OCS Study

BOEM 2020-010

U.S. Department of the Interior

Bureau of Ocean Energy Management

New Orleans Office

The Movement and Habitat Associations

of Sea Turtles in the Northern 

Gulf of Mexico
OCS Study

BOEM 2020-010

Published by

U.S. Department of the Interior

Bureau of Ocean Energy Management

New Orleans Office

New Orleans, LA

January 2020

The Movement and Habitat Associations

of Sea Turtles in the Northern

Gulf of Mexico

Authors

Lance P. Garrison

Donald W. Glenn, III

Hayley Karrigan

Prepared under BOEM Interagency Agreements

M10PG00088

by

NOAA National Marine Fisheries Service

Southeast Fisheries Science Center

75 Virginia Beach Drive

Miami, FL 33149
DISCLAIMER

This study was funded, in part, by the US Department of the Interior, Bureau of Ocean Energy 

Management (BOEM), Environmental Studies Program, Washington, DC, through Interagency 

Agreement Number M10PG00088 with the National Marine Fisheries Service (NMFS). This report has 

been technically reviewed by BOEM, and it has been approved for publication. The views and 

conclusions contained in this document are those of the authors and should not be interpreted as 

representing the opinions or policies of the US Government, nor does mention of trade names or 

commercial products constitute endorsement or recommendation for use.

REPORT AVAILABILITY

To download a PDF file of this report, go to the US Department of the Interior, Bureau of Ocean Energy 

Management Data and Information Systems webpage (http://www.boem.gov/Environmental-StudiesEnvData/), click on the link for the Environmental Studies Program Information System (ESPIS), and 

search on 2020-010. The report is also available at the National Technical Reports Library at 

https://ntrl.ntis.gov/NTRL/. 

CITATION

Garrison LP, Glenn III DW, Karrigan H. 2019. The movement and habitat associations of sea turtles in

the Northern Gulf of Mexico. New Orleans (LA): US Department of the Interior, Bureau of Ocean 

Energy Management. 69 p. Interagency Agreement No.: M10PG00088. Report No.: OCS Study 

BOEM 2020-010. 

ABOUT THE COVER

Photo of a satellite tagged loggerhead ready for release. Photo by C. McClellan, Duke University.
i

CONTENTS

List of Figures.......................................................................................................................................ii

List of Tables........................................................................................................................................iv

List of Abbreviations and Acronyms..................................................................................................v

1.0 Introduction.....................................................................................................................................6

1.1 Background ..................................................................................................................................6

1.2 Study Objectives ..........................................................................................................................9

2.0 Materials and Methods.................................................................................................................10

2.1 Tag Deployments .......................................................................................................................10

2.2 Tag Attachment..........................................................................................................................11

2.3 Tag Types and Configuration.....................................................................................................15

2.4 Location data processing ...........................................................................................................18

3.0 Results...........................................................................................................................................20

3.1 Deployments and Movement Patterns.......................................................................................20

3.1.1 Loggerhead turtle movements ............................................................................................................20

3.2.1 Kemp’s ridley turtle movements..........................................................................................................27

3.2 Summary of Core Use Areas .....................................................................................................31

3.2.1. Evaluation of core use areas .............................................................................................................31

3.2.2 Loggerhead turtle core use areas.......................................................................................................32

3.2.3 Kemp’s ridley core use areas. ............................................................................................................33

3.3 Dive Behaviors and Seasonal Movements ................................................................................36

3.3.1 Loggerhead turtles..............................................................................................................................36

3.3.2 Kemp’s ridley turtles ...........................................................................................................................48

3.4 Surface Availability.....................................................................................................................52

3.4.1. Estimating surface availability............................................................................................................52

3.4.2 Loggerhead turtles..............................................................................................................................53

3.4.3 Kemp’s ridley turtles ...........................................................................................................................58

4.0 Discussion.....................................................................................................................................61

4.1 Movement Patterns and Habitat Use.........................................................................................61

4.1.1 Loggerhead turtles..............................................................................................................................61

4.1.2 Kemp’s ridley turtles ...........................................................................................................................62

4.2 Dive-surface Behaviors and Availability.....................................................................................63

4.2.1 Loggerhead turtles..............................................................................................................................63

4.2.2 Kemp’s ridley turtles ...........................................................................................................................63

Further Discussion.......................................................................................................................................64

5.0 Conclusions ..................................................................................................................................66

5.1 Movement Patterns ....................................................................................................................66

5.2 Dive-surface Behaviors..............................................................................................................66

References ..........................................................................................................................................68
ii

LIST OF FIGURES

Figure 1. Tag deployment locations for all turtles. ......................................................................................11

Figure 2. Position of satellite transmitter attachment on turtle’s carapace. ................................................14

Figure 3. A satellite tagged loggerhead ready for release..........................................................................14

Figure 4. MK-10A Wildlife Computers GPS telemetry tag. .........................................................................15

Figure 5. SMRU Satellite Relay Data Logging tag......................................................................................15

Figure 6. Position of Kemp's ridley 106340 that moved into Atlantic waters after tagging.........................19

Figure 7. Loggerhead turtle locations. ........................................................................................................20

Figure 8. Kemp's ridley turtle locations. ......................................................................................................21

Figure 9. Location quality for Kemp's ridley and loggerhead turtle positions. ............................................21

Figure 10. Positions of loggerhead turtles occupying intermediate depth waters of the west Florida 

shelf.......................................................................................................................................24

Figure 11. Positions of loggerhead turtles occupying waters of the outer west Florida continental shelf. .25

Figure 12. Positions of loggerhead turtles from southwest Florida and the north central GOM.................26

Figure 13. Positions of loggerhead turtles with limited tracking data..........................................................27

Figure 14. Positions of Kemp's ridley turtles near St. Joseph's Bay...........................................................28

Figure 15. Positions of Kemp's ridley turtles near Tampa Bay and southwest Florida...............................29

Figure 16. Positions of Kemp's ridley turtles along the Texas coast. .........................................................30

Figure 17. Positions of Kemp's ridley turtles near Texas estuaries............................................................31

Figure 18. Counts of loggerhead turtle locations in 5km cells. ...................................................................32

Figure 19. Utilization distributions for loggerhead turtles in the eastern GOM. ..........................................33

Figure 20. Location counts for Kemp's ridley turtles in 5km cells. ..............................................................34

Figure 21. Utilization distributions for Kemp's ridley turtles. .......................................................................35

Figure 22. Percentage of time in depth ranges for "shallow" depth loggerhead turtles..............................37

Figure 23. Percentage of time in depth ranges for "intermediate" depth loggerhead turtles......................37

Figure 24. Percentage of time in depth ranges for "deep" depth loggerhead turtles..................................38

Figure 25. Spatial distribution of loggerhead turtles with “shallow” dive behaviors. ...................................39

Figure 26. Spatial distribution of loggerhead turtles with "intermediate" dive behaviors. ...........................40

Figure 27. Spatial distribution of loggerhead turtles with "deep" dive behaviors........................................41

Figure 28. Seasonal movements and depth behavior for loggerhead turtle 100604..................................42

Figure 29. Seasonal movements and depth behaviors for loggerhead turtle 100605................................43

Figure 30. Seasonal movement and depth behavior for loggerhead turtle 106354....................................44

Figure 31. Seasonal movement and depth behavior for loggerhead turtle 100614....................................45

Figure 32. Seasonal movement and depth behavior for loggerhead turtle 106338....................................46

Figure 33. Seasonal movement and depth behavior for loggerhead turtle 106349....................................47

Figure 34. Percentage of time in depth bins for Kemp's ridley turtles occupying waters offshore of 

Mississippi Sound..................................................................................................................49

Figure 35. Percentage of time in depth bins for Kemp's ridley turtles occupying waters of Southwest 

Florida. ..................................................................................................................................49

Figure 36. Percentage of time in depth bins for turtles occupying waters along the Texas coast and 

estuaries................................................................................................................................50

Figure 37. Percentage of time in depth bins for turtles occupying waters off the Florida Panhandle.........50

Figure 38. Seasonal movements of Kemp's ridley turtles tagged along the Texas coast. .........................51
iii

Figure 39. Percentage of time at surface for loggerhead turtles by depth, region, season, and day 

compared to night. ................................................................................................................55

Figure 40. Mean percentage time at surface for loggerhead turtles...........................................................57

Figure 41. Percentage time at surface for Kemp's ridley turtles. ................................................................59

Figure 42. Percentage of time at surface for Kemp's ridley turtles.............................................................60
iv

LIST OF TABLES

Table 1. Tag Deployments on Loggerhead Turtles ....................................................................................12

Table 2. Tag Deployments on Kemp's Ridley Turtles.................................................................................13

Table 3. Settings for Wildlife Computers MK10A Tags...............................................................................16

Table 4. Distance Travelled and Location Quality from Loggerhead Turtle Tag Deployments..................22

Table 5. Distance Travelled and Location Quality for Kemp's Ridley Turtle Tag Deployments .................23

Table 6. Average Percentage of Time in Depth Intervals (m) and Behavior Classes for Loggerhead 

Turtles ...................................................................................................................................36

Table 7. Average percentage of time in depth intervals (m) by region for Kemp's ridley turtles ................48

Table 8. Mean and Standard Error of Percentage Time at Surface for Loggerhead Turtles......................53

Table 9. Tests of Fixed Factors in GLM Mixed Model of Percentage Time at Surface for Loggerhead 

Turtles ...................................................................................................................................56

Table 10. Mean and Standard Error of Percent Time at Surface for Loggerhead Turtles..........................56

Table 11. Mean and Standard Error of Percent Time at Surface for Kemp's Ridley Turtles......................58

Table 12. Tests of Fixed Factors in GLM Mixed Model of Percentage Time at Surface for Kemp's 

Ridley Turtles ........................................................................................................................59

Table 13. Mean and Standard Error of Percent Time at Surface for Kemp's Ridley Turtles......................60
v

LIST OF ABBREVIATIONS AND ACRONYMS

Short Form Long Form

AMAPPS Atlantic Marine Assessment Program for Protected Species

ARGOS satellite tracking system for telemetry tags

DPS distinct population segment

DWH Deepwater Horizon 

ESA Endangered Species Act

GOM Gulf of Mexico

GPS global positioning system

NEFSC Northeast Fisheries Science Center

NMFS National Marine Fisheries Service

NOAA National Oceanic and Atmospheric Administration

NRDA Natural Resources Damage Assessment

SEFSC Southeast Fisheries Science Center

SMRU Sea Mammal Research Unit

TED turtle excluder device
6

1.0 INTRODUCTION 

1.1 Background 

The Northern Gulf of Mexico (GOM) is home to five species of sea turtles (or just turtles) occupying US 

waters: Northwest Atlantic Ocean distinct population segment (DPS) loggerhead (Caretta caretta); 

Kemp’s ridley (Lepidochelys kempii); North Atlantic DPS green (Chelonia mydas); Northwest Atlantic 

DPS (proposed threatened) leatherback (Dermochelys coriacea); and hawksbill (Eretmochelys imbricata). 

The loggerhead and green sea turtle DPSs occupying US waters are listed as threatened under the 

Endangered Species Act (ESA; US Fish and Wildlife Service and National Oceanic and Atmospheric 

Administration 2019), and the other species are currently listed as endangered. The GOM includes major 

nesting beaches for loggerhead turtles including several nesting subpopulations along the Florida coast 

(Turtle Expert Working Group 2009). The sole nesting habitat for Kemp’s ridley turtles is on the western 

GOM with nesting areas in Texas and at Rancho Nuevo Mexico (Turtle Expert Working Group 1998; 

Turtle Expert Working Group 2000). Estuarine, continental shelf, and oceanic waters of the GOM are 

important habitats for multiple life history stages. 

A diverse suite of anthropogenic threats are present within the heavily used and highly industrialized 

waters of the GOM. A primary focus of management efforts for sea turtles in the GOM has been to reduce 

the threat due to commercial fisheries. For example, turtle excluder devices (TEDs) are mandated for 

shrimp otter trawl fisheries to reduce bycatch mortality (Epperly et al. 2002). Similarly, the US Atlantic 

pelagic longline fishery is required to use “circle” hooks in an effort to reduce the incidental bycatch and 

mortality of loggerhead and leatherback turtles through Atlantic waters including the GOM (Watson et al. 

2005). Bottom longline in the eastern GOM has also been the focus of management efforts to reduce the 

bycatch of sea turtles including implementations of restrictions on fishing in water depths with high rates 

of loggerhead turtle interactions (National Marine Fisheries Service 2010).

