Survivorship and Movements of Sea Turtles Caught and Released

from Longline Fishing Gear

Yonat Swimmer, Richard Brill, Lianne Mailloux

University of HawaiiVIMS-NMFS

PFRP PI Workshop-2002

Hard-shelled turtlesGenerally hooked Federally threatened

Leatherback turtleGenerally entangled Federally endangered

Question: What is fate of sea turtles post-release??

Pop-up satellite archival tags (PSATs)

To determine post-release survivorship

To determine post-release pelagic behavior (e.g. geolocation, dive depths/duration, migratory corridors)

Deployed by at-sea observers

Why Use PSATs over conventional satellite transmitters?

Cons• Expensive• Questionable

geolocation data• Delay in receiving

data• Difficult to attach to

turtle

Pros

• Can retrieve data in event of mortality!!

PSATs:

Internal clock & sensors to record:

*geographic location (via sunrise/sunset times)

*dive depth, duration

*temperature

How do we get the data?

PSATs release at pre-set date...

tags float to the surface...

data transmitted to satellite…

data received on our computers.

When will PSATs float to surface?1) At pre-set pop-up date

2) After tag has been at constant depth for 4 days*

3) After tag has exceeded 1,500 m depth*

4) If tag and/or baseplate are shed

*these parameters exceed what is expected to occur in a live turtle (we assume mortality)

Attaching PSAT on a hard-shelled turtle

Marine epoxy and syntatic foam base-plate

Marine epoxies to adhere base-plate to hard-shell turtles

• Easy to use

• Safe to use on boat(both for turtle and operator)

• Base-plate and tag will float if tag is shed prematurely

To better understand the impact of a turtle-longlineencounter, PSAT data (e.g. survivorship & behavior) will be correlated with observations noted, such as:

– Hook location– Severity of Injury– Assessment of health

How do we know the system will work??

Lessons learned from a blue shark…

Depth/Temp Data

-4000.00

-3500.00

-3000.00

-2500.00

-2000.00

-1500.00

-1000.00

-500.00

0.00

500.00

4/10 4/11 4/12 4/13 4/14 4/15 4/16 4/17 4/18 4/19 4/20

0

5

10

15

20

25

30

Depth(ft)

Temp(C)

PSAT Blue Shark (Musyl & Brill)

Temp (oC)Depth (ft)

PSAT deployed

PSATs in the Hawaii Longline Fishery• Since March 2001, ~60 Scientific Technicians

(Observers) trained to attach PSATs on hard shelled turtles

• HI: 21% coverage (each observer has tag kit)

• 2 turtles caught in LL gear and released with PSAT– Olive Ridley, tracked for ~ 4 months– Loggerhead, tag shed immediately

Geolocations determined by PSATs• Based on raw data obtained from tag/satellite

• Most probable track predicted from state-space model via the Kalman filter [done by A. Nielsen].

- Each point on this track is computed as the weighted average of the model predictions from all other observations and the observation at the point.

~ 4 months at liberty post-release

Olive Ridley (13202): Hooked in mouth

___________________________1,874 n mi

PSAT deployedPop-off location

Olive Ridley (13202)

Depth data suggest tag was shed rather than a mortality

Percentage Time at DepthDay and Night

010203040506070

0 10 50 100 150 250 350 450 550

Depth (m)

% f

req

uec

y

Night

Day

Min-Max Depth for Olive ridley (13202)

050

100150200250300350400450500550

Time

Dep

th (

m)

minimum

maximum

Aug. 15, 2001 Nov. 15, 2001

Turtle’s Movements and Oceanic Fronts

Were oceanographic features associated with the turtle’s movements?

• No correlations were found between turtle movements and temperature- and chlorophyll-fronts.

• Data suggest turtle’s horizontal movements were correlated with the Northern Equatorial currents. [Keith Bigelow]

Turtle 13202

Hawaiian Islands

Power of Tagging: What we learned from 1 Turtle

• Turtle survived min. 4 months post-release after deep hooking in mouth, swam nearly 1,900 nmi.

• Turtle spent nearly 60% of it’s time within the top 50 m during day, remained deeper at night.

