Title Page
 Table of Contents
 List of Tables
 List of Figures
 Nesting, renesting, migration and...
 Internesting behavior
 Nesting density, beach preferences...
 Influence of physical and biotic...
 Summary and conclusions
 Biographical sketch

Title: Reproductive ecology of the green turtle, Chelonia Mydas, at Ascension Island /
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00099236/00001
 Material Information
Title: Reproductive ecology of the green turtle, Chelonia Mydas, at Ascension Island /
Physical Description: xiii, 163 leaves : ill., maps ; 28 cm.
Language: English
Creator: Mortimer, Jeanne A
Publication Date: 1981
Copyright Date: 1981
Subject: Green turtle   ( lcsh )
Sea turtles -- Ascension Island   ( lcsh )
Zoology thesis Ph. D
Dissertations, Academic -- Zoology -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Thesis: Thesis (Ph. D.)--University of Florida, 1981.
Bibliography: Bibliography: leaves 155-162.
Statement of Responsibility: by Jeanne A. Mortimer.
General Note: Typescript.
General Note: Vita.
 Record Information
Bibliographic ID: UF00099236
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000294685
oclc - 07784876
notis - ABS1020


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Table of Contents
    Title Page
        Page i
        Page ii
        Page iii
        Page iv
    Table of Contents
        Page v
        Page vi
    List of Tables
        Page vii
    List of Figures
        Page viii
        Page ix
        Page x
        Page xi
        Page xii
        Page xiii
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
    Nesting, renesting, migration and remigration
        Page 12
        Page 13
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        Page 15
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        Page 57
        Page 58
    Internesting behavior
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
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    Nesting density, beach preferences and population estimate
        Page 101
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        Page 103
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        Page 123
    Influence of physical and biotic factors on egg and hatchling viability
        Page 124
        Page 125
        Page 126
        Page 127
        Page 128
        Page 129
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    Summary and conclusions
        Page 152
        Page 153
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    Biographical sketch
        Page 163
        Page 164
        Page 165
        Page 166
Full Text








Most especially I want to thank my committee chairman, Dr. Archie

Carr, who was a source of inspiration during every phase of the study.

I am grateful to the other members of my committee who read the thesis

and made constructive comments: Dr. Walter Auffenberg, Dr. Thomas Emmel,

and Dr. Hugh Popenoe. Thanks also are due to Dr. Karen Bjorndal and

Dr. Jack Ewel. Ross Alford and Tim Breen patiently assisted me with the

statistical analyses. Assistance in analyzing the beach sands was pro-

vided by the staff of the Soil Characterization Lab (Frank Sodek, Dave

Cantlin and Bill Pothier), and by Dr. Victor Carlisle, Dr. P. S. Rao and

Dr. Luther Hammond in the Soils Department. Other people in Gainesville

who provided help at various stages of the project are: Dennis Ojima,

Anne Meylan, Peter Meylan, Dr. Frank Nordlie, Faye Benedict, Carol Brown

and Esta Belcher. Donna Gillis skillfully typed the dissertation.

The government officials and agencies on Ascension Island generously

provided me with lodging and allowed me access to the island facilities.

For this I am grateful to the St. Helenian Government, Property Services

Agency, Cable and Wireless, British Broadcasting Corporation, and the U.S.

Air Force Base and N.A.S.A. Tracking Station. I realize that the presence

of a scientist on the island for such an extended period--16 months--was

very irregular and I appreciate their indulgence. I am particularly

thankful to the administrators who served on the island during my stay--

Gov. Geoffrey Guy, the late Brig. Gordon MacDonald, Simon Gillett and

Brian Kendall.

It is impossible to name all the people on Ascension who assisted

me in the various stages of my work. I am especially grateful to those

who were willing to stay up all night with me and track the movements

of turtles out at sea. Special thanks go to Chuck Belaski (RCA) who,

helped me with nearly every track. Other faithful tracking companions

included: Carole and Keith Pearce (PSA), Dave Lovell (BBC), lan Calvert

(BBC), Eric "Moses" Joshua (PAA), Charlie Leo (C&W), Woody and Rex (RCA),

lan and Avalon, and Geoff Gartside (BBC). Without the muscle-power of

the following people it would have been impossible to make the deep

excavations necessary to determine hatching success: Eric "Moses"

Joshua (PAA), Sid Youde (PSA), "Peaches" Coleman (PSA), Phil Wadsworth

(BBC) and Brian Yon (PAA). I am grateful to my diving partners who on

short notice and sometimes under somewhat dangerous circumstances were

willing to accompany me: "Jimmy" Young (PAA), Gerald Hercules (C&W),

Phil Wadsworth (BBC), lan Calvert (BBC), Chuck Belaski (RCA), Eric

"Moses" Joshua (PAA), "Buffalo" Young (C&W), Chris Royale (C&W) and

Brian Yon (PAA). The following people tagged turtles for me: Eric

"Moses" Joshua (PAA), the late Robin Hannay (CSO), lan Calvert (BBC)

and Bill Stinnet (PAA). Transportation is always a problem at Ascension,

and I am grateful to those who lent me vehicles, gave me rides, or

fixed my own vehicles when they were broken down--which was often:

the Georgetown Police, Peter and Phyllis Corker (BBC), the N.A.S.A.

Motorpool, Eric "Moses" Joshua (PAA), "Small Change" (PAA), "Skunk"

Benjamin (PAA), "Duck" Joshua (PAA) and Brian "Dutch" Lawrence (C&W).

Very special thanks go to my parents Jeanne and Stirling Mortimer

who supported me in so many ways over the years.

My work at Ascension was primarily financed by a grant to Archie

Carr from the National Geographic Society. Partial funding was also

received from the National Marine Fisheries Service (FSE-43-8Q-125-134),

the Caribbean Conservation Corporation, and National Science Foundation

(DES 73 06453).


ACKNOWLEDGMENTS . . . . . . . . . ... .

LIST OF TABLES . . . . . . . . . .. .. . .

LIST OF FIGURES . . . . . . . . . ... .

ABSTRACT . . . . . . . . . . . . . .


S INTRODUCTION . . . . . . . . . . .

Background for the Study . . . . . . . .
The Island . . . . . . . . . .


Introduction ....
Methods .. . ...
Results ...
Discussion . . .

3 INTERESTING BEHAVIOR . . . . . . ... .

Introduction . . .
Materials and Methods.
Results and Discussion

POPULATION ESTIMATE . . . . . . .... .

Introduction . . . . . . . . . . .
Methods . . . . . . . . . . . .
Results . . . ...........
Discussion . . . . . . . . . . .
Population Estimate . . . . . . ...


Introduction . . . . . . . . . . .
Methods . . . . . . . . . . .
Results ....... ........................
Discussion . . . . . . . . . . .

. . . . . . .

. . . . . .
. . . . . . . . .