In addition to fishery bycatch, activities associated with energy exploration and extraction in the GOM 

have been identified as potential threats to protected turtles. The primary focus has been upon the role of 

explosive platform removal and the associated potential impact on sea turtles. Platforms and other 

structures may act to aggregate turtles and result in locally high densities of animals. When these 

platforms are removed, visual observations are made within the expected zone of impact to ensure that 

turtles and other protected species are not in the immediate area (Gitschlag et al. 1997; Vida et al. 2008). 

However, additional activities associated with energy activities may also have impacts on sea turtles. The 

Deepwater Horizon (DWH) oil spill in 2010 highlighted the potential risks to sea turtles due to both large 

scale and small scale accidental events. Oil from the DWH spill impacted oceanic waters, continental 

shelf waters, and beaches that are important habitats for sea turtles in the northern GOM (NOAA GOM 

Spill Restoration 2012 [now Deepwater Horizon Natural Resource Damage Assessment Trustees 

(NRDA) 2016]). In addition to impacting nesting beach habitats, oil may also impact sargassum, which 

has been recently identified as a critical habitat features for oceanic juvenile loggerhead turtles (National

Marine Fisheries Service 2013a). 

One significant factor limiting the ability to assess the impacts of anthropogenic threats to sea turtles is a 

lack of information on spatial distribution, habitat use, and abundance (Turtle Expert Working National 

Marine Fisheries Service 2013b). Because sea turtles occupy such a diverse range of habitats at different 

life history stages, obtaining a comprehensive assessment of population size would require a suite of inwater studies. Visual line transect surveys from aircraft are valuable because they have the capability to 

rapidly cover large geographic areas to obtain estimates of density based upon the “distance sampling” 

framework. Aerial line transect surveys have been conducted infrequently in the GOM. The most 
7

complete surveys were conducted during 1992–1994 which covered the entire GOM continental shelf and 

within estuarine waters during September–October of each year (SEFSC, unpublished data). Data derived 

from these surveys, and a partial survey conducted in 1996, were used to estimate turtle densities and 

potential interactions with shrimp fisheries (Epperly et al. 2002). Partial surveys of the eastern GOM were 

also conducted during the summer and winter of 2007 (SEFSC, unpublished data). Neither of these 

surveys included independent observer approaches or other tools to address the known negative biases 

associated with the assumption of complete detection of animals on the trackline that is part of the 

standard distance analysis approach (Laake and Borchers 2004). Abundance estimates derived from these 

past surveys, then, are known to be negatively biased. More recently, broadscale seasonal aerial surveys 

of the GOM were conducted as part of the NRDA associated with the DWH oil spill. These surveys 

included two independent observer teams and therefore collected data specifically to quantify “perception 

bias”, or the probability of the observers missing a turtle conditional on its presence at the surface (March 

and Sinclair 1989). However, these studies require additional information to fully correct for known 

biases.

In addition to perception bias, visual surveys suffer from known negative biases including 1) the inability 

to detect small turtles, 2) difficulty in reliable visual identification of turtles to species, and 3) the limited 

presence of turtles at the surface where they are available to be counted by visual observers (National 

Marine Fisheries Service 2013b). Limited studies have been conducted to examine the size of detection 

from survey aircraft operating at altitudes of 500–600 feet, and these suggest that turtles less than 30cm in 

length are unlikely to be reliably detected by visual observers (SEFSC, unpublished data). The problem of 

species identification is addressed primarily through training and the use of experienced observers, and 

species identification guides have been developed in order to improve this effort (e.g., Goodman and 

Belskis 2012). 

Satellite telemetry tags that record and report dive-surface behavior are the primary tool available for 

addressing the problem of negative biases associated with availability at the surface. However, there is 

very little data on turtle dive-surface behaviors in waters of the GOM. Available dive-surface behavior 

data from telemetry tags was reviewed by the Loggerhead Turtle Expert Working Group (Turtle Expert 

Working Group 2009) and found a number of studies for Atlantic waters ranging from Cape Canaveral, 

Florida to Savannah, Georgia. These studies showed a considerable range in the percentage of time at the 

surface both spatially and seasonally with values ranging from 3.8% to 48.6% over this spatial range and 

in multiple seasons (Turtle Expert Working Group 2009). More recent data collected along the Atlantic 

coast was part of the Atlantic Marine Assessment Program for Protected Species (AMAPPS), which also 

showed a broad range in time at surface for loggerhead turtles and apparent seasonal and spatial 

variability likely related to migration patterns and/or water temperatures (Northeast and Southeast

Fisheries Science Centers 2011). Similarly, tags deployed on loggerhead turtles in coastal and estuarine 

waters of North Carolina demonstrated that turtles spent, on average, <1% of their time in the upper 1m 

of the water column in estuarine waters and 2.4% of their time at the surface in coastal waters with some 

evidence for seasonal variability (Braun-McNeil et al. 2010). When these estimates of time at surface 

were applied to previous abundance estimates, it resulted in 4–100 fold increases in the estimates of turtle 

density within their respective habitats. 
8

There are very few studies of turtle dive-surface behavior in the GOM for either loggerhead or Kemp’s 

ridley turtles. The primary study for loggerheads was conducted by Renaud and Carpenter (1994) in 

coastal waters of the western GOM. This study found seasonal differences in dive behaviors with turtles 

spending a larger amount of time at the surface during the winter and a lower amount of time during 

summer. Due to the extreme spatial and temporal variability in dive-surface behavior on the Atlantic 

coast, it is likely that there is similar complexity in the GOM. In order to develop accurate abundance 

estimates of turtle abundance from visual surveys in the GOM, improved information on dive-surface 

behaviors is necessary. 

In addition to providing data on dive-surface behaviors, tag telemetry studies provide insight into 

movement patterns and habitat use. Telemetry studies of nesting loggerhead turtles on the Southwest 

Florida coast demonstrated a broad range of movement patterns post-nesting including movements onto 

the nearby continental shelf, migration to South Florida, migration into the north-central GOM, and large 

scale movements into waters of the Caribbean Sea and beyond (Girard et al. 2009). In each case, the 

larger scale migratory movements were followed by extended periods where animals were occupying a 

relatively small area, presumably reflecting important foraging habitats (Girard et al. 2009). Nesting 

loggerhead turtles tagged in St. Joseph Bay, Florida and near the Dry Tortugas during 2008, 2009, and 

2010 also showed movements into foraging areas on the continental shelf and off the Yucatan peninsula. 

Turtles stayed within these foraging areas for an average of at least 61 days and foraging areas were in 

waters generally less than 50m in depth (Hart et al. 2012). Similarly, telemetry studies of nesting female 

loggerheads in Gulf Shores, Alabama and St. Joseph Bay demonstrated a range of movement patterns 

during inter-nesting periods which included both large scale movements between emergences on different 

nesting beaches and smaller scale restricted area search movements in nearshore coastal waters (Hart et 

al. 2013). These inter-nesting areas are most typically in waters <50m in depth with a mean of 31.6m 

(Hart et al. 2013). These studies have generally shown that loggerhead turtles tagged in the eastern half of 

the GOM stay in that area with relatively little movement west of the Mississippi River. 

Satellite telemetry tag studies have also examined large scale movements and identified foraging habitats 

for nesting Kemp’s ridley turtles in the western GOM. Kemp’s ridley turtles nesting at Padre Island 

National Seashore in Texas and in Rancho Nuevo, Mexico travelled long distances over continental shelf 

waters to the Florida Gulf coast (Seney and Landry 2008, Shaver and Rubio 2008, Shaver et al. 2013). 

The habitat for Kemp’s ridley turtles was generally shallow waters relatively close to shore in water 

depths of less than 40m (Shaver and Rubio 2008). Foraging sites were identified in waters offshore of 

Louisiana and Texas in discrete depth zones of the outer continental shelf in waters depths from 20–60m. 

Foraging areas were also identified in the north-central GOM outside of the Chandeleur islands. As with 

loggerhead turtles, these foraging zones were areas of restricted movements and residency times of 

several months (Shaver et al. 2013). 
9

1.2 Study Objectives 

The primary objective of this study was to collect data, through satellite telemetry tagging, on divesurface behaviors and seasonal movements on loggerhead, green, and Kemp’s ridley sea turtles occupying 

continental shelf waters of the northern GOM. In addition, the position information obtained from the tags 

provides information on movement and habitat use, with a particular focus on the spatial and temporal 

changes in dive behaviors. The study focused on late juvenile, sub-adult to adult sea turtles that are the 

primary targets of visual surveys. Previous studies have focused on nesting female turtles, therefore 

efforts were made to conduct in-water captures of sub-adults so as to provide additional information about 

the behaviors and movement patterns of these life history stages. These data will add to the knowledge of 

movement patterns and important habitats for sea turtles in the GOM and will be used to support 

estimates of abundance from visual line transect surveys. 

This study was initially funded in 2010; any language and interpretation thereof should be considered a 

description in time around the year 2015 when the draft of this study was presented. 
10

2.0 MATERIALS AND METHODS 

2.1 Tag Deployments 

Due to permit restrictions on directed captures of turtles, tags were deployed on individuals captured 

using a variety of methods associated with sampling efforts by collaborating researchers and are described 

below. A total of 37 telemetry tags were deployed during the study (2011 to 2013). Thirty-four of these 

were Wildlife Computers MK-10 GPS tags, and 3 were Sea Mammal Research Unit (SMRU, St. 

Andrews University, Scotland) instruments, which were deployed for comparison to the Wildlife 

Computers tags deployed at other sites. Turtles were tagged on nesting beaches and in-water in the Gulf 

of Mexico (GOM). In all tagging efforts, animals were held for approximately two hours while the epoxy 

cured and then allowed to return to the water. Tag deployments were as follows:

• For turtles on the beach, tags were attached with epoxy while the animal was held on the beach in 

a temporary enclosure after she had finished laying her eggs. 

• Turtles captured in-water in conjunction with the Corps of Engineers dredging operations 

(Sarasota, Florida and Gulfport, Mississippi) were caught in trawls operating in front of the 

dredge to prevent turtles from interacting with the dredge. 

• Turtles captured offshore of Sarasota, Charlotte Harbor, and in St. Joseph Bay were captured by 

hand with a large dip net or strike net. Three nesting female loggerhead turtle (SMRU) tags were 

deployed at Keewaydin Island in Naples, Florida during July 2011. 

• Tags on 1 loggerhead and 3 Kemp’s ridley turtles were deployed during May 2012 in the northern 

GOM outside of Mississippi Sound using animals incidentally captured during studies of Turtle 

Excluder Device (TED) effectiveness conducted aboard the R/V Caretta by researchers at the 

Southeast Fisheries Science Center (SEFSC) Pascagoula laboratory. An additional sampling 

effort of this type was attempted during September 2012, but no turtles were encountered.

• Sampling efforts were also conducted in coastal waters south of Louisiana during July 22–25, 

2013 and September 3–6, 2013 collaborating with In-water Research Group. During these efforts, 

day trips were staged out of Venice, Louisiana aboard a 27 foot research vessel targeting high 

density areas for Kemp’s ridley turtles in waters between 20–40m depth. Netting or hand captures 

of observed turtles were attempted. Weather conditions were marginal during the July trip, and 

few sea days were accomplished. Weather conditions were improved during the September trip 

and turtles were encountered; however, there were no successful captures or tags deployed.

• Tags were deployed on Adult and Sub-Adult Kemp’s ridley turtles in estuarine and nearshore 

coastal waters along the Texas coast by researchers from SEFSC’s Galveston, Texas laboratory 

during April–September 2013. These included turtles that were incidentally hooked at fishing 

piers during recreational fishing. In addition, Kemp’s ridley turtles were captured in-water in 

Texas in collaboration with Texas A&M Galveston with a tangle net.

In total, 37 tags were deployed during the study: 18 loggerhead turtles and 19 Kemp’s ridley turtles 

(Table 1, Table 2, and Figure 1). No green sea turtle tags were deployed for this study. 
11

Figure 1. Tag deployment locations for all turtles. 

