n02:51

ENDANGERED SPECIES RESEARCH

Endang Spec Res

INTRODUCTION

Within the Caribbean, centuries of commercial

exploitation have resulted in reduction or extirpation

of many marine turtle rookeries (Groombridge 1982,

Groombridge & Luxmoore 1989, Jackson 1997, Mc-

Clenachan et al. 2006). The Cayman Islands epitomize

this history of Caribbean marine turtle exploitation.

Despite their small size, the islands once supported

one of the largest ever green turtle Chelonia mydas

rookeries (Groombridge 1982), as well as abundant

nesting by loggerhead Caretta caretta and hawksbill

Eretmochelys imbricata turtles (Lewis 1940). It is

believed that every summer, marine turtles migrated to

the isolated islands to nest, leading to reports that ves-

sels, which have lost their latitude in hazy weather,

have steered entirely by the noise which these crea-

tures make in swimming to attain the Caymana isles

(Long 1774, cited in Lewis 1940 p. 57). By the early

1800s, massive exploitation caused a huge decline in

the Cayman Islands green turtle rookery (Lewis 1940),

and by the 20th century, rookeries here were consid-

ered extinct (Groombridge 1982). However, recent sur-

veys have revealed that nesting by green and logger-

head turtles persists at low levels (Wood & Wood 1994,

Aiken et al. 2001, Bell et al. in press). Additionally,

Satellite tracking highlights the need for

international cooperation in marine turtle

management

Janice M. Blumenthal

1, 2,

, Joni L. Solomon

, Catherine D. Bell

, Timothy J. Austin

Gina Ebanks-Petrie

, Michael S. Coyne

, Annette C. Broderick

, Brendan J. Godley

Department of Environment, PO Box 486, Grand Cayman KY1–1106, Cayman Islands

Marine Turtle Research Group, Centre for Ecology and Conservation, University of Exeter, Cornwall Campus,

Penryn TR10 9EZ, UK

Marine Geospatial Ecology Lab, Nicholas School of the Environment and Earth Sciences, Duke University, A321 LSRC,

PO Box 90328, Durham, North Carolina 27708, USA

ABSTRACT: We present detailed results of a satellite tracking project following 10 adult female tur-

tles from the Cayman Islands, thought to have once been one of the world’s largest rookeries. By

tracking the movements of 7 green turtles Chelonia mydas and 3 loggerhead turtles Caretta caretta

from now critically reduced rookeries we defined key habitats for internesting movement, migration,

and foraging in a range of Caribbean jurisdictions. Turtles tracked from the Cayman Islands traveled

to foraging grounds in Belize, Guatemala, Honduras, Mexico, Nicaragua and the USA. This range

encompasses a >2000 km stretch of Caribbean coastline and the Florida Keys, highlighting the need

for international cooperation in identifying and mitigating foraging ground threats. For one of the

green turtles, foraging site fidelity was elucidated over the course of two reproductive seasons, and

oceanic internesting intervals/post-nesting oceanic circles were defined for the first time in Atlantic

loggerhead turtles. In addition to fundamental and applied insights into the biology of the 2 species,

this research elucidates geographic scale for potential ecological effects of past decimation of rook-

eries in the Cayman Islands and highlights the effectiveness of community efforts in support of

conservation research.

KEY WORDS: Satellite tracking · Spatial ecology · Marine turtle · Chelonia mydas · Caretta caretta

Resale or republication not permitted without written consent of the publisher

Vol. 2: 51–61, 2006

Previously ESR 7: 1–11, 2006

Printed December 2006

Published online November 1, 2006

Endang Spec Res 2: 51–61, 2006

nesting by green turtles released from the Cayman

Turtle Farm as hatchlings or yearlings has been docu-

mented (Bell et al. 2005).

Green turtle rookeries in the Cayman Islands have

been reduced from a pre-exploitation estimate of 6.5

million adults (Jackson 1997), to near extirpation (less

than 26 nesting females of each species; Bell et al. in

press). Conservation of these critically reduced rook-

eries necessitates delineation of critical habitat and

identification of threats. Indeed, research on such

rookeries has recently been called for as part of a

regional review (McClenachan et al. 2006). However,

while nesting beaches in the Cayman Islands are com-

prehensively monitored (Bell et al. in press), marine

turtles spend most of their lives at sea. Over the past

few decades, application of flipper tags has been a

widely-utilized methodology for studying migration

and demographic parameters. However, this method is

not ideally suited to monitoring migration for small

rookeries, as the likelihood of tag recovery in such sit-

uations is extremely small. Additionally, tag recovery

locations may be biased toward areas with active

marine turtle fisheries, and it may be difficult to deter-

mine whether tags were recovered from final destina-

tions or locations en route (Godley et al. 2003,

Schroeder et al. 2003).

