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Sea Turtles and Longline Fisheries: Impacts and Mitigation Experiments
Yonat Swimmer, Mike Musyl, Lianne McNaughton, Anders Nielson, Richard Brill, Randall Arauz
PFRP P.I. MeetingDec. 9, 2003
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Species Population Trend Major Nesting Beaches
Leatherback Turtle Declining Mexico Costa Rica Malaysia
Loggerhead Turtle Declining Australia Japan
Green Turtle Declining (except in Hawaii & Australia)
Hawaii
Black Turtle Declining Mexico Galapagos
Hawksbill Turtle Unknown Hawaii
Olive Ridley Turtle Declining (except in Oaxaca)
Mexico Costa Rica Malaysia Thailand Irian Jaya India
Sea Turtles in the Pacific
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• Destruction of nesting beaches
• Long generation times– 15-20 years until adulthood
• High mortality of eggs – Egg harvesting (poaching)– Egg predation (mammals)
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•High natural predation of hatchlings and juveniles at Sea
•Adult harvest by humans
•Disease
•Pollution
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• Entanglement and ingestion of marine
debris
• Incidental capture in fisheries
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Generally entangled or foul-hooked (snagged)
Status: Endangered*
Leatherback turtle(Dermochelys coriacea)
Longline Fishing and Sea Turtle Interactions:
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e.g. loggerhead (Carettacaretta) and olive ridley (Lepidochelys olivacea)
Generally hooked -opportunistic feeders bite baited hooks.
Status: Threatened
Hard-shelled turtles
Longline Fishing and Sea Turtle Interactions:
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What is fate of turtles after their release from longline-fishing gear?
Our chosen tool…
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Pop-up satellite archival tags (PSATs)
To determine -- survivorship -- geolocation(& migratory corridors)
-- dive depths--temperature
Deployed by at-sea observers
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How can PSATs determine survivorship??
PSATs set to release/report:
At pre-set pop-up dateor
After tag has been at constant depth for 4 days*or
After tag has exceeded 1,500 m depth*or
If tag and/or baseplate are shed, will float to surface
*these parameters exceed what is expected to occur in a live turtle (we assume mortality)
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PSAT concerns
• Early tag shedding observed in fish and turtles
• Data quantity relatively low
• Light-based geolocations require additional filtering to data (e.g. Kalman filter)
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Most probable track predicted from state-space model via the Kalman filter (Sibert and Nielson).
Geolocations determined by PSATs
Incorporation of SST data is in progress.
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California LLFishery (6)
Costa Rica14-olive ridley1 green
HawaiiLL Fishery
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~ 4 months at liberty post-release
Olive Ridley (13202): Hooked in mouth
___________________________1,874 n mi
PSAT deployedPop-off location
PSATs in Hawaii:
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Min-Max Depth for Olive ridley (13202)
050
100150200250300350400450500550
Time
Dept
h (m
)
minimummaximum
Aug. 15, 2001 Nov. 15, 2001
Max.=544m@ 4oC
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Depths for Longline-caught and released olive ridley (13202) in North Pacific Ocean
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PSATs released from California Fishery 2002-2003
•15 trips, 6 PSATs deployed
Hawaiian IslandsN
K. Bigelow
• One dud, 2 still out
• One possible mortality 6 mos. later---data inconclusive.
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�
��
180°
180°-180
-180
-170
-170
-160
-160
-150
-150
-140
-140
0 0
10 10
20 20
30 300
0 0
196159
72
21134
21288
22052
Main Hawaiian Islands
N
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• Turtles 21134 & 22052: no depth data, geolocation only.
Time at Depth for Loggerhead Turtle #21288
75
25
58
42
0
20
40
60
80
0 - 10 10.5 - 50
Depth Bins (m)
% F
requ
ency
DayNight
• Turtle 21288: Depth data for first three months. Only geolocation data btwn. 3-6 mos., then 1,108 m dive.
Mortality??
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YES!!
Loggerhead spent 100% total time < 50 m Olive ridley spent 90% total time <100 m
Is there a “turtle layer” in the North Pacific??
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Costa Rica Sea turtles= 8% total catch longline fishery
Collaboration:Univ. of Hawaii, PRETOMA,NMFS, Sea Turtle RestorationProgram
Cooperative fishers!!
10 Caught and released from longline gear
5 Controls (free swimming)
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Tags on CR olive ridley turtles stayed on for only ~ 60 days
Are tags removed by fishers?
Are turtles mating and knocking tags off?
