Satellite tracking large numbers of individuals to infer population level dispersal and core areas...

BIODIVERSITYRESEARCH

Satellite tracking large numbers ofindividuals to infer population leveldispersal and core areas for theprotection of an endangered speciesGail Schofield1*, Alexandra Dimadi2, Sabrina Fossette1,3, Kostas

A. Katselidis2,4, Drosos Koutsoubas2,5, Martin K. S. Lilley1,6, Adrian

Luckman7, John D. Pantis8, Amalia D. Karagouni9 and Graeme C. Hays1,10

1Department of Biosciences, Swansea

University, Singleton Park, Swansea, SA2

8PP, UK, 2National Marine Park of

Zakynthos, 1 El. Venizelou Str., GR-29100,

Zakynthos, Greece, 3Environmental Research

Division, Southwest Fisheries Science Center,

National Marine Fisheries Service, National

Oceanic and Atmospheric Administration,

Pacific Grove, CA 93950, USA, 4Department

of Environmental & Natural Resources

Management, University of Ioannina,

G. Seferi 2, GR-30100, Agrinio, Greece,5Department of Marine Sciences, University

of the Aegean, 81100, Mytilini, Greece,6M�editerran�een Institut d’Oc�eanographie,

Aix-Marseille Universit�e, 163 Av. de

Luminy, 13288 Marseille Cedex 9, Mytilini,

France, 7Department of Geography, Swansea

University, Swansea, UK, 8Department of

Ecology, School of Biology, Aristotle

University of Thessaloniki, UP Box 119,

54006, Thessaloniki, Greece, 9Department of

Botany, Faculty of Biology, Microbiology

Group, National Kapodistrian University of

Athens, Athens, 15781, Greece, 10Centre for

Integrative Ecology, School of Life and

Environmental Sciences, Deakin University,

Warrnambool, Vic., 3280, Australia

*Correspondence: Gail Schofield, Department

of Biosciences, Swansea University, Singleton

Park, Swansea SA2 8PP, UK.

E-mail: [email protected]

ABSTRACT

Aim Tracking the dispersal patterns and habitat use of migratory species is

necessary to delineate optimal areas for protection, with large sample sizes

being more representative of the population. Here, we examine the dispersal

patterns of a key Mediterranean loggerhead turtle (Caretta caretta) breeding

population to identify priority foraging sites for protection.

Location Zakynthos Island, Greece and the wider Mediterranean.

Method We examined the dispersal patterns and foraging sites of 75 adult

loggerheads (n = 38 males and 37 females) tracked from the breeding area of

Zakynthos Island (Greece) from 2004 to 2011. We then combined our data

with published sea turtle literature to identify key foraging sites for protection.

Results While both males and females exhibited similar dispersal patterns,

about 25% males remained < 100 km of Zakynthos, whereas all females (except

one) migrated > 200 km. Integration of our data with the wider literature

isolated 10 core sites in proximity to existing protected areas, which could

potentially protect 64% of the Zakynthos population, while five sites support

individuals from at least 10 other loggerhead breeding populations.

Main conclusions Due to the widespread availability of neritic foraging

grounds across the Mediterranean, sea turtles from Zakynthos exhibit disparate

dispersal patterns. However, protecting only a few objectively defined important

sites can encompass a large proportion of the foraging areas used and hence

have considerable conservation benefit.

Keywords

Adaptive behaviour, conservation management, dispersal, predictive models,

sample size, spatial ecology, telemetry.

INTRODUCTION

Many animal populations invest in long-distance migration

to reduce foraging competition when food resources are

scarce at breeding sites (e.g. Greenwood, 1980; Alerstam

et al., 2003; Fryxell et al., 2004). Hence, while a population

may aggregate at one site to breed, many disparate foraging

sites may be used depending on resource availability and the

pattern of dispersal which may be influenced by factors such

as wind direction, sea currents or land barriers in avian,

marine and terrestrial migrants, respectively (e.g. �Akesson &

Hedenstrom, 2007). Consequently, important habitats for

protection may be distributed across wide regions, often tra-

versing international borders or economic exclusion zones

(e.g. Hannah et al., 2002; Bradshaw et al., 2010). At present,

of the 150,000 protected areas across the world, just 3% are

DOI: 10.1111/ddi.12077834 http://wileyonlinelibrary.com/journal/ddi ª 2013 John Wiley & Sons Ltd

Diversity and Distributions, (Diversity Distrib.) (2013) 19, 834–844A

Jou

rnal

of

Cons

erva

tion

Bio

geog

raph

yD

iver

sity

and

Dis

trib

utio

ns

in the oceans (c. 5000 marine protected areas) (Bradshaw

et al., 2010). Hence, as countries introduce measures to

improve protection along their coastlines (Bradshaw et al.,

2010), it is important to ensure that governments and

environmental agencies select optimal sites for regulation

(Ferrier, 2002).

Remote tracking systems of animals, using, for example,

GPS or ARGOS, may generate extensive datasets that directly

show the placement of individuals within ecosystems, por-

traying habitat use and migratory patterns. This technology

provides an opportunity to collect fine-scale spatio-temporal

information about species that would otherwise be difficult

to study (i.e. tuna, Block et al., 2005; shearwaters, Shaffer

et al., 2006; leopards, Gavashelishvili & Lukarevskiy, 2008).

For instance, tracking studies of sea turtles, which are of

world-wide conservation concern, have gained momentum

over the last 20 years (Godley et al., 2008), with datasets of

> 30 (max. 186) turtles from individual populations gradu-

ally emerging; however, these works are primarily focused on

females and juveniles (e.g. Polovina et al., 2006; Hawkes

et al., 2011), rather than males (but see Arendt et al., 2012a,

b). In general, tracking studies of sea turtles have inferred

(1) high fidelity of adults to foraging sites (e.g. Broderick

et al., 2007; Schofield et al., 2010a), (2) seasonal variability

in dispersal to foraging sites (e.g. van Dam et al., 2008;

Hawkes et al., 2011; Zbinden et al., 2011), (3) male and

female differences in dispersal and foraging site use (e.g. van

Dam et al., 2008; Arendt et al., 2012a) and (4) phenotypic

variation in foraging habitat (coastal versus oceanic) use

within populations (e.g. Hatase et al., 2002, 2010; Hawkes

et al., 2006). Several theories have been proposed to explain

these differences, including (1) hatchling drift influenced by

sea currents (Hays et al., 2010b; Gaspar et al., 2012), (2) the

evolutionary context of food abundance predictability

(Drakare et al., 2006; van Dam et al., 2008) and (3) possible

adult mortality risk of migratory routes and foraging sites

(van Dam et al., 2008).

