MARINE ECOLOGY PROGRESS SERIESMar Ecol Prog Ser

Vol. 433: 261–272, 2011
doi: 10.3354/meps09152

Published July 18

Post-capture movements of loggerhead turtles
in the southeastern Pacific Ocean
assessed by satellite tracking
Jeffrey C. Mangel1, 2,*, Joanna Alfaro-Shigueto1, 2, Matthew J. Witt2,
Peter H. Dutton3, Jeffrey A. Seminoff3, Brendan J. Godley2
1

Pro Delphinus, Octavio Bernal 572-5, Lima 11, Peru
Center for Ecology and Conservation, University of Exeter, Penryn, Cornwall TR10 9EZ, UK

2
3

Protected Resources Division, Southwest Fisheries Science Center, National Marine Fisheries Service,
NOAA, La Jolla, California 92037, USA

ABSTRACT: The post-capture movements made by loggerhead sea turtles Caretta caretta in thesoutheastern Pacific Ocean were monitored from 2003 to 2007. Fourteen loggerhead turtles were fitted with satellite transmitters and released off the coast of Peru. All turtles were juveniles (curved
carapace length range: 40.5 to 68.5 cm) incidentally captured by small-scale longline fishing vessels
from southern or central Peru. Track durations were highly variable (mean ± SD: 143 ± 90 d; range: 8
to 297 d) with no clear signs of immediate post-release mortality. Upon release, all turtles moved offshore beyond the continental shelf. Eight of 11 turtles tracked for > 60 d had final displacements of< 750 km, suggesting that loggerhead turtles often maintain extended residency in these waters andthat this area is an important foraging zone for loggerhead turtles of southwest Pacific origin. Satellite
tracks also showed a substantial overlap of areas used by turtles with known Peruvian longline fishing effort. Turtles spent 75% of their time within the area fished by this fleet (based upon observedsets). This suggests that turtles are vulnerable to fishery interactions and that bycatch mitigation measures should be employed to minimize fishery impacts on loggerhead turtles. The loggerhead turtles
tracked during this study spent ca. 51% of their time in Peruvian waters, 39% in international waters
and 9% in Chilean waters, which emphasizes the need for a multinational approach to sea turtle conservation and fisheries management in the region.
KEY WORDS: Caretta caretta · Peru · Chile · Small-scale fisheries · Bycatch · Habitat · Governance
Resale or republication not permitted without written consent of the publisher

Many large marine vertebrates such as sharks, sea
turtles, seabirds and marine mammals have complex
life histories that encompass wide spatiotemporalscales. This situation places them at repeated risk ofinteraction with multiple anthropogenic threats thathave been associated with the population declines
seen in many species (e.g. Tasker et al. 2000, Baum etal. 2003, Read et al. 2006, Wallace et al. 2010). Keyamong these threats is incidental capture (bycatch) inmarine fisheries gear (e.g. longlines and driftnets)

operating in pelagic zones (Hall et al. 2000). The loggerhead sea turtle Caretta caretta, which is foundworldwide in temperate and tropical waters (Bolten2003), is one such species affected by bycatch and is in
decline in many parts of its range (Lewison et al. 2004,
Wallace et al. 2008).
The life history of loggerhead sea turtles operates at
oceanic scales, with nesting sites, juvenile developmental habitats and adult foraging grounds for thesame population often separated by thousands of kilometers (Bolten 2003). In the North Pacific Ocean, loggerhead turtle nesting, which is confined to Japan, has*Email: jcm210@exeter.ac.uk© Inter-Research 2011 · www.int-res.com