More recently, molecular genetic methods have

demonstrated that many foraging aggregations sup-

port turtles from multiple rookeries, and these methods

have proven to be of great utility in linking aggrega-

tions with their nesting beach origins (loggerhead tur-

tles: e.g. Engstrom et al. 2002, Bass et al. 2004, Roberts

et al. 2005, Maffucci et al. 2006, Reece et al. 2006;

green turtles: e.g. Lahanas et al. 1998, Bass & Witzell

2000, Luke et al. 2004). However, with the notable

exception of a green turtle foraging ground in

Nicaragua (Bass et al. 1998), adult foraging grounds in

the Caribbean are largely unsurveyed (Bowen 2003),

and if such surveys were undertaken, it

is unlikely that contributions from the

smallest rookeries would be detected.

Therefore, for these rookeries, satellite

tracking represents the only viable

technique for locating adult foraging

grounds.

Migrations of mature marine turtles

typically span hundreds or thousands of

kilometers (reviewed by Plotkin 2003).

Reproductively valuable adults are often

harvested and incidentally captured

during migration (Witherington 2003,

Seminoff 2004 Chelonia mydas. In:

IUCN 2006 IUCN Red List of Threatened

Species. Available at: www.redlist.org),

necessitating documentation of threats

on migration routes and foraging grounds (Morreale et

al. 1996, Lutcavage et al. 1997, Schroeder et al. 2003,

James et al. 2005). Satellite tracking facilitates rapid

identification of critical habitat (e.g. Horrocks et al. 2001,

James et al. 2005, Troëng et al. 2005), thus representing

a valuable tool for elucidating management require-

ments. In the case of small threatened rookeries the

methodology is particularly useful, as with moderate

capital investment detailed information can be gathered

very quickly.

By tracking wild green and loggerhead turtles, and a

green turtle reared in captivity, we set out to rapidly

delineate habitats (nesting beaches, internesting areas

migratory routes, and foraging grounds) utilized by

turtles originating from the Cayman Islands. In this

way, we aimed to highlight priorities for conservation.

MATERIALS AND METHODS

Study area. The Cayman Islands are located south of

Cuba in the Caribbean Sea (Fig. 1. Grand Cayman,

19.3° N, 81.4° W; Little Cayman, 19.7°N, 81.1° W; Cay-

man Brac, 19.7° N, 79.9° W). The 3 low-lying oceanic

islands are exposed carbonate peaks on the Cayman

Ridge with near-vertical slopes dropping to depths in

excess of 2000 m on all sides (Roberts 1994). The

islands provide approximately 55 km of shoreline suit-

able for marine turtle nesting (Aiken et al. 2001).

Platform Terminal Transmitter deployment. We

attached Platform Terminal Transmitters (PTTs) to 7

post-nesting green turtles (G1 to G7) and 3 post-nest-

ing loggerhead turtles (L1 to L3) from June to August

2003 (3 transmitters deployed), 2004 (5 transmitters

deployed) and 2005 (3 transmitters deployed). All log-

gerhead turtles and 6 of the green turtles were tagged

in Grand Cayman, while 1 green turtle was tagged in

Cayman Brac (Fig. 1). G1 was tracked for 2 reproduc-

Fig. 1. Cayman Islands, showing location of nesting sites for loggerhead tur-

tles (L1 to 3: filled circles) and green turtles (G1 to G7: open circles). 1000 m

contours are indicated

Blumenthal et al.: Satellite tracking of Cayman turtles

tive migrations; originally in 2003 (G1a), and again in

2004 after a 1 yr remigration interval (G1b). The turtle

was identified via inconel flipper tags applied the pre-

vious year and, as the first PTT had detached, we

deployed a new unit in order to track the turtle for a

second season. One of the green turtles (G4) had been

released from the Cayman Turtle Farm as a yearling in

1988, marked with a ‘living tag’ (implantation of a

4 mm disk of lightly colored plastron (lower shell) into

the darker carapace, with location of the tag coding for

year class) (Bell et al. 2005). At the time of transmitter

deployment in 2005, this turtle nested on Seven Mile

Beach, Grand Cayman (Cayman Islands Department

of Environment unpubl. data).