2.2 Tag Attachment 

After capture, the animal’s carapace was prepared by removing epibionts (barnacles, algae, etc.) at the 

mounting and bonding site of transmitter. The ideal location to place the transmitter was the point where 

the first and second vertebral scutes meet. This section of the carapace rises to a maximum point above 

the sea surface each time the turtle breathes, and the base antenna on the transmitter will break the plane 

of the water’s surface (Figure 2). Attachment media (slow curing epoxy) encompassed sections of the 

first and third vertebral scutes, as well as the first and second costal scutes. These areas were thoroughly 

scrubbed with a scrub brush, rinsed with fresh water, dried with a towel, and then lightly sanded with 

sandpaper. When smooth, the entire area was lightly wiped with an alcohol pad or a small amount of 

acetone. The tag was then adhered with epoxy and allowed to cure before returning the turtle to the water 

(Figure 3). All turtle handling and tag attachment methods were consistent with SEFSC field protocols 

(National Marine Fisheries Service 2008). 
12

Table 1. Tag Deployments on Loggerhead Turtles 

Tag ID Life Stage Type First 

Latitude

First 

Longitude First Date Last Latitude

Last 

Longitude Last Date Number of Days

Number of 

Locations

106355 Sub-Adult MK10 27.9510 -82.801 5/14/2011 27.2240 -82.582 7/10/2011 57 133

106354 Adult MK10 27.6070 -82.849 5/21/2011 25.1020 -83.329 10/29/2011 161 166

106344 Adult MK10 27.5433 -82.776 5/26/2011 27.5710 -82.743 9/26/2011 123 407

100604 Adult MK10 29.7313 -85.393 6/12/2011 28.4960 -83.360 2/2/2012 235 1343

100611 Adult MK10 29.6852 -85.369 6/12/2011 26.0320 -83.007 9/28/2012 474 4001

106342 Adult MK10 27.5880 -82.706 6/12/2011 27.4900 -82.771 11/13/2012 520 1477

100600 Adult MK10 29.6855 -85.370 6/13/2011 29.3340 -83.499 7/27/2012 410 3701

100605 Adult MK10 29.6889 -85.372 6/13/2011 27.2710 -83.799 1/27/2012 228 601

100614 Adult MK10 29.6870 -85.370 6/13/2011 28.4000 -83.744 11/13/2012 519 4039

100227 Adult SMRU 26.1740 -81.944 7/2/2011 29.0490 -83.817 9/23/2011 83 628

106349 Adult MK10 30.1070 -89.077 7/2/2011 29.6066 -88.069 4/20/2012 293 411

100226 Adult SMRU 25.6670 -81.450 7/3/2011 25.5310 -81.259 9/3/2011 62 401

100225 Adult SMRU 26.0200 -81.785 7/7/2011 28.5170 -83.674 10/8/2011 93 376

106363 Sub-Adult MK10 27.1310 -83.010 7/12/2011 27.1150 -83.004 9/8/2011 58 83

106338 Sub-Adult MK10 26.7070 -83.292 7/13/2011 26.2080 -83.248 1/21/2012 192 298

100608 Sub-Adult MK10 29.7298 -85.332 10/27/2011 29.7570 -85.316 4/23/2012 179 357

106350 Adult MK10 27.9480 -82.756 5/22/2012 30.0710 -88.838 7/20/2012 59 287

106364 Sub-Adult MK10 30.0730 -88.866 5/23/2012 30.0670 -88.864 7/13/2012 51 598
13

Table 2. Tag Deployments on Kemp's Ridley Turtles

Tag ID Life Stage Type First 

Latitude

First 

Longitude First Date Last Latitude

Last 

Longitude Last Date Number of Days

Number 

of 

Locations

106365 Sub-Adult MK10 27.9470 -82.7560 8/15/2011 26.7200 82.1710 2/20/2012 189 115

106356 Sub-Adult MK10 26.5010 -82.1890 9/21/2011 26.3360 82.3070 10/29/2011 38 140

106340 Adult MK10 26.5937 -82.1318 9/23/2011 25.5980 81.2840 10/11/2011 18 79

100597 Sub-Adult MK10 29.7269 -85.3225 10/14/2011 29.9180 85.3790 11/7/2011 24 235

100613 Sub-Adult MK10 29.7310 -85.3050 10/15/2011 29.8700 85.4010 11/15/2011 31 207

100601 Sub-Adult MK10 29.7282 -85.3730 10/22/2011 29.7540 85.3810 2/1/2012 102 428

100596 Sub-Adult MK10 29.7259 -85.3229 10/28/2011 29.8520 85.3800 11/5/2011 8 62

100609 Juvenile MK10 29.7550 -85.3970 11/17/2011 29.7470 85.2880 4/1/2012 136 317

110811 Sub-Adult MK10 26.5920 -82.1350 11/18/2011 26.6028 82.2641 3/24/2012 127 105

100598 Sub-Adult MK10 30.1050 -89.0150 4/10/2013 29.2840 94.8990 5/23/2013 43 189

110810 Sub-Adult MK10 30.0500 -88.9150 5/23/2012 30.1050 89.0640 6/13/2012 21 50

106357 Sub-Adult MK10 27.9470 -82.7630 5/25/2012 29.9790 88.6310 6/13/2012 19 187

110809 Sub-Adult MK10 30.1839 -88.9488 5/25/2012 29.9770 87.9950 6/10/2012 16 21

122185 Adult MK10 29.2031 -94.9442 11/8/2012 28.7630 95.5890 4/26/2013 169 799

122187 Adult MK10 29.4910 -94.5360 4/10/2013 29.5510 94.3680 7/18/2013 99 1004

128367 Adult MK10 29.2416 -94.8750 5/16/2013 29.2370 94.8840 8/5/2013 81 884

128373 Adult MK10 29.2014 -94.9381 5/16/2013 28.4420 96.4440 5/28/2013 12 178

128376 Sub-Adult MK10 29.0401 -95.1585 5/31/2013 29.2820 94.7590 7/1/2013 31 328

128375 Sub-Adult MK10 29.2050 -94.7840 9/5/2013 29.4060 94.6890 10/13/2013 38 342
14

Figure 2. Position of satellite transmitter attachment on turtle’s carapace. 

Diagram by C. McClellan, Duke University. 

Figure 3. A satellite tagged loggerhead ready for release.

Photo by C. McClellan, Duke University.
15

2.3 Tag Types and Configuration

Two different types of telemetry tags were deployed during this project. The primary tag was the MK10A GPS telemetry tag produced by Wildlife computers (Figure 4) with 34 deployed during the project, 

and the remaining three tags were Satellite Relay Data Logging (SRDL) tags produced by the St. 

Andrew’s University Marine Research Unit (Figure 5). Both of these tags use the ARGOS satellite 

system to transmit information on location and summaries of dive behavior throughout the life cycle of 

the tag. In addition, both tag types include FastLOC GPS technology which allows the collection and then 

transmission of highly accurate GPS-derived locations. Position information derived solely from ARGOS 

triangulation is only rarely accurate to less than 250m; therefore, the FastLOC GPS provides at least a 

subsample of highly accurate locations.

Figure 4. MK-10A Wildlife Computers GPS telemetry tag. 

(http://wildlifecomputers.com/products/tdr10)

Figure 5. SMRU Satellite Relay Data Logging tag. 

(http://www.smru.st-andrews.ac.uk/Instrumentation/GPSArgosTag/)

These tag types each include a depth sensor and reports information on the amount of time the animal 

spent within each depth interval. Settings for recording and reporting location and depth information are 

shown in Table 3. The reported histograms report the maximum dive depths, dive duration, and time at 

depth within the specified bins. Data were summarized and reported during six-hour intervals and were 

transmitted daily. Dive data were collected if the tag depth exceeded 1m.
16

Table 3. Settings for Wildlife Computers MK10A Tags 

The reporting program for the SMRU tags matched these settings.

Fastloc Settings

Fastloc sampling interval 360 minutes

Deployment Latitude 29.29 degrees

Deployment Longitude -94.787 degrees

Deployment Altitude 0 m

Transmit hours 0–23

Fastloc Collection Days

January 1–31

February 1–28

March 1–31

April 1–30

May 1–31

June 1–30

July 1–31

August 1–31

September 1–30

October 1–31

November 1–30

December 1–31

Fastloc Control

Maximum successful Fastloc attempts 1 per hour; 4 per day

Maximum failed Fastloc attempts 10 per hour

Overall maximum Fastloc attempts 50 per day

Suppress Fastloc after good haulout location enabled

Don't abort Fastloc processing if tag measures wet 

on next wakeup

Percentage of the battery capacity already used for 

Fastloc 0%

Data to Transmit Settings

Histogram Selection

Histogram Data sampling interval 10 seconds

Dive Maximum Depth (m), 12 bins 0; 1; 2; 5; 10; 20; 30; 40; 50; 100; 200; >200

Dive Duration, 14 bins 

1 min ; 2 mins ; 3 mins ; 4 mins ; 5 mins ; 10 mins 

; 15 mins ; 20 mins ; 25 mins ; 30 mins ; 40 mins ; 

50 mins ; 60 mins ; >60 mins 

Time-at-Temperature (C), 14 bins 8; 10; 12; 14; 16; 18; 20; 22; 24; 26; 28; 30; 32; 

>32

Time-at-Depth (m), 14 bins 0; 1; 2; 3; 4; 5; 10; 20; 30; 40; 50; 100; 200; >200

20-min time-line disabled

Hourly % time-line enabled

PAT-style depth-temperature profiles enabled with low resolution

Histogram Collection

Hours of data summarized in each histogram 6
17

Histograms start at GMT 00:00

Do not create new Histogram-style messages if a 

tag is continuously dry throughout a Histogram 

collection period

is disabled

Time-Series Messages

Generation of time-series (TS) messages is enabled

Time interval between TS samples 10 mins 

Channels sampled Depth

Start with 255 days on

then Duty Cycle with 0 days off

and 255 days on

Dive & Timeline Definition

Depth reading to determine start and end of dive Wet/Dry

Ignore dives shallower than 1m

Ignore dives shorter than 1m 

Depth threshold for timelines Wet/Dry

Behavior Messages

Generation of behavior messages is enabled

Transmission Control

Transmit data collected over these last days 7

Pause transmissions if haulout exceeds 48 hours

Transmit every eighth day if transmissions are 

paused is enabled

Collection days

January 1–31

February 1–29

March 1–31

April 1–30

May 1–31

June 1–30

July 1–31

August 1–31

September 1–30

October 1–31

November 1–30

December 1–31

Relative transmit Priorities

Histogram, Profiles, Time-lines, Stomach 

Temperature high (3 transmission(s))

Fastloc and Light-level Locations med (2 transmission(s))

Behavior and Time-Series med (2 transmission(s))

Status Every 20 transmissions

When to Transmit Settings
18

Initially transmit for these hours regardless of 

settings below 24

Transmit hours 0 - 23

Transmit days

January 1–31

February 1–29

March 1–31

April 1–30

May 1–31

June 1–30

July 1–31

August 1–31

September 1–30

October 1–31

November 1–30

December 1–31

2.4 Location data processing 

The raw data provided through both ARGOS and GPS determination of location underwent an initial 

filtering and screening prior to analysis to remove data outliers. First, all records with an ARGOS location 

quality of “Z” were removed, as these positions are considered to be inaccurate and low‐quality locations. 

Second, the remaining location data were imported into ArcGIS® and plotted over a land map. Positions 

plotting on land were removed from the data set. Position data for one Kemp’s ridley turtle that moved 

into Atlantic waters was also removed to retain only those records within the GOM (Figure 6). Finally, 

the displacement distance between successive locations was calculated, and the average speed between 

successive points was calculated based upon the elapsed time between time stamps. If the speed exceeded 

4 km/hr, the position was removed from the record as this speed is not within reasonable expectations for 

turtle movements. The resulting filtered dataset was used for all subsequent analyses. 
19

Figure 6. Position of Kemp's ridley 106340 that moved into Atlantic waters after tagging. 
20

3.0 RESULTS

3.1 Deployments and Movement Patterns

Tags were deployed on loggerhead turtles along the Florida west coast and in the north-central Gulf of 

Mexico (GOM) south of Mississippi. During the active periods of the tags, turtles generally moved from 

nearshore waters to offshore waters and occupied waters over the inner continental shelf (Figure 7). 

Average duration for loggerhead turtle deployments was 210.9 days (sd = 165.7) with a range of 51 to 

520 days. The mean total distance travelled was 2,350 km with an average speed of 0.9 km/hr (Table 4). 

Loggerhead turtles did not move into the western GOM during the tag deployments, nor did any animals 

leave the GOM or move into deeper, offshore waters. 

Figure 7. Loggerhead turtle locations. 