INTRODUCTION

262

Mar Ecol Prog Ser 433: 261–272, 2011

been linked through genetic analyses and satellite
tracking to aggregations of juveniles and subadults
found in the central and eastern Pacific (Bowen 1995,
Nichols et al. 2000, Polovina et al. 2006, Howell et al.
2010). In the South Pacific Ocean, decades of intensemonitoring in eastern Australia has helped in defining
many aspects of the nesting and oceanic ecology ofloggerhead turtles in the western South Pacific region
and in describing declining trends in abundance ofthat population (Limpus & Limpus 2003a). However, it
was not until 2004 that the species was confirmed in
the southeastern Pacific Ocean (SEP) through a combination of onboard and shore-based fisheries monitoring (Alfaro-Shigueto et al. 2004). Genetic studies haveshown that the juvenile loggerhead turtles found in the
SEP originate from Australian and New Caledonian
rookeries (Alfaro-Shigueto et al. 2004, Boyle et al.
2009). Additional reports now also confirm the occurrence of loggerhead turtles off Ecuador and Columbia(Alava 2008) and Chile to a latitude of 32° S (Donoso &Dutton 2010). Alfaro-Shigueto et al. (2008) report primarily small- to medium-sized juveniles and subadultsized turtles found off the Peruvian coast (curved carapace length [CCL] range: 35.9 to 86.3 cm) while Donoso& Dutton (2010) and Alava (2008) reported similarsized, and perhaps somewhat larger, loggerhead turtles
captured by industrial swordfish longline vessels inChile (CCL range: 47 to 84 cm) and small-scale longline
vessels in Ecuador (CCL range: 50 to 80 cm). However,each of these studies was fishery dependent and thus
may only represent those sizes of turtles vulnerable tocapture by these particular fishing gears.
The wide dispersal of loggerhead turtles combinedwith their omnivorous feeding habits (which result inopportunistic foraging on fishing bait), leads to highlevels of bycatch in coastal and pelagic fisheries, particularly near-surface longlines (Lewison et al. 2004,
Peckham et al. 2008, Tomás et al. 2008, Wallace et al.
2008). These fishery interactions have led to sizeable
takes of loggerhead turtles globally (Lewison et al.
2004, Gilman et al. 2006, Wallace et al. 2008). As aresult of this situation, the need to improve our understanding of the pelagic life stages of sea turtles andtheir interactions with fisheries have been identified as
research priorities (Hamann et al. 2010).
There has also been growing awareness of the needto assess and address the issue of post-release mortality, that is, the potential for animals to die from fisheryrelated injury after being released from fishing gear
(Bjorndal et al. 2003, Hays et al. 2003). Such information is necessary in determining fishery-related morality rates but is particularly challenging to evaluate
without a means to track animals after their release.
Assessments of post-release mortality based uponsatellite tracking of released animals has been

attempted with sea turtles, including loggerhead turtles (Chaloupka et al. 2004, Swimmer et al. 2006, Sasso& Epperly 2007, Howell et al. 2010, Snoddy & Southwood Williard 2010) as well as with other marine
megafauna including blue sharks Prionace glauca(Moyes et al. 2006) and blue marlin Makaira nigricans(Graves et al. 2002).
The SEP (Fig. 1) is 1 of 4 eastern boundary current
systems on earth and is a highly dynamic and productive marine ecosystem (Carr 2001). It is dominated by
the Humboldt Current System (HCS), which is a windinduced coastal upwelling system. Winds in this system move along the Peruvian coast toward the equator
before turning westward into the Pacific Ocean andresult in year-round, nutrient-rich upwelling (Bakun &Weeks 2008). This cold, nutrient-rich coastal upwellingyields high levels of primary and secondary productivity and makes the HCS one of the world’s most productive marine ecosystems (Carr 2001, Taylor et al. 2008).
Aside from supporting a considerable abundance offlora and fauna, the HCS also supports large fishingindustries (Bertrand et al. 2004, Jahncke et al. 2004,
Thiel et al. 2007). Indeed, ~16 to 20% of global annual
fish production is derived from the region (Heileman etal. 2009). There are also very large and dispersed
small-scale fleets, with ~40 000 small-scale vessels
fishing the coastal and offshore waters of Ecuador,
Peru and Chile (Arriaga & Martinez 2003, OECD 2009,
Alfaro-Shigueto et al. 2010). Bycatch of seabirds,
cetaceans and sea turtles, including loggerhead turtles, has been documented in these small-scale fisheries in Peru (Awkerman et al. 2006, Alfaro-Shigueto
et al. 2010, Gilman et al. 2010, Mangel et al. 2010). This
is of concern given the 86% decline in loggerhead turtle nesting reported for eastern Australia nesting
beaches over a 23 yr period, despite local conservation
efforts including nesting beach and in-water protectedareas, and hatchling management and controls onsome fisheries known to affect the species (Limpus &Limpus 2003b).
The purpose of the present study was to improve ourunderstanding of the ecology of loggerhead turtles in
the SEP region. More specifically, we were interestedin (1) assessing loggerhead turtle at-sea movements
and distribution, (2) determining their habitat selectionand (3) gaining preliminary insights into the effects of
injury and potential for post-hooking mortality.

MATERIALS AND METHODS
Turtle characteristics. Fourteen loggerhead turtles
were fitted with satellite transmitters between March
2003 and February 2007 (Table 1). The turtles wereincidentally entangled or hooked by longline gear set