For a summary of deployment information, biomet-

rics, and satellite transmitter performance for all indi-

viduals see Table 1. Sirtrack KiwiSat 101 PTTs were

used on all individuals with the exception of 1 Sea

Mammal Research Unit (SMRU) Satellite Relay Data

Logger tag, which was deployed on L3. To attach the

units, a portable wooden corral was erected around

each turtle following nesting. The carapace of each

turtle was prepared by scrubbing to remove epibionts,

sanding lightly, and cleaning with acetone, and a PTT

was attached with 2-part epoxy (based on the methods

of Godley et al. 2003).

Data filtering. For all transmitters, data were down-

loaded from the ARGOS satellite system and analyzed

via a dedicated program known as the Satellite Track-

ing and Analysis Tool (STAT: Coyne & Godley 2005).

Location accuracy fell into 6 categories (location class

(LC) 3, 2, 1, 0, A, and B). The most accurate positions

(LC 3, 2, 1, A; cf. Hays et al. 2001) and biologically real-

istic speeds (<5 km h

–1

; cf. Luschi et al. 1998) were

used to reconstruct routes and calculate distances

traveled, although for loggerheads during migration

we also included LC B subject to a speed filter in cases

where fewer locations were available. Bathymetric

data were sampled from the General Bathymetric

Chart of the Oceans GEBCO 1-Minute Global Bathy-

metry Grid (www.bodc.ac.uk/projects/international/

gebco/gebco_digital_atlas).

RESULTS

Longevity and tracking

Green turtles were tracked for an extended period

from release to last transmission (mean ± SD 164 d ±

71, range 67 to 281, n = 8). In contrast, loggerhead

turtles were tracked for a consistently longer period

(mean ± SD 685 d ± 311, range 379 to 1000, n = 3).

Foraging destination was ascertained for all animals,

defined as >30 d at a fixed locale (<200 km in

diameter).

Green turtles

Movements between satellite transmitter deploy-

ment and the beginning of directed migration were

documented for green turtles (time in internesting

habitat, mean ± SD 17 d ± 14, range 0 to 34, n = 8). Prior

to commencing migrations to foraging habitat, the

majority of green turtles remained in the vicinity of the

nesting beach. However, 1 green turtle (G6) circled

Grand Cayman (Fig. 2a), and another (G7: the only

individual tagged in Cayman Brac) moved to the vicin-

ity of Grand Cayman (maximum distance from nesting

Turtle CCL PTT Tag Displacement Distance Migration Countries Foraging

(cm) deployment duration (km) traveled duration transited destination

date (d) (km) (d) (n)

G1a 104.0 2003-07-27 136 855 874 12 4 Guatemala

G1b 105.5 2004-08-28 67 856 1023 20 5 Guatemala

G2 107.0 2003-08-22 281 691 712 11 4 Belize & Mexico

G3 109.0 2004-08-19 144 768 1265 31 3 Mexico

G4 110.5 2005-07-24 112 745 991 18 3 Belize

G5 107.0 2005-08-28 88 632 466 19 3 Florida Keys

G6 110.0 2005-08-19 214 623 812 19 3 Mexico

G7 110.0 2004-08-31 269 520 548 11 2 Honduras

L1 100.0 2003-07-28 1000 791 1159 49 3 Nicaragua

L2 105.0 2004-07-14 675 535 886 39 3 Nicaragua

L3 100.0 2004-06-23 379 485 1020 27 3 Nicaragua

Table 1. Chelonia mydas and Caretta caretta. Summary of biometric, PTT deployment, and migration information for all turtles.