The Mediterranean Sea has been the focus of extensive sea

turtle research, including satellite tracking and by-catch stud-

ies (e.g. Broderick et al., 2007; Zbinden et al., 2008; Schofield

et al., 2009; Casale et al., 2010; Schofield et al., 2010a; Zbin-

den et al., 2011). This work has resulted in the delineation

of two Regional Management Units (RMU) for loggerhead

sea turtles, representing populations from the Mediterranean

and north-west Atlantic (Wallace et al., 2010), with green

turtle (Chelonia mydas) populations also being resident to

the region. Interestingly, while juvenile loggerheads from

Atlantic populations enter the western Mediterranean basin

(via the Strait of Gibraltar) for development (Casale et al.,

2008; Eckert et al., 2008), the breeding and foraging habitats

of permanent Mediterranean loggerhead and green popula-

tions are primarily concentrated in the central and eastern

basins, with Zakynthos Island (Greece) in the central basin

hosting the largest known breeding site for loggerhead turtles

(Fig. 1a; Margaritoulis et al., 2003). Initial stranding data of

dead turtles from Zakynthos (based on external flipper tag

returns) that were washed ashore or entangled in nets indi-

cated potentially broad dispersal to foraging sites (Margari-

toulis et al., 2003); yet, this observation could have been an

artefact of oceanic drift by dead or injured animals. How-

ever, subsequent satellite tracking studies began to support

the stranding data, but indicated differences in movement

patterns. For instance, a tracking study of 18 female logger-

heads from Zakynthos (Zbinden et al., 2011) showed a clear

dispersal pattern to foraging sites, either north (to the Adri-

atic) or south (to the Gulf of Gabes). In contrast, a tracking

study of 10 males from the same site (Schofield et al., 2010a)

showed primarily northerly dispersal to the Adriatic and

Aegean. This raised the question of whether males and

females use different foraging sites, or whether this was

simply an artefact of sample size.

Hence, in this study, we assessed the dispersal and forag-

ing destinations of 75 adult male and female loggerheads that

were captured and tracked from the key Mediterranean

breeding area of Zakynthos between 2004 and 2011. Based

on our tracking data, we suggest where suitable neritic forag-

ing habitat may lie in winter and summer months, enabling

prioritization for conservation. Finally, we combine our data

with published literature from other sea turtle (green and

loggerhead) populations across the Mediterranean, to identify

key foraging sites according to contributions of species,

breeding population, sex and age class. This study supports

the importance of using large datasets to correctly infer pop-

ulation level dispersal patterns and foraging habitat use, as

well as to delineate important areas for the protection of sea

turtles inhabiting the Mediterranean Sea.

METHODS

Instrumentation

Between 2004 and 2011, 75 adult loggerhead turtles from

Zakynthos, Greece, in the central Mediterranean basin

(Fig. 1a; Table S1a, b; 37° 43′ N, 20° 52′ E), were instrumen-

ted with satellite transmitters (n = 38 males, of which five

were tracked for more than one breeding season; n = 37

females, of which one was tracked for more than one breed-

ing season). During May of 2007–2011, the Swansea Univer-

sity team attached 32 transmitters, and a further 25

transmitters were attached by the National Marine Park of

Zakynthos (NMPZ) from 2008 to 2010 (combined total:

n = 38 males; n = 19 females), when males and females

aggregate to mate before the start of the nesting season. All

turtles were captured at sea, within 1 km of shore, in the

vicinity of the nesting beaches (for methodology see

Schofield et al., 2010a). When possible, transmitters were

retrieved one year after attachment, during in-water surveys

or on the nesting beaches. Units provided either Global Posi-

tioning System (GPS) quality locations and/or Argos quality

locations relayed either via the Argos satellite system or the

mobile phone network. Table S1 lists the tracking devices

used, with information on device programming, performance

Diversity and Distributions, 19, 834–844, ª 2013 John Wiley & Sons Ltd 835

Tracking an endangered species for conservation

metrics and weights being available in our previous publica-

tions (e.g. Schofield et al., 2010a). The data were filtered

using a maximum rate of travel of 5 km h�1 between succes-

sive locations (Luschi et al., 1998). Foraging sites were iden-

tified by individuals slowing down and remaining in fixed

areas for extended periods of time (minimum of 5 days; see

Hays et al., 2010a), using a combination of displacement

distance and changes in speed of travel (Blumenthal et al.,

2006; Schofield et al., 2010a). In addition, we digitized the

previously published tracks of 18 female loggerhead turtles

satellite tracked from 2004 to 2007 on the nesting beaches of

Zakynthos (Zbinden et al., 2011), which are also listed in

Table S1. This paper presents previously unpublished track-

ing information for 38 turtles (n = 22 males; n = 16

females).

All tracked turtles (males and females) were identified using

a previously validated photo-identification system (Schofield

et al., 2008) and external flipper tags (females only), with all

turtles captured from 2008 onwards also receiving passive inte-

grated transponders (PITs). From May 2009 onwards, follow-

ing confirmation that males (Hays et al., 2010a), like females

(see Broderick et al., 2007), return to their primary foraging

sites, transmitters were only attached to previously untracked

individuals, using the combined methods of identification. In

the event of capturing previously tracked turtles, the individual

was measured, photographed, identified, marked with paint

(to avoid repeat captures in the same two-week period) and

returned to the sea. Transmitters were not attached to turtles

with signs of recent injury, large numbers of leeches, emacia-

tion or flipper trauma/loss.

(a)

(b)

(c)

Figure 1 (a) The location of the

breeding area of Zakynthos in the

Mediterranean compared with other

loggerhead (stars) and green (triangles)

turtle nesting areas in the Mediterranean.

The main seas of the Mediterranean that

are cited in this study are indicated. (b)

Migration of male (black, n = 31) and

female (red n = 29) loggerhead turtles

from the breeding area of Zakynthos in

Greece to the primary foraging sites.

Excluded tracks: five retracked (repeat

tracked, either through the device

operating for more than one year, or a

new transmitter being attached) males;

one male and five females without

locations between the breeding and

foraging sites. White star = Zakynthos.

(c) Schematic showing the patterns

(as actual numbers of turtles) of initial

dispersal by male (n = 27) and female

(n = 33) turtles on departing the

breeding area (excluding residents,

n = 5). Note: diagram not to scale.

836 Diversity and Distributions, 19, 834–844, ª 2013 John Wiley & Sons Ltd

G. Schofield et al.

Dispersal

The direction of departure from Zakynthos was recorded for all

turtles. The dispersal directions were grouped into five ‘regions’

of the Mediterranean Sea: (1) Region A, north, towards Amv-

rakikos and the Adriatic, (2) Region B, south-west, towards

Tunisia (Gulf of Gabes) and Libya, (3) Region C, the vicinity of

Zakynthos (the Ionian Sea), (4) Region D, to the Aegean Sea;

and (5) Region E, to the western Mediterranean (Fig. 1a;

Table 1). We compared the dispersal directions of the tracking

datasets against published female stable isotope analyses from

Zakynthos (Zbinden et al., 2011) and female strandings for

Zakynthos (Margaritoulis et al., 2003) (Table 1). To avoid

pseudoreplication in the analyses, for the six turtles tracked

across two years, only data from the first year were used.