Kemp’s ridley turtle tags were deployed at several locations along the Florida west coast and in nearshore 

waters of coastal Texas. The movements of tagged Kemp’s ridley turtles were typically more limited than 

those of loggerhead turtles, though that may be a function of overall shorter tag durations. The average 

duration for Kemp’s ridley tags was 63.3 days (sd = 57.0) with a range of 8 to 189 days. The mean total 

distance travelled was 619.5 km with an average speed of 1.0 km/hr (Table 5). Animals tagged in the 

eastern GOM largely remained in nearshore waters relatively close to their release site. In the western 

GOM, animals likewise stayed in nearshore coastal waters and moved along the Texas coast (Figure 8).

3.1.1 Loggerhead turtle movements

There were four distinct groupings of loggerhead turtle tracks and movements into continental shelf 

waters. Five turtles, two deployed near St. Joseph’s Bay and three deployed in southwest Florida, moved 

offshore into intermediate depth waters of the continental shelf and remained in depths generally 

shallower than 25m. Each of these turtles underwent directed movements before remaining in a localized 

area (Figure 10).
21

Figure 8. Kemp's ridley turtle locations. 

The ARGOS location quality indices for both species were dominated by relatively low-quality “A” and 

“B” type positions. Seventy-nine percent (79%) of loggerhead turtle locations and 76% of Kemp’s ridley 

turtle locations were of the “A” or “B” type quality, which are considered to be accurate locations, but 

they do not have sufficient information available to calculate uncertainty in the position. 17.4% of the 

loggerhead turtle locations and 16.5% of the Kemp’s ridley locations were of class 1 or higher (including 

GPS locations), which have sufficient information to estimate position accuracy which is typically within 

500m (Figure 9). These rates are typical for ARGOS data collected in the GOM. 

Figure 9. Location quality for Kemp's ridley and loggerhead turtle positions. 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

GPS 3 2 1 0 A B

Proportion of Locations

Location Quality

Kemp's

Loggerhead
22

Table 4. Distance Travelled and Location Quality from Loggerhead Turtle Tag Deployments 

Turtle ID Number of 

Locations

Total Distance 

(km)

Avg. Speed 

(km/hr)

Location Quality

0 1 2 3 A B GPS

100225 376 1141.9 0.90 8 12 5 2 42 307

100226 401 735.1 0.80 0 1 0 0 12 388

100227 628 1633.0 1.05 20 17 7 3 144 437

100600 3701 4440.2 0.53 127 163 88 38 601 2653 31

100604 1343 2800.9 1.11 45 39 22 7 137 970 123

100605 601 2683.6 1.16 59 61 22 13 74 364 8

100608 357 733.7 0.65 15 24 7 5 40 224 42

100611 4001 6552.9 0.56 473 669 383 175 671 1611 19

100614 4039 7147.5 0.64 418 387 218 73 783 2146 14

106338 298 2217.3 1.18 50 49 21 13 41 86 38

106342 1477 1884.4 0.39 54 58 45 11 75 1180 54

106344 407 1218.3 0.88 1 1 0 0 26 368 11

106349 411 2297.7 1.00 20 16 11 7 62 269 26

106350 287 2564.3 0.64 21 11 0 0 43 197 15

106354 166 2656.0 1.37 10 12 8 3 23 84 26

106355 133 398.9 1.29 3 3 1 1 17 97 11

106363 83 632.3 1.16 9 14 3 22 13 22

106364 598 576.6 0.54 5 4 3 2 36 527 21
23

Table 5. Distance Travelled and Location Quality for Kemp's Ridley Turtle Tag Deployments

Turtle

ID

Number of 

Locations

Total Distance 

(km)

Avg. Speed 

(km/hr)

Location Quality

0 1 2 3 A B GPS

100596 62 113.2 0.947 3 1 1 3 11 34 9

100597 235 268.4 0.698 5 5 2 1 36 157 29

100598 188 442.4 0.999 3 8 7 1 17 134 18

100601 428 772.4 0.670 11 14 7 3 49 257 87

100609 317 1107.4 0.966 27 39 21 6 41 144 39

100613 207 368.5 0.938 7 5 6 3 24 131 31

106340 79 219.3 1.128 0 0 0 0 7 66 6

106356 140 174.3 0.773 1 6 7 8 5 99 14

106357 187 388.7 0.500 6 9 7 7 35 109 14

106365 114 548.7 1.007 3 3 1 1 28 60 18

110809 20 155.9 0.351 0 3 2 0 3 10 2

110810 50 337.1 1.494 1 2 0 0 14 25 8

110811 105 828.1 0.973 9 3 3 4 28 41 17

122185 799 2444.3 1.012 89 92 57 34 119 294 114

122187 1004 1423.7 0.939 9 15 5 1 103 797 74

128367 884 1379.9 1.021 5 3 0 0 28 807 41

128373 178 265.6 1.298 2 5 4 3 16 142 6

128374 6 22.5 1.415 0 1 0 0 1 4 0

128375 342 576.8 0.846 0 3 0 0 8 315 16

128376 328 552.6 1.113 0 1 3 3 10 294 17
24

Figure 10. Positions of loggerhead turtles occupying intermediate depth waters of the west Florida shelf. 

A second group of five turtles, all captured in the Florida panhandle, moved rapidly offshore and south 

into deeper waters over the outer portion of the west Florida continental shelf. After tagging, these turtles 

underwent a short period of residence near the tagging location, then moved relatively quickly into 

offshore waters before settling into a localized region in depths generally deeper than 30m (Figure 11).
25

Figure 11. Positions of loggerhead turtles occupying waters of the outer west Florida continental shelf. 

Two loggerhead turtles captured in waters of the North Central GOM (106349 and 106350) remained 

close to their capture location in waters offshore of the Chandeleur Islands and near the barrier islands of 

Mississippi Sound. The tag duration for 106349 was 291 days, so this track indicates a relatively long 

residence period within a localized region. 
26

Figure 12. Positions of loggerhead turtles from southwest Florida and the north central GOM. 

Similarly, turtle ID 106344 and 106342 remained very close to the tagging site or in waters just offshore 

of the central west Florida coast despite very long tag durations (Figure 12). In contrast, ID 106354 was 

tagged in roughly the same location; however, this animal transited a long distance to the north-central 

GOM before returning south and settling in an apparent foraging habitat in deep waters of the southwest 

Florida continental shelf (Figure 12). 

Finally, three loggerhead turtles had relatively short durations of approximately 50 days, and each of 

these animals remained relatively close to the tagging site throughout their deployment periods (Figure 

13).
27

Figure 13. Positions of loggerhead turtles with limited tracking data. 

3.2.1 Kemp’s ridley turtle movements

In contrast to loggerhead turtles, Kemp’s ridley turtles in the eastern GOM remained in waters close to 

shore and near the tagging location. To some extent, this limited movement is related to the overall 

shorter duration of tags deployed on Kemp’s. However, this pattern may also be related to overall 

movement patterns of the species which involve larger scale east-west seasonal migrations from nesting 

beaches in the western GOM to nearshore foraging grounds in the eastern GOM. 

Five animals tagged near St. Joseph’s Bay, Florida remained close to shore and within estuarine waters 

throughout their deployment period, which averaged 60 days (range 8–132, Figure 13). The animal with 

the longest duration (ID 100609, 132 days) also remained in and around St. Joseph’s Bay.
28

Figure 14. Positions of Kemp's ridley turtles near St. Joseph's Bay. 

Kemp’s tagged and released near Tampa Bay, Florida likewise had restricted movements during their 

deployment periods. The animal with the longest duration (ID 106365, 189 days) remained within 

estuarine waters throughout the six-month deployment (Figure 15). ID 106340, in contrast, moved 

southeast into the Atlantic Ocean in the months after its tagging (Figure 6). 
29

Figure 15. Positions of Kemp's ridley turtles near Tampa Bay and southwest Florida. 

There were two distinct movement patterns in Kemp’s ridley turtles captured in nearshore waters off 

Texas. Four animals underwent relatively large scale movements staying nearshore and moving south 

along the Texas coast. This includes ID 122185, which had the longest deployment period of 169 days 

and moved south into Mexican waters (Figure 16). Animals tagged within estuarine waters had shorter 

durations of approximately 30 days and remained within the estuaries (Figure 17). 
30

Figure 16. Positions of Kemp's ridley turtles along the Texas coast. 
31

Figure 17. Positions of Kemp's ridley turtles near Texas estuaries. 

3.2 Summary of Core Use Areas

3.2.1. Evaluation of core use areas

Position data from tagged loggerhead and Kemp’s ridley turtles were used to evaluate core-use areas by 

combining information across individuals. The objective of these analyses is to identify regions where 

turtles have relatively long duration periods and restricted area movements. These areas may represent 

important foraging or inter-nesting habitats. It is important to note that the high variability in behaviors 

between individual animals makes large scale inferences about important foraging habitats difficult. To 

make wider inferences, one would need to sample larger numbers of turtles over much longer durations. 

However, the examination of common areas where turtles aggregated during their tagging period provides 

insight into the types of habitats that may serve as foraging areas. 

The first approach to this analysis used turtle location counts occurring within a gridded area covering 

waters from the nearshore (including estuaries) out to the 200m isobaths. The grid used 5x5 km square 

cells, and total turtle location counts within each grid cell were summarized for both loggerhead and 

Kemp’s ridley turtles. The second approach was to evaluate the Utilization Distribution (distribution of 

areas of movement and longer duration stays) using Kernel density methods (Worton 1989) and using the 

package adehabitat in the R statistics package (Calenge 2011). In brief, the Kernel density method uses a 

bivariate normal function to estimate the probability of detection within the range of a given position 

based upon the spatial distribution of the relocation points. The resulting surface provides a map of the 
32

relocation probability of a given animal. In this case, the 50% and 90% kernel density maps are used to 

display the utilization distribution for each individual. The movement data were not filtered to distinguish 

between “foraging” and “moving” modes of behavior, thus these surfaces represent the overall 

distribution ranges for the animals accounting for both types of behavior. As such, they should be 

considered general summaries of movement ranges. 

3.2.2 Loggerhead turtle core use areas

As indicated in the maps of turtle movements, there appear to be two aggregation regions for loggerhead 

turtles in the eastern GOM. The position counts within 5x5 km grid cells indicate discrete areas on the 

outer portion of the central west Florida continental shelf and in shallower waters just south of the Florida 

panhandle with high counts of turtle locations. These areas reflect the areas that turtles migrated to and 

then stayed within a localized area for long potions of their tag deployments (Figure 18). In addition, the 

region south of Mississippi Sound in the north-central GOM also seemed to be an aggregation area with 

high numbers (Figure 18).

Figure 18. Counts of loggerhead turtle locations in 5km cells. 
33

The overlay of Utilization Distribution areas from the Kernel density analysis similarly show that 

loggerhead turtles tagged in the eastern GOM move over fairly large ranges (equivalent to the 90% 

density area) that include the majority of the continental shelf waters. However, within that range, there 

are discrete areas where turtles congregate and have a higher level of residence. These areas are most 

typically in intermediate depth waters along the west Florida shelf (Figure 19).

Figure 19. Utilization distributions for loggerhead turtles in the eastern GOM. 

3.2.3 Kemp’s ridley core use areas.

In contrast to the tagged loggerhead turtles, Kemp’s ridley turtles had more restricted use areas, 

particularly in the eastern GOM. Counts of locations in grid cells show that animals had very limited 

movement ranges and were restricted to nearshore waters close to the tagging locations (Figure 20).
34

Figure 20. Location counts for Kemp's ridley turtles in 5km cells. 

Turtles tagged along the Texas coast showed a broader range of movement with some areas of concentration within their utilization distribution 

(Figure 21). In both cases, the tagged Kemp’s ridley turtles used nearshore habitats and did not move offshore into deeper waters of the 

continental shelf during their deployment period.
35

Figure 21. Utilization distributions for Kemp's ridley turtles. 
36

3.3 Dive Behaviors and Seasonal Movements

3.3.1 Loggerhead turtles

Dive behavior information derived from histograms reported from the tags were summarized to evaluate 

variation in dive behavior among loggerhead turtles and temporal changes in behaviors during the 

movements from nearshore to offshore waters noted above. Examination of the data from loggerhead 

turtles indicated that there were three groups of animals based upon their average dive behavior patterns 

termed, “shallow”, “intermediate” and “deep” animals. The “shallow” animals were generally restricted 

to dive depths of less than 20m (Figure 22). “Intermediate” depth animals tended to have a more bimodal 

average dive behavior with peak rates in the 20–30m depth range and in the 40–50m depth range (Figure 

23). Deep” animals had dive records dominated by depths of 40m or greater (Figure 24, Table 6).