Information includes curved carapace length (CCL), PTT deployment date, straight-line distance from nesting beach to foraging

ground (displacement), total distance traveled, duration of migration, number of countries passed through during migration, and

final foraging destination for all tracked turtles. Turtle G1 was tracked in 2003 (G1a) and 2004 (G1b)

Endang Spec Res 2: 51–61, 2006

beach 197 km, mean depth of locations 2940 m) before

returning to Cayman Brac (Fig. 2b). While re-nesting

was not confirmed by beach patrol staff, it is likely that

these local movements occurred over the course of

internesting intervals. G7 reached Grand Cayman 10 d

after leaving Cayman Brac, and returned to Cayman

Brac after an additional 10 d. As this period represents

a typical internesting interval for green turtles in the

Cayman Islands (Cayman Islands Department of

Environment, unpubl. data), G7 may have shifted

nesting sites, nesting in Grand Cayman before return-

ing to Cayman Brac. Similarly, G6 returned to the

vicinity of the nesting beach on 2 occasions (after 10

and 12 d, respectively), suggesting that movements

may also have occurred over the course of 2 inter-

nesting intervals.

After beginning directed migration, 6 of the 7

tracked green turtles oriented toward the Central

American or Mexican mainland, while 1 individual

(G5) oriented northward toward Cuba and the Florida

Keys (Fig. 3a). Two movement patterns were

observed: direct movement to foraging habitat (Fig.

3b, Individuals 2 and 7) and oceanic crossing fol-

lowed by coastal migration (Fig. 3c, Individuals 3, 4, 5

and 6). One individual (G1: tracked for 2 reproduc-

tive migrations) completed a direct oceanic migration

on the first occasion, and an indirect oceanic crossing

followed by coastal migration on the second. Duration

of migration for green turtles varied from 11 d

(entirely oceanic movement), to 31 d (9 d oceanic,

and 22 d in coastal waters). Of the 7 green turtles, 6

were tracked to shallow nearshore foraging areas,

while the green turtle tracked from Cayman Brac

(G7) took up residence in an offshore area (Gorda

Bank, Honduras).

Loggerhead turtles

Movements between satellite transmitter deploy-

ment and the beginning of directed migration were

documented for all loggerhead turtles (time in inter-

nesting habitat, mean ± SD 22 d ± 15, range 9 to 38,

n = 3). L1 remained near shore, while L2 displayed

entirely oceanic movements, circling Cayman Brac

and Little Cayman before returning to the vicinity of

Grand Cayman (Fig. 2c; maximum distance from the

nesting beach 135 km, mean depth of locations

2760 m). As duration of oceanic movement was 23 d,

and nesting does not appear to have occurred in

the other islands, this may represent a post-nesting

oceanic loop rather than an internesting interval. The

third individual (L3) initially circled offshore banks

(10 d), then remained in the vicinity of Grand Cayman

(15 d), and finally circled Cayman Brac and Little Cay-

man (10 d). While nesting was not confirmed, this

Fig. 2. Chelonia mydas and Caretta caretta. Post-nesting oceanic movements around the Cayman Islands for green and

loggerhead turtles (a) G6, (b) G7, (c) L2 and (d) L3. Other tracked turtles remained in the vicinity of the nesting beach prior

to beginning directed movements

Blumenthal et al.: Satellite tracking of Cayman turtles

movement pattern, and the seasonality of the move-

ments, suggests oceanic internesting intervals (Fig. 2d;

maximum distance from the nesting beach 211 km,

mean depth of locations 1900 m).

After beginning directed migration, all 3 loggerhead

turtles moved through oceanic waters toward the

mainland coast of Central America (Fig. 4). Logger-

head turtles utilized an indirect migratory strategy,

migrating along the coastal shelf to foraging destina-

tions. Two individuals (L1 and L2) encountered the

coastal shelf at the mouth of the Patuca River, Hon-

duras, and subsequently traveled east and south along

the shelf (in waters of <30 m). L2 initially took up resi-

dence near the Miskito Bank, Nicaragua, and L1 pro-

ceeded south to the vicinity of the Corn Islands,

Nicaragua. For L3, the complete post-nesting migra-

tory route could not be reconstructed due to a period of

few transmissions during migration. However, forag-

ing destination was obtained for this individual on the

edge of the Nicaraguan shelf in close proximity to L2.

The 3 loggerhead turtles utilized

Nicaraguan foraging grounds through-

out extended tracking, with L2 under-

taking a 200 km habitat shift to the

southern Nicaraguan shelf after more

than 4 mo at her initial foraging site.

After a 1 yr remigration interval, L3

returned to the vicinity of the Cayman

Islands and is presumed to have nested.

However, as the PTT was functioning

intermittently, a detailed return migra-

tory route could not be plotted.