Mangel et al.: Loggerhead movements in the southeastern Pacific263

Shigueto et al. 2010). The precise locationof capture is known for 11 of the 14 turtles.
The study animals ranged in size from 40.5
to 68.5 cm CCL, measured from nuchal
notch to posterior most tip, and were thusclassified as juveniles, as reported by
Alfaro-Shigueto et al. (2008).
The turtles used in our study were captured by collaborating fishers during thefinal set of each fishing trip to allow prompt
return to port for transmitter attachment.
To further minimize time in captivity, turtles were released within ~30 min of thecompletion of transmitter attachment several kilometers offshore, typically within
24 h of their original capture. All loggerhead turtles used in the study were active
at time of capture (not moribund or comatose) and fishers were given detailed
instructions on how to safely handle andmaintain the turtles aboard. All visible fishing hooks and entangling line were removed from the turtles before release.
We assigned an injury score to each turtle based upon the location and severity ofany visible injuries sustained during thecapture process following criteria described by Chaloupka et al. (2004). We
used a 3 point injury scale in which level 1
referred to turtles with external injuries
only (including those that were only entangled in longline branchlines), level 2 indicated minor injuries to the mouth cavity or
lower mandible and level 3 indicated more
severe injuries including turtles deeply
hooked in the esophagus or soft palate.
Fig. 1. Caretta caretta. All turtle track locations (turtles tracked for 60+ d) bylevel of injury and showing a polygon of longline fishing effort monitored This examination was primarily external infrom 8 ports (242 trips, 1771 sets) collected by fisheries observers from 2000 to nature (except in those cases of level 3 in2007 (Alfaro-Shigueto et al. 2008). Color shading of tracks indicates injury juries) and was not meant as an overall turscores. Red: injury score 1 (n = 7); blue: injury score 2 (n = 4); green = injury tle health assessment (as in Heithaus et al.
score 3 (n = 3). The termination points of tracks of injury scores 2 and 3 are2007), but rather as a scoring of the injuries
also marked with colored squares and triangles, respectively. Tracked loggerhead positions were within fishing area boundaries from 75 ± 33% of the time associated with the turtle’s capture.
(range, 13 to 100%) (500 and 2000 m bathymetric contours are also shown).
Transmitter application and data analyInset shows the predominant current patterns (arrows) of the southeastern sis. We used satellite transmitters (platform
Pacific Ocean. MCP: minimum convex polygon
transmitter terminals [PTTs] from Telonics
and from Wildlife Computers) in the study(Table 1). We attached PTTs to the anterior central
from small-scale fishing vessels targeting sharks
scutes of the carapace using the fiberglass cloth and(mainly blue sharks and short-fin mako sharks Isuruspolyester resin method described by Balazs et al. (1996)
oxyrinchus) and dolphin fish Coryphaena hippurusor with PowerFast™ 2-part marine epoxy (Coyne et al.
in oceanic waters. The vessels operated out of the ports
2009; Table 1). PTTs had one of 2 laddered duty cyclesof Ilo (71.33° W, 17.63° S) and Pucusana (76.78° W,(Table 1) where Duty Cycle 1 was set to transmit 24 h on
12.48° S) in southern and central Peru, respectively(Month 1), 6 h on and 13 h off (Months 2 to 3) and 6 h on
(Fig. 1). These vessels used Mustad classic J type fishand 25 h off (>Month 3). Duty Cycle 2 was set to transing hooks with a 10° offset and ranged in size from 1 tomit 24 h on (Month 1), 24 h on and 48 h off (Months 2
3 (for a detailed description of the fishery see Alfaro-

248 | 71
89 | 85
118 | 55
249
229
593
124
117
126

228 | 5142 | 8187 | 8162 | 18
48 | 458 | 3498
245

25 | 3101 | 7to 3), 24 h on and 72 h off (Months 4 to 5) and 24 hon and 96 h off (>Month 6).
Positional data were received from Service
ARGOS and managed with the Satellite Tracking and Analysis Tool (STAT, Coyne & Godley2005). Argos positional data are accompanied
by indicators of their spatial accuracy where
positions assigned location Class 3 are of greatest accuracy (< 350 m), and those with location
Class 0 are the least accurate (>1 km). Positions
assigned Classes A and B have no estimateof their accuracy. These data were subjected to
a combination of filtering procedures to eliminate potential outliers. Argos-derived location
Classes 3, 2, 1, 0, A and B for turtle positions
were retained for this analysis (Witt et al. 2010)
and filtered based upon speed (> 5 km h–1
excluded, Luschi et al. 1998) and turning angle(< 25° excluded). Tracks were also reduced to
one location per day to produce an unbiased
data set of all environmental and behavioral
variables (see De Solla et al. 1999 for further discussion of handling autocorrelation in animal
movement data sets). For days when more than
one location was obtained, the position of highest quality Argos location class was retained. If
multiple positions for a given day were of thesame highest quality, the location nearest to
12:00 h local time was selected. Following track
filtering, the first 7 d of each track after release
were eliminated to minimize any artifact introduced by transporting and releasing turtles
relatively close to the coast. We used ArcMap
9.2 (ESRI) to display turtle positions and the
Hawth’s Tools Extension (www.spatialecology.
com/htools) to create minimum convex polygonsof longline fishing effort.
Longline fishing effort data detailed in Alfaro
Shigueto et al. (2008) was used to examine theoverlap with the turtles tracked in this study.
Trained onboard observers collected data on
fishing effort and catch, including set positions(using handheld GPS), aboard fishing vessels
from 8 ports (242 trips, 1773 sets) for the years
2004 to 2007. This is the same fleet from which
the loggerhead turtles in this study were captured. A polygon of Peruvian fishing effort was
created by combining minimum convex polygons of fishing effort from the 8 ports.
Satellite tracking data were compared withbathymetry and sea surface temperature (SST)
data. Bathymetric values were obtained from the
Global Bathymetric Chart of the Oceans(GEBCO, www.gebco.net; IOCIHO 2003). An
8 d composite 4 km spatial resolution Nighttime