Table 6. Average Percentage of Time in Depth Intervals (m) and Behavior Classes for Loggerhead Turtles

DeployID 0-10 10-20 20-30 30-40 40-50 50-100 >100 Type

100605 14.007 15.083 2.893 3.746 1.877 15.040 47.270 Deep

106354 18.640 3.345 12.968 9.195 3.423 1.720 50.597 Deep

106363 10.454 1.019 1.654 13.824 72.957 0.000 0.000 Deep

100604 8.860 26.312 31.542 14.687 15.008 3.539 0.014 Intermediate

100600 12.241 5.711 80.454 1.502 0.000 0.000 0.000 Intermediate

100611 21.837 7.953 16.178 1.406 9.903 42.137 0.528 Intermediate

100614 25.790 1.822 3.692 2.236 61.281 0.712 4.386 Intermediate

106338 22.870 2.529 7.324 10.302 3.889 31.323 21.723 Intermediate

106342 27.895 27.510 5.231 0.328 38.981 0.000 0.000 Intermediate

106344 22.839 71.740 5.371 0.000 0.000 0.000 0.000 Intermediate

106349 21.074 23.446 16.558 4.859 13.664 11.836 8.502 Intermediate

106355 22.734 60.160 17.069 0.000 0.000 0.000 0.000 Intermediate

100608 61.294 31.718 0.879 0.000 0.000 0.000 0.000 Shallow

106350 39.072 30.716 16.741 4.519 8.934 0.000 0.000 Shallow

106364 35.806 64.166 0.004 0.000 0.000 0.000 0.000 Shallow
37

Figure 22. Percentage of time in depth ranges for "shallow" depth loggerhead turtles. 

Figure 23. Percentage of time in depth ranges for "intermediate" depth loggerhead turtles. 

0

10

20

30

40

50

60

70

0-10 10-20 20-30 30-40 40-50 50-100 >100

Percentage of Time

Depth Range (m)

100608

106350

106364

0

10

20

30

40

50

60

70

80

90

0-10 10-20 20-30 30-40 40-50 50-100 >100

Percentage of Time

Depth Range (m)

100611 100614

106338 106342

106344 106349

106355 100600

100604
38

Figure 24. Percentage of time in depth ranges for "deep" depth loggerhead turtles. 

The depth behavior groupings are related to the spatial distribution and habitat use of the turtles during 

their tag deployments. The “shallow” group turtles included one animal with a restricted range off of the 

Florida panhandle and two animals from the north-central GOM that remained in shallow waters south of 

Mississippi Sound throughout their deployment period (Figure 25).

0

10

20

30

40

50

60

70

80

0-10 10-20 20-30 30-40 40-50 50-100 >100

Percentage of Time

Depth Range (m)

100605

106354

106363
39

Figure 25. Spatial distribution of loggerhead turtles with “shallow” dive behaviors. 

The “intermediate” depth turtles included animals that had some portion of their distribution in nearshore 

water and then moved to establish restricted area movements in intermediate depths. One of the turtles 

tagged in the central GOM (106349), for example, spent a portion of its deployment just south of 

Mississippi Sound and then moved into adjacent continental shelf waters (Figure 26). 
40

Figure 26. Spatial distribution of loggerhead turtles with "intermediate" dive behaviors. 

The “deep” loggerhead turtles, in contrast, spent relatively little of their deployment period in nearshore 

shallow waters and instead moved onto the outer continental shelf. This group also includes turtle 106354 

which undertook a larger scale movement before settling in offshore waters off of southwest Florida 

(Figure 27). 
41

Figure 27. Spatial distribution of loggerhead turtles with "deep" dive behaviors. 

For those turtles that had long deployments and had intermediate depth behaviors, there was a common 

seasonality to their movement patterns and depth behaviors. Monthly movement and depth behaviors for 

individual turtles are shown in Figure 28–Figure 33. In general, animals remained in nearshore waters 

during the warmest months of the year (June–July), and had high percentages of their time in depths of 

20m or less. Typically, during August these animals transitioned from nearshore habitats to habitats 

further offshore. During this transition period when the turtle is travelling, the proportion of time spent in 

relatively shallow depths remained high. This pattern was seen in turtles 100604 (Figure 28) and 100614 

(Figure 31), for example. During the fall and winter months, turtles typically occupied deep water 

habitats and spent a large portion of their time (>80%) at depth (e.g., 100605, Figure 29). Though most of 

these turtles occupied waters over the west Florida shelf, a similar seasonal pattern was observed in turtle 

106349 (Figure 33) in the north central GOM. 
42

Figure 28. Seasonal movements and depth behavior for loggerhead turtle 100604. 

0

10

20

30

40

50

60

70

80

0-10 10-20 20-30 30-40 40-50 50-100 >100

Percentage of Time

Depth Bin (m)

Turtle ID: 100604 June

July

Augus

t

Sept

Oct
43

Figure 29. Seasonal movements and depth behaviors for loggerhead turtle 100605. 

0

10

20

30

40

50

60

70

80

90

100

0-10 10-20 20-30 30-40 40-50 50-100 >100

Percentage of Time

Depth Bin (m)

Turtle ID: 100605 June

July

August

Sept

Oct

Nov

Dec

Jan
44

Figure 30. Seasonal movement and depth behavior for loggerhead turtle 106354. 

0

10

20

30

40

50

60

70

80

90

0-10 10-20 20-30 30-40 40-50 50-100 >100

Percentage of Time

Depth Bin (m)

Turtle ID: 106354

June

July

Augus

t
45

Figure 31. Seasonal movement and depth behavior for loggerhead turtle 100614. 

0

10

20

30

40

50

60

70

80

90

100

0-10 10-20 20-30 30-40 40-50 50-100 >100

Percentage of Time

Depth Bin (m)

Turtle ID: 100614 Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep
46

Figure 32. Seasonal movement and depth behavior for loggerhead turtle 106338. 

0

10

20

30

40

50

60

70

0-10 10-20 20-30 30-40 40-50 50-100 >100

Percentage of Time

Depth Bin (m)

Turtle ID: 106338

Jul

Aug

Sep

Oct

Nov

Dec

Jan
47

Figure 33. Seasonal movement and depth behavior for loggerhead turtle 106349. 

0

20

40

60

80

100

0-10 10-20 20-30 30-40 40-50 50-100 >100

Percentage of Time

Depth Bin (m)

Turtle ID: 106349 Jul

Au

g

Sep

Oct

No

v
48

3.3.2 Kemp’s ridley turtles

Unlike loggerhead turtles, the Kemp’s ridley turtles tagged in this study had less variability in habitats 

and movement patterns, and therefore less variation in depth behaviors. The turtles remained in shallow 

waters and spent the majority of their time in depths less than 20m (Table 7).

Table 7. Average percentage of time in depth intervals (m) by region for Kemp's ridley turtles

DeployID 0–10 10–20 20–30 30–40 40–50 Region

122185 22.4 2.7 45.0 25.7 4.0 Coastal TX

122187 62.5 37.5 0.0 0.0 0.0 Coastal TX

128367 39.7 58.1 2.1 0.0 0.0 Coastal TX

128373 92.2 5.6 2.2 0.0 0.0 Coastal TX

128374 92.0 6.9 1.1 0.0 0.0 Estuarine TX

128375 69.9 18.8 11.2 0.0 0.0 Estuarine TX

128376 51.2 41.7 7.1 0.0 0.0 Estuarine TX

100596 30.9 69.1 0.0 0.0 0.0 FL Panhandle

100597 65.1 34.7 0.2 0.0 0.0 FL Panhandle

100601 28.2 64.1 1.9 0.0 0.0 FL Panhandle

100609 51.9 38.6 9.5 0.0 0.0 FL Panhandle

100613 80.9 19.0 0.1 0.0 0.0 FL Panhandle

100598 87.1 7.9 4.9 0.0 0.0 Mississippi

106357 45.8 36.3 14.3 3.4 0.1 Mississippi

110809 79.4 7.8 7.5 0.0 0.0 Mississippi

110810 84.2 8.8 0.0 0.1 0.0 Mississippi

106340 48.5 9.6 14.0 20.1 4.2 Southwest FL

106356 72.8 11.4 15.7 0.0 0.0 Southwest FL

106365 100.0 0.0 0.0 0.0 0.0 Southwest FL

110811 47.9 21.3 30.8 0.0 0.0 Southwest FL

The Kemp’s ridley turtles occurring in waters off Mississippi Sound and in Southwest Florida spent the 

majority (typically >70%) of their time in water depths from 0–10m (Figure 34, Figure 35); those in 

Texas and the Florida Panhandle more evenly split their time between the 0–10m and 10–20m depth bins 

(Figure 36, Figure 37). Turtles occupying waters in coastal waters of Texas occurred more frequently in 

deeper bins than those within estuarine habitats (Table 7).
49

Figure 34. Percentage of time in depth bins for Kemp's ridley turtles occupying waters offshore of 

Mississippi Sound. 

Figure 35. Percentage of time in depth bins for Kemp's ridley turtles occupying waters of Southwest Florida. 

0

10

20

30

40

50

60

70

80

90

100

0-10 10-20 20-30 30-40 40-50

Percentage of Time

Depth Bin (m)

100598

106357

110809

110810

0

10

20

30

40

50

60

70

80

90

100

0-10 10-20 20-30 30-40 40-50

Percentage of Time

Depth Bin (m)

106340

106356

106365

110811
50

Figure 36. Percentage of time in depth bins for turtles occupying waters along the Texas coast and estuaries. 

Figure 37. Percentage of time in depth bins for turtles occupying waters off the Florida Panhandle. 

Along the Texas coast, where some individuals undertook larger scale movements, there was evidence for 

seasonal migration from several individuals. In general, animals moved further south to waters off of 

Southern Texas and Mexico during late winter (Jan–Mar) and remained further north during the springfall (Figure 38).

0

10

20

30

40

50

60

70

80

90

100

0-10 10-20 20-30 30-40 40-50

Percentage of Time

Depth Bin (m)

122185

122187

128367

128373

128374

128375

128376

0

10

20

30

40

50

60

70

80

90

0-10 10-20 20-30 30-40 40-50

Percentage of Time

Depthh Bin (m)

100596

100597

100601

100609

100613
51

Figure 38. Seasonal movements of Kemp's ridley turtles tagged along the Texas coast. 
52

3.4 Surface Availability

3.4.1. Estimating surface availability

A primary application for the dive-surface behavior data collected during this study is estimation of 

surface availability for sea turtles to improve the accuracy and precision of abundance estimates for sea 

turtles derived from visual survey data, in particular aerial surveys. Line transect surveys using the 

Distance approach (Buckland et al. 2001) use an assumption that all animals occurring on the survey 

trackline are observed so as to convert the observed relationship between the number of sightings and the 

perpendicular distance from the trackline to an estimate of detection probability of individual animals 

within the surveyed strip. In the absence of an estimate of the probability of detection on the trackline, 

termed g(0), the assumption is made that g(0) = 1, and this assumption results in a negative bias in 

resulting abundance estimates. This visibility bias results from two components of detection: 1) the 

detection of animals on the surface by observers, and 2) the presence of animals at the surface. The 

former, termed perception bias, can be quantified by deploying two independent teams aboard the survey 

platform (e.g. Laake and Borchers 2004). However, aboard fast moving aerial platforms, animals that are 

available to one team are also available to the other team, and hence there is no mechanism to account for 

the probability that animals will be on the surface. To account for this, additional information is needed 

about the duration of surface-dive behavior to calculate the probability of animals being on the surface. 

This is particularly important for sea turtles that, as shown in the data collected in this and previous 

studies, spend upwards of 90% of their time beneath the surface and hence are unavailable to survey 

platforms. In addition, results from this study demonstrate that there are both seasonal and spatial 

differences in dive behaviors as turtles move between nearshore and offshore habitats. Thus, it would be 

expected that there is a change in the availability of turtles to aerial surveys over space and time. Failing 

to account for this variability would result in incorrect inferences about seasonal and spatial variation in 

animal density derived from visual surveys.

The formulation for estimating availability is derived from Laake et al. (1997). Availability at the surface 

is given by: 

(1)

where s is the duration of surfacing intervals, d is the duration of dive intervals, and w(x) is:

(2) 

and r is the search radius, x is the distance of the observed object, and v is the speed that the platform is 

moving. The first term in equation 1 reduces to the percentage of time at the surface. The second term 

describes the probability that an animal beneath the surface will come to the surface during the period of 

time when its location is being observed by the aircraft, which is estimated by equation 2. Due to the high 

speed of the aircraft, the narrow field of vision on either side of the aircraft, and the long dive times of 

turtles, this value is extremely small. Therefore, availability at the surface for aerial surveys can be 

estimated directly as the percentage of time at the surface.

