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

�

�

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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

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.