Foraging

The shortest (i.e. straight line) distance between the primary

foraging sites and the breeding site was calculated. Foraging

sites were classified as: (1) oceanic (> 200 m) (Seminoff et al.,

2008), (2) neritic coastal (< 200 m seabed depth, < 2 km from

shore) and (3) neritic open sea (< 200 m seabed depth,

> 2 km from shore) (Schofield et al., 2010a). For the purposes

of this study, discrete sites were given arbitrary numbers; how-

ever, they remain an artefact of sample size, whereby as sample

size increases, so certain sites will merge. Here, we defined a

foraging site as a single site or group of overlapping sites that

are separated from adjacent sites by a minimum distance of

36 km, which reflects the mean migration speed (1.5 km h�1;

SD � 0.57; Schofield et al., 2010a) over a 24 h period, indicat-

ing directional movement. We recorded the location (lati-

tude), mean depth (GEBCO, http://www.gebco.net/) and the

category of all foraging sites (i.e. whether it was the first, sec-

ond, etc. to be used after migrating from the breeding site) that

were used by all turtles over the study period. Home ranges

were not calculated, due to the different types of transmitters

used, and differences in transmission frequency and accuracy.

We used ARCMAP v9.1 (ERSI, Redlands, CA, USA; http://www.

esri.com/software/arcview) to show the location of all foraging

sites used by the tracked turtles across the Mediterranean.

Where possible, we recorded the date that turtles shifted forag-

ing sites and compared the frequency of movement according

to geographical location and temperature. We also assessed the

data for any differences in sex and body size [curved carapace

length (CCL), from the nuchal scute to the tip of the longest

supracaudal scute] with respect to migratory distances and the

latitude of the foraging sites.

Following Hawkes et al. (2007), we modelled the potential

available foraging habitat for loggerheads in the Mediterra-

nean during summer (August) and winter (February). We

used a maximum seabed depth of 100 m (as 60 of 61 turtles

foraged at sites shallower than 100 m depth) and a mini-

mum temperature of 13 °C, based on minimum Mediterra-

nean wintering temperatures recorded by Hochscheid et al.

(2007), and the fact that no turtles in this study inhabited

waters below this temperature. Bathymetric data were

derived from GEBCO. Sea surface temperature (SST) data

were derived from MODIS (Moderate Resolution Imaging

Spectrometer) satellite data products (http://oceancolor.gsfc.

nasa.gov/). We used the mean February SST from 2000 to

2010. These freely available gridded data products were

resampled to the UTM map projection to facilitate the mea-

surement of habitat area under SST and depth constraints.

The general foraging ground locations of all turtles (except

one) in each season clearly fell within the model parameters

for each season; therefore, it was not necessary to further val-

idate the model using filtered satellite location data (as per-

formed by Hawkes et al., 2011) and was not possible here

due to the use of different tracking units, with different

quantities of locations at very different resolutions.

Protection

We evaluated the relative importance of the identified foraging

sites based on available published data, with the aim to guide

managers regarding the sites requiring immediate protection

focus. As the Mediterranean is an almost enclosed sea that hosts

around 24 known sea turtle (loggerhead and green) nesting

areas across around 16 countries (Margaritoulis et al., 2003),

we assimilated published literature on adult sea turtles for this

region (see Table S2) that provided evidence for the presence of

foraging sites, in addition to the use of known adult foraging

sites by juvenile turtles. Data were assimilated from tracking,

genetic, capture-recapture, tagging, by-catch and stranding

studies. We then arranged the foraging sites according to species

Table 1 Numbers of turtles tracked to

foraging areas in each of the five regions

in Fig. 1(a). Data are compared with the

proportions of stranded loggerheads

recorded in each region (Margaritoulis

et al., 2003) and inferred foraging areas

from stable isotope data (Zbinden et al.,

2011).

Region Location

TrackingStrandings

Females

Stable isotope

FemalesTotal Males Females

A Adriatic & Amvrakikos 28 10 18 45 22

B Gulf of Gabes & Libya 21 10 11 30 25

C Ionian (including residents) 9 8 1 3 0

D Aegean 6 3 3 19 0

E West Mediterranean 1 1 0 2 0

F Other 0 0 0 1 0

Total 65 32 33 100 47



(green/loggerhead), sex (male/female), size class (adult/juve-

nile), number of represented breeding populations, seasonality

of site (i.e. summer, winter or year-round use) and existing pro-

tection status of the site. Finally, we considered the likelihood of

these sites receiving protection based on local, national and

regional status in relation to the breeding area.

RESULTS

Turtles

The mean CCL of male loggerheads was 82.9 cm (n = 33,

SD � 7, range: 71–102 cm), while that of females was

83.7 cm (n = 35, SD � 4.5, range: 74–91 cm). Four trans-

mitters stopped working when turtles were still within the

breeding area and were excluded from the dataset, leaving 32

males and 33 females for the dispersal analysis. Of the

remaining transmitters, four stopped working during the

post-breeding migration, which were excluded from the for-

aging site analyses, leaving 29 males and 32 females.

Dispersal

In general, males and females exhibited similar dispersal pat-

terns from Zakynthos, with 70% travelling south-west and 30%

travelling south-east (Fig. 1b, c). Most turtles migrated either

north to the Adriatic Sea and Amvrakikos Gulf (Region A,

42%) or south-west to Libya and Tunisia (Region B, 32%), with

the remainder staying in the Ionian Sea (Region C) or migrating

to less frequented areas in the east (Region D) and west (Region

E) Mediterranean. Significantly more males than females

remained within 100 km of Zakynthos (G test, P < 0.001; 24%

and 3%, respectively). This difference in use of the Ionian Sea

between males and females was reflected in the comparison of

the proportion of turtles in each of the five regions for the male

and female tracking (n = 65), female stable isotope (n = 47;

Zbinden et al., 2011) and female stranding (n = 100; Margari-

toulis et al., 2003) datasets. The correlation coefficient of male

tracking data with the female stranding data was much lower

(0.72) than the female tracking data with the female stranding

data (0.97) or the stable isotope data (0.87).

Foraging

After breeding, all turtles migrated to neritic sites shallower

than 100 m, except one male that travelled directly to an

oceanic site. In total, six turtles (male n = 4; female n = 2)

frequented both neritic and oceanic sites during the tracking

period. Foraging sites were widely dispersed across the three

basins (Fig. 2a; Table S2; see Supporting information for

detailed description); however, sites used by 65% of turtles

were primarily concentrated in the north and south parts of

the central basin, supporting the habitat model indicating

that the central basin has the greatest percentage of available

foraging habitat of < 100 m seabed depth (Fig. 2b; Table 2).