For this analysis, we made the assumption that turtles would be visible to an aircraft at depths up to 2 m 

below the surface. This is consistent with observations from the field and the frequent observation and 

identification of turtles just below the surface. The tags in this study were configured to include bins at 1 

and 2m depth, therefore allowing the direct estimation of the percentage of time in the upper 2m of the 

water column at each reporting interval. For this analysis, each four hour reporting interval for depth data 

s d

w x

s d

s

p x a ++

+ = ( ) ( )

2

2 2

( )

v

r x

w x − =
53

was treated as a sample to estimate the average percentage of time at the surface. However, a dependency 

is introduced between these samples because there are repeated measures from the same turtle. 

To analyze these data and estimate the mean (and associated variance) of percentage time at the surface, a 

generalized linear mixed model was used. A random effect for turtle ID was included in each of these 

models to account for dependence between samples within a turtle. The mixed model included four fixed 

factors: Season (Winter, Spring, Summer, and Fall), Day or Night, Region (Western, Eastern, and Central 

GOM), and depth (less than 25m or greater than 25m). Data were analyzed separately for loggerhead and 

Kemp’s ridley turtles. 

The depth factor was analyzed only for loggerhead turtles due to the limited depth range observed in 

Kemp’s ridley turtles. The 25m isobaths was chosen as the depth break based upon initial analyses of the 

bimodal distribution of animals with respect to depth. 

The regional factor also differed between species. For loggerheads, the regional factor tested behaviors 

between the central (Mississippi Sound) and eastern (Florida coast) regions. For Kemp’s ridley turtles, the 

region factor tested differences between animals occupying the western GOM (Texas coast) and the 

eastern GOM (Mississippi Sound and Florida).

3.4.2 Loggerhead turtles

The overall average percentage of time spent at the surface for loggerhead turtles was 11.45% (95% 

confidence interval: 8.59 – 14.31). However, there was significant variation in the percentage time at the 

surface for each of the factors tested in this analysis. Most notably, there were important seasonal effects 

with a lower time at the surface during winter months compared to the other seasons. In addition, day 

compared to night effects were important in some seasons, with higher average time spent at the surface 

during night. Finally, the average time at the surface was generally higher in shallow waters compared to 

deep waters (Table 8, Figure 39). There was limited ability to evaluate regional differences due to small 

sample sizes. There were insufficient samples to estimate means and variances particularly in the central 

region, and few records in the “deep” stratum for the central area. Therefore, data were collapsed across 

regions for subsequent analyses. 

Table 8. Mean and Standard Error of Percentage Time at Surface for Loggerhead Turtles 

Missing values indicate cells with too few samples to estimate means or standard errors.

Depth Season Day Area N Mean StdErr

Shallow Win Night Central

Shallow Spr Night Central 7 13.99 6.02

Shallow Sum Night Central 30 6.37 0.94

Shallow Fal Night Central

Shallow Win Day Central

Shallow Spr Day Central 14 7.13 2.16

Shallow Sum Day Central 62 6.55 0.68

Shallow Fal Day Central 1 9.70

Deep Win Night Central 9 5.11

Deep Spr Night Central
54

Depth Season Day Area N Mean StdErr

Deep Sum Night Central 1 18.60

Deep Fal Night Central 21 7.01

Deep Win Day Central 16 9.91

Deep Spr Day Central 4 65.45

Deep Sum Day Central 9 6.62 0.07

Deep Fal Day Central 37 22.01

Shallow Win Night Eastern 46 6.74 1.02

Shallow Spr Night Eastern 51 11.12 3.40

Shallow Sum Night Eastern 229 10.27 2.05

Shallow Fal Night Eastern 93 8.97 1.73

Shallow Win Day Eastern 87 7.80 1.03

Shallow Spr Day Eastern 88 11.41 1.79

Shallow Sum Day Eastern 464 7.32 0.76

Shallow Fal Day Eastern 180 9.08 2.17

Deep Win Night Eastern 107 4.98 0.76

Deep Spr Night Eastern 102 13.97 4.20

Deep Sum Night Eastern 376 23.20 3.47

Deep Fal Night Eastern 209 15.49 3.69

Deep Win Day Eastern 242 7.01 1.15

Deep Spr Day Eastern 190 11.54 0.98

Deep Sum Day Eastern 711 11.36 1.51

Deep Fal Day Eastern 429 11.00 1.50
55

Figure 39. Percentage of time at surface for loggerhead turtles by depth, region, season, and day compared 

to night. 

Error bars indicate 95% confidence intervals.

The generalized linear mixed model indicated significant effects for all main effects and interaction terms 

(Table 9). The seasonal effects remained strong with lower surface availability during winter months 

compared to the other three seasons. Day and/or night effects were also generally consistent across 

regions and depth strata with higher presence at the surface during night hours compared to daylight 

hours. For the purposes of correcting visual aerial survey data, the means for daylight hours are most 

relevant, and demonstrate that both seasonal and regional differences in surface availability must be 

accounted for when developing correction factors for abundance estimation. These values range between 

7.19 and 12.65%, resulting in approximately 10-fold increases in estimated abundance compared to 

uncorrected estimates (Table 10, Figure 40). 

0

5

10

15

20

25

30

Win Spr Sum Fal

Percent Time at Surface

Season

Night

Day

0

10

20

30

40

50

60

70

Win Spr Sum Fal

Season

0

2

4

6

8

10

12

14

16

18

20

Win Spr Sum Fal

Percent Time at Surface

Season

0

5

10

15

20

25

30

35

Win Spr Sum Fal

Season

A. Central-Shallow

B. Central-Deep

C. Eastern-Shallow D. Eastern-Deep
56

Table 9. Tests of Fixed Factors in GLM Mixed Model of Percentage Time at Surface for Loggerhead Turtles 

Data were collapsed across regions due to small sample sizes. SEAS represent seasonal effects and DAY 

represents day/night effects.

Effect Num DF Den DF F p-value

SEAS 3 3785 27.20 <0.0001

DAY 1 3785 15.99 <0.0001

SEAS*DAY 3 3785 22.37 <0.0001

DEPTH 1 3785 6.25 0.0125

SEAS*DEPTH 3 3785 14.02 <0.0001

DAY * DEPTH 1 3785 6.47 0.0110

DAY * SEAS * DEPTH 3 3785 8.99 <0.0001

Table 10. Mean and Standard Error of Percent Time at Surface for Loggerhead Turtles 

Data were collapsed across regions due to small sample sizes. 

Depth Season Day N Mean StdErr

Shallow Win Night 46 6.74 1.02

Shallow Spr Night 58 11.46 3.19

Shallow Sum Night 259 9.82 1.92

Shallow Fal Night 93 8.97 1.73

Shallow Win Day 87 7.80 1.03

Shallow Spr Day 102 10.82 1.48

Shallow Sum Day 526 7.23 0.68

Shallow Fal Day 181 9.08 2.16

Deep Win Night 116 4.99 0.70

Deep Spr Night 102 13.97 4.20

Deep Sum Night 377 23.18 3.46

Deep Fal Night 230 14.72 3.57

Deep Win Day 258 7.19 1.10

Deep Spr Day 194 12.65 1.72

Deep Sum Day 720 11.30 1.50

Deep Fal Day 466 11.87 1.61
57

A. Shallow

B. Deep

Figure 40. Mean percentage time at surface for loggerhead turtles. 

Data are collapsed across regions. Error bars indicate 95% confidence intervals.

0

2

4

6

8

10

12

14

16

18

20

Win Spr Sum Fal

Percent Time at Surface

Season

Night Day

0

5

10

15

20

25

30

35

Win Spr Sum Fal

Percent Time at Surface

Season
58

3.4.3 Kemp’s ridley turtles

The overall average percentage time at the surface for Kemp’s ridley turtles was 15.14% (95% confidence 

limit: 10.44–19.84%). Initial analyses indicated generally higher availability at the surface during daylight 

hours compared to night (average 17.00% compared to 10.54%). The seasonal pattern was weaker than 

that observed in loggerhead turtles, and there was little overall difference in the mean time at surface 

between the western and eastern regions (Table 11, Figure 41). There were limited numbers of samples 

in winter months, particularly in the western region. Data were collapsed across regions in subsequent 

analyses. 

Table 11. Mean and Standard Error of Percent Time at Surface for Kemp's Ridley Turtles

Area SEAS DAY N Mean StdErr

West Winter Night 39 9.50 .

West Spring Night 67 9.92 1.84

West Summer Night 50 8.67 1.30

West Fall Night 27 8.87 3.38

East Winter Night 24 4.31 1.55

East Spring Night 11 13.97 7.46

East Summer Night 8 24.96 9.54

East Fall Night 72 13.55 4.58

West Winter Day 92 33.62 .

West Spring Day 148 15.26 2.61

West Summer Day 123 7.58 0.93

West Fall Day 81 12.42 4.73

East Winter Day 83 11.42 5.16

East Spring Day 40 25.74 12.23

East Summer Day 21 30.69 7.02

East Fall Day 147 17.61 4.61
59

A. Eastern region 

B. Western region

Figure 41. Percentage time at surface for Kemp's ridley turtles. 

Error bars indicate 95% confidence limits.

The generalized linear mixed model for data collapsed across regions indicated a non-significant main 

effect for season. The strongest effect was day compared to night, and there was a significant interaction 

term between season and day (Table 12). 

Table 12. Tests of Fixed Factors in GLM Mixed Model of Percentage Time at Surface for Kemp's Ridley 

Turtles 

Data were collapsed across regions due to small sample sizes.

Effect Num 

DF

Den 

DF F p-value

SEAS 3 1006 1.63 0.1804

DAY 1 1006 21.24 <0.0001

SEAS*DAY 3 1006 4.24 0.0055

0

10

20

30

40

50

60

Winter Spring Summer Fall

Percent Time at Surface

Season

Day

Night

0

5

10

15

20

25

30

35

40

Winter Spring Summer Fall

Percent Time at Surface

Season
60

Table 13. Mean and Standard Error of Percent Time at Surface for Kemp's Ridley Turtles 

Data were collapsed across region due to small sample sizes.

Season Day N Mean StdErr

Win Night 63 7.52 1.55

Spr Night 78 10.49 2.00

Sum Night 58 10.92 2.20

Fal Night 99 12.28 3.52

Win Day 175 23.09 6.60

Spr Day 188 17.49 3.65

Sum Day 144 10.95 3.32

Fal Day 228 15.77 3.63

The difference between day and night was most pronounced during the winter and spring months, when 

the time at surface was higher during daylight hours. During the warmer months, the difference between 

daylight and night hours was not significant (Table 13, Figure 42). Availability at the surface was 

highest during the cooler seasons and lower during warm seasons. As with loggerhead turtles, the means 

and variances for daylight hours are most relevant for deriving corrections for visual survey abundance 

estimates. The range of mean values is from 10.95 to 23.09%, resulting in significant correction factors 

for abundance estimates that vary strongly by season.

Figure 42. Percentage of time at surface for Kemp's ridley turtles. 

Error bars indicate 95% confidence intervals.

0

5

10

15

20

25

30

Win Spr Sum Fal

Percent Time at Surface

Season

Night Day
61

4.0 DISCUSSION 

4.1 Movement Patterns and Habitat Use 

4.1.1 Loggerhead turtles 

The loggerhead turtles tagged in the eastern Gulf of Mexico (GOM) along the coast of Florida displayed 

distinct seasonal movement patterns between nearshore and intermediate depth coastal environments. 

Turtles tagged in nearshore waters or on nesting beaches during summer months typically remained in 

nearshore environments with fairly restricted movements through early summer. These animals typically 

began offshore movements during August to intermediate depth habitats moving distances of 50–300 km 

over the course of several weeks. The route between nearshore and offshore habitats was direct for most 

of the tagged individuals; however, one animal (106354) underwent a much larger scale migration 

moving first to the northwest into the central GOM before returning to the southeast and finishing its 

migratory movements off the southwest Florida coast (Figure 30). The relatively large kernel utilization 

distribution observed for turtles tagged in the eastern GOM reflects this broadscale movement (Figure 

19). 

In contrast, turtles tagged in the north central GOM near Mississippi Sound had more limited movement 

ranges. Though there was a smaller sample size, the turtles tagged on the beach or in nearshore waters 

near Mississippi Sound made their migratory movements with a similar seasonal timing, but travelled 

much smaller distances in moving to intermediate depth habitats adjacent to the nearshore waters where 

they were tagged (e.g., turtle 106349, Figure 33). This may be a function of the proximity of appropriate 

foraging areas to the nearshore waters relative to the west Florida shelf. Despite the small sample size, 

these data do suggest some degree of residency in the north central GOM, at least for the turtles tagged in 

this study.