DISCUSSION

Within 3 yr, through deployment of

satellite transmitters on 10 turtles, we

gained significant insights into the

movement of 2 critically reduced rook-

eries of Caribbean marine turtles. Esti-

mates of rookery size in the Cayman

Islands by Bell et al. (in press) suggest

that approximately 10 to 20% of

female loggerhead turtles and 30 to

40% of female green turtles were

tagged and tracked to foraging destina-

tions. Satellite tracking results may

therefore be representative of previ-

ously unknown migratory patterns for

the rookeries, providing swift insight

into movement across areas under a

range of jurisdictions.

Local habitat utilization

While some Cayman Islands green and loggerhead

turtles remained within a few km of the nesting

beach, others ranged through oceanic waters up to

200 km away. In prior studies, green and loggerhead

turtles generally remained in shallow areas near

nesting beaches before beginning migrations (green

turtles: Liew & Chan 1992, Meylan 1995, Hays et al.

2002a; loggerhead turtles: Hays et al. 1991, Godley

et al. 2003), though it should be noted that rookeries

in the Cayman Islands are in close proximity to

oceanic waters. For loggerhead turtles, oceanic habi-

tat utilization during the internesting interval has

been documented only in Japan (Sakamoto et al.

1990); however, the highly plastic behavior of this

species is gradually being revealed,with an in-

creasing number of studies showing oceanic resi-

dence in post-nesting adults (Hatase et al. 2002,

Hawkes et al. 2006).

Fig. 3. Chelonia mydas. (a) Green turtle migration routes to foraging grounds

in Central America, Mexico, and the USA. G1 was tracked for 2 successive

nesting seasons, 2003 (1a, solid line) and 2004 (1b, dashed line). Routes were

constructed utilizing positions of location class 3, 2, 1, A, and speeds less than

5 km h

–1

. The 200 m contour is indicated. (b,c) Displacement plots indicating

representative (b) oceanic (G2) and (c) coastal (G3) movement patterns. Slope of

the line is indicative of speed

Endang Spec Res 2: 51–61, 2006

For green turtles, post-nesting oceanic

loops (following the final nesting of the

season, yet prior to directed migration)

have recently been documented in Tor-

tuguero (Troëng et al. 2005) and Taiwan

(Cheng 2000). Looping behavior could be

associated with oceanic foraging (Troëng

et al. 2005) or attempts to locate a new

foraging ground (Luschi et al. 1998).

Although turtles from the Cayman

Islands briefly encountered shallower

waters, it is unlikely that benthic foraging

occurred, as mean depth of locations

during oceanic movements was greater

than 2500 m.

Oceanic movements in turtles from the

Cayman Islands may constitute oceanic

internesting intervals, shifts in nesting

beach utilization, or post-nesting oceanic

loops. Historically in the Cayman Islands,

exploitation on and near the nesting

beach brought an immense rookery to the

brink of extinction. During the nesting

season, reproductive individuals are typi-

cally concentrated in a small area within

a single jurisdiction, increasing vulnera-

bility to exploitation (Meylan 1995). For

rookeries which underwent heavy ex-

ploitation on and near the nesting beach,

oceanic movements during the internest-

ing period may have been advantageous.

It has been suggested that some turtles

nesting in the Cayman Islands may repre-

sent recent recruits, following the near

extirpation of the historical rookery

(Wood & Wood 1994, Aiken et al. 2001). If

this is the case, these colonizing individuals might be

expected to possess low nesting site fidelity, which

could increase the frequency of behaviors such as

oceanic movements during the internesting interval or

shifting between island nesting sites.

Migration

For post-nesting migration, 2 movement patterns

were observed: direct movements from the nesting

beach to the foraging ground and indirect oceanic

crossing followed by extended migration along the

coast or coastal shelf. Coastal migrations may serve 2

purposes: (1) facilitating navigation and (2) reducing

cost of migration by permitting benthic foraging (God-

ley et al. 2002, Hays et al. 2002b). Therefore, turtles

may minimize the duration of open ocean crossing,

even at the expense of increasing total migratory dis-

tance (Cheng 2000, Godley et al. 2002, Hays et al.

2002b). Movement patterns do not appear to be fixed

for individuals: the green turtle (G1) tracked for 2 con-

secutive reproductive migrations completed a direct

oceanic migration on one occasion and a coastal migra-

tion following an indirect ocean crossing on the other.