Mar Ecol Prog Ser 433: 261–272, 2011

394
399
295
100
39
55
20
13
100
100
98
100
100
100
100
70
61
2
27
15
67
93
67
41
32
23
37
9
0
0
64
82
0
7
4
0
0
0
0
11
63
75
0
3
1
16
73
78
29
7
33
59
68
66
0
16
100
97
35
2.00
3.52
4.18
7.87
5.74
4.57
5.10
5.55
4.71
7.74
7.53
7.50
5.96
7.04
446
479
593
2 337
1 658
672
581
522
372
395
361
60
721
1 752
223
136
142
297
289
147
114
94
79
51
48
8
121
249
1
1
1
3
3
1
1
1
1
2
2
3
2
2
1
1
1
1
1
1
1
1
2
2
2
2
1
1

PTT
model

CC1
CC2
CC3
CC4
CC5
CC6
CC7
CC8
CC9
CC10
CC11
CC12
CC13
CC14

25 Mar 03
24 Oct 03
24 Oct 03
7 Apr 05
14 Jul 05
3 Feb 06
5 Feb 06
14 Nov 06
13 Jan 07
13 Jan 07
13 Jan 07
16 Jan 07
5 Feb 07
8 Feb 07

ST-18
ST-18
ST-18
ST-20
SDR-T16
ST-18
ST-18
ST-20D
SPOT5
SPOT5
SPOT5
SPOT5
A-1010A-1010

F
F
F
F
F
F
F
F
F
P
P
P
P
P

Maritime zone (%) Time in
Capture to Closest approach
Peru Chile High fishingreleaseto captureseas zone (%) distance (km)(km) | (d)Deployment Portdate

Attachment Duty Injury
Track
MaximumDmethodcycle score duration
D
rate
(d)
(km)
(km d–1)
Turtle CCL
no.
(cm)

I
I
I
I
I
P
P
P
I
I
I
I
I
I
63.2
64.0
68.0
61.5
65.9
56.5
54.2
68.5
65.5
64.1
40.5
60.8
51.3
65.0

264

Table 1. Caretta caretta. Summary of environmental and tracking variables for 14 loggerhead turtles captured as bycatch off the coast of Peru. Ports are Ilo (I) and Pucusana(P). Platform transmitter terminal (PTT) models SPOT5 and SDR-T16 were obtained from Wildlife Computers, while the remainder (ST-18, ST-20, ST-20D, A1010) were from
Telonics. Attachment methods referred to used fiberglass resin (F) or Powerfast epoxy (P). Duty cycle 1 was a laddered program set to transmit 24 h on (Month 1), 6 h on and
13 h off (Months 2 to 3) and 6 h on and 25 h off (>Month 3). Duty cycle 2 was a laddered program set to transmit 24 h on (Month 1), 24 h on and 48 h off (Months 2 to 3), 24 hon and 72 h off (Months 4 to 5) and 24 h on and 96 h off (>Month 6). Injury score 1: external injuries (including entanglement); injury score 2: minor internal injuries to mouth
or lower mandible; injury score 3: severe injuries due to deep hooking. D refers to displacement (Columns 10 and 11). CCL = curved carapace length

Mangel et al.: Loggerhead movements in the southeastern Pacific(4 micron) Sea Surface Temperature Dataset from the
MODIS-Aqua satellite was used to determine SST at
the location of each turtle’s daily position (Feldman &McClain 2009). Maritime political boundaries wereobtained from the Flanders Marine Institute maritime
boundaries geodatabase v. 5.0 (www.vliz.be). Timewithin a given boundary was calculated by tabulating
entry and exit dates and times from the tracking data
and assigning those time periods to their appropriate
polygons. Any period > 7 d that could not be accounted
for owing to lack of positions was discarded (2% ofcases), but times < 7 d were attributed to the dominant
polygon (7% of cases). Data regarding environmental
variables, as well as speed of movement, displacementfrom release location (including 7 d release period) andpolitical boundaries were limited to turtles tracked for
60 d or more (n = 11). Swim speeds are reported as‘minimum overall average’ since our speed calculations assume straight line travel between consecutive
positions. Descriptive statistics are presented as mean
± SD.

RESULTS
Environmental variables
After their release, all turtles returned to oceanic
waters (Fig. 1) and did not appear to return to coastal
waters (< 200 m). The overall mean depth of the waters
occupied was 4286 ± 376 m (range of means: 3392 to
4704 m, median = 4352 m, n = 11). The average SST
was 21.1 ± 2.2°C (range of means: 16.2 to 23.8°C,
median = 21.6°C, n = 11; Fig. 2), with only 4% of SST
values being <15°C.

