooked? - general overview with 2004-2007 data. 3) What may influence the hooking location ?

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Hook locations in sea turtles where and why? Michelle Sims Duke University

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  1. Hook locationsin sea turtleswhere and why?Michelle SimsDuke University

  2. Overview 1) Definitions - hook locations, ports, fisheries 2) Where are turtles hooked? - general overview with 2004-2007 data 3) What may influence the hooking location? - bait, hook characteristics, turtle species/length 4) Ways to explore data - keep data separate by port and fishery - combine data - advantages and information required

  3. Definitions • Hook locations: • External (Head, Neck, flippers, axilla, tail, shell) • Lower jaw • Jaw commissure • Upper jaw • Tongue • Swallowed • Fisheries: • Surface:Tuna, Mahi and Shark • Port: • Given codes: 102, 104, 105, 106, 108, 109, 110

  4. “Good” hookings ? “Bad” hookings ? Where are turtles hooked?

  5. J hooks

  6. What may influence the hooking location? • Hook characteristics - type (e.g. C), size (e.g. 16), ring, offset • Gear characteristics - bait (e.g. squid vs fish), mainline material (?), distance between hooks (?), hook depth (?) • Turtle characteristics - Species, size

  7. What may influence the hooking location? • Hook characteristics - type (e.g. C), size (e.g. 16), ring, offset

  8. Available information on hooks and bait type: Old forms: • Hook type - C or J • Size of C hook (e.g. C16) • Species of bait used on line • Extra information from new forms: • Size and shaft angle of J • Presence of ring on J and C • Offset size • Manufacturer • % of each species of bait used on line

  9. Options for exploration • Keep data separate by port and fishery

  10. Options for exploration • Keep data separate by port and fishery All examples - looking at probability that hook is swallowed

  11. % of swallowed J hooks is significantly higher than C16 hooks Mahi fishery - port 104 • Used data from lines with 100% squid • Data from 2005-2006 (old forms) • Compare hooking locations in C15, C16 to J * Based on two sample Z-Test of proportions (vs J), one-sided, alpha=0.05

  12. % of swallowed J hooks is NOT significantly higher than C16 hooks Tuna fishery – port 105 • Used data from lines with 100% squid • Years 2004-2006 (from old forms) • Compare hooking locations in C16 vs J * Based on two sample Z-Test of proportions (vs J), one-sided, alpha=0.05

  13. Questions 1) Why differences in J vs C16 effects between ports? • Small sample size ? • Differences in size of J or C16 hooks ? 2) Why differences in % swallowed between ports even with same bait and same hook? • Other gear or hook characteristics ?

  14. Available information on hooks and bait type: Old forms: • Hook type - C or J • Size of C hook (e.g. C16) • Species of bait used on line • Extra information from new forms: • Size and shaft angle of J • Presence of ring on J and C • Offset size • % of each species of bait used on line

  15. Effect of ring on hooking location

  16. Number swallowed 0 1 0 0 9 0 ~20 % 0 % Tuna fishery – port 110 • Year 2007 (from new form) • Only use data from lines with >90% fish • Compare hooking locations by - Hook type and size - c15, c16, J (all angled) - Presence of ring Number of turtles : * On new form - Js with ring called “J8”. Js with no ring called “J”

  17. Number swallowed 0 1 0 0 9 0 Tuna fishery – port 110 • Year 2007 (from new form) • Only use data from lines with >90% fish • Compare hooking locations by - Hook type and size - c15, c16, J (all angled) - Presence of ring Number of turtles : No difference in % J hooks swallowed (p=0.06*) *Based on randomisation test

  18. % of swallowed C13 hooks is NOT significantly higher than C14 or C15 hooks Mahi fishery – port 110 Analysis 1: • Data from new forms • Data from lines with100% fish • Compare hooking locations in C13, C14 and C15 * Based on two sample Z-Test of proportions (vs J), one-sided, alpha=0.05

  19. No difference in swallow rates among C hook sizes Increase in % fish on line drop in % of hooks swallowed Mahi fishery – port 110 Analysis 2: • Data from new forms • Data from all lines with bait information • Compare differences in swallow rates using: - % fish on line (0% if all squid) - C13, C14 and C15 hooks • Based on logistic regression with hook type and % fish on line as covariates. • One-sided z test, alpha = 0.05

  20. Conclusions • Evidence of bait effect • Ring may increase rate of hooked turtles swallowing hook? • Limitations: Small sample within a port x fishery to explore further

  21. Requires complete information on hooks and gear - gear information and hook type - old and new forms - more information about hooks - new form Options for exploration • Keep data separate by port and fishery • Combining data from ports and/or fisheries - meta-analysis - increase understanding of factors influencing location - more comparisons (e.g. ring x hook size x bait type)

  22. Questions for each port: Can you provide more information about and J and C hooks for years when old forms were used? e.g. ring, offset, shaft angle and size of J

  23. Questions for each port: For each target fishery, is the size of J hooks similar : 1) Among years? 2) To other target fisheries within your port? • To the same fishery in other ports? • To other target fisheries in other ports?

  24. Questions for each port: For each target fishery, is the size of J hooks similar : 1) Among years? 2) To other target fisheries within your port ? • To the same fishery in other ports? • To other target fisheries in other ports?

  25. What may influence the hooking location? • Hook characteristics - type (e.g. C), size (e.g. 16), ring, offset • Gear characteristics - bait (e.g. squid vs fish), mainline material (?), distance between hooks (?), hook depth (?) • Turtle characteristics - Species, size

  26. Hooked locations by species Total = 1891 539 76 30 28 4

  27. ? ? ? Unknown Logger- head Green/ Black Leather-back Olive Ridley Hawksbill Turtle lengths x species

  28. Turtle lengths x port - all years 2004-2007

  29. Turtle lengths x field office - data from 2007

  30. C12 C13 C14 C15 C16 C18 J J2 J38 J8 102 mahi 0 0 3 0 0 0 1 0 0 0 102 shark 0 0 0 0 1 0 0 0 0 0 104 tuna 0 0 0 27 64 0 43 0 0 0 104 mahi 0 0 0 281 381 0 134 61 0 0 104 shark 0 0 0 70 80 0 31 5 0 0 105 tuna 0 0 0 0 84 2 131 0 10 0 105 mahi 27 14 15 19 0 0 42 0 0 0 105 shark 0 0 0 0 1 0 0 0 5 0 106 mahi 0 0 22 24 0 0 17 0 0 0 108 mahi 0 0 11 5 4 0 17 0 0 0 108 shark 0 0 0 0 8 0 5 0 0 0 109 mahi 0 2 6 4 0 0 20 0 0 0 109 shark 0 0 0 0 3 0 1 0 0 0 110 tuna 0 0 16 26 50 0 88 0 0 79 110 mahi 0 70 359 233 24 0 6 0 0 0 110 shark 0 0 0 0 3 0 1 0 0 0

  31. Comparison of tuna fishery in office 105 and mahi in office 104

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