Does an olive ridley carapace form a weaker epoxy bond as compared to loggerheads??
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�
�
�
�
�
�
��
N
EW
S
29480
13211
13207
29489
29474
13198
13117
30484
-95
-95
-90
-90
-85
-85
-80
-80
-75
-75
0 0
5 5
10 10
15 15
Longline-caught olive ridley turtles (n=8)
Costa Rica
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�
�
��
N
EW
S
38604
13204
1311213108
-100
-100
-95
-95
-90
-90
-85
-85
-80
-80
-75
-75
-5 -5
0 0
5 5
10 10
15 15
Control olive ridley turtles (n=4)
Costa Rica
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Depth(m) for Tag 29474
-250
-200
-150
-100
-50
0
8/22/02 9/1/02 9/11/02 9/21/02 10/1/02 10/11/02 10/21/02 10/31/02 11/10/02 11/20/02
Date
Dep
th (m
)
PSAT deployed
64 days at liberty
-- Hooked in mouth
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Free-swimming controlDive Depth for CR 13112
(Two months at liberty)
Depth (m)
300
60
90
120150
180
210
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• 90% time turtles’ within top 80m
• Turtles more shallow at night.
• Longline-caught turtles remain deeper
Day Depths
Night Depths
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Average Hourly Temperature
222324252627282930
18 20 22 0 2 4 6 8 10 12 14 16
GMT -6 Hrs.
Tem
pera
ture
(C)
Control Longline
Average Hourly Depth
515253545556575
18 20 22 0 2 4 6 8 10 12 14 16
GMT -6 Hrs.
Dept
h (m
)
Control Longline
Longline-caught turtles remain deeper and in colder water during the day.
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Night Depths & Lunar Illumination (#29474)
(0=New moon, 1=Full moon; r=0.55)
0
20
40
60
80
100
Avg
. Dep
th (m
)
0.00
0.20
0.40
0.60
0.80
1.00
Luna
r Illu
min
atio
n
Date
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CR-Olive Ridley 13112: Chlorophyll
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Survivorship• Longline-caught olive ridley (8) and
loggerhead turtles (4) were tracked from 35-196 days, & no mortalities were
confirmed.
• One turtle that was deeply-hooked had the longest track (72 days) for all CR olive ridleys.
• 4 control turtles were successfully tracked from 40-68 days.
• One “control” turtle died.
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Depth (m) for Olive Ridley (#38604)
-1000
-900
-800
-700
-600
-500
-400
-300
-200
-100
0
6/8/03 6/18/03 6/28/03 7/8/03 7/18/03 7/28/03 8/7/03 8/17/03 8/27/03
Date
Dep
th (m
)
4 days at constant pressure
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Depth (m) for Olive Ridley (#38604)
-120
-100
-80
-60
-40
-20
0
6/7/03 6/17/03 6/27/03 7/7/03 7/17/03 7/27/03 8/6/03 8/16/03
Date
Depth (m)
Possible fisheries Interaction?
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On
off
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Drilling method
(based on Epperly et al. 2003)
#38604
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• Most sea turtles survive longline hooking.
• Multiple interactions could contribute to mortality.
• Turtles released after capture in longline gear have markedly different dive patterns…
• …that could affect turtles’ foraging or reproductive ecology.
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• PRETOMA (CR), NMFS, Papagayo Seafoods (CR), Sea Turtle Restoration Program (USA), University of Hawaii.
• Happening Now! – Test of blue dyed bait in
shallow mahi mahi fishery within the EEZ of Costa Rica
Fishing Experiments on Sea Turtle Bycatch Reduction
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Kemp’s ridley, loggerhead and green turtles avoided blue-foods in laboratory studies
Why blue bait???
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Olive ridley turtle CPUE approx. 7 (per 1,000 hooks)
Why Costa Rica??
Cooperative Fishers
Daytime, shallow fishery
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Experimental Design– Two boats fishing within same general area
– 12-16 sets/ boat (1 trip/boat)
– Treated or untreated squid randomly determined
– Ideally, treated and untreated # days equal
– Statistical tests will be done to determine mahi mahi CPUE and turtle BPUE by treatment.
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Acknowledgements• Funding and facilities provided by the National
Marine Fisheries Service and the Pelagic Fisheries Research Program at the University of Hawaii.
• Collaborators include: NMFS observers and observer program, Don Peterson, R. Arauz, STRP, Dave Foley, Keith Bigelow, Lucas Moxey, Mike Laurs (PFEL/NOAA), Marti McCracken.