Fig. 2. Caretta caretta. Pooled monthly sea surface temperature (SST) for all turtles tracked for > 60 d (n = 11)

265

Track durations
Track durations ranged from 8 to 297 d (mean duration: 143 ± 90 d, median = 129 d, n = 14; Table 1). The
minimum overall average swim speed was 0.70 ±0.11 km h–1 (range: 0.57 to 0.90 km h–1, median =0.66 km h–1, n = 11). There was no effect of turtle sizeon track duration (randomization test with 10 000 iterations and within and between group randomization:
2-tailed p = 0.96; Fig. 3a). Likewise, there was no effectof level of injury upon track duration (Randomization
test: 2-tailed p = 0.99; Fig 3b). There was also no effectof either turtle size (Randomization test: 2-tailed p =0.96; Fig 3c) or injury score on minimum overall average swim speed (Randomization test: 2-tailed p = 0.12;
Fig 3d).
The number of uplinks received per day for eachturtle was also examined because an increase indaily signals received could indicate that an animal
is floating injured or dead at the surface (Hays et al.
2007). There was no evidence of an increase in daily
signals received for any of the tracked turtles (Fig. S1in the supplement at www.int-res.com/articles/suppl/
m433p261_supp.pdf). We also reviewed the battery
voltage information for the 4 SPOT5 tags (the only
tags for which this information was available) toassess transmitter battery life as a possible reason for
termination of the tracks for those turtles. There wasno sign of voltage declines sufficient to halt transmission toward the end of the track periods for any of
the 4 tags.

Displacement
Maximum displacement ranged from 372 to 2337 km(mean: 921 ± 667 km, median = 593 km; Table 1, Fig. 1& Fig. S3 in the supplement). Eight of the 11 turtles
with tracks lasting > 60 d (track duration range: 79 to
223 d) had a final displacement of < 750 km. The
remaining 3 turtles had track durations ranging from
249 to 297 d and maximum displacements from 1607 to
2337 km.
There was no effect of turtle size on displacement
rate (Randomization test: 2-tailed p = 0.64; Fig. 3e), nor
was there an effect of capture to release distance on
maximum displacement (r = 0.07; Fig. S2a in the supplement). However, there was an effect of level of
injury upon displacement rate (Randomization test: 2tailed p = 0.002; Figs. 3f & S3) in which turtles withinjury scores of 2 and 3 had greater displacement rates
than those with an injury score of 1.
Logistical constraints meant that turtles could neither
be fitted with transmitters in situ nor returned tocapture location for release. The average distance266

Mar Ecol Prog Ser 433: 261–272, 2011

Fisheries and governanceAlthough captured and released in
Peruvian waters, our study turtles also
moved within Chilean and international waters during tracking periods(Peru: mean = 51 ± 29%, median =59%, range for individuals = 7 to 97%;
Chile: mean = 10 ± 24%, median =1%, range = 0 to 82%; international
waters: mean = 39 ± 30%, median =32%, range = 0 to 93%; Table 1, Fig.
1). The combined tracks of all turtles
covered an area of ~2500 km from east
to west and 1600 km from north tosouth. There was also a large overlapof turtle movements with longline fishing areas. Turtles spent 75 ± 33%(range: 13 to 100%, median = 99%) of
their time within previously defined
Peruvian small-scale longline fishinggrounds (Alfaro-Shigueto et al. 2008).
There was no effect of turtle size ontime spent within the fishing grounds(Randomization test: 2-tailed p = 0.86;
Fig. 3g).

DISCUSSION
This work offers insights into postcapture movements of loggerhead turtles in the SEP and represents the firstwork of its kind with sea turtles in theregion. As such, while based upon arelatively small sample, it provides avaluable point of comparison with simFig. 3. Caretta caretta. Track durations, minimum overall average swim speeds,
ilar studies of conspecifics elsewheredisplacement rates and time within fishing grounds minimum convex polygon
and can help inform regional and(MCP) grouped by turtle size (curved carapace length, CCL) and injury scoreglobal efforts to better understandfishery impacts on sea turtles (Lewison
between capture and release locations was 261 ±et al. 2004, Blumenthal et al. 2006, Wallace et al. 2008,
153 km, (range: 98 to 593 km, median = 245 km, n =McClellan et al. 2009, Alessandro & Antonello 2010)11), but there was no correlation between capture toand their post-release mortality (Bjorndal et al. 2003,
release distance and distance traveled after 1 mo from
Hays et al. 2003, Chaloupka et al. 2004, Swimmer et al.
the release date (r = 0.02, p = 0.96; Fig. S2b). There was2006, Sasso & Epperly 2007).
no clear evidence of high precision homing per se
although turtles approached to within 119 ± 75 km(range of minimum distances: 25 to 248 km, median =Environmental factors
101 km, n = 11) of their capture location and did so 34± 33 d post-release (range: 3 to 85 d, median = 18 d)
Our work indicates that many of these turtles were(Table 1). As would be expected, there was a correla‘resident’ in the waters off Peru and Chile, where theytion between capture to release distance and nearest
maintained a pelagic lifestyle for the duration of trackapproach to capture location (r = 0.66, p < 0.05;
ing. Turtles spent > 97% of their time in waters in
Fig. S2c).
excess of 1000 m depth. Moreover, 8 of 11 turtles had