After both reproductive migrations, G1 maintained

fidelity to the same foraging site, suggesting orienta-

tion toward a distinct and fixed foraging ground rather

than selection of suitable habitat from year to year. In a

previous study, a green turtle satellite tracked through

successive breeding seasons did not return to her ini-

tial foraging site during the tracking period (Cheng

2000), although similar fidelity has been suggested in

adult female turtles in Australia via flipper tag returns

(Limpus et al. 1992, Limpus & Limpus 2001). In com-

parison to other turtles, the captive-bred green turtle

tracked in this study displayed no apparent anomalous

movements.

Fig. 4. Caretta caretta. (a) Loggerhead turtle migration routes to foraging grounds

in Central America. Routes were constructed utilizing positions of location class 3,

2, 1, A, B and speeds less than 5 km h

–1

. L2 initially foraged on the northern

Nicaraguan shelf (2

) before migrating 200 km south to forage on the southern

shelf (2

). The 200 m contour is indicated. (b) Displacement plot indicating re-

presentative indirect movement pattern of L1. (c) Combined displacement plots

for all loggerhead turtles, showing habitat shift from a northerly to a southerly

foraging site for L2

Blumenthal et al.: Satellite tracking of Cayman turtles

Lessons for regional conservation

Migration routes of turtles from the Cayman Islands

exemplify the problems of managing threatened

marine turtle rookeries, as turtles from a small area

dispersed widely through a wide range of habitats and

came under the jurisdiction of many nations. Green

turtles traveled to foraging grounds in Belize,

Guatemala, Honduras, Mexico, and the USA, with

their range encompassing a >2000 km stretch of

Caribbean coastline and the Florida Keys. This dis-

persion highlights the importance of broad and collab-

orative marine turtle management. In contrast, all 3

loggerhead turtles were tracked to foraging habitats in

Nicaragua, underscoring the necessity of identifying

key habitats and targeting action.

Anthropogenic impacts vary greatly with habitat and

jurisdiction: longline fisheries may threaten marine

turtles during oceanic movements, while directed take

and incidental capture in shrimp trawls and gill nets

are critical threats in the neritic zone (Lutcavage et al.

1997). For rookeries in the Cayman Islands, mortality

experienced on coastal migratory routes and foraging

grounds may represent a greater danger than, for

example, longlining, which generally occurs in oceanic

waters (Lewison et al. 2004). In the Gulf of Mexico and

the Caribbean Sea, shrimp trawls present a significant

threat (Groombridge & Luxmoore 1989, NRC 1990,

Henwood et al. 1992). Estimates based on 1987 shrimp

landings (Henwood et. al 1992) suggest that at the time

over 48000 turtles might have been incidentally cap-

tured in Mexican shrimp trawls each year, while over

15000 turtles might have been captured annually in

Central America (Henwood et al. 1992) (Table 2).

Accuracy of these estimates, species composition of

captured turtles, and current magnitude of this threat

are unknown, though these data are urgently required

to inform regional management.

In addition to experiencing a diversity of threats

during the course of reproductive migrations, green

and loggerhead turtles from rookeries in the Cayman

Islands are subject to many national and international

policies and legal instruments. Belize, Guatemala,

Honduras, Mexico, Nicaragua, and the USA are signa-

tories to the Convention on International Trade in

Endangered Species of Wild Fauna and Flora (CITES,

Chacón 2002), which prohibits international trade in

marine turtle products but does not regulate domestic

trade or habitat protection (Wold 2002). Other interna-

tional agreements — such as the Convention on the

Conservation of Migratory Species of Wild Animals

(CMS), the SPAW (Specially Protected Areas and

Wildlife) Protocol to the Cartagena Convention, and

the Inter-American Convention for the Protection and

Conservation of Sea Turtles (IAC) — have the potential

to effect international cooperation in marine turtle

management, but have not yet been consistently

adopted across the Caribbean region (Table 3). Addi-

tionally, the nature of national legislation and the

effectiveness of its enforcement varies greatly among

jurisdictions. Illegal turtle products are commonly mar-

keted in Belize, Guatemala, Honduras, and Mexico

(Chacón 2002, Fleming 2001) and in Nicaragua, which

appears to be key foraging habitat, it has been esti-

mated that a minimum of 10 000 to 11 000 green turtles

are taken annually, loggerhead turtles are taken inci-

dentally (Lagueux 1998).