Several turtles (n = 11 males; n = 12 females) used up to

four separate sites, most of which frequented primary sites at

40–45°N latitude (n = 16 northern sites versus n = 7

southern sites) and moved south to latitudes < 40°N where

the temperature remained above 13 °C year-round (Fig. 2c;

Table 2).

Excluding residents to Zakynthos island (n = 5), foraging

sites were on average 777 � 334 km (range 50–1537) distant

from the breeding site. Migratory distance was not correlated

with CCL (F1,60 = 2.6, r2 = 0.05; P = 0.1). Furthermore,

there was no difference in the mean (and SD) CCL between

neritic versus oceanic foragers (mean 84 � 2 vs. 82 � 8 cm

CCL, respectively); however, the sample size of the latter

group was small (n = 6), with five individuals investing in

both oceanic and neritic foraging. In addition, we found that

the latitude of the primary foraging site was associated with

CCL, with possible longitudinal variation in CCL too (see

the supplementary information and Fig. S1 for more details.)

Protection

Figure 2a shows that about one-third of identified foraging

sites (n = 10) used by the Zakynthos population are near to

(< 20 km; n = 3 sites) or directly overlapping (n = 7 sites)

existing MPAs and/or national parks (Abdulla et al., 2008;

Table 3; Table S2). If the protection area and associated

measures were extended to these 10 locations, 64% of turtles

(62% males and 64% females) from Zakynthos could poten-

tially be protected, at least for part of the year, with limited

additional management effort. Unfortunately, half of these

sites are only used during the summer by turtles, with win-

tering sites at unprotected locations. The improvement of

protection measures at three existing protected areas in

Greece (Sites 16, 19 and 20, all in the Ionian Sea) could safe-

guard 20% of turtles (28% males and 12% females) from

Zakynthos, in addition to adult turtles from other breeding

populations and juvenile green and loggerhead populations

(Table 3; Table S2). At a regional scale, there are two focal

areas for foraging site protection, the Gulf of Gabes and the

Adriatic. In the Adriatic, the establishment of protection

measures at Site 25 could safeguard 18% of turtles (20%

males and 16% females) from Zakynthos; however, this site

was only used by turtles during the winter months, although

turtles from other adult breeding populations, as well as

juvenile loggerheads (and possibly greens), have been docu-

mented in this area (Table 3; Table S2). In comparison, the

protection of Sites 4 and 5 in the Gulf of Gabes could safe-

guard 31% (30% males and 34% females) of turtles through-

out the year, with loggerhead turtles from up to 10 other

breeding populations, as well as juvenile loggerheads, also

frequenting these two sites (Table 3; Table S2).

DISCUSSION

The present study shows that turtles from a key loggerhead

sea turtle population in the Mediterranean exhibit variable

dispersal patterns, due to the large availability of neritic


G. Schofield et al.

foraging habitat throughout the region. As we tracked over

30 males and 30 females in the current study, the observed

dispersal patterns are considered to be representative for this

population, allowing any differences between the sexes to be

clearly defined. However, while the sample size of the current

study is large compared with the majority of existing sea tur-

tle studies (see Godley et al., 2008), the tracked individuals

in this study still only represented about 9% of this breeding

population (Schofield et al., 2010b). Hence, it was necessary

to draw on available tracking, stranding and genetic informa-

tion from the wider literature to delineate core foraging areas

for protection.

It is possible that we may have missed foraging areas that

are rarely used by the Zakynthos adult breeding population,

despite the size of the tracking dataset. For instance, adult

turtles foraging in the Bay of Naples have been tracked to

foraging and breeding sites in the central Mediterranean

(Bentivegna, 2002; Hochscheid et al., 2007). Furthermore,

(a)

(b)

(c)

Figure 2 (a) Discrete foraging sites frequented by male (black triangles) and female (grey triangles) loggerheads from Zakynthos (with

some turtles frequenting more than one site). The foraging sites are indicated and numbered; orange numbers = foraging sites

overlapping or in close proximity to existing marine protected areas and/or national parks. Discrete foraging sites are arbitrary and

defined as a single site or group of overlapping sites that are separated from adjacent sites by a minimum distance of 36 km, which

reflects the mean migration speed of loggerhead turtles (1.5 km h�1; Schofield et al., 2010a, b) over a 24 h period. In addition, other

known loggerhead (filled dark grey circles) and green turtle (filled grey circles) foraging sites are shown based on the published literature

(Bentivegna, 2002; Margaritoulis et al., 2003; Broderick et al., 2007; Hochscheid et al., 2007; Casale et al., 2008). Note: solely juvenile

foraging sites of the West Mediterranean have not been included here. (b) Available foraging habitat for loggerheads in the

Mediterranean to 100 m seabed depth (yellow contour) and 200 m seabed depth (blue contour) derived from GEBCO. For percentages,

please see Table 2. (c) Sea surface temperature data delineating the 13 °C minimum temperature limit (pink contour) in February from

2000 to 2010 using MODIS. For percentage of 100 m seabed depth lost to loggerheads in winter, please see Table 2.



increased tracking is revealing increased behavioural plasticity

(e.g. Hatase et al., 2007; Seminoff et al., 2008; Rees et al.,

2010; Schofield et al., 2010a), which confers some resilience

against change, despite complicating the identification of all

core foraging areas.

Interestingly, while our previous work using n = 10 males

(Schofield et al., 2010a) indicated a bias of male movement

towards northerly foraging sites, once the sample size

exceeded 20 individuals, similar numbers dispersed north as

south, more closely reflecting that observed for females from

the same population. Furthermore, the current study

supported adult female tag returns from the stranding datasets

(Margaritoulis et al., 2003), as well as hatchling drift scenarios

(Hays et al., 2010b). However, this consistency across studies

was stronger for tracked females compared with tracked

males. Male dispersal deviated from that of females in that

24% of males remained resident or close (< 100 km) to the

breeding area, supporting recently published studies (Shaver

et al., 2005; van Dam et al., 2008; Arendt et al., 2012a). Yet,

studies on Cyprus (loggerheads, Broderick et al., 2007) and

the Galapagos (green turtles, Seminoff et al., 2008) have

recorded females resident to the general area; hence, we may

have just not yet tracked a resident female. The observed dif-

ference in migratory pattern between the sexes at Zakynthos,

and other areas, may be due to males facing much lower

reproductive costs/investment compared with females

(Clutton-Brock & Vincent, 1991). Similar differences in

movement patterns and habitat use between the sexes have

also been recorded for other species (e.g. wandering

albatrosses, Weimerskirch et al., 1997; fur seals, Boyd et al.,

1998). This behaviour might facilitate more opportunistic

foraging strategies by males, as well as allow annual reproduc-

tive activity and greater (earlier) access to returning females

(for review see Morbey & Ydenberg, 2008).