Mangel et al.: Loggerhead movements in the southeastern Pacificfinal displacements of < 750 km from their release point
even though track durations extended up to 223 d.
These results, while based upon instrumented animals
released at locations distinct from their site of capture,
support findings from other regions indicating thatjuvenile loggerhead turtles may be actively selecting
key pelagic habitats and are not simply passively
distributed by ocean currents (Polovina et al. 2006,
Monzón-Argüello et al. 2009, Hays et al. 2010, McCarthy et al. 2010). Furthermore, given the sizes of turtles in this study, this would also be consistent with atransition by juvenile loggerhead turtles from passiveto active swimmers at ~40 to 60 cm straight carapace
length, as has been reported in the Atlantic Ocean andMediterranean Sea (Bolten 2003, Cardona et al. 2005,
Revelles et al. 2007). However, 3 loggerhead turtles,
nos. CC4, CC5 and CC14, did make relatively long
movements both north and west, which match the general surface current patterns in the region (Fig. 1).
Therefore, loggerhead turtle movements may comprise a combination of active station holding and passive current-driven drifting (Cardona et al. 2005, Hayset al. 2010).
Studies off the Baja California Peninsula indicatethat juvenile loggerhead turtles may take up residency
for extended periods before returning to the western
Pacific Ocean (Nichols et al. 2000, Peckham & Nichols
2003, Seminoff et al. 2004, Etnoyer et al. 2006). Ourfindings suggest that a similar scenario occurs in thewaters off Peru and northern Chile. Moreover, as has
been observed in several studies of juvenile loggerhead turtles in the Mediterranean Sea, the animals inour study appeared to avoid the waters of the continental shelf (Cardona et al. 2005, Revelles et al. 2007,
Monzón-Argüello et al. 2009). This observation is reinforced by similar findings by Donoso & Dutton (2010)
who report loggerhead turtles in pelagic waters offshore from northern Chile. Given the size class of turtles in the present study and for the region (AlfaroShigueto et al. 2008), which is primarily the oceanic
juvenile stage (Bolten 2003, Limpus & Limpus 2003a),this may be as expected. The findings of Howell et al.
(2010) that juvenile loggerhead turtles in the central
North Pacific Ocean spent > 90% of their time in theupper 15 m of the water column supports the notion ofa pelagic foraging lifestyle for this life history stage inthis species. Furthermore, if these juvenile turtles havepoorly developed diving abilities (Bolten 2003, Cardona et al. 2005, Revelles et al. 2007) then they would
not be able to exploit benthic prey found over the shelfand may therefore specialize in pelagic prey, similar to
Baja California where the loggerhead turtle population
feeds primarily or exclusively upon pelagic red crab
Pleuroncodes planipes (Nichols et al. 2000, Peckham &Nichols 2003).

267

The mean SST of 21.1 ± 2.2°C experienced by theseturtles was well within their thermal tolerance (Witherington & Ehrhart 1989, Coles & Musick 2000, Milton &Lutz 2003), but the minimum SST experienced by someindividuals reached <15°C on several occasions andcould therefore be approaching the species’ lower
thermal tolerance (Coles & Musick 2000, Milton & Lutz
2003). As Howell et al. (2010) note, however, this lower
limit may be better considered as a species preference
and less as an absolute value. But these cool temperatures do suggest the potential for seasonal north–south
movements, as seen in the western Atlantic Ocean(Coles & Musick 2000, Hawkes et al. 2007, Mansfield
et al. 2009) and Mediterranean Sea (Bentivegna et al.
2007), that in cooler months probably bring loggerhead
turtles that have been recorded in waters off northern
Chile (Donoso & Dutton 2010) north into the relatively
warmer waters of Peru. It is also interesting to note that
Donoso & Dutton (2010) report an increase in loggerhead turtle bycatch associated with an incursion of a
21°C warm zone for the year 2001, and also found abimodal association of SST (18 and 21°C) with theoccurrence of loggerhead turtles off Chile. This coincides closely with the mean SST for the loggerhead turtles tracked in our study and with findings in the central North Pacific Ocean that loggerhead turtle bycatchby the Hawaii-based longline fleet was highest whensetting at oceanic fronts of 17 and 20°C (Polovina et al.
2000). That loggerhead turtles may aggregate inwaters of certain temperatures may also help explain
their absence from continental shelf waters in Peru.
These areas are dominated by cold, coastal upwelling
waters ranging from 15 to 17°C in the winter and 15 to
19°C in the summer months (Bertrand et al. 2004). The
apparent avoidance of the continental shelf by loggerhead turtles in our study may therefore be driven by
one or more of the (possibly related) drivers of avoidance of cold coastal waters, active selection of preferred foraging habitat or lower risk of predation(Bolten 2003, Hawkes et al. 2007, Eckert et al. 2008).
Additional studies to further detail loggerhead turtle
prey species and foraging behavior in the SEP would
help resolve this question.

