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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
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
• Destruction of nesting beaches
• Long generation times– 15-20 years until adulthood
• High mortality of eggs – Egg harvesting (poaching)– Egg predation (mammals)
•High natural predation of hatchlings and juveniles at Sea
•Adult harvest by humans
•Disease
•Pollution
• Entanglement and ingestion of marine
debris
• Incidental capture in fisheries
Generally entangled or foul-hooked (snagged)
Status: Endangered*
Leatherback turtle(Dermochelys coriacea)
Longline Fishing and Sea Turtle Interactions:
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:
What is fate of turtles after their release from longline-fishing gear?
Our chosen tool…
Pop-up satellite archival tags (PSATs)
To determine -- survivorship -- geolocation(& migratory corridors)
-- dive depths--temperature
Deployed by at-sea observers
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)
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)
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.
California LLFishery (6)
Costa Rica14-olive ridley1 green
HawaiiLL Fishery
~ 4 months at liberty post-release
Olive Ridley (13202): Hooked in mouth
___________________________1,874 n mi
PSAT deployedPop-off location
PSATs in Hawaii:
Min-Max Depth for Olive ridley (13202)
050
100150200250300350400450500550
Time
Dept
h (m
)
minimummaximum
Aug. 15, 2001 Nov. 15, 2001
Max.=544m@ 4oC
Depths for Longline-caught and released olive ridley (13202) in North Pacific Ocean
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
• 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??
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??
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)
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
�
�
��
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
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
Free-swimming controlDive Depth for CR 13112
(Two months at liberty)
Depth (m)
300
60
90
120150
180
210
• 90% time turtles’ within top 80m
• Turtles more shallow at night.
• Longline-caught turtles remain deeper
Day Depths
Night Depths
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.
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
CR-Olive Ridley 13112: Chlorophyll
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.
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
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?
On
off
Drilling method
(based on Epperly et al. 2003)
#38604
• 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.
• 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
Kemp’s ridley, loggerhead and green turtles avoided blue-foods in laboratory studies
Why blue bait???
Olive ridley turtle CPUE approx. 7 (per 1,000 hooks)
Why Costa Rica??
Cooperative Fishers
Daytime, shallow fishery
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.
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.
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