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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

Hook locationsin sea turtleswhere and why?Michelle SimsDuke University


Overview
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


Definitions
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


Hook locations in sea turtles where and why michelle sims duke university

“Good” hookings ?

“Bad” hookings ?

Where are turtles hooked?



What may influence the hooking location
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 location1
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
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
Options for exploration

  • Keep data separate by port and fishery


Options for exploration1
Options for exploration

  • Keep data separate by port and fishery

    All examples - looking at probability that hook is swallowed


Mahi fishery port 104

% 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


Tuna fishery port 105

% 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


Questions
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 type1
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
Effect of ring on hooking location


Tuna fishery port 110

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”


Tuna fishery port 1101

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


Mahi fishery port 110

% 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


Mahi fishery port 1101

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


Conclusions
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


Options for exploration2

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)


Questions for each port
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


Questions for each port1
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?


Questions for each port2
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?


What may influence the hooking location2
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
Hooked locations by species

Total = 1891 539 76 30 28 4


Hook locations in sea turtles where and why michelle sims duke university

?

?

?

Unknown

Logger-

head

Green/

Black

Leather-back

Olive

Ridley

Hawksbill

Turtle lengths x species


Hook locations in sea turtles where and why michelle sims duke university

Turtle lengths x port

- all years 2004-2007



Hook locations in sea turtles where and why michelle sims duke university

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