Hook locationsHook locationsin sea turtlesin sea turtleswhere and why?where and why?

Michelle SimsMichelle SimsDuke UniversityDuke University

OverviewOverview

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

1) Definitions

- hook locations, ports, fisheries

DefinitionsDefinitions

• Hook locations: External (Head, Neck, flippers, axilla, tail,

shell) Lower jaw

Jaw commissureUpper jawTongueSwallowed

• Fisheries: Surface: Tuna, Mahi and Shark

• Port:Given codes: 102, 104, 105, 106, 108, 109,

110

Where are turtles hooked?Where are turtles hooked?

“Good” hookings ?

“Bad” hookings ?

C13 hooks

Hook location

Pro

port

ion

hook

ed

0.0

0.2

0.4

0.6

external jaw comm. lower jaw swallow tongue upper jaw

C14 hooks

Hook location

Pro

port

ion

hook

ed

0.0

0.2

0.4

0.6

external jaw comm. lower jaw swallow tongue upper jaw

C15 hooks

Hook location

Pro

po

rtio

n h

oo

ked

0.0

0.2

0.4

0.6

external jaw comm. lower jaw swallow tongue upper jaw

C16 hooks

Hook location

Pro

po

rtio

n h

oo

ked

0.0

0.2

0.4

0.6

external jaw comm. lower jaw swallow tongue upper jaw

J hooks

Hook location

Pro

po

rtio

n h

oo

ked

0.0

0.1

0.2

0.3

0.4

external jaw comm. lower jaw swallow tongue upper jaw

J hooks

What may influence the What may influence the hooking location?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 What may influence the hooking location?hooking location?

•Hook characteristics - type (e.g. C), size (e.g. 16), ring, offset

Available information on Available information on hooks and bait type: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 COffset size Manufacturer % of each species of bait used on line

Options for explorationOptions for exploration

Keep data separate by port and fishery

Options for explorationOptions for exploration

Keep data separate by port and fishery

All examples - looking at probability that hook is swallowed

Mahi fishery - port 104Mahi fishery - port 104• Used data from lines with 100% squid• Data from 2005-2006 (old forms)• Compare hooking locations in C15, C16 to J

Number of hookings

Hook type Percentageswallowed

Difference in % swallowed (vs J)

53 J 15.1%

94 C15 22.3% No

92 C16 5.4% 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 105Tuna fishery – port 105• Used data from lines with 100% squid• Years 2004-2006 (from old forms)• Compare hooking locations in C16 vs J

Number of hookings

Hook type Percentageswallowed

Difference in % swallowed (vs J)

94 J 45.7%

50 C16 38% 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

QuestionsQuestions

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 Available information on hooks and bait type: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 COffset size % of each species of bait used on line

Hook type and Ring

Pro

po

rtio

n s

wa

llow

ed

0.0

00

.05

0.1

00

.15

0.2

00

.25

0.3

0

C15 C15 C16 C16 J J

RingNo Ring

Effect of ring on Effect of ring on hooking locationhooking 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 110Tuna fishery – port 110

Ring: YES NO

C15 11 4

C16 7 19

J* 48 16

* On new form - Js with ring called “J8”. Js with no ring called “J”

9 0

Number swallowed

00

01

Number of turtles :

~20 %~20 % 0 %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 110Tuna fishery – port 110

Ring: YES NO

C15 11 4

C16 7 19

J* 48 16 9 0

Number swallowed

00

01

Number of turtles :

*Based on randomisation test

No difference in % J hooks swallowed (p=0.06*)

Mahi fishery – port 110Mahi fishery – port 110Analysis 1:• Data from new forms• Data from lines with 100% fish• Compare hooking locations in C13, C14 and C15

Number of hookings

Hook type Percentageswallowed

Difference in % swallowed (vs C13)

30 C13 3.3%

29 C14 13.8% No

61 C15 0% 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 110Mahi fishery – port 110Analysis 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

ConclusionsConclusions

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 explorationOptions for exploration

Keep data separate by port and fishery

Questions for each port:Questions for each port:

Can you provide more information about andJ 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) Among 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: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 ?

3) To the same fishery in other ports?

4) To other target fisheries in other ports?

Questions for each port:Questions for each port:

What may influence the What may influence the hooking location?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 Hooked locations by speciesspecies

Olive Ridley

Green /Black

Unknown

Logger-head

Hawksbill

Leatherback

External 436 (23%)

151(28%)

10 7 5 4

Lower jaw 724 (38%)

179 (33%)

25 7 7 0

Jaw commissure

78 (4%) 28 (5%) 5 4 2 0

Swallowed 325 (17%)

54 (10%) 4 8 9 0

Tongue 129 (7%)

60 (11%) 1 4 0 0

Upper jaw 199 (11%)

67 (13%) 31 0 5 0

Total = 1891 539 76 30 28 4

160 161 162 163 164 165

02

04

06

08

01

00

12

01

40

Species Code

Tu

rtle

len

gth

s (c

m)

Unknown OliveRidley

Logger-head

Green/Black

Leather-back

Hawksbill

?

?

?

Turtle lengths x species

102 104 105 106 108 109 110

20

40

60

80

100

120

Green/Black

field office

Turt

le length

s (

cm

)

102 104 105 106 108 109 110

020

40

60

80

120

Olive Ridley

field officeT

urt

le length

s (

cm

)

Turtle lengths x port - all years 2004-2007

104 105 106 108 110

40

50

60

70

80

Green/Black

field office

Turt

le length

s (

cm

)

104 105 106 108 110

020

40

60

80

100

Olive Ridley

field officeT

urt

le length

s (

cm

)

Turtle lengths x field office - data from 2007

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

1042C15 1042C16 1042J 1051C16 1051J

10

15

20

25

30

35

40

port x fishery x hook type

Dis

tanc

e bw

n ho

oks

1042C15 1042C16 1042J 1051C16 1051J

10

12

14

16

18

port x fishery x hook type

Hoo

k de

pth

1042C15 1042C16 1042J 1051C16 1051J

40

06

00

80

01

000

12

00

port x fishery x hook type

Soa

k du

ratio

n

1042C15 1042C16 1042J 1051C16 1051J

40

60

80

10

0

port x fishery x hook type

Tur

tle le

ngth

s

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

10 20 30 40 50 60

02

04

06

08

01

00

12

01

40

hook depth (fathoms)

turt

le le

ng

th (

cm)