6 SUMMARY AND CONCLUSIONS. . . . . . . . ... 152

LITERATURE CITED ..... . . . . . . . 155

BIOGRAPHICAL SKETCH .. .. .. .. .. .... .. .... 163



1 Comparison of total numbers of observed nestings by
turtles first encountered at South West Bay beach in
January and February of 1977 and 1978. . . . . ... 26

2 Locations of the last observed emergences of the previous
season, and the first observed emergences after
remigration, for the 67 remigrant turtles. . . . ... 28

3 Accuracy with which turtles returned to the same cluster
of beaches to nest . . . . . . . . . 31

4 Locations of the members of each pair of successive
nesting emergences separated by intervals of less
than seven days. . . . . . . . . ... . 32

5 Locations of the members of each pair of successive
nesting emergences separated by intervals of seven
or more days .. . . . . . . . ..... 33

6 Accuracy with which turtles returned to the same beach
to nest. . . . . . . . .... ....... 35

7 Number of turtles tagged at Ascension Island each year 55

8 Recorded emergences of turtles on the nesting beaches
before and after they were tracked . . . . . . 89

9 Physical characteristics of each of the Ascension
Island nesting beaches . . . . . . . ... .106

10 Number of turtles and the percentage of total
turtles nesting at each beach during the 1976-77 and
1977-78 nesting seasons. . . . . . . . ... 115

11 Fates of eggs in 76 nests from which hatchlings emerged. 129

12 Percentages and causes of mortality in eggs and hatch-
lings at Ascension beaches studied . . . . .... 130

13 Physical parameters of beach sand. . . . . . ... 132



1 Nesting beaches of Ascension Island. . . . . . . 6

2 Average monthly precipitation between 1962 and 1978
recorded by the U.S. Base Weather Station near the airstrip. 8

3 Monthly temperature maxima and minima for Georgetown,
during the years 1899-1954 . . . . . . . 10

4 Relationship between the average number of body pits
per turtle emergence and the average mean particle size
of the sand at each of the seven beaches . . . ... 20

5 Time intervals separating consecutive emergences by
Ascension turtles, recorded between 1960 and 1978. . . 22

6 Number of days between the first and last observed
emergences of turtles tagged during the first six weeks
of the 1977-78 nesting seasons . . . . . . .. 24

7 Comparison of numbers of observed nestings by remigrant
turtles and the previously untagged recruit turtles. ... 25

8 Means and standard deviations of the average distances
between successive nesting emergences of turtles
encountered on the three major beaches of Ascension Island 36

9 Relationship between the numbers of eggs laid by
turtles at each recorded nesting, and the number of
days elapsed since their first observed nesting
during the season. . . . . . . . ... . 38

10 Remigration intervals between successive nesting
seasons recorded for Ascension turtles . . . .... 40

11 Number of years between last sightings of turtles
on nesting beach and their capture off the coast of
Brazil . . . . . . . . .. . . . . . 41

12 Location of long distance recoveries at Brazil ...... 42

13 Movements of turtle 15426 during the first 5.6 hours after
laying eggs at North East Bay beach in the second egg
chamber that she dug .... . . . . . . . 65


14 Movements of turtle 15139 during the first six hours
after laying on South West Bay beach. . . . . ... 67

15 Movements of turtle 15153 during the first 38 hours
after laying eggs at South West Bay beach . . . ... 69

16 Movements of turtle 15206 during the first 17.3 hours
after she abandoned a nesting attempt at South West
Bay beach . . . . . . . . . . . 71

17 Movements of turtle 15206 during the first 36.3 hours
after laying eggs at South West Bay beach, in her
sixth egg chamber .. . . . . . . . .... 73

18 Movements of turtle 15985 during the first 7.2 hours
after having been frightened away from her second
nest hole at North East Bay beach . . . . .... 76

19 Movements of turtle 15900 during the first 20.3 hours
after having been frightened away from her second
nest hole at North East Bay beach . . . . .... 78

20 Movements of turtle 15516 during the first 10.3 hours
after having been frightened away from her third
nest hole on South West Bay beach . . . . .... .80

21 Movements of turtle 15923 during the first two hours
after having been frightened away from her second
egg chamber at South West Bay beach . . . . .... .82

22 Movements of turtle 15465 during the first 8.2 hours
after abandoning her nest hole at South West Bay beach. . 84

23 Movements of turtle 16019 during the first 3.3 hours
after having been frightened away from her first egg
chamber at South West Bay beach . . . . . .... .86

24 Movements of turtle 15415 during the first two hours
after having been frightened away from her fifth nest
hole at South West Bay beach. . . . . . . ... 88

25 Seasonal distribution of nesting activity on Ascension's
three major nesting beaches--South West Bay, Long Beach
and North East Bay--as shown by morning track counts. . 105

26 Relationship between estimated number of egg clutches
laid on each beach during a season, and beach length,
for 26 beaches at Ascension Island. ... . . . 108


27 Relationship between physical characteristics of
Ascension beaches and nesting density. . . . . .. 110

28 Relationship between combinations of beach characteristics
and nesting density at Ascension Island. . . . . ... Ill

29 Relationship between nesting density along the shoreline,
and the position of the offshore contour lines,at the
three major Ascension beaches. . . . . . . ... 112

30 Relationship between mean particle size and sorting
coefficient, and average emergence success of clutches . 134

31 Average mean particle diameter plotted against the
average sorting coefficient of sand collected at each of
the 32 Ascension Island beaches. . . . . . . ... 135

Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy



Jeanne A. Mortimer

March 1981

Chairman: Archie Carr
Major Department: Zoology

The reproductive ecology and behavior of the green turtle, Chelonia

mydas, were studied at Ascension Island, an isolated peak in the Central

Equatorial Atlantic Ocean. Physical characteristics of the 32 cove-head

beaches of the island were measured, and their influence on beach-choice

by gravid females, on the behavior of females during nest construction,

and on viability of the eggs and hatchlings was examined. Characteris-

tics of the offshore approaches exert more influence on beach selection

by nesting females than do features above the high tide line. Nesting

is most dense on beaches with approaches unobstructed by submerged rocks.

The turtles avoid beaches with foreshores cluttered by rocks, or where

there is artificial lighting nearby.

Females have difficulty digging egg chambers in the coarse, dry

Ascension sand. Typically, they emerge repeatedly, on two or three

successive nights, and dig multiple trial nest holes before depositing

eggs. Successive egg clutches are laid at intervals of about 14 days.

Although females may lay as many as seven clutches in a season, the

average number recorded was between two and three. The numbers of eggs

laid by individual females during a season decreases with successive

nestings; the average clutch size measured was 120.9 eggs. Four years,

followed by three years, are the predominant remigratory intervals

recorded in Ascension turtles.

During renesting emergences, the females usually land at the same

beach, often to within a few meters of their previous nesting place, or

at an adjacent beach. Stronger site tenacity was evident in renestings

separated by less than seven days (assumed to be repeated attempts to

lay the same clutch of eggs), than in those separated by longer time

intervals. These differences correlate with predictable patterns of

behavior observed in females, the movements of which were visually tracked

during their interesting intervals. After successful oviposition,

tracked females travelled to a shallow area off the northwest coast of

the island. The frustrated nesters remained in the vicinity of the

nesting beach that they had just abandoned. Both rarely entered water

more than 18 m deep.

Nesting occurs on all the beaches, although on some,hatching

success approaches zero. No correlation between nesting density and

percent hatchling emergence on the beaches was found. Reproductive

success is influenced by characteristics of the beach sand, especially

particle size distribution. Sand that is too fine, or too poorly sorted

inhibits gas diffusion. Coarse sand causes cave-ins. A positive

correlation between hatching success and depth of the nest was observed,

probably because higher moisture levels occur at great depths. Elevated

levels of salinity in the sand, most frequently seen in poorly sorted

sand, may induce desiccation through osmotic stress. The positive

correlation between hatching success and distance from the sea may be

related to inundation by rollers. There is a relative dearth of both

terrestrial and offshore predation upon the eggs and hatchlings. Heavy

mortality is caused by edaphic and density-dependent factors--beach

erosion, inundation, and females digging up previously laid clutches.