In contrast to Hatase et al. (2010) in the Pacific, but simi-

lar to Hawkes et al. (2011) in the Atlantic, the majority of

male and female loggerheads frequented neritic foraging sites

of < 100 m seabed depth in the central Mediterranean, either

to the north (Adriatic) or south (Gulf of Gabes), with only a

Table 2 Potential available neritic foraging habitat in the

western, central and eastern Mediterranean at a maximum

seabed depth of 100 m (as all neritic study sites were within

100 m depth, except one) and showing the reduction in habitat

availability during winter (based on minimum Mediterranean

wintering temperatures of 13 °C determined by Hochscheid

et al., 2007). Bathymetric data were derived from GEBCO. Sea

surface temperature (SST) data were derived from Moderate

Resolution Imaging Spectrometer (MODIS) satellite data

products (http://oceancolor.gsfc.nasa.gov/).

Basin

Total area

(km2)

% Total area

< 100 m seabed

depth

% Total area < 100 m

seabed depth with

February SST > 13 °C

West 831,300 6.8 3.5

Central 861,200 16.4 9.5

East 765,400 7.7 4.5

Total 2,457,900 10.5 5.9

Table 3 Summary table of the focal foraging sites of Zakynthos (Greece) loggerheads in the Mediterranean, and potential overlap with

other breeding and juvenile populations based on evidence from the published literature (satellite tracking, live and dead strandings,

mark–recapture, by-catch, genetic analyses). See Table S2 for full listing and associated references and Fig 2a. for foraging site locations.

Site is the foraging site number listed in Fig. 2a. Breeding no. is the number of loggerhead breeding areas represented at each foraging

site frequented by Zakynthos turtles.

Site Basin Country

Foraging

category

Thermal

availability

Protection

in vicinity

Recorded

species

Gender/age class

Loggerhead breeding

populations

SourcesLoggerhead Green No. Location

4 Central Tunisia NC/NO Year-round No Log M/F/Juv n/a ~11 Zak; Kyp; Cyp; Turk;

Mess, Lib; Tunis;

? Cal,?Is,?It

1, 2, 3, 4, 5

6, 7, 8, 9, 12

5 Central Tunisia NC/NO Year-round No Log M/F /Juv n/a ~6 Zak; Kyp; Cyp; Turk;

Tunis; Lib

1, 2, 3, 4,

5, 6, 7, 13

16 Central Greece NC Year-round Yes Log M n/a 1 Zak 1

20 Central Greece NC Year-round Yes Log/Gre M/F /Juv Juv ~4 Zak; Syr; ?Kyp,

Unknown

1, 2, 3,5, 10

25 Central Croatia NO Seasonal

(summer)

Yes Log M/F/Juv n/a ~2 Zak; Kyp 1, 5, 11

Foraging category, NO, neritic open sea; NC, neritic coastal. Recorded species, Log, loggerhead; Gre, Green; Gender/age class, M, adult male;

F, adult female; Juv, juveniles, with gender not differentiated. Breeding populations, ?, unconfirmed; Zak, Zakynthos, Greece; Kyp, Kyparissia,

Greece; Cyp, Cyprus; Syr, Syria; T, Turkey; Mess, Messina; Lib, Libya; Tunis, Tunisia; Cal, Calabria; Is, Israel; It, Italy. Sources, 1, this paper; 2,

Bentivegna (2002); 3, Margaritoulis et al. (2003); 4, Broderick et al. (2007); 5, Casale et al. (2007); 6, Hochscheid et al. (2007); 7, Echwikhi et al.

(2010); 8, Chaeib et al., (2012); 9, Casale et al. (2012, 2013); 10, Rees et al. (2013); 11, Lazar et al. (2004a, b); 12, Casale et al. (2012, 2013); 13,

Saied et al., 2012.


G. Schofield et al.

few individuals using oceanic sites. This north versus south

division is similar to that recorded by Hawkes et al. (2011)

in the Atlantic. Furthermore, our habitat model showed that

these two areas of the Mediterranean support the greatest

areas of available foraging habitat in the Mediterranean. Due

to sea temperatures dropping below 13 °C in winter (i.e. the

minimum Mediterranean wintering temperatures recorded

by Hochscheid et al., 2007) in the northern area, turtles were

more likely to use more than one foraging/wintering site and

move southward compared with those inhabiting the

southern area.

High neritic habitat availability, multi foraging site use

and temperature regulated shifts to wintering sites make

establishing focal areas for protection in the Mediterranean

extremely challenging. Despite this, tracking datasets from

the current study combined with existing publications, based

on tracking and other techniques (i.e. stranding, capture-

recapture and genetics), produced baseline information

identifying key foraging sites for protection at national and

regional levels. At a regional scale, pressure to protect the

Zakynthos population is extremely difficult due to the com-

plexity of national boundaries and competition between

governments and government agencies regarding jurisdic-

tional responsibility (Agardy, 1994). Furthermore, detailed

by-catch studies, from the Adriatic to the Gulf of Gabes

(Casale et al., 2008, 2010; Echwikhi et al., 2010; Chaieb

et al., 2012), clearly indicate the high risk of mortality to

sea turtles as a result of intensive fisheries activities in these

key foraging sites. However, in both regions, we identified

key areas for protection that would also safeguard adult and

juvenile turtles from at least 10 other breeding sites. At

northern sites, which are primarily used by turtles in the

summer, seasonal protection measures could be introduced,

with different levels of fisheries activity being permitted in

different seasons (Hannah et al., 2002). At a national scale,

within the Ionian Sea of Greece, we reaffirm the need to

establish a large multiple use protected area, with an inte-

grated coordinated management system providing varying

levels of protection. Within this framework of small MPAs

(L�opez Ornat, 2006), six foraging and/or breeding sites

(including Zakynthos) would receive protection, which are

frequented by year-round resident males, sexually active

males shuttling between breeding sites (Schofield et al.,

2010a, b) and reproductive females conducting forays

among sites (Schofield et al., 2010a, b). Furthermore, we

recommend that protective legislation and effective manage-

ment should be strengthened in Amvrakikos Gulf, as the

existing national park primarily focuses its protection

actions in the northern section (transitional ecosystems/wet-

lands) of the marine area (see also Rees et al., 2013). To

further refine important areas for conservation planning, it

is important to assimilate all available environmental criteria

(e.g. Edwards & Richardson, 2004; Coll et al., 2010), includ-

ing areas of seasonal use and how the distribution of sea

turtle foraging sites might change over time (Hannah et al.,

2002; Ara�ujo et al., 2004).

In conclusion, our study provides a good example of a sea

turtle population with high variability in dispersal and forag-

ing habitat use, demonstrating the importance of having

large tracking sample sizes to infer core areas for protection

at an ocean basin scale.