As only the Cayman Islands are party to CMS, and

other national and international policies and instru-

ments are inconsistently applied, a thorough assess-

ment of the uptake and effectiveness of legislation is

needed to prioritize regional action. For green turtles

from the Cayman Islands, our results indicate that prio-

rities are in Central America and Mexico, while for

loggerhead turtles Honduras and Nicaragua appear to

be priority nations.

Longlines Shrimp trawls Incidental capture Directed take

Impact Species Impact Species Impact Species Impact Species

Cayman – – – – <5 Cc, Cm <5 Cc, Cm

Belize Un – 153

– Un – 500–800

Cc, Cm, Ei

Guatemala Un – 636

–Un– Un –

Honduras Un – 2899

–Un– Un –

Mexico Un – 48779

–Un– Un –

Nicaragua Un – 610

– Un – 10 000–11 000

USA 7891

Cc 5000–50 000

Cc 500–5000

Cc 5–50

Sources:

NOAA Fisheries (2001);

Henwood et al (1992);

NRC (1990);

Smith et al. (1992);

Lagueux (1998)

Table 2. Estimated annual marine turtle captures in jurisdictions utilized by mature green and loggerhead turtles from the

Cayman Islands. Nesting: Cayman Islands; Foraging: USA, Mexico, Belize, Guatemala, Honduras, and Nicaragua. Un: number

of marine turtle captures not quantified; Cc: loggerhead (Caretta caretta); Cm: green (Chelonia mydas); Ei: hawksbill

(Eretmochelys imbricata). –: threat does not occur

Endang Spec Res 2: 51–61, 2006

Ecological impacts

Although historical harvesting in the Cayman

Islands took place within the confines of a tiny geo-

graphic area and a single life-history stage, congrega-

tion of reproductive individuals allowed rookeries to

be decimated within a few decades (Lewis 1940). As

this ecological extinction occurred well before the

advent of scientific studies of the marine environment,

consequences for seagrass beds and other Caribbean

marine habitats are difficult to assess. However, histor-

ically, abundant marine turtles undoubtedly played a

major role in Caribbean marine ecosystems, acting as

grazers and consumers (Bjorndal & Jackson 2003,

Moran & Bjorndal 2005) and it is therefore presumed

that their loss had a drastic impact on the balance of

such ecosystems (McClenachan et al. 2006).

Additionally, the near extirpation of nesting turtles

in the Cayman Islands may have had demographic

consequences for other Caribbean rookeries: a den-

sity-dependent effect on foraging grounds (Bjorndal

et al. 2000) may have facilitated compensatory popu-

lation growth in extant Caribbean green turtle rook-

eries, such as Tortuguero, which has experienced a

positive population trend (Troëng & Rankin 2005).

Patterns of dispersion of remnant rookeries must be

interpreted with caution, but by tracking surviving

members of what may have been one of the largest

ever green turtle rookeries (Groombridge 1982) and a

significant Caribbean loggerhead rookery (Lewis

1940), we may be able to glimpse historical range and

trace impacts of ecological extinction through wide-

spread ecosystems.

In addition to impacting foraging grounds in a range

of Caribbean jurisdictions, the extirpation of rookeries

from the Cayman Islands is likely to have profoundly

impacted local ecosystems. As turtles mediate signifi-

cant energy flow from nutrient-rich foraging grounds

to nutrient-poor nesting beaches (Bouchard & Bjorndal

2000), abundant nesting by green and loggerhead tur-

tles is likely to have affected the growth of native

beach vegetation and the nutrient content of lagoonal

waters off nesting beaches. Therefore, near extinction

of these rookeries will have brought about significant

shifts in ecosystem dynamics prior to modern surveys

of reef environments.

Insights into local conservation: community-

sponsored conservation efforts

While rookeries in the Cayman Islands are now

critically small (Bell et al. in press), resident juvenile

hawksbill and green turtles are often sighted around

all 3 islands. Due to this apparent ‘abundance’ of

turtles, management requirements for rookeries can

be difficult to convey (J. M. Blumenthal pers. obs.).

Reproductively valuable adult and sub-adult green

and loggerhead turtles are targeted in a legal fish-

ery, and illegal take of eggs and nesting females

continues in the Cayman Islands (Bell et al. 2006).