An estimated 2,600 females nested at Ascension during the 1976-77

season, and 1,800 during the 1977-78 season.


Background for the Study

When Linnaeus introduced Chelonia to science in 1758, he based his

description on a specimen from Ascension Island. It probably did not

occur to Linnaeus that the population on which he based his new genus

was, biologically, probably the most interesting in the world. Ascension

lies in the Central Equatorial Atlantic, midway between the coasts of

Africa and Brazil. It is a true oceanic island with no littoral platform

to support the marine vegetation on which green turtles (Chelonia mydas)

normally feed. The fact that turtles show up there each season poses a

number of biological questions: Where do they come from? Why do they

go out there to nest? By what route do they travel? By what mechanism

is the open-sea travel guided? To what extent has speciation been

induced by isolation and the selective demands of their long migration

to a mid-ocean speck of an island?

It was to shed light on these questions that the tagging program of

the University of Florida was extended in 1958 from Tortuguero, Costa

Rica to Ascension. The origin of the seasonal nesting colony was soon

shown to be the coast of Brazil. In the Spring of 1960, Harold Hirth

spent nine weeks on the island. Of 206 turtles that he tagged, four were

recovered in Brazil (Carr and Hirth, 1962). During the years between

1960 and 1976, a total of 2,236 turtles were tagged by other collabor-

ators--students sent to the island for brief periods, local residents

who tagged during spare time--and by personnel of the Mariculture, Ltd.

turtle farm who visited the island in 1972, 1973 and 1974 to collect

turtle eggs for the farm. Morphometric data on the adult turtles and

descriptions of the nesting behavior of the population are given by

Carr and Hirth (1962) and Simon and Parkes (1976). Carr and Hirth (1962)

and Carr (1975) reported on nesting periodicity. Stancyk and Ross

(1978) correlated physical characteristics of each beach sand at Ascension

with density of nesting observed on the beaches. Carr et aZ. (1974)

described movements of a few turtles tracked in the interesting


As tag returns accumulated, Carr published several papers document-

ing the Brazil-Ascension migratory pattern, and suggested possible

sensory mechanisms for the open sea navigation involved (Carr, 1962;

1964; 1967a; 1972; 1975 and Koch et aZ., 1969) and theories to explain

the evolution of such long distance migration (Carr and Coleman, 1974).

These studies have shown the migration of the Ascension colony to be one

of the most remarkable in the animal world. Although it is not as

extensive as that of some birds (ex. the golden plover or arctic tern)

there can be no doubt that it entails true open sea navigation; the

turtles have access to no landmarks. Tracking experiments with Ascension

females to test the sensory mechanisms involved in open sea navigation

were discontinued because equipment failed (Carr, 1972).

I chose the Ascension Island colony as the subject of my research

because of these unique attributes and the many unanswered biological

questions that they pose. A major asset is that the colony is un-

exploited, having in 1926 become the first sea turtle population in

history to receive complete protection from human depredation on the

nesting beach (Hart-Davis, 1972). Moreover, the island is the sole

breeding place for the turtles nesting there, and is small enough that

nesting activity can be effectively monitored.

The nesting ground at Ascension is discontinuous, being divided

into a series of covehead beaches. These differ from each other in

terms of their size and shape, offshore configuration and approach,

and sand characteristics. A central effort of my research was to

determine what effect these variables may have on nesting density and

beach preferences, on reproductive homing, on the process of nest

construction, and on hatching success. In every phase of the study,

I looked for behavioral characteristics that could be used to distin-

guish the members of the Ascension Island population from those of the

other major green turtle populations in the Atlantic Ocean system--the

mainland Tortuguero, Costa Rica, and Surinam populations. I studied

interesting movements of turtles in the sea by tracking (Carr et al.,

1974) and have compared the interesting behavior of the insular

Ascension population with that recorded for the mainland Tortuguero


My work has materially supplemented the meagre data previously

gathered on within-season nesting periodicity and remigration intervals.

The record of long distance migration has also been extended--although

not beyond the borders of Brazil. The Ascension Island green turtle

colony is now the best documented insular sea turtle population in the

world. It is still by no means thoroughly understood, however, and

continued research at Ascension would surely be very rewarding.

The Island

Geology and Topography

Ascension Island is an isolated volcanic peak on the mid-Atlantic

ridge in the South Atlantic Ocean (757'S, 14022,W). It is roughly

triangular in shape, covering an area of about 97 km and measuring

approximately 14.0 km from east to west and 11.2 km from north to south

(Fig. 1). The nearest points of land are the island of St. Helena,

1304 km to the south, Liberia on the African continent, 1536 km to the

northeast, and the easternmost bulge of Brazil, 2200 km due west. The

highest elevation, 860 m, is the Peak of Green Mountain; about two-thirds

of the island is below 255 m (Duffey, 1964). The terrestrial ecology

of the island is described in detail by Duffey (1964), and its geology

by Darwin (1896) and Daly (1925). More than half of the island--

principally the coastal areas and the flat northern portion--is covered

with flows of basaltic or trachdoleritic lava, forming an extremely

rough terrain (Daly, 1925). There is no continental shelf, and the sea

bottom drops away abruptly on all sides. The central equatorial current

flows past the island from the east at speeds averaging from 0.4 to

0.9 knots (Anon., 1975).

Along the northern and western coastline are scattered 32 cove-

head beaches, ranging in length from 10 m to 915 m and in area from
2 2
110 m to 63,064 m2. The topography of the beaches is described in

Chapter 4. On most of them the sand is a combination of crushed shells

and algae nodules. On some, however, the sand is derived from

pulverized lava and volcanic ash. Physical characteristics of the

various beach sands are described in Chapter 5.

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Seasonality of Climate and Turtle Nesting

Ascension lies in the zone of steady southeasterly trade winds.

Wave action is exceptionally heavy. At times, huge swells called

"rollers," believed to originate from distant storm centers, pound the

shoreline, coming in predominantly from the northwest and less commonly

from the southwest. The roller season coincides with the turtle nest-

ing season (Chapter 5).

The average annual precipitation measured by the weather station

near the airstrip (see map, Fig. 1) between 1962 and 1978 was 193.7 mm

(S.D. = 129.6). Figure 2 shows the average monthly precipitation

recorded there. For comparative purposes I mounted raingauges behind

South West Bay beach, Long Beach, English Bay beach and North East Bay

beach (Fig. 1). Rainfall measured by the weather station at an altitude

of about 75 m, is similar to what I measured at nearby South West Bay

beach and Long Beach, and to what the Cable and Wireless Office measured

in Georgetown. Rainfall was somewhat higher at North East Bay beach,

and lower at English Bay beach than at the other sites.

Predictable levels of precipitation occur during most of the year,

but the months of December, March and April are subject to unusually

heavy downpours. Five out of the 16 months of March for which pre-

cipitation was measured, and three of the 17 months of April, received

more than 55 m of rainfall (ranging from 57.4 to 294.6 mm). During

one of the Decembers, 176.5 mm of rain fell. In no other single month

was there more than 55 mm (Fig. 2). The heavy rains are not predictable

on an annual basis, but they seem to be so over longer periods of time.

It is not surprising that the turtle nesting season (December through






110 -

100 -

2 90

- 80








Figure 2. Average monthly precipitation between 1962 and 1978
recorded by the U.S. Base Weather Station near the

May) coincides with the wettest time of the year (cf. Figs. 2 and 25),

in view of the low levels of precipitation that occur at Ascension,

and the difficulty turtles have in constructing their egg chambers in

the dry sand (Chapter 2).