ACKNOWLEDGEMENTS

The authors thank the National Marine Park of Zakynthos

(NMPZ) for the permission to conduct this research, and the

sponsors of the Management Agent’s termed Caretta’s Odys-

sey which spanned 2008 to 2010 for 25 transmitters. The 32

Swansea University transmitters were financed by the AXA

Research Fund, Boyd Lyon Sea Turtle Fund, British Chelonia

Group, People’s Trust for Endangered Species, Project Aware,

Swansea University and Thermadap. We thank Suzanne

Bevan, who pre-processed the MODIS SST product. We

thank the many people who provided in-water capture assis-

tance, including the NMPZ coast guards. We acknowledge

use of the Maptool program (http://www.seaturtle.org).

REFERENCES

Abdulla, A., Gomei, M., Maison, E. & Piante, C. (2008) Sta-

tus of marine protected areas in the Mediterranean Sea.

IUCN, Malaga and WWF, France., 152 p.

Agardy, T. (1994) Advances in marine conservation: the role

of marine protected areas. Trends in Ecology & Evolution,

9, 267–270.�Akesson, S. & Hedenstrom, A. (2007) How migrants get

there: migratory performance and orientation. BioScience,

57, 123–133.

Alerstam, T., Hedenstrom, A. & Akesson, S. (2003) Long-

distance migration: evolution and determinants. Oikos,

103, 247–260.

Ara�ujo, M.B., Cabeza, M., Thuiller, W., Hannah, L. &

Williams, P.H. (2004) Would climate change drive species

out of reserves? An assessment of existing reserve-selection

methods. Global Change Biology, 10, 1618–1626.

Arendt, M.D., Segars, A.L., Byrd, J.I., Boynton, J., Schwenter,

J.A., Whitaker, J.D. & Parker, L. (2012a) Migration, distri-

bution, and diving behavior of adult male loggerhead sea

turtles (Caretta caretta) following dispersal from a major

breeding aggregation in the Western North Atlantic.

Marine Biology, 159, 113–125.

Arendt, M.D., Segars, A.L., Byrd, J.I., Boynton, J., Whitaker,

J.D., Parker, L., Owens, D.W., Blanvillain, G., Quattro,

J.M. & Roberts, M.A. (2012b) Distributional patterns of

adult male loggerhead sea turtles (Caretta caretta) in the

vicinity of Cape Canaveral, Florida, USA during and after

a major annual breeding aggregation. Marine Biology, 159,

101–112.

Bentivegna, F. (2002) Intra-Mediterranean migrations of log-

gerhead sea turtles (Caretta caretta) monitored by satellite

telemetry. Marine Biology, 141, 795–800.



Block, B., Teo, S.L.H., Walli, A., Boustany, A., Stokesbury,

M.J.W., Farwell, C.J., Weng, K.C., Dewar, H. & Williams,

T.D. (2005) Electronic tagging and population structure of

Atlantic bluefin tuna. Nature, 434, 1121–1127.

Blumenthal, J.M., Solomon, J.L., Bell, C.D., Austin, T.J.,

Ebanks-Petrie, G., Coyne, M.S., Broderick, A.C. & Godley,

B.J. (2006) Satellite tracking highlights the need for inter-

national cooperation in marine turtle management. Endan-

gered Species Research, 2, 51–61.

Boyd, I.L., McCafferty, D., Reid, K., Taylor, R. & Walker,

T.R. (1998) Dispersal of male and female Antarctic fur

seals (Arctocephalus gazelle). Canadian Journal of Fisheries

and Aquatic Sciences, 55, 845–852.

Bradshaw, C.J.A., Giam, X. & Sodhi, N.S. (2010) Evaluating

the relative environmental impact of countries. PLoS ONE,

5, e10440.

Broderick, A.C., Coyne, M.S., Fuller, W.J., Glen, F. & Godley,

B.J. (2007) Fidelity and overwintering of sea turtles.

Proceedings of the Royal Society B: Biological Sciences, 274,

1533–1538.

Casale, P., Freggi, D., Basso, R., Vallini, C. & Argano, R.

(2007) A model of area fidelity, nomadism, and distribu-

tion patterns of loggerhead sea turtles (Caretta caretta)

in the Mediterranean Sea. Marine Biology, 152, 1039–

1049.

Casale, P., Abbate, G., Freggi, D., Conte, N., Oliverio, M. &

Argano, R. (2008) Foraging ecology of loggerhead sea

turtles Caretta caretta in the central Mediterranean Sea:

evidence for a relaxed life history model. Marine Ecology

Progress Series, 372, 265–276.

Casale, P., Affronte, M., Insacco, G., Freggi, D., Vallini, C.,

d’Astore, P.P., Basso, R., Paolillo, G., Abbatte, G. &

Argano, R. (2010) Sea turtle strandings reveal high anthro-

pogenic mortality in Italian waters. Aquatic Conservation:

Marine and Freshwater Ecosystems, 20, 611–620.

Casale, P., Freggi, D., Cin�a, A. & Rocco, M. (2013) Spatio-

temporal distribution and migration of adult male logger-

head sea turtles (Caretta caretta) in the Mediterranean Sea:

further evidence of the importance of neritic habitats off

North Africa. Marine Biology, 160, 703–718. doi:10.1007/

s00227-012-2125-0.

Casale, P., Broderick, A.C., Freggi, D., Mencacci, R., Fuller,

W.J., Godley, B.J. & Luschi, P. (2012) Long-term residence

of juvenile loggerhead turtles to foraging grounds: a poten-

tial conservation hotspot in the Mediterranean. Aquatic

Conservation: Marine and Freshwater Ecosystems, 22, 144–

154. doi: 10.1002/aqc.2222

Chaieb, O., Elouaer, A., Maffucci, F., Karaa, S., Bradai,

M.N., ElHili, H., Bentivegna, F., Said, K. & Chatti, N.

(2012) Population structure and dispersal patterns of log-

gerhead sea turtles Caretta caretta in Tunisian coastal

waters, Central Mediterranean. Endangered Species

Research, 18, 35–45.

Clutton-Brock, T.H. & Vincent, A.C.J. (1991) Sexual selec-

tion and the potential reproductive rates of males and

females. Nature, 351, 58–60.

Coll, M., Piroddi, C., Steenbeek, J. et al. (2010) The biodi-

versity of the Mediterranean Sea: estimates, patterns, and

threats. PLoS ONE, 5, e11842.

van Dam, R.P., Diez, C.E., Balazs, G.H., Colon, L.A.C.,

McMillan, W.O. & Schroeder, B. (2008) Sex-specific migra-

tion patterns of hawksbill turtles from Mona Island, Puerto

Rico. Endangered Species Research, 4, 85–94.

Drakare, S., Lennon, J.L. & Hillebrand, H. (2006) The

imprint of the geographical, evolutionary and ecological

context on species–area relationships. Ecology Letters, 9,

215–227.