Satellite tracking has demonstrated the migratory

nature of marine turtle rookeries (versus the year-

round presence of juveniles), and has facilitated

scientific and community discussion of the re-

productive value of mature turtles. This concept has

great applicability throughout the Caribbean region,

as management legislation is often focused on mi-

nimum rather than maximum size limits, aimed at

protecting juveniles rather than adults (Richardson

et al. 2006).

As charismatic species, marine turtles provide an

ideal flagship for introducing communities to conser-

vation concepts. Funds for satellite tracking turtles

CITES CMS Cartagena SPAW IAC CBD

Party Party Signed Ratified Signed Ratified Signed Ratified Signed Ratified

Cayman Is. Yes Yes Yes Yes No No No No Yes Yes

Belize Yes No – Yes No No Yes Yes Yes Yes

Guatemala Yes No Yes Yes Yes No Yes Yes Yes Yes

Honduras Yes No Yes No No No Yes Yes Yes Yes

Mexico Yes No Yes Yes Yes No Yes Yes Yes Yes

Nicaragua Yes No Yes No No No Yes No Yes Yes

USA Yes No Yes Yes Yes Yes Yes Yes Yes No

Table 3. Participation in Multilateral Environmental Agreements (MEAs) in jurisdictions utilized by adult female green and

loggerhead turtles from the Cayman Islands. Nesting: Cayman Islands; foraging: USA, Mexico, Belize, Guatemala, Honduras,

Nicaragua. MEA abbreviations: CITES: Convention on International Trade in Endangered Species of Wild Fauna and Flora;

CMS: Convention on the Conservation of Migratory Species of Wild Animals; Cartagena: Convention for the Protection and

Development of the Marine Environment of the Wider Caribbean Region (Cartagena Convention); SPAW: protocol concerning

Specially Protected Areas and Wildlife (SPAW Protocol to the Cartagena Convention); IAC: Inter-American Convention for

the Protection and Conservation of Sea Turtles; CBD: Convention on Biological Diversity

Blumenthal et al.: Satellite tracking of Cayman turtles

from the Cayman Islands were largely raised by school

fundraisers and from community sponsors, and migra-

tory paths were made available to the public in near

real time on the SEATURTLE.ORG satellite tracking

website (www.seaturtle.org/tracking). In the past 3 yr,

the tracking website as a whole has received more

than 3.5 million visits from over 155 countries. With this

participatory approach, we aimed to focus awareness

on the need for international cooperation in marine

turtle management.

Overall, satellite tracking marine turtles from the

Cayman Islands across international boundaries pro-

vided an accessible introduction to issues of interna-

tional law surrounding migratory species and offered

an unparalleled opportunity to increase awareness

among the public and policy makers. This research has

enabled us to develop and communicate an under-

standing of management requirements for threatened

marine turtle rookeries, while providing a case study in

the difficulties of managing highly-migratory endan-

gered species.

Acknowledgements. Graphics were produced using the

Maptool program (a product of SEATURTLE.ORG: www.

seaturtle.org/maptool). All tracks were made available to

the public in near real time on the SEATURTLE.ORG track-

ing website: www.seaturtle.org/tracking. We thank Cayman

Islands volunteers and sponsors, particularly M. Orr, E.

Blanco, G. Oberholtzer, G. Kwong, J. Porter, M. Fowlds, the

Olde family, the Richardson family, St. Ignatius High

School, Ocean Frontiers Ltd, Jacques Scott Ltd, DiveTech

Kids Camp Outreach Program, the Brakka Trakkas, the

Ritz-Carlton Grand Cayman’s Ambassadors of the Environ-

ment program, and Department of Environment research,

enforcement, and operations staff. Work in the Cayman

Islands was supported by the National Fish and Wildlife

Foundation (NFWF), and work in the UK was supported by

the Darwin Initiative, European Social Fund, Overseas Ter-

ritories Environment Programme, Turtles in the UK Over-

seas Territories (TUKOT) and the National Environment

Research Council (NERC). J.B. is supported by a University

of Exeter Postgraduate Studentship. The manuscript was

improved by the input of 3 anonymous reviewers.

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Submitted: June 14, 2006; Accepted: September 23, 2006

Proofs received from author(s): October 15, 2006