Fisheries and governance
The turtle movements we describe overlapped withthe area operated by the Peruvian small-scale longline
fishery (Alfaro-Shigueto et al. 2008; our Fig. 1). Indeed,
they fell within the fishing grounds of vessels monitored from 8 ports for 75% of their track durations andone-half of the study turtles spent the entire track
period within the fishing zone. This profoundly underestimates the extent of overlap with this one fishery268

Mar Ecol Prog Ser 433: 261–272, 2011

since it operates from at least 19 ports and sets an estimated 80 million hooks per annum (Alfaro-Shigueto etal. 2010). Alfaro-Shigueto et al. (2010) also note that
the Peruvian small-scale longline fleet sets their mainline at the ocean surface. Therefore, if juvenile loggerhead turtles spend > 90% of their time within the upper
15 m, as has been reported in the central North Pacific
Ocean (Howell et al. 2010), then they have a heightened risk of interacting with this fishing gear. There
are, in addition, other fisheries such as driftnets, industrial purse-seines, and longline fleets in international
waters that have not been assessed but are of concern
because of their potential for interactions with loggerhead turtles in the region.
Chaloupka & Limpus (1997, 2001) have reported on
fisheries in the western Pacific Ocean that have bycatchof loggerhead turtles. But it is now clear that at least
some of the loggerhead turtles from the Australian and
New Caledonian stocks spend extended periods of timeoutside the western Pacific region. Research has shownthat loggerhead turtle maturation, and the oceanic
movements that accompany it, may take decades, withage at maturity estimates ranging from 10 to > 30 yr(Zug et al. 1995, Parham & Zug 1997, Chaloupka 1998,
Bjorndal et al. 2000, Bjorndal & Bolten 2001, Casale etal. 2009). This implies extended periods, possibly
decades, in a given life stage and its accompanying
habitat during which pelagic juveniles in particular are
exposed to contact with the other fisheries operating ininternational waters. While there is some information
for the central North Pacific Ocean for loggerhead turtle interactions with the Hawaii-based longline fleet,similar information is absent for the central South
Pacific. However, Domingo et al. (2010) observed a
bycatch of loggerhead turtles by Uruguayan-flagged
vessels operating in this region. Donoso & Dutton (2010)
document loggerhead turtle interactions with the
Chilean industrial swordfish longline fishery, but also
note the lack of information on other fleets in the area,
including the Spanish longline fleet operating out ofsouthern Peru. Peckham et al. (2007, 2008) have shownfor the North Pacific region that fisheries impacts onloggerhead turtles, including small-scale (or artisanal)
fisheries, can be severe. Likewise, in other regions andwith other sea turtles species, similar, but not fully
understood, trends of prolonged exposure to fisheryinteractions, including small-scale fisheries, have beenreported (Lewison et al. 2004, Alfaro-Shigueto et al.
2007, Casale 2010, Wallace et al. 2010). There is clearlya need for a full, detailed assessment of bycatch andpotential mitigation measures in the Peruvian smallscale fleet as well as the full suite of substantial industrial and small-scale fisheries operating in the region,
especially given the rapid and sustained decline of thisspecies in Australia (Limpus & Limpus 2003b).

Injury effects
One of the objectives of this study was to use satellite
tracking movement data to gain insights into theeffects of injury to bycaught sea turtles. We found noeffect of injury on track duration. However, there
appears to have been an effect of injury on the rate ofdisplacement. Turtles we scored as having minor orsevere injuries (scores 2 and 3) displaced at a much
faster rate than turtles with only external injuries(score 1). The reason for this difference is not clear.
Turtles with the fastest displacements tended to movein the same general direction as main surface currents
in the region (Fig. 1 inset) so they could be exhibitingsome passive drifting. But the long duration and characteristics of the tracks (i.e. battery voltage, uplinks perday) suggest that injuries were not fatal. We also
acknowledge that the turtles in this study may have
had pre-existing injuries that were not visible oraccounted for in our ranking. Thus our results, while
indicative of a turtle’s injury status, do not represent acomplete understanding. Similar to the findings ofHowell et al. (2010) 2 of our longest track durations
came from animals we categorized as having severe
injuries. Sasso & Epperly (2007), reporting on juvenile
loggerhead turtles in the North Atlantic Ocean, also
observed that lightly hooked loggerhead turtles intheir study had a similar survival rate to uninjured,control turtles. While acknowledging the small sample
size of the present study, these results suggest that loggerhead turtles are able to survive for extended periods with injuries, including severe injuries. Or theymight indicate that our understanding of what entails aminor or severe injury to a sea turtle is incomplete. One
transmitter failed after only 8 d but could not be attributed to death of the turtle, nor could death be attributed to any of the remaining turtles, which transmitted
from 48 to 297 d. Use of PTTs or pop-up satellitearchival tags (PSAT) with dive data or depth sensors
could help investigators make more informed determinations, but still do not provide clarity in revealing aturtle’s fate (Chaloupka et al. 2004, Swimmer et al.
2006). Future studies in this fishery should determine
the prevalence of entanglements as well as minor andsevere hookings of turtles in order to help evaluate
their likelihood of survival and the relative risk posedby the fishery. The effects of sublethal injuries alsoneed to be explored further as these could lead to
reduced fitness as a result of tissue damage, infection,
impaired feeding or swimming, or lead to a greater riskof predation (Watson et al. 2005, Sasso & Epperly
2007). Such effects may be particularly important inareas where turtle habitat strongly overlaps fishinggrounds and turtles thus may face repeated capture
and injury. Studies of longline fisheries bycatch of log-