After their movement offshore, the tagged individuals undertook maintained smaller scale movements 

within intermediate depth waters between 30-100m on the west Florida continental shelf. There did 

appear to be distinct groups of individuals with some animals taking up occupancy in shallow waters (30–

50m depth) and others in deeper waters (>100m depth). This difference in habitat use was not strongly 

related to tagging location, as some individuals tagged in the same place ended up using different habitats. 

This restricted area movement was maintained for several months, typically throughout the cooler portion 

of the year. The patchy distribution observed in maps of location counts (Figure 18) reflects these 

extended periods of fine-scale movement in intermediate depth waters.

These patterns are similar to those reported for ten loggerhead turtles tagged in southwest Florida and the 

Florida panhandle (Hart et al. 2012). In that study, animals likewise maintained a short (1-2 month) 

duration in nearshore waters following tagging and then moved into intermediate continental shelf waters 

where they undertook more restricted area movements. The individuals tagged off of southwest Florida 

moved to offshore habitats adjacent to the tagging area. However, the individuals tagged in the current 

study used a broader range of habitats as presumptive foraging areas across a broader range of water 

depths. In addition, the two individuals tagged in the Florida panhandle in Hart et al. (2012) did not 

establish foraging behavior in the eastern GOM, but rather moved into much deeper waters off the 

Yucatan Peninsula. In the current study, animals tagged in this area did remain in the northern GOM and 

established both shallow and intermediate depth foraging areas over the continental shelf. In combination, 

these studies demonstrate considerable variability in habitat use among individual turtles using the same 

reproductive habitats. These data also suggest, however, that a broad range of habitats over the 

continental shelf serve as important foraging habitats for loggerhead turtles which are resident (for lack of 
62

a better term) in restricted areas for periods of several months, primarily during cooler water periods from 

fall through winter. 

4.1.2 Kemp’s ridley turtles 

The Kemp’s ridley turtles tagged in this study generally underwent very small scale movements and did 

not migrate into offshore waters or foraging areas as seen in the loggerhead turtles. In the animals tagged 

along the Florida coast and in the north-central GOM, the utilization distribution maps reflect this very 

restricted movement pattern (Figure 21) as animals remained within 20 km of their tagging location 

throughout the duration of the tags. Though the sample size was small, and the range of tag durations was 

variable, the longest duration tags of 5–6 months also showed this restricted area movement, suggesting a 

degree of residency within these nearshore habitats of the eastern GOM for extended periods of time. The 

vast majority of locations was in waters less than 20m depth, and any movement into adjacent deeper 

waters were of very short duration and did not result in establishing long duration foraging habitats. There 

was an exception to this general pattern as turtle 106340 moved away from the tagging location and 

moved around the Florida peninsula and into waters of the Atlantic near Cape Canaveral, Florida. As with 

loggerhead turtles, there is a high degree of individual variation in behaviors, and at least some 

individuals undertake large scale movements out of the GOM.

The Kemp’s ridley turtles tagged in the western GOM had a broader utilization distribution than those in 

the eastern GOM (Figure 21) but also remained in nearshore coastal waters rather than moving into 

offshore habitats. These animals either stayed near the tagging location or undertook seasonal latitudinal 

movements along the Texas coast moving south from the tagging locations in the summer into waters of 

southern Texas and Mexican waters during the cooler months (Figure 38). This may reflect movements 

between different nesting areas along the Texas and Mexican coasts, but does not appear to be consistent 

with the establishment of clear foraging areas as was observed in the loggerhead turtles of the eastern 

GOM.

The movement patterns of the turtles in this study were notably different from those observed in a recent 

review of tagging data from 31 Kemp’s ridley turtles in the GOM (Shaver et al. 2013). The previous study 

summarized the movement patterns of nesting turtles that were tagged either at San Padre Island in Texas 

or in Rancho Nuevo, Mexico. These animals undertook movements to the west after tagging and 

established foraging areas along the southern coast of Louisiana and in waters of the north-central GOM 

in Chandeleur Sound and offshore of Mississippi Sound. The areas south of Louisiana were along the 

outer edge of the continental shelf in depths less than 68m (Shaver et al. 2013). These turtles were 

“resident” in the foraging areas for an average of 101 days (range 40–263 days), but most individuals 

moved between multiple foraging zones within this region during that period. 

The contrast between the findings of this study and those of Shaver et al. (2013) likely reflects differences 

in life history stages and behavioral mode of the individuals tagged in the two studies. The turtles tagged 

in the current study were from in-water captures in nearshore waters rather than from nesting females. 

The observed variability suggests distinct modes of behavior as a function of life-history stage and 

differential use of nearshore (10–20m depth) coastal waters and intermediate depth waters by Kemp’s 

ridley turtles in the eastern and western GOM.
63

4.2 Dive-surface Behaviors and Availability 

The dive-surface behaviors for both loggerhead and Kemp’s ridley turtles indicated important seasonal, 

diurnal, and spatial effects on the time available at the surface. 

4.2.1 Loggerhead turtles 

In loggerhead turtles, the spatial and seasonal variation represents the shift in habitats and behavioral 

modes across seasons with animals moving into deeper waters and spending progressively less time at the 

surface during cooler months. The time available at the surface was notably lower during winter months, 

with an average time at the surface of 6–8% during winter months compared to 10–12% during summer 

and fall. This difference in behavior may be associated with thermal considerations in the respective 

habitats or may reflect behavioral differences. The animals occupying deeper waters in the winter months 

are presumably foraging, and hence spend a larger portion of their time making deep dives. In contrast, 

one would expect that shallower dives made in nearshore waters, or at a time when animals are not 

foraging, would result in less time beneath the surface. The concordance between behavior and spatial 

distribution results in significant differences in availability between nearshore and continental shelf 

habitats. The availability at the surface averaged from 8–12% in shallow habitats and 6–10% in deeper 

habitats. However, within a given season, the difference in surface availability between deep and shallow 

habitats was not consistent. During summer months, for example, the availability at the surface was 

higher in deep waters, particularly at night, compared to the availability in shallow waters (Figure 40). 

Finally, the diurnal differences were also generally consistent across habitats and seasons with higher 

availability at night than during the day. The variability in these data likely reflects complexity in the 

behavioral and physiological requirements of loggerhead turtles as they move between nearshore internesting habitats and offshore foraging habitats. 

The current study is the first detailed analysis of loggerhead turtle dive behaviors in the GOM. Previous

reviews from the Atlantic coast have demonstrated very high variation in dive-surface behaviors in 

different habitats and seasons with ranges from 3.8% to 48.6%. Thus, the overall average value of 11.45% 

of time spent at the surface in the GOM is well within this expected range for loggerhead turtles in coastal 

and continental shelf habitats. The only previous study of loggerhead turtle surfacing behavior was 

Renaud and Carpenter (1994) from western GOM coastal waters which indicated that turtles spent a 

larger amount of time at the surface during winter months and less time during summer months. However, 

the seasonal patterns observed in this study are opposite to those observed in this previous study, which 

may be a result of differences in habitat and life history stage.

4.2.2 Kemp’s ridley turtles

For Kemp’s ridley turtles, the overall patterns are less variable than those for loggerhead turtles owing to 

the more restricted, shallow habitats occupied by the turtles tagged in the current study. However, there 

was a significant interaction term between season and day indicating that the diurnal effects were 

different among the different seasons. Most notably, during the winter and spring, Kemp’s ridleys spent a 

larger amount of time near the surface during daylight hours compared to night hours. During the 

summer, the time at surface was the same for both day and night, and was not significantly different 

during the fall (Figure 42). Because the animals were occupying similar nearshore habitats during each 

season, this may result from differences in thermal requirements among the different seasons. The high 

presence at the surface during winter months may reflect a requirement for animals in relatively cool 

nearshore waters to warm themselves during the day. The resulting seasonal patterns in day-time 

availability at the surface are significant with an average of 23% during winter months falling to 11% 

during summer months. 
64

Surface availability is a critical parameter for estimating the abundance of turtles using visual linetransect surveys from either airplanes or vessel based studies. The inability to correct for availability bias 

in these estimates (i.e., the probability that an animal will be available to be observed by the platform) 

results in a direct negative bias in the resulting abundance estimates. For fast moving aircraft, the 

percentage time at the surface is the variable of interest that is required to correct this known bias. For the 

only current coastwide estimate of loggerhead turtle abundance on the Atlantic coast, availability bias 

corrections based upon tag data were applied. This study found very strong regional differences in dive 

behavior, such that animals occurring in mid-Atlantic waters spent a median of 67% of their time at the 

surface while those in the south Atlantic (south of Cape Hatteras, North Carolina) spent only 7% of their 

time near the surface. The coastwide abundance estimate based only on turtles at the surface was 

approximately 60,000 animals; however, accounting for the low availability of turtles in the south 

Atlantic where the sightings per unit effort was also higher resulted in a nearly 10-fold increase in the 

abundance estimate resulting in an estimate of ~588,000 turtles (Northeast and Southeast Fisheries 

Science Center 2010). This study clearly demonstrates two critical components of applying surface 

availability corrections to aerial survey data. First, the expected magnitude of the correction is very high 

due to the large amount of time turtles spend beneath the surface. Second, the potential for seasonal and 

spatial variation in behavior that is specific to the surveyed habitat is required. The strong regional 

differences in surface availability between the mid- and southern Atlantic had a very strong impact on the 

observed abundance estimates.

Further Discussion 

In the GOM, there has been less regular aerial survey effort and, until this study, little examination of 

turtle dive-surface behaviors. Broad-scale estimates of abundance for loggerhead and Kemp’s ridley 

turtles have not been made for the GOM in recent years; however, Epperly et al. (2002) present turtle 

density estimates based upon aerial surveys conducted in 1992–1996. These aerial surveys estimated 

loggerhead turtle densities of approximately 0.05 animals/km2 in the eastern GOM and much lower 

densities of loggerheads in the western GOM ranging from 0.01 animals/km2 in shallow waters (< 20m) 

to 0.003 animals/km2 in deeper waters (20–200m). Estimates of Kemp’s ridley turtles were lower than 

those for loggerheads ranging from 0.008 animals/km2 in nearshore waters of the eastern GOM to very 

low densities of 0.0004 animals/km2 in the western GOM. There are several sources of negative bias in 

these estimates, including availability bias. 

Aerial surveys of the eastern GOM were conducted by SEFSC in the summer and winter of 2007 and 

resulted in similar density estimates to those provided by Epperly et al. (2002) for loggerhead turtles. This 

survey covered waters from the shoreline to the 200m isobath between Key West Florida and the 

Mississippi River delta. Density estimates for loggerhead turtles in the eastern GOM during summer 

averaged 0.0567 animals/km2 resulting in an abundance estimate of 11,302 (95% CI 9,028-14,148), and 

the density during winter was very similar at 0.057 animals/km2 (N = 11,433; 7,346 – 17,793 95% CI). 

For Kemp’s ridley turtles, the estimated density for winter was 0.047 animals/km2 (N = 9,366; p5% CI 

6,132-14,306), but was much lower during the summer with a density of 0.009 animals/km2 and an 

abundance estimate of 2,045 (1,30 –3,208; SEFSC unpublished data). 

Each of these previous abundance estimates was known to be negatively biased and was limited by the 

availability of appropriate data on dive-surface behaviors. Based on the range of values observed in the 

current study of average percent time at the surface for loggerhead turtles of 11.45% and for Kemp’s 

ridley turtles of 15.14%, these density estimates are negatively biased by approximately 8.7x for 

loggerhead turtles and 6.6x for Kemp’s ridley turtles. However, more in depth seasonal and spatially 

stratified analyses are required to fully correct available abundance estimates for dive-surface behavior.
65

In addition to correcting bias in abundance estimates, spatial and seasonal information on surface 

behaviors is critical for deriving spatially explicit models of turtle density from visual survey data. 

Density maps that provide estimates of animal density as a function of habitat variables are increasingly 

an important tool for management and environmental planning. For turtles, the spatial and temporal 

variability in dive behaviors has the potential to obscure habitat relationships. For example, failing to 

correct for the differences in dive behaviors between shallow and deep habitats would confound any 

calculations of the relationship between turtle density and water depth. The resulting density surfaces are 

therefore less reliable when this variability is ignored. The data provided in this study and similar large 

scale tag studies is therefore a critical component in improving density estimation and understanding of 

turtle habitats in the GOM. 
66

5 CONCLUSIONS 

5.1 Movement Patterns 

- Loggerhead turtles in this study were typically found in shallow water in late spring/early summer, then 

migrated into deeper water for fall and/or winter months. 