Relative humidity measured on the southwest side of the island at

an elevation of about 50 m, ranges from 56-61% during the day, to the

70's and 80's at night (Duffey, 1964). Air temperatures remain relatively

constant from month to month throughout the year. Figure 3 shows the

average daily maximal and minimal temperatures per month recorded at

Georgetown. The turtle nesting season, which peaks in February, March

and April, coincides with the warmest part of the year (cf. Figs. 3

and 25).

Human Inhabitants

Ascension Island was not permanently inhabited until 1815, when the

British erected a Garrison at what is presently Georgetown. In 1899

the first submarine cable was laid to Ascension, and from then until

1964 the island was administrated by the Eastern Telegraph Company

(later Cable and Wireless Co.). During World War II the airstrip was

built, and Ascension served as a stop-over point for aircraft flying

between South America and Africa. About 4,000 U.S. servicemen were

stationed on the island. In 1957 the island became part of the Air

Force Eastern Test Range, and various satellite tracking installations

were erected.

Today Ascension Island is part of the British colony of St. Helena,

which includes the islands of Ascension, St. Helena and Tristan da

Cunha. The human population consists of approximately 1,000 people--St.




1 I I

Figure 3. Monthly temperature maxima and minima for Georgetown, during
the years 1899-1954 (Duffey, 1964).


Helenian, British, American and South American--who live in the British

villages of Georgetown and Two Boats, on the U.S. Air Force Base, and

near the top of Green Mountain (Fig. 1).



The nesting behavior of female sea turtles at the beach is well

documented (see review by Ehrhart, in press). Behavioral studies of

nesting turtles along with tagging studies have yielded information

about nesting periodicity, reproductive homing, clutch size, long-

distance migration and remigratory intervals.

Nesting Periodicity

During a nesting season, green turtles usually lay from one to

seven clutches of eggs. There is strong evidence, however, that some

females may lay only once or twice (Hendrickson, 1958; Bustard, 1972;

Schulz, 1975; Carr et al., 1978; Balazs, 1980). The average interval

between nestings varies among green turtle populations. The following

interesting intervals (in days) were recorded at other nesting grounds:

Sarawak (Hendrickson, 1958)--10.5 (8-17); Heron Island, Australia

(Bustard, 1972)--14.5 (9-21); French Frigate Shoals, Hawaii (Balazs,

1980)--13.2 (11-18); Surinam (Schulz, 1975)--13.4 (11-16); and at

Tortuguero, Costa Rica (Carr et aZ., 1978)--12.1 (9-15). Carr and

Hirth (1962) estimated the interesting interval for Ascension turtles

as 14.5 days, with a range of 10 to 17 days (N = 76). Simon and

Parkes (1976) did not calculate the average number of days between

nestings at Ascension, but observed that 41.0% of the turtles (N = 75)


nested after intervals of 11 to 12 days, and 25.3% after 13 to 14 days.

I was the first investigator to tag intensively at Ascension throughout

an entire nesting season, and my data thus make possible the first

estimate of the number of clutches laid by individuals during a season,

and also enhance knowledge of interesting periodicity.

Clutch Size

Average clutch size varies among populations of green turtles and has

been found to be: 104.7 in Sarawak (Hendrickson, 1958); 110 at Tortuguero,

Costa Rica (Carr and Hirth, 1962); 115.5 at Ascension (Carr and Hirth,

1962); 78.0 in the Galapagos Islands (Pritchard, 1971a); 110 at Heron

Island, Australia (Bustard, 1972); 138 in Surinam (Shculz, 1975); and

104 in Hawaii (Balazs, 1980). Clutch size has been shown to be positively

correlated with the size of the turtle both within and between populations

(see review by Hirth, 1980). Carr and Hirth (1962) and Pritchard (1971a)

observed that the sizes of successive clutches laid by individual

females tend to decrease during the season. At Tortuguero, Bjorndal

(1980) found evidence that the egg clutches of remigrant turtles are

larger than those of untagged "recruit" turtles.

Reproductive Homing

Most populations of green turtles have been shown to have homing

urge and ability (Hendrickson, 1958; Carr and Ogren, 1960; Carr and Hirth,

1962; Carr and Carr, 1972; Schulz, 1975; Carr, 1975; Balazs, 1980). At

the linear coastline rookery at Tortuguero, Costa Rica, three levels of

reproductive place-finding, perhaps involving three different sets of

orienting cues, have been identified. These have been designated as

regional return, philopatry and site-fixity by Carr et at. (1978). The

ability of Tortuguero turtles to find the coast of Costa Rica represents

the regional return. Although most of the Atlantic coastline of Costa

Rica is a nearly uniform stretch of beach, green turtles nest only on one

35 km segment of the shoreline, bounded at each end by a river mouth.

Site discrimination at this level is termed philopatry. The phrase

site-fixity refers to the tendency of individual turtles to make emergences

modally no more than 0.2 km from previous emergence sites (Carr and Carr,

1972). The Tortuguero analysis is at least partly applicable to the

levels of nest-site discrimination shown by members of other populations

of turtles, even where the topography of the nesting grounds differ

greatly from that at Tortuguero. At Ascension the nesting grounds

consist of a series of covehead beaches that vary in size and shape,

and are located at irregular intervals along the leeward side of the

tiny island and are separated from each other by rugged rock promentories.

Thus at Ascension the island-finding phase of the reproductive migration,

which involves crossing more than 2,000 km of open sea that separate the

island from the feeding grounds on the coast of Brazil can be considered

the regional return (Carr, 1975). The term philopatry can logically be

applied to the selection of a particular covehead beach, as previously

documented by Carr and Hirth (1962) and by Carr (1967a; 1975), or of a

cluster of beaches. Moving clockwise around the island from South West

Bay, four clusters of beaches are easily identified. They are the

South West Bay cluster, the Long Beach cluster, the English Bay cluster,

and the North East Bay cluster (Fig. 1). Site-fixity in the restrictive

sense would be the tendency to return to approximately the same place on

one of the island beaches during successive nestings.

The present study does not address the problem of explaining the

mechanisms by which the regional return to Ascension from the Brazilian

coast is made. However, I have gathered considerable data on the two

other levels of place-discrimination--the tendencies to return in

successive nestings (a) to given beach or cluster of beaches, and (b)

to a specific section of the beach selected. I have reassessed and

tried to define the precision with which Ascension turtles are site-

fixed in their three types of renesting emergences, as follows: after

roughly 14-day intervals; after abandoned nesting attempts; and after

remigration intervals of two or more years. I have also attempted to

examine possible sensory mechanisms by which such close range homing

orientation is achieved.

Long Distance Migration

Meylan (in press b) summarizes available tag return data bearing

on the migration of adult marine turtles. The migratory pattern of the

Ascension turtles--along with those of the populations that nest at

Tortuguero, Costa Rica (Carr et at., 1978) and in Surinam (Schulz, 1975)--

is more thoroughly documented than that of any other green turtle colony

in the world.

Remigratory Intervals

The most commonly observed multi-annual renesting intervals for

Chelonia are two, three and four years. The predominant interval varies

among populations: two years in Surinam (Schulz, 1975) and in Hawaii

(Balazs, 1980); three years in the South China Sea (Harrisson, 1956;

Hendrickson, 1958) and at Tortuguero, Costa Rica (Carr et al., 1978);

and four years in Australia (Bustard and Tognetti, 1969). Carr (1975)

reported three years as the predominant remigratory interval in

Ascension turtles. Returns that have accumulated since that 1975 report,

however, suggest that longer intervals may be more typical.


