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

Overview 2) Where are turtles hooked? - general overview with 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 1) Definitions - hook locations, ports, fisheries

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

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

J hooks

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

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

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

Options for exploration  Keep data separate by port and fishery

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

Mahi fishery - port 104 Used data from lines with 100% squid Data from (old forms) Compare hooking locations in C15, C16 to J Number of hookings Hook typePercentage swallowed Difference in % swallowed (vs J) 53J15.1% 94C1522.3%No 92C165.4%Yes * Based on two sample Z-Test of proportions (vs J), one-sided, alpha=0.05 % of swallowed J hooks is significantly higher than C16 hooks

Tuna fishery – port 105 Used data from lines with 100% squid Years (from old forms) Compare hooking locations in C16 vs J Number of hookings Hook typePercentage swallowed Difference in % swallowed (vs J) 94J45.7% 50C1638%No * Based on two sample Z-Test of proportions (vs J), one-sided, alpha=0.05 % of swallowed J hooks is NOT significantly higher than C16 hooks

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 ?

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

Effect of ring on hooking location

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 Tuna fishery – port 110 Ring:YESNO C15114 C16719 J*4816 * On new form - Js with ring called “J8”. Js with no ring called “J” 90 Number swallowed Number of turtles : ~20 % 0 %

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 Tuna fishery – port 110 Ring:YESNO C15114 C16719 J* Number swallowed Number of turtles : *Based on randomisation test No difference in % J hooks swallowed (p=0.06*)

Mahi fishery – port 110 Analysis 1 : Data from new forms Data from lines with 100% fish Compare hooking locations in C13, C14 and C15 Number of hookings Hook typePercentage swallowed Difference in % swallowed (vs C13) 30C133.3% 29C1413.8%No 61C150%No * Based on two sample Z-Test of proportions (vs J), one-sided, alpha=0.05 % of swallowed C13 hooks is NOT significantly higher than C14 or C15 hooks

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 No difference in swallow rates among C hook sizes Increase in % fish on line drop in % of hooks swallowed

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

 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) 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

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

For each target fishery, is the size of J hooks similar : 1) A mong years ? 2) To other target fisheries within your port ? 3)To the same fishery in other ports ? 4)To other target fisheries in other ports ? Questions for each port:

For each target fishery, is the size of J hooks similar : 1) A mong years ? 2) To other target fisheries within your port ? 3)To the same fishery in other ports ? 4)To other target fisheries in other ports ? Questions for each port:

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

Hooked locations by species Olive Ridley Green / Black UnknownLogger- head HawksbillLeatherback External436 (23%) 151 (28%) Lower jaw724 (38%) 179 (33%) Jaw commissure 78 (4%) 28 (5%) 5420 Swallowed325 (17%) 54 (10%) 4890 Tongue129 (7%) 60 (11%) 1400 Upper jaw199 (11%) 67 (13%) Total =

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

Turtle lengths x port - all years

Turtle lengths x field office - data from 2007

C12 C13 C14 C15 C16 C18 J J2 J38 J8 102 mahi shark tuna mahi shark tuna mahi shark mahi mahi shark mahi shark tuna mahi shark

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