Mangel et al.: Loggerhead movements in the southeastern Pacificgerhead turtles in the region do indicate that the
majority of bycaught turtles are released alive (AlfaroShigueto et al. 2008, Donoso & Dutton 2010), as doreports of longline fisheries in other regions (Kotas etal. 2004, Gilman et al. 2007, Casale 2010). This situation could be further improved through fisher training
in sea turtle safe handling and release methods and theadoption of bycatch mitigation measures such as theuse of circle hooks or mackerel type bait, which havebeen shown to reduce sea turtle bycatch and injury
type and severity in other fisheries (Watson et al. 2005,
Gilman et al. 2007, Yokota et al. 2009).
The pelagic distribution of loggerhead turtles observed in the present study highlights the challenges ofresearch on this species in the SEP region, and generally of other highly mobile, pelagic species. Monitoring
through the use of onboard observers on fishing vessels has provided valuable information on size classes
and distribution (Alfaro-Shigueto et al. 2004, 2008). But
this type of fishery-dependent data does not necessarily describe the full ecology of the species in the region.
Here we have reported on the movements of loggerhead turtles bycaught by small-scale longline fishingvessels. While we have limited our analyses to only
those turtles that have tracks of 60 d or more (as ameans to control for potentially aberrant behavior by
injured animals), it is possible that these tracks do not
fully represent the normal habitat or behavior of thespecies in the region. We also recognize that othervariables could have an effect on track duration (e.g.
attachment method, location of capture, transmittertype), but small sample size limits the degree to whichthese variables can be fully explored. However, given
the extremely high level of fishing effort in the region(Alfaro-Shigueto et al. 2010) and the resulting highlikelihood of interactions between fisheries and loggerhead turtles, this information is extremely valuable in
improving our understanding of the species in the SEP
and its interactions with fisheries.

Future directions269

use and further assessing their vulnerability to fisheries bycatch. Such research can also provide information to help manage these fisheries to minimize opportunities for sea turtle bycatch (Blumenthal et al. 2006,
McClellan et al. 2009, Godley et al. 2010).
As we have noted, recent work has helped to bettercharacterize some Peruvian and Chilean fisheries andtheir sea turtle interactions (Alfaro-Shigueto et al.
2008, 2010, Donoso & Dutton 2010), but almost nothingis known about those interactions in the other smallscale and industrial fleets from many nations operatingin the southern Pacific Ocean. Evidence of interactions
with Uruguayan-flagged commercial longliners operating in the Pacific Ocean have been reported(Domingo et al. 2010), but there remains a vast swathof the central South Pacific Ocean that loggerhead turtles most probably inhabit for many years before they
return to neritic habitats in the western Pacific Ocean.
There is clearly a need for a more complete assessmentof the fisheries that loggerhead turtles are likely to
encounter during that time to better identify, categorize and rank the threats they face and to identify andimplement effective mitigation strategies.
Acknowledgements. We warmly thank the participating fishers, Captains Miguel Cuentas and Francisco Bernedo in particular, for their generous collaboration. Pro Delphinus biologists and veterinarians D. Montes and M. Pajuelo provided
superb field work. The artisanal fisher association from theport of Ilo (SUBCABPI) provided excellent logistical support.
The manuscript benefitted from helpful comments by 4
anonymous reviewers. Project funding and equipment wasprovided by NOAA National Marine Fisheries Service Southwest Fisheries Science Center and the National Fish andWildlife Foundation. J.C.M. and J.A.S. are Overseas Researchand Students Awards Scheme (ORSAS) and University of Exeter scholarship awardees, respectively. J.C.M., J.A.S. and
B.J.G. received funding from the Darwin Initiative. M.J.W. isfunded by the Peninsula Research Institute for Marine Renewable Energy (PRIMaRE). Research was authorized underInstituto Nacional de Recursos Naturales (INRENA) permits
015-2002-INRENA-J-DGFFS-DCB, 070-2003-INRENA-IFFSDCB, 068-2004-INRENA-IFFS-DCB, 025-2005-INRENA-IFFSDCB and 002-2006-INRENA-IFFS-DCB.
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Submitted: November 24, 2010; Accepted: March 27, 2011
Proofs received from author(s): July 7, 2011