Beach Patrols and Tagging

The beaches were patrolled nightly and all turtles encountered

were tagged on the trailing edge of the right front flipper, with cow

ear tags of monel metal (Carr and Giovanolli, 1957). When previously

tagged turtles were encountered, tag numbers were recorded. During the

1977-78 season all turtles were routinely checked for old tag scars.

During the previous season, tag scars were only recorded when noticed

by chance. In all cases, the point along the beach where the turtle

was observed was recorded, and the stage of her nest digging process

was recorded. An effort was made to estimate the number of trial pits

that she had excavated when encountered.

Turtle taggers working on nesting beaches elsewhere (for example

at Tortuguero, Costa Rica, and in Florida) routinely wait until a turtle

has begun laying before they apply the tag. This is impractical at

Ascension where successful nesting is delayed by the apparent difficulty

turtles have excavating nests in the coarse dry island sand (see follow-

ing section). Fortunately, Ascension turtles, which have evolved in an

environment free of large terrestrial predators, tend not to be as

skittish as their counterparts on the mainland. For this reason I was

able to devise a unique method of tagging. I found that if I approached

a turtle quietly, from behind, while crawling on my belly, and avoided

shining light in her face (I used a mouth-held penlight flashlight for

illumination, and turned it on only to read the tag number) I could, in

most cases, apply the tag during any stage of nest construction without

frightening the turtle back into the sea.

Because of the long distances between them, I could not give equal

attention to each of the 32 beaches, but instead tagged most intensively

on beaches with the heaviest nesting activity. During the 1976-77

nesting season I tagged regularly on South West Bay beach, and visited

the other beaches only sporadically. Twice during that season, for a

period of about a week each time, I made all night patrols on South West

Bay beach to monitor all the activities of the turtles which came up

there. In order to recognize individuals from a distance without dis-

turbing them, I painted a number on the rear of the carapace of each

turtle with an orange cattle marking crayon, and applied the tag only

after oviposition. Some turtles were also marked with crayon in the

hope that divers might recognize them underwater. During the 1977-78

season I tagged regularly on South West Bay beach, Long Beach, North

East Bay beach and Hannay beach, and patrolled most of the other beaches

at less frequent intervals. Nesting activity on individual beaches

was monitored over a period of several successive nights to determine

the average number of times females emerge before laying eggs.

My aim to compare nesting behavior, in particular with respect to

the number of trial nest holes dug, at different beaches with varying

sand types, was hindered by the fact that nesting turtles making trial

holes frequently remain on the beach all night long. Accordingly, during

my early morning track counts, I estimated the number of abandoned nest

holes by counting pits associated with individual tracks. The high

nesting density and looseness of the dry Ascension sand made it difficult

to follow tracks above high tide line. For this reason I was usually

able to count pits only at the beginning or at the end of the season,

when fewer turtles were nesting, or at other times when I encountered

isolated tracks. By counting pits I was also able to identify emergences

during which no digging occurred.

Long Distance Tag Recoveries, Remigration Intervals and Clutch Size

The present paper compiles all published and unpublished data on long

distance tag recoveries and remigratory intervals accumulated by inves-

tigators at Ascension since 1960. The data on clutch size for the 1976-

77 and 1977-78 nesting seasons were gathered during my hatching success

study (see Chapter 5). Most of what we know about clutch sizes of

Ascension turtles, however, was determined during previous seasons--

especially during Harold Hirth's visit in 1960, and during the seasons

that Mariculture Ltd. took eggs for the turtle farm on Grand Cayman.


Behavior on the Nesting Beach

The nesting process of Ascension turtles follows the same general

pattern as that at Tortuguero (Carr and Hirth, 1962) and at green turtle

nesting grounds elsewhere. With the foreflippers the turtle digs a body

pit, and when this has reached sufficient depth she delicately excavates

an urn-shaped egg chamber, using only the hind flippers. Into this the

eggs are laid and then with the rear flippers, the nest is carefully

filled with sand. When the egg chamber is covered, she uses her front

flippers to throw large quantities of sand backwards over the nest site

while slowly moving herself and her body pit forward.

The most noticeable differences between the behavior of Ascension

females and those nesting at Tortuguero, are that at Ascension the body

pits are deeper, and more than one body pit and egg chamber are usually

dug before the eggs are laid (Fig. 4). The island turtles may remain on

the beach from a few minutes to nine hours, and then return to the sea

without laying eggs. As many as twelve body pits, with egg chambers in

the bottom of most of them, may be dug. Presumably this activity is

exhausting, and on occasion I have come upon females apparently asleep

on the sand.

Figure 4 shows that the turtles dig more nest pits on beaches with

coarse sand than on beaches with fine sand. The relationship between the

average number of pits and the average mean sand particle diameter is

also shown (see Chapter 5).

To estimate the numbers of emergences made prior to successful egg

laying, over periods of three to seven successive nights I monitored

nesting activity on South West Bay beach, where the sand texture is more

or less typical for the island, and at Hannay beach which has very coarse

grained sand. From each cohort of turtles observed nesting on a given

night, I recorded the numbers that returned to the same beach on the

second, third, fourth and fifth nights. I adjusted the latter figures

upwards, using my percent tagging efficiency for those nights, computed







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by comparing the number of turtles tagged each night with the morning

track count (see Chapter 4). I found that about 79% of the turtles came

back to nest at South West Bay beach a second night, 25% returned a

third night, 12% a fourth night and 5% a fifth night. This gives an

average of 2.2 emergences per turtle per nesting period. At Hannay

beach, there was evidence that nearly 90% of the turtles returned the

second night, 75% the third night, 50% the fourth night and almost 20%

the fifth night--for an average of 3.3 emergences per turtle per nesting


There may be considerable error in these calculations. My tagging

efficiency was rarely 100%, and site fixity is not perfect in Ascension

turtles (see following section); turtles that may have returned to nest

on any beaches other than South West Bay or Hannay would not have been

recorded. Also, turtles that I recorded as first-night nesters might

have emerged unrecorded on previous nights. In spite of these sources of

possible error I feel that the figures are useful estimates.

Exploratory Crawls

Emergences during which no digging occurred were recorded most

often early in the nesting season. They also occurred commonly after

rollers had smoothed the beaches (see Chapters 1 and 5). During these

emergences the turtles would crawl high up onto the beach platform. In

the early part of the 1978 season, I counted 0.2 such emergences for

each track associated with body pits.

Internesting Periodicity

Figure 5 shows time intervals between observed nesting emergences

at Ascension. Of these returns, 67% were observed by me during the


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nesting seasons of 1976-77 and 1977-78, and the remainder were recorded

during 1960, 1964, 1966, 1967 and 1969.

Numbers of Nestings per Female

The numbers of days between the first and last observed emergences

of turtles are shown in Figure 6. The longest interval is 92 days.

Because my tagging efficiency never approached 100%, the intervals

recorded are underestimates. The x-axis shows 14-day intervals correspond-

ing to the interesting periodicity of the Ascension turtles. It is

noteworthy that the bars on the histogram denoting the second through

sixth nesting periods are nearly equal.

To improve the accuracy of the estimate of the number of nestings

by each female, I restricted the sample to turtles tagged at South West

Bay beach during the first 50 days of the 1977-78 season. My most

consistent tagging effort was exerted there during the first four months

of that season. Table I compares the total number of observed nestings

by turtles first encountered in January (x = 2.18; 2.08 in 1977 and 2.27

in 1978) with those first seen in February (x = 1.65; 1.66 in 1977 and

1.63 in 1978). The average number of extrapolated nestings, derived

by assuming that nesting occurs at regular 14-day intervals between

the first and last observed nestings, was 2.82 (2.65 in 1977, and 3.0

in 1978).