Echwikhi, K., Jrib, I., Bradai, M.N. & Bouain, A. (2010)

Gillnet fishery-loggerhead turtle interactions in the Gulf of

Gabes, Tunisia. Herpetological Journal, 20, 25–30.

Eckert, S.A., Moore, J.E., Dunn, D.C., Van Buiten, R.S.,

Eckert, K.L. & Halpin, P.N. (2008) Modeling loggerhead

turtle movement in the Mediterranean: importance of body

size and oceanography. Ecological Applications, 18, 290–308.

Edwards, M. & Richardson, A.J. (2004) Impact of climate

change on marine pelagic phenology and trophic mis-

match. Nature, 430, 881–884.

Ferrier, S. (2002) Mapping spatial pattern in biodiversity for

regional conservation planning: where to from here?

Systematic Biology, 51, 331–363.

Fryxell, J.M., Wilmshurst, J.F. & Sinclair, A.R.E. (2004) Pre-

dictive models of movement by Serengeti grazers. Ecology,

85, 2429–2435.

Gaspar, P., Benson, S.R., Dutton, P.H., Reveillere, A., Jacob,

G., Meetoo, C., Deheck, A. & Fossette, S. (2012) Oceanic

dispersal of juvenile leatherback turtles: going beyond pas-

sive drift modelling. Marine Ecology Progress Series, 457,

265–284.

Gavashelishvili, A. & Lukarevskiy, V. (2008) Modelling the

habitat requirements of leopard Panthera pardus in west

and central Asia. Journal of Applied Ecology, 45, 579–588.

Godley, B.J., Blumenthal, J.M., Broderick, A.C., Coyne, M.S.,

Godfrey, M.H., Hawkes, L.A. & Witt, M.J. (2008) Satellite

tracking of sea turtles: where have we been and where do

we go next? Endangered Species Research, 4, 3–22.

Greenwood, P.J. (1980) Mating systems, philopatry and dis-

persal in birds and mammals. Animal Behavior, 28, 1140–

1162.

Hannah, L., Midgley, G.F. & Millar, D. (2002) Climate

change-integrated conservation strategies. Global Ecology &

Biogeography, 11, 485–495.

Hatase, H., Takai, N., Matsuzawa, Y., Sakamoto, W., Omuta,

K., Goto, K., Arai, N. & Fujiwara, T. (2002) Size-related

differences in feeding habitat use of adult female logger-

head turtles Caretta caretta around Japan determined by

stable isotope analyses and satellite telemetry. Marine Ecol-

ogy Progress Series, 233, 273–281.

Hatase, H., Omuta, K. & Tsukamoto, K. (2007) Bottom or

midwater: alternative foraging behaviours in adult female

loggerhead sea turtles. Journal of Zoology, 273, 46–55.

Hatase, H., Omuta, K. & Tsukamoto, K. (2010) Oceanic resi-

dents, neritic migrants: a possible mechanism underlying


G. Schofield et al.

foraging dichotomy in adult female loggerhead turtles

(Caretta caretta). Marine Biology, 157, 1337–1342.

Hawkes, L.A., Broderick, A.C., Coyne, M.S., Godfrey, M.H.,

Lopez-Jurado, L., Lopez-Suarez, P., Merino, S.E., Varo-

Cruz, N. & Godley, B.J. (2006) Phenotypically linked

dichotomy in sea turtle foraging requires multiple conser-

vation approaches. Current Biology, 16, 990–995.

Hawkes, L.A., Broderick, A.C., Coyne, M.S., Godfrey, M.H.

& Godley, B.J. (2007) Only some like it hot – quantifying

the environmental niche of the loggerhead sea turtle.

Diversity and Distributions, 13, 447–457.

Hawkes, L.A., Witt, M.J., Broderick, A.C., Coker, J.W.,

Coyne, M.S., Dodd, M., Frick, M.G., Godfrey, M.H.,

Griffin, D.B., Murphy, S.R., Murphy, T.M., Williams, K.L.

& Godley, B.J. (2011) Home on the range: spatial ecology

of loggerhead turtles in Atlantic waters of the USA.

Diversity & Distributions, 17, 624–640.

Hays, G.C., Fossette, S., Katselidis, K.A., Schofield, G. &

Gravenor, M.B. (2010a) Breeding periodicity for male sea

turtles: good news for conservation in the face of climate

change. Conservation Biology, 24, 1636–1643.

Hays, G.C., Fossette, S., Katselidis, K.A., Mariani, P. &

Schofield, G. (2010b) Ontogenetic development of

migration: Lagrangian drift trajectories suggest a new para-

digm for sea turtles. Journal of the Royal Society Interface,

7, 1319–1327.

Hochscheid, S., Bentivegna, F., Hamza, A. & Hays, G.C.

(2007) When surfacers do not dive: multiple significance

of extended surface times in marine turtles. The Journal of

Experimental Biology, 213, 1328–1337.

Lazar, B., Margaritoulis, D. & Tvrtkovic, N. (2004a) Tag

recoveries of the loggerhead sea turtle Caretta caretta in

the eastern Adriatic Sea: implications for conservation.

Journal of the Marine Biological Association of the UK, 84,

475–480.

Lazar, B., Casale, P., Tvrtkovic, N., Kozul, V., Tutman, P. &

Glavic, N. (2004b) The presence of the green sea turtle,

Chelonia mydas, in the Adriatic Sea. Herpetological Journal,

14, 143–147.

L�opez Ornat, A. (2006). Guidelines for the establishment and

management of Mediterranean marine and coastal protected

areas. MedMPA project, UNEP-MAP RAC\SPA, Tunis.

Luschi, P., Hays, G.C., Del Seppia, C., Marsh, R. & Papi, F.

(1998) The navigational feats of green sea turtles migrating

from Ascension Island investigated by satellite telemetry.

Proceedings of the Royal Society B: Biological Sciences, 265,

2279–2284.

Margaritoulis, D., Argano, R., Baran, I., Bentivegna, F.,

Bradai, M.N., Cami~nas, J.A., Casale, P., Metrio, G.D.,

Demetropoulos, A., Gerosa, G., Godley, B.J., Haddoud,

D.A., Houghton, J., Laurent, L. & Lazar, B. (2003) Logger-

head turtles in the Mediterranean Sea: present knowledge

and conservation perspectives. Loggerhead sea turtles (ed.

by B.E. Witherington), pp. 175–198. Smithsonian Institu-

tion, Washington.

Morbey, Y.E. & Ydenberg, R.C. (2008) Protandrous arrival

timing to breeding areas: a review. Ecology Letters, 4,

663–673.

Polovina, J.J., Uchida, I., Balazs, G., Howell, E.A., Parker, D.

& Dutton, P. (2006) The Kuroshio Extension Bifurcation

Region: a pelagic hotspot for juvenile loggerhead sea tur-

tles. Deep-Sea Research II, 53, 326–339.