• Turtle did not exceed depths of 250 m, except on a few rare occasions.

• The maximum dive depth was recorded at 544 m, with a corresponding temperature of 4.0 oC.

• Turtle’s horizontal movements appear correlated with the Northern Equatorial currents.

Depth (ft) for Loggerhead (CR 13107)

-100

-80

-60

-40

-20

0

4/30/02 5/02/02 5/04/02 5/06/02 5/08/02 5/10/02 5/12/02 5/14/02 5/16/02

PSAT deployed

No change in pressure suggests tag was shed immediately after release—an attachment problem

Depth (ft)

Costa RicaSea turtles= 8% total catch longline fishery

Collaboration:U. of Hawaii, NMFS, Sea Turtle Restoration Project

6 Caught and released from longline gear -5 olive ridleys, 1 green turtle

3 Controls (free swimming)- 3 olive ridleys

Horizontal Movements of 2 Turtles Hooked and Released from Longline Fishing Gear

Turtles at liberty ~6 weeks

Olive Ridley—deeply hooked in mouth

(6 weeks at liberty, 82 n mi straight distance)

Time at Depth Day and Night (CR 13198)

0

10

20

30

40

50

60

0 10 50 100 150 250 350 450 550

meters

% F

req

uen

cy

% Day Frequency

% Night Frequency

Dive Depth (ft) for Olive Ridley (CR 13117)

-600

-500

-400

-300

-200

-100

0

11/25/01 12/05/01 12/15/01 12/25/01 1/04/02 1/14/02 1/24/02

Deeply hooked in mouth

(6 weeks at liberty, 195 n mi straight distance)

PSAT deployed

Depth (Ft)

Movements of 3 Free-Swimming (control) Turtles

Turtles at liberty 6-8 weeks

Olive Ridley—Free swimming control

(6 weeks at liberty, 477 n mi straight distance)

Time at Depth Day and Night (CR 13204)

0

20

40

60

80

0 10 50 100 150 250 350 450

meters

% F

req

uen

cy

% Day% Night

Dive Depth (ft) for Olive Ridley (CR 13112)

-900

-800

-700

-600

-500

-400

-300

-200

-100

0

11/25/01 12/05/01 12/15/01 12/25/01 1/04/02 1/14/02 1/24/02 2/03/02 2/13/02 2/23/02

Free-swimming control

(Two months at liberty)

PSAT deployed

Depth (Ft)

Dive Depth (ft) for Olive Ridley (CR 13108)

-900

-800

-700

-600

-500

-400

-300

-200

-100

0

11/25/01 12/05/01 12/15/01 12/25/01 1/04/02 1/14/02 1/24/02 2/03/02 2/13/02

Free-swimming control

(Two months at liberty)

PSAT deployed

Depth (Ft)

Summary of PSATs Deployed at Sea

• 1 of 2 PSATs deployed in Hawaii longlinerecorded data ~ 4 months. Data suggest tag shed rather than mortality.

• 5 of 7 PSAT deployed in Costa Rica shed early (6-8 weeks). Depth data suggest all tags were shed.

• Will investigate potential that hooked turtles remain more shallow (0-100m) than controls.

Efforts/collaborations to deploy PSATson Longline-caught hard-shelled turtles

• Contract with PRETOMA in Costa Rica to continue observer coverage

• California longline-observer program trained in PSAT attachment

• Collaboration in planning to deploy PSATs in Brazilian longline fishery

Leatherbacks & PSATs• Current attachment

methods (e.g. harness) not feasible for at-sea application by observers

• Direct-carapace method tested on 5 nesting females(P.I: Molly Lutcavage. Puerto Rico, June 2002)

• Could ideally be refined for use by observers

Current Research Goals

• Determine source for early shedding of tags (PSAT or attachment??)

• Refine attachment procedures accordingly

• Continue extensive collaborations to increase tagging opportunities

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, A. Nielsen, J. Sibert, R. Arauz, STRP, L. Mailloux, D. Gremminger, G. Balazs, M. Lutcavage, S. Sadove, A. Rhodin, Saltwater Inc., R. Morris, and T. Gorgas.