A comparison of the total number of observed nestings by turtles

bearing tags from previous seasons (remigrants) with the total number

that arrived tagless (recruits) is shown in Figure 7. In both 1976-77

and 1977-78 more nestings were recorded for remigrants.




S60 -////




20 -


0-6 7-21 22-35 36-49 50-63 64-77 78-92
Figure 6. Number of days between the first and last observed emergences
of turtles tagged during the first six weeks of the 1977-78
nesting seasons. The x-axis shows 14-day intervals corresponding
to the interesting periodicity of Ascension turtles.



I 2 3


Figure 7. Comparison of numbers of observed nestings by remigrant
turtles (those bearing tags or tag scars from a prior
season) and the previously untagged recruit turtles.
Data were collected during the 1976-77 and 1977-78




z 30

W 20

Table 1. Comparison of total numbers of observed
nestings by turtles first encountered at
South West Bay beach in January and
February of 1977 and 1978.

Turtles First
in January

n %

23 29.5

29 37.2

17 21.8

7 9.0

2 2.6

78 100

Turtles First
in February

n %

36 57.1

15 23.8

10 15.9

2 3.2

0 0

63 100

Mean Number of
Observed Nestings 2.18 1.65

Number of


Reproductive Homing

During the 1976-77 and 1977-78 nesting seasons at Ascension I

tagged 1,100 turtles. Of these, 371 were observed nesting at later

dates, and were involved in a total of 973 multiple emergences, ranging

from two to ten per turtle. Emergences separated by fewer than seven

days were assumed to involve returns after aborted nesting attempts.

Those occurring after intervals of seven or more days were considered

to be successful nestings. In analyzing the data, I considered these

two types of emergences separately. A third class of re-emergence is

that made whan a remigrant returns after an absence of two or more years.

Although data are not extensive, reproductive homing is also evident in

those returns. At Ascension Island the turtles show site fidelity for

a cluster of adjacently located beaches; for a particular beach within

a cluster; or to a less clearly demonstrable extent, for a restricted

section of a beach.

Site fidelity in remigratory returns

At other nesting grounds site fidelity in return nestings has been

clearly proved for remigratory as well as renesting emergences. At

Ascension, data on the former are meagre. For each remigrant turtle

recorded at Ascension between 1960 and the present time, Table 2

indicates the cluster of beaches at which the last observed nesting

during an earlier season occurred. The number of years separating

emergences are also indicated. Many of the remigratory recoveries at

Ascension have been made by part time collaborators, who did not

usually keep precise locality records.

Table 2. Locations of the last observed emergences of the
previous season, and the first observed emergences
after remigration, for the 67 remigrant turtles.
One turtle was recorded after two remigrations.
The numbers indicate the years between each pair
of sightings. The percentages indicate what
portions of the total number of remigrants
recovered at the beach clusters listed along the
top row, were last seen at the beach clusters
listed along the left hand side of the table.



South West

Long Beach

North East


South West







Long Beach


North East









Total number of
remigrants recorded
per cluster 29 16 23

Site fidelity in within-season returns

Re-emergences occurring within a single nesting season are examined

in terms of site fidelity for a beach cluster, for a given beach, and

for points along a single beach.

Movements between clusters of beaches. In a preliminary assess-

ment of site fixity, I assigned each re-emergence of each turtle a rating

for "success" or "failure" depending on whether the turtle emerged at

the same cluster of beaches on which it previously came out. Using a

normal approximation of the binomial distribution (Mendenhall, 1975),

I determined the 95% confidence interval for percentages of successful

emergences, according to the formula:

limit + 2 -1 P ; where S = number of successes,
0.95 S + F
F = number of failures, and

S+ F

The 95% confidence interval for the proportion of successive emergences

on the same beach cluster separated by seven or more days was 84.1-90.6%.

For those separated by less than seven days it was 91.0-97.9%. These

data corroborate earlier evidence of philopatry at Ascension.

I then considered all the emergences of each turtle, and determined

the beach cluster on which each nested most frequently. More than half

of the emergences of each of 334 of the 371 turtles were confined to one

cluster. Emergences of 37 turtles could not be categorized because only

two were recorded, each at a different beach cluster.

I again assigned each re-emergence a score of "success" or "fail-

ure," this time depending on whether it occurred at the dominant beach

cluster. To see whether there were differences between the site-fidelity

of turtles that nested predominantly at one cluster or another, I

separated the turtles into four groups according to their dominant

beach clusters, and used the same formula to determine the 95% confidence

interval for the percentage of successful emergences within each group of

turtles (Table 3). There was little difference between the performances

of the four groups. However, emergences separated by less than seven

days were more likely to occur within the same cluster of beaches, than

those separated by greater time intervals.

Table 4 shows the location of each pair of consecutive emergences

by individual turtles, separated by intervals of fewer than seven days;

and Table 5 shows the same for those separated by intervals of seven or

more days. In most cases, the two emergences occurred at the same cluster

of beaches. In those instances in which a turtle strayed from the

original cluster, she was more likely to re-emerge at a neighboring

cluster than at one farther away. There was a greater tendency to re-

appear at the same beach cluster when emergences were separated by less

than seven days (Table 3).

Movements between beaches. For each turtle I determined which

beach, if any, was used most often. Each emergence was given a score

of "success" or "failure" depending on whether it occurred at the dominant

beach. I then used the above formula to determine the 95% confidence

interval for the percentage of "successful" emergences which occurred.

When all the turtles are considered together, 77.4-85.1% of returns after

seven or more days, and 81.6-91.7% of returns within a seven day

interval, were successfully site-fixed.






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Table 4. Locations of the members of each pair of successive
nesting emergences separated by intervals of less
than seven days. The beach clusters are listed in the
order in which they occur at Ascension, moving clock-
wise along the shoreline, starting at South West Bay.
English Bay cluster is not listed because no turtles
were recovered there within a seven day interval. The
percentages indicate what portions of the total number
of turtles recovered at the beach clusters listed
along the top row, were last seen at the beach clusters
listed along the left-hand side of the table. The
percentages across each row decrease as distance from
the original cluster increases.




South West
U Bay

S Long Beach

j North East

Total number of
re-emergences recorded
per cluster

South West

107/109 =

1/109 =

1/109 =

Long Beach

6/21 =

14/21 =

1/21 =

109 21

North East

1/51 =

0/51 =

50/51 =

Table 5. Locations of the members of each pair of successive
nesting emergences separated by intervals of seven
or more days. The beach clusters are listed in the
same order in which they occur at the island, moving
clockwise along the shoreline, starting at South
West Bay. The percentages indicate what portions of
the total number of turtles recovered at the beach
clusters listed along the top row, were last seen at
the beach clusters listed along the left-hand side
of the table. The percentages in each row decrease
as distance from the original cluster increases.




South West

South West 240/254 =
Bay 94.5%

Long Beach

English Bay

North East

9/254 =

0/254 =

5/254 =

Long Beach English Bay

14/67 =

42/67 =

2/67 =

9/67 =

1/13 =

5/13 =

4/13 =

3/13 =

Total number of
recorded per

254 67 13 82

North East

6/82 =

2/82 =

1/82 =

73/82 =

254 67

13 82

To determine whether site tenacity was greater at one beach than

at another, I first grouped the turtles according to the cluster to which

their dominant beach belonged. For each group the 95% confidence intervals

were determined for the percentage of emergences which were site-fixed to

the dominant beaches of the individual turtles (Table 6). A chi-square

test was used to compare the proportions of successes and failures by

each group of turtles--except the group nesting predominantly at the

English Bay cluster for which too few data were gathered. No significant

difference (p < 0.05) was found between the performances of the three

groups of turtles when emergences separated by intervals of fewer than

seven days were considered. The chi-square test showed, however, that

when renestings separated by seven or more days were considered, the

turtles of the North East Bay cluster had significantly more failures

than did those from the other clusters (p < 0.001).

Site-fixity within the boundaries of a given beach. For each

turtle recorded more than once on either South West Bay beach, Long

Beach or North East Bay beach, an index of site-fixity was calculated.

First, I determined the midpoint between the positions of her two most

widely separated landings. Then I measured the distance of each

emergence from that point, summed the distances, and divided by the

total number of emergences made by that turtle. Figure 8 compares

the indices calculated for turtles observed nesting at South West Bay

beach, Long Beach, and North East Bay beach. It also compares site

tenacity in emergences separated by less than seven days, with that

of those separated by seven or more days. A z-test (Steel and Torrie,

1960) showed no significant difference between emergences occurring

during the 1976-77 and 1977-78 seasons (p < 0.05). At each beach a




j i


m 0N

L- 4- -


* -C rC C

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i0 n i c

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.m 0 m
0 0

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ce 0

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,-o o0
u u4-

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-0 m
(4- 0 Ln
'4 -n






(- 4
0 U




(350 m)

cn 100
z 90

C 80
2 70
0 60


z 40

(915 m)


Figure 8. Means and standard deviations of the average distances
between successive nesting emergences of turtles encountered
on the three major beaches of Ascension Island. The distances
were calculated by determining the average deviation of the
emergences of each turtle from a point midway between her
two most distant landings.





120 -


C t

(480 m)

greater degree of site fixity tended to occur in consecutive emergences

separated by less than seven days than in those separated by longer time

intervals. However, a z-test showed these differences to be statistically

significant only at South West Bay beach, where I had the largest sample

size (N = 231; z = -2.31; p < 0.05).

Clutch Size

All available published and unpublished data on clutch size were

compiled and the average clutch was found to be 120.9 eggs (N = 548;

S.D. = 26.8). The average varied from year to year: 115.5 eggs, N =

140, in 1960 (Carr and Hirth, 1962); 116.3 eggs, N = 169, in 1973, and

127.0 eggs, N= 163, in 1974 (Simon and Parkes, 1976); 128.9 eggs, N = 58,

in 1977; and 125.6 eggs, N = 18, in 1978. A. Carr made available to me

for recalculation, the raw data from Carr and Hirth (1962) in which

clutch size in Ascension turtles is discussed. Egg counts of two clutches

fromeach of 26 females were made by Hirth in 1960. The average egg

number in the earlier of the two sets of clutches was 123 (S.D. = 15.7);

in that of the later clutches it was 103 (S.D. = 20.91). A paired t-test

showed a highly significant tendency for the second clutch to be smaller

(t = 4.40; N = 26; p < o0.00).

For an additional twelve individuals, Hirth counted the eggs of

three or more clutches: for eight turtles, three counts were made; for

two, four counts were made; and for two others five counts were made.

In Figure 9 the number of eggs in each clutch is plotted against the

number of days since the first observed laying by the corresponding

female. A significant correlation was found (r = -0.55; N = 42;


140- *

40 0

120 *

rr 0 .

w 90-, *

S80 \ p<0.001

z 70
C* *


S 10 20 30 40 50 60

Figure 9. Relationship between the number of eggs laid by
turtles at each recorded nesting, and the number
of days elapsed since their first observed nesting
during the season. Only cases involving three or
more clutches with known egg count laid by the same
turtle are considered.

p < 0.001) between number of eggs laid and the number of days elapsed

since the first observed nesting.

I then compared all the egg complements counted by Hirth during the

first part of the 1960 season (February 21-March 20), with those laid

later in the season (March 21-April 30). A z-test (Steel and Torrie,

1960) showed no significant difference (z = -0.80; df = 79; p = 0.21).

Remigration Intervals and Tag Loss

Since the initiation of the Ascension study in 1960, return

migratory visits have been recorded for 68 tagged Ascension green turtles.

Figure 10 shows the remigration intervals of these animals. Three and

four year cycles predominate. During the 1977-78 season I systematically

checked each turtle for old tag scars and found that 78% of the 42

remigrants had lost their tags.

Long Distance Recoveries

Since 1960, 3,384 turtles have been tagged at Ascension Island. At

the present time, a total of 64 long distance tag recoveries have been

made, all from the coast of Brazil (Fig.11) where the turtles forage on

benthic algae (Ferreira, 1968). The 39 Brazilian recoveries made prior

to 1973 are summarized by Carr (1975). Elapsed time between the last

recorded appearance of each turtle on the nesting beach and its capture

on the coast of Brazil is shown in Fig. 12. Most recoveries occurred

within three years after the turtle was tagged.

1 2 3 4




Figure 10. Remigration intervals between successive nesting
seasons recorded for Ascension turtles.

5 6 7 8 9






0 .. ,--. .,- r,* ,.

I 2 3 4 5 6


Figure 11. Number of years between last sightings of turtles on
nesting beach and their capture off the coast of

450 400 350

50- 2 1

/. 6





C 0 500

) KM

Figure 12. Location of long distance recoveries at Brazil. Circled
numerals show number of returns from each locality. Arrows
indicate recoveries made within 100 days of the last sight-
ing of the turtle on a nesting beach at Ascension.


Behavior on the Nesting Beach

All the Ascension beaches are characterized by coarse, dry and

loose sand (Table 13). On the biogenic beaches in particular, the sand

grains are rounded and slip over each other easily. It would obviously

be difficult to form an egg chamber with nearly vertical walls in such

a medium. Because the angle of repose increases with moisture content,

and because water content increases with depth, it is reasonable that

the Ascension turtles would have to dig deep body pits. In addition,

the higher moisture levels found at greater depths would benefit the

incubating eggs, which at Ascension are subject to dehydration (see

Chapter 5). Possibly their need for deeper body pits, and their long

distance migratory patterns explain why the turtles of the Ascension

colony are larger than those of other green turtle populations (Hirth,


Because cave-ins are frequent, it is not surprising that turtles

dig more trial nest holes in beach sands with larger mean particle

diameters (Figure 4). An exception was found at North East Bay beach,

where the turtles dig more nest pits in the relatively fine sand than

would be expected based on the observations made at the other beaches

(Figure 4). Perhaps this is explained by the low moisture content of

the North East Bay sand (Table 13), a condition which would decrease

the angle of repose. Bustard (1972) and Balazs (1980) believe that

at Heron Island, Australia,and at French Frigate Shoals low moisture

content of the sand impedes digging.

It was sometimes obvious why a turtle stopped digging a particular

egg chamber; the walls had caved in. Often, however, the original egg

chamber appeared well formed and some other quality of the sand or site

must have prompted her to move out of the body pit and resume digging

a few meters away. One wonders whether the viability of egg clutches

laid in such egg chambers would have been significantly lowered. In

Sarawak, Hendrickson (1958) found evidence that vibrations in the sand

caused by the activities of females digging nearby cause turtles to

abandon egg chambers. I doubt that this is a major cause of abandonment

by Ascension turtles, because multiple nest holes are often dug by

isolated individuals.

Many egg clutches at Ascension are destroyed by turtles digging

new nests, as was observed at Heron Island, Australia,by Bustard and

Tognetti (1969). Such density dependent mortality is greatest on the

beaches with coarser grained sand, where more trial nest holes are

constructed. In light of this, it seems curious that a strong site

fixity (see following section) should be a characteristic of the

Ascension population. If a turtle returns to lay eggs at the same

point on the beach where she laid another clutch two weeks earlier,

and if she makes numerous trial nest pits there, she obviously risks

digging up her own eggs. It also seems curious that a turtle once

having failed to construct a suitable nest on a given night, should

return to the same point on the same beach the following night. There

is also the question, what happens if a turtle is never able to con-

struct a suitable egg chamber. Does she drop her eggs in the sea, as

has been suggested by Simon and Parkes (1976) and Balazs (1980), or

does urgency force her to accept a suboptimal egg chamber?

Exploratory Crawls

"False crawl" is a somewhat misleading term that for want of a

better phrase has been used to indicate an emergence during which eggs

are not laid. Carr et aZ. (1978) discussed the various degrees of

completion to which unrealized nestings advance at Tortuguero, and

recognized three distinct types. These are, in order of their prevalence

at Tortuguero, the smooth arcing "half-moon" and the angular "half-

moon" (in which a turtle emerges to a point on or just beyond the

wave-washed flat and then returns to the sea), and the abandoned prospect-

ing venture far up into nesting sand. Only rarely do turtles at

Tortuguero dig complete nest cavities and then abandon them, as occurs

so commonly at Ascension. Somewhat more frequently, Tortuguero turtles

crawl up onto the beach, make a few trial scrapes, and then return to

the sea without nesting. This type of behavior is observed more commonly

at Ascension, especially early in the season when one finds long,

meandering tracks high on the beach platform, with little or no

evidence of digging except for a shallow body pit. Possibly, these

tracks only seem to be more numerous at that time because later on,

as nesting activity increases, they are not as easily discernible

among the tracks left by other turtles. However, I found other evidence

that recent nesting activity on a beach may encourage turtles that

arrive later to begin nest construction.

Virtually without exception, as soon as an Ascension turtle,

crawling along a beach, begins to descend into a body pit left by

another turtle, she will start throwing sand with her front flippers,

and often will construct her own body pit and egg chamber there.

Similar behavior was also observed by Hendrickson (1958) in Sarawak. It

seems possible that a turtle encountering only smooth sand, might

actually be discouraged from nesting because she receives no possible

stimulus to dig. In any case, after wandering about, such individuals

return to the sea. This reluctance to dig in smooth sand might be

adaptive. For example, the body pit left by a turtle after she covers

her nest is usually located one or two meters from the site of the egg

clutch. Turtles subsequently nesting in that pit will therefore not

threaten the eggs (Hendrickson, 1958). A second advantage may be that

segments of beach regularly subjected to smoothing by inundation would

be avoided. For example, one night after a series of rollers had

smoothed the surface of an Ascension beach, the only four turtles that

emerged that night, wandered extensively over the beach without digging

nest holes.

It is noteworthy that the two most frequent types of false crawl

occurring at Tortuguero, the half-moons, are the least prevalent both

at Ascension and in Hawaii (Balazs, 1980). The smooth arcing half-

moon, which leaves a curving track on the wave-washed flat seems to be

a pre-programmed sensory appraisal of the shore. In the other type,

the angular half-moon, the two limbs of the track meet at an angle,

suggesting that the turtle abandoned the emergence after receiving some

discouraging stimuli. In neither case is there any evidence of digging,

nor that the turtles aborted the emergence because they had been

startled. Half-moons seem to be sensory, probably chemical or tactile,

appraisals of the shore (Carr et at., 1978).

During the 1979 season at Tortuguero, approximately 1.1 false

crawls were recorded for each complete nesting emergence. At Ascension

they were less prevalent. Carr and Hirth (1962) discuss differences

in the topography of the two nesting grounds which may account for the

divergent behavior. In 1978, during the first month of the season at

Ascension, when false crawls are most commonly observed and most easily

discernible, I counted only 0.2 false crawls for each normal emergence.

Because Ascension beaches are steeper than that at Tortuguero the

wave-washed littoral zone is also less extensive. For this reason,

most of the exploratory emergences that occur at Ascension may go

unrecorded. On many occasions I saw turtles crawl distances of one or

two meters onto the wave-washed sand, in the classic half-moon pattern,

but their tracks were erased by waves within seconds. On nights when

the moon was full, I could sometimes see turtles swimming back and forth

in the surf just offshore. Presumably these were females investigating

the shoreline prior to making a landfall (see Chapter 3).

Internesting Periodicity

Carr and Hirth (1962) based their estimate of the average inter-

nesting interval at Ascension (14.5 days) on 76 observations. I calcu-

lated a new estimate using all the re-emergences observed at Ascension

since 1960 (Fig. 5). The majority of the 405 turtles represented in

the first peak in Figure 5 nested after intervals of 11 to 18 days

(range 7-20). The predominant interval was 13, followed by 14 days, and

the average interval was 13.9 days. Lesser peaks can be seen in Figure

5 at points roughly corresponding to multiples of 13-14 days. Nesting

emergences observed within six or fewer days were assumed to be re-

emergences after aborted nesting attempts.

Figure 5 shows the intervals between recorded nesting emergences,

but in most cases egg laying was not observed. To test the accuracy of

my estimate, I examined the 53 emergences recorded during the 1960, 1970,

1977 and 1978 seasons, in which eggs were known to have been deposited

after intervals ranging from seven to 20 days. The average of these,

14.1 days (S.D. = 2.49), is very close to the 13.9-day estimate derived

from Figure 5.

Number of Nestings per Female

In Surinam, where the tagging efficiency was reported to be nearly

perfect, Schulz (1975) estimated that the average green turtle nested

2.9 times in a season. Turtles first observed nesting during the initial

six weeks of the season laid more clutches--an average of 3.6 nests.

At other localities where it has been impossible to monitor every

emergence, the minimum average number of clutches laid per female must

be estimated. At Tortuguero, Costa Rica, Carr et aT. (1978) estimated

that turtles first encountered early in the season lay an average of

2.8 clutches.

At Ascension, the longest interval between the first and last

observed emergence by a turtle was 92 days, during which time she could

have laid seven egg clutches at 14-day intervals. The nesting season

lasts approximately six months, so individuals nesting early in the

season are not the same that nest at the end of the season. I recorded

an average minimum of 2.2 clutches per season laid by turtles first

observed early in the season, and like Schulz (1975) and Carr et at.

(1978), I found evidence that more clutches are laid by turtles first

observed at the beginning of the season than later in the season (Table


It is important to realize that my numbers are probably under-

estimates because my beach coverage was by necessity incomplete. My

estimate increases to 2.8 clutches per season when the number of nestings

is extrapolated on the assumption that nesting occurs at regular 14-day

intervals. In the past, some investigators have assumed that to calculate

the number of actual nestings, it was only necessary to divide the time

between the first and last observed emergences, by the known interesting

interval. In Surinam, Schulz (1975) recorded large numbers of turtles

nesting at intervals corresponding to multiples of the average two-week

interesting interval. One might assume such extended intervals to be

artifacts of the sampling caused by unrecorded emergences. Schulz,

however, believes that his monitoring of the nesting beach is so

complete that the tagging crew could not have missed that many nestings.

Thus, it would appear at least in Surinam, and maybe at other