- Loggerhead turtles tagged in the north central Gulf of Mexico (GOM) near Mississippi Sound had more 

limited movement ranges with a similar seasonal timing, but travelled much smaller distances in moving 

to intermediate depth habitats adjacent to the nearshore waters where they were tagged.

- After their movement offshore, the tagged individuals undertook maintained smaller scale movements 

within intermediate depth waters between 30–100m on the west Florida continental shelf. There did 

appear to be distinct groups of individuals with some animals taking up occupancy in shallow waters (30–

50m depth) and others in deeper waters (>100m depth). This restricted area movement was maintained 

for several months, typically throughout the cooler portion of the year. 

- In combination with previous studies, these data suggest that a broad range of habitats over the 

continental shelf serve as important foraging habitats for loggerhead turtles which are resident in limited 

areas for periods of several months, primarily during cooler water periods from fall through winter. 

- The Kemp’s ridley turtles tagged in this study in the eastern GOM generally undertook very small scale 

movements and did not migrate into offshore waters or foraging areas as seen in the loggerhead turtles. 

Animals remained within 20km of their tagging location throughout the duration of the tags. 

- The Kemp’s ridley turtles tagged in the western GOM had a broader utilization distribution than those in 

the eastern GOM but also remained in nearshore coastal waters rather than moving into offshore habitats. 

These animals either stayed near the tagging location or undertook seasonal latitudinal movements along 

the Texas coast, moving south from the tagging locations in the summer into waters of southern Texas 

and Mexican waters during the cooler months.

- The movement patterns of the turtles in this study were very different from those observed in a recent 

review of tagging data from 31 Kemp’s ridley turtles in the GOM which undertook movements to the 

west after tagging and established foraging areas along the southern coast of Louisiana and in waters of 

the north-central GOM in Chandeleur Sound and offshore of Mississippi Sound. The contrast between the 

findings of this study and those of Shaver et al. (2013) likely reflects differences in life history stages and 

behavioral mode of the individuals tagged in the two studies. The turtles tagged in the current study were 

from in-water captures in nearshore waters rather than from nesting females. 

5.2 Dive-surface Behaviors 

- The dive-surface behaviors for both loggerhead and Kemp’s ridley turtles indicated important seasonal, 

diurnal, and spatial effects on the time available at the surface. 

- In loggerhead turtles, the spatial and seasonal variation represents the shift in habitats and behavioral 

modes across seasons with animals moving into deeper waters and spending progressively less time at the 

surface during cooler months. The time available at the surface was notably lower during winter months, 

with an average time at the surface of 6–8% during winter months compared to 10–12% during summer 

and fall. 
67

- The current study is the first detailed analysis of loggerhead turtle dive behaviors in the GOM. 

Previousreviews from the Atlantic coast have demonstrated very high variation in dive-surface behaviors 

in different habitats and seasons, with ranges from 3.8% to 48.6%. Thus, the overall average value of 

11.45% of time spent at the surface in the GOM is well within this expected range for loggerhead turtles 

in coastal and continental shelf habitats. 

- For Kemp’s ridley turtles, there was a significant interaction between season and day indicating that the 

diurnal effects were different among the different seasons. Most notably, during the winter and spring, 

Kemp’s ridleys spent a larger amount of time near the surface during daylight hours compared to night 

hours. During the summer, the time at surface was the same for both day and night, and was not 

significantly different during the fall.

- The resulting seasonal patterns in day-time availability for Kemp’s ridley turtles at the surface are 

significant with an average of 23% during winter months falling to 11% during summer months. 

- Based on the range of values observed in the current study of average percent time at the surface for 

loggerhead turtles of 11.45% and for Kemp’s ridley turtles of 15.14%, previous density estimates for the 

GOM for these species are negatively biased by approximately 8.7x for loggerhead turtles and 6.6x for 

Kemp’s ridley turtles. However, additional seasonal and spatial analyses are required to fully account for 

availability bias in survey estimates.

- Spatial and seasonal information on dive-surface behaviors is critical for deriving spatially explicit 

models of turtle density from visual survey data to avoid biases in presumed habitat relationships that are 

driven by behavioral differences.

- The data derived from this study will inform spatial models and in-water abundance estimates of 

loggerhead and Kemp’s ridley turtles in the GOM. 
68

REFERENCES

Braun-McNeil J, Goodman MA, Patton BW. 2010. Surfacing behavior of loggerhead (Caretta caretta) 

sea turtles in estuarine and coastal waters of North Carolina. Beaufort (NC): Southeast Fisheries 

Science Center. 88 p. NOAA Technical Memorandum. NMFS-SEFSC-605. 

Buckland ST, Anderson DR, Burnham KP, Laake JL, Borchers DL, et al. 2001. Introduction to distance 

sampling. Oxford (GB): Oxford University Press. 448 p.

Calenge C. 2011. Home range estimation in R. The adehabitatHR Package. Auffargis (FR): n.p. 61 p. 

http://cran.r-project.org/web/packages/adehabitatHR/adehabitatHR.pdf

Deepwater Horizon Natural Resource Damage Assessment Trustees. 2016. Deepwater Horizon oil spill: 

Final Programmatic Damage Assessment and Restoration Plan and Final Programmatic 

Environmental Impact Statement. Silver Spring (MD): National Oceanic and Atmospheric 

Administration. 70 p.Retrieved from http://www.gulfspillrestoration.noaa.gov/restorationplanning/gulf-plan

Epperly S, Avens L, Garrison L, Henwood T, Hoggard W, et al. 2002. Analysis of sea turtle bycatch in 

the commercial shrimp fisheries of Southeast U.S. waters and the Gulf of Mexico. Miami (FL): 

Southeast Fisheries Science Center. 88 p. NOAA Technical Memorandum NMFS-SEFSC-490.

Girard C, Tucker AD, Calmettes B. 2009. Post-nesting migrations of loggerhead sea turtles in the Gulf of 

Mexico: dispersal in highly dynamic conditions. Mar Biol. 156:1827–1839.

Gitschlag GR, Herczeg BA, Barcak TR. 1997. Observations of sea turtles and other marine life at the 

explosive removal of offshore oil and gas structures in the Gulf of Mexico. Gulf Res Rep. 9(4):1–16.

Goodman Hall A, Belskis LC. 2012. Guide to aerial identification of sea turtles in the U.S. Atlantic and 

Gulf of Mexico. Miami (FL): Southeast Fisheries Science Center. 31 p. NOAA Technical 

Memorandum NMFS-SEFSC-633. https://repository.library.noaa.gov/view/noaa/4325

Hart KM, Lamont MM, Sartain AR, Fujisaki I, Stephens BS. 2013. Movements and habitat use of 

loggerhead sea turtles in the Northern Gulf of Mexico during the reproductive period. PLoS ONE. 

8(7):e66921. doi:10.1371/journal.pone.0066921.

Hart KM, Lamont MM, Fjuisaki I, Tucker AD, Carthy RR. 2012. Common coastal foraging areas for 

loggerhead turtles in the Gulf of Mexico: opportunities for marine conservation. Biol Conserv. 

145:185–194.

Laake JL, Borchers DL. 2004. Methods for incomplete detection at distance zero. In: Buckland ST, 

Anderson DR, Burnham KP, Laake JL, Borchers DL, et al, editors. Advanced distance sampling. 

Oxford (GB): Oxford University Press. 434 p.

Laake JL, Calambokidis JC, Osmeks SD, Rugh JD. 1997. Probability of detecting harbor porpoises from 

aerial surveys: estimating g(0). J Wildl Manage. 61:63–75. 
69

NOAA Gulf Spill Restoration. 2012. Natural Resource Damage Assessment April 2012 status update for 

the Deepwater Horizon oil spill. 91 p. 

https://www.gulfspillrestoration.noaa.gov/sites/default/files/wpcontent/uploads/FINAL_NRDA_StatusUpdate_April2012.pdf

National Marine Fisheries Service. 2008. Southeast Fisheries Science Center sea turtle research 

techniques manual. Miami (FL): Southeast Fisheries Science Center. 92 p. NOAA Technical 

Memorandum NMFS SEFSC-579. https://repository.library.noaa.gov/view/noaa/3626

National Marine Fisheries Service. 2010 January 15. Fisheries of the Caribbean, Gulf of Mexico, and 

south Atlantic; reef fish fishery of the Gulf of Mexico; Amendment 31. A proposed rule by the 

National Oceanic and Atmospheric Administration. 75 FR [Federal Register] 2469. Doc. No.: 2010-

287. p. 2469–2474.

National Marine Fisheries Service. 2013a. Biological report on the designation of marine critical habitat 

for the loggerhead sea turtle, Caretta caretta. Washington (DC): National Marine Fisheries Service. 

166 p. https://repository.library.noaa.gov/view/noaa/16867 

National Marine Fisheries Service. 2013b. Sea turtle assessment status and research needs. Washington 

(DC): National Marine Fisheries Service. 62 p. NOAA Technical Memorandum NMFS-F/SPO-131. 

Northeast Fisheries Science Center and Southeast Fisheries Science Center. 2011. Preliminary summer 

2010 regional abundance estimate of loggerhead turtles (Caretta caretta) in northwestern Atlantic 

Ocean continental shelf waters. Woods Hole (MA): Northeast Fisheries Science Center. 38p. 

Northeast Fisheries Science Center Reference Document 11-03. 

https://www.nefsc.noaa.gov/publications/crd/crd1103/1103.pdf 

Renaud ML, Carpenter JA. 1994. Movements and submergence patterns of loggerhead turtles (Caretta 

caretta) in the Gulf of Mexico determined through satellite telemetry. Bull Mar Sci. 55:1–15.

Seney EE, Landry AM. 2008. Movements of Kemp’s ridley sea turtles nesting on the upper Texas coast: 

implications for management. Endangered Spec Res. 4:73–84.

Shaver DJ, Hart KM, Fujisaki I, Rubio C, Sartain AR, et al. 2013. Foraging area fidelity for Kemp’s 

ridleys in the Gulf of Mexico. Ecol Evol. 3:2002–2012.

Shaver DJ, Rubio C. 2008. Post-nesting movements of wild and head-started Kemp’s ridley sea turtles 

Lepidochelys kempii in the Gulf of Mexico. Endangered Spec Res. 4:43–55.

Turtle Expert Working Group [Southeast Fisheries Science Center]. 1998. An assessment of the Kemp’s 

ridley (Lepidochelys kempii) and loggerhead (Caretta caretta) sea turtle populations in the Western 

North Atlantic. Miami (FL): National Marine Fisheries Service, Southeast Fisheries Science Center. 

105 p.NOAA Technical Memorandum, NMFS-SEFSC-409.

Turtle Expert Working Group [Southeast Fisheries Science Center]. 2000. Assessment update for the 

Kemp’s ridley and loggerhead sea turtle populations in the Western North Atlantic. Miami (FL): 

National Marine Fisheries Service, Southeast Fisheries Science Center. 132 p. NOAA Technical 

Memorandum NMFS-SEFSC-444.
70

Turtle Expert Working Group [Southeast Fisheries Science Center]. 2009. An assessment of the 

loggerhead turtle population in the Western North Atlantic Ocean. Miami (FL): National Marine 

Fisheries Service, Southeast Fisheries Science Center. 145 p. NOAA Technical Memorandum 

NMFS-SEFSC-575. https://repository.library.noaa.gov/view/noaa/3714

US Fish and Wildlife Service and National Oceanic and Atmospheric Administration. 2010. Endangered 

and threatened species; proposed listing of nine distinct population segments of loggerhead sea turtles 

as endangered or threatened. Federal Register 75(50): 12598–12656.

Waston JW, Epperly SP, Foster DG, Shah AK. 2005. Fishing methods to reduce sea turtle mortality 

associated with pelagic longlines. Can J Fish Aquat Sci. 62:965–981.

Vida ST, Hammer RM, Racca R, Hannay D, Thompson MJ, et al. 2008. Review of potential impacts to 

sea turtles from underwater explosive removal of offshore structures. Environ Impact Assess Rev.

28:267–285.

Worton BJ. 1989. Kernel methods for estimating the utilization distribution in home-range studies. 

Ecology. 70:164–168.
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