Rees, A.F., Al Saady, S., Broderick, A.C., Coyne, M.S.,

Papathanasopoulou, N. & Godley, B.J. (2010) Behavioural

polymorphism in one of the world’s largest populations of

loggerhead sea turtles, Caretta caretta. Marine Ecology

Progress Series, 418, 201–212.

Rees, A.F., Margaritoulis, D., Newman, R., Riggall, T.E.,

Tsaros, P., Zbinden, J.A. & Godley, B.J. (2013) Ecology of

loggerhead marine turtles Caretta caretta in a neritic forag-

ing habitat: movements, sex ratios and growth rates. Mar-

ine Biology, 160, 519–529. doi:10.1007/s00227-012-2107-2.

Saied, A., Maffucci, F., Hochscheid, S., Dryag, S., Swayeb, B.,

Borra, M., Ouerghi, A., Procaccini, G. & Bentivegna, F.

(2012) Loggerhead turtles nesting in Libya: an important

management unit for the Mediterranean stock. Marine

Ecology Progress Series, 450, 207–218.

Schofield, G., Katselidis, K.A., Dimopoulos, P. & Pantis, J.D.

(2008) Investigating the viability of photo-identification as

an objective tool to study endangered sea turtle popula-

tions. Journal of Experimental Marine Biology & Ecology,

360, 103–108.

Schofield, G., Lilley, M.K.S., Bishop, C.M., Brown, P.,

Katselidis, K.A., Dimopoulos, P., Pantis, J.D. & Hays,

G.C. (2009) Conservation hotspots: intense space use by

breeding male and female loggerheads at the Mediterra-

nean’s largest rookery. Endangered Species Research, 10,

191–202.

Schofield, G., Hobson, V.J., Fossette, S., Lilley, M.K.S.,

Katselidis, K.A. & Hays, G.C. (2010a) Fidelity to foraging

sites, consistency of migration routes and habitat modula-

tion of home range by sea turtles. Diversity & Distributions,

16, 840–853.

Schofield, G., Hobson, V.J., Lilley, M.K.S., Katselidis, K.A.,

Bishop, C.M., Brown, P. & Hays, G.C. (2010b) Inter-

annual variability in the home range of breeding turtles:

implications for current and future conservation manage-

ment. Biological Conservation, 143, 722–730.

Seminoff, J.A., Zarate, P., Coyne, M., Foley, D., Parker, D.,

Lyon, B.N. & Dutton, P.H. (2008) Post-nesting migrations

of Galapagos green turtles, Chelonia mydas, in relation to

oceanographic conditions: integrating satellite telemetry

with remotely-sensed ocean data. Endangered Species

Research, 4, 57–72.

Shaffer, S.A., Tremblay, Y., Weimerskirch, H., Scott, D.,

Thompson, D.R., Sagar, P.M., Moller, H., Taylor, G.A.,

Foley, D.G., Block, B.A. & Costa, D.P. (2006) Migratory

shearwaters integrate oceanic resources across the Pacific

Ocean in an endless summer. Proceedings of the National

Academy of Sciences USA, 10, 12799–12802.



Shaver, D.J., Schroeder, B.A., Byles, R.A., Burchfield, P.M.,

Pe~na, J., M�arquez, R. & Martinez, H.J. (2005) Movements

and home ranges of adult male Kemps Ridley sea turtles

(Lepidochelys kempii) in the Gulf of Mexico investigated by

satellite telemetry. Chelonian Conservation & Biology, 4,

817–827.

Wallace, B.P., DiMatteo, A.D., Hurley, B.J. et al. (2010)

Regional management units for marine turtles: a novel

framework for prioritizing conservation and research across

multiple scales. PLoS ONE, 5, e15465.

Weimerskirch, H., Cuenot-Chaillet, Y.C.F. & Ridoux, V.

(1997) Alternative foraging strategies and resource alloca-

tion by male and female wandering albatrosses. Ecology, 78,

2051–2063.

Zbinden, J.A., Aebischer, A., Margaritoulis, D. & Arlettaz, R.

(2008) Important areas at sea for adult loggerhead sea tur-

tles in the Mediterranean Sea: satellite tracking corrobo-

rates findings from potentially biased sources. Marine

Biology, 153, 899–906.

Zbinden, J.A., Bearhop, S., Bradshaw, P., Gill, B.,

Margaritoulis, D., Newton, J. & Godley, B.J. (2011)

Migratory dichotomy and associated phenotypic variation

in marine turtles revealed by satellite tracking and stable

isotope analysis. Marine Ecology Progress Series, 421,

291–302.

SUPPORTING INFORMATION

Additional Supporting Information may be found in the

online version of this article:

Figure S1 Variation in sea turtle body size (CCL) with lati-

tude of foraging area (F1,60 = 15.05, r2 = 0.2; P < 0.001).

Table S1 Deployment details for the 75 tracked turtles: (a)

male (n = 38, of which five were tracked for more than one

breeding season) and (b) female (n = 37, of which one was

tracked for more than one breeding season).

Table S2a. Summary information of the foraging sites identi-

fied across the Mediterranean using adult male and female

loggerheads tracked from Zakynthos, Greece. S2b. Published

literature used to identify overlap in foraging sites with Zak-

ynthos turtles (A) based on tracking datasets and (B) based

on genetic data.

BIOSKETCH

Gail Schofield is a behavioural ecologist, whose work

focuses on applying scientific research to conservation prac-

tice using direct and indirect techniques, such as satellite tele-

metry and videography. Her work has investigated the effects

of various parameters effect both small and large scale move-

ment patterns of vertebrates, including breeding, foraging and

migration ecology. This work constituted a major collabora-

tive effort combining data assimilated by GS and colleagues

at Swansea University with the National Marine Park of

Zakynthos Management Agency (http://www.nmp-zak.org/).

Further information about GS and publications can be found

at http://scholar.google.gr/citations?user=JuAIkOoAAAAJ&h-

l=en and http://www.swan.ac.uk/bs/turtle/hays_publications2.

htm.

Author contributions: G.S., S.F. and G.C.H. conceived the

study; A.D.K. obtained the funding for the 25 NMPZ trans-

mitters; G.C.H., G.S. and S.F. obtained the funding for the

32 Swansea University transmitters; G.S., S.F. and M.K.S.L.

conducted the fieldwork attaching all 57 transmitters; G.S.,

K.A.K. and A.D. compiled the data; G.S. and G.C.H. led the

data analyses and interpretation with contributions from all

authors; A.L. conducted the GIS analysis; G.S. wrote the

paper with contributions from all authors.

Editor: Reuben Keller


G. Schofield et al.

Satellite tracking large numbers of individuals to infer population level dispersal and core areas...

Documents

Transcript of Satellite tracking large numbers of individuals to infer population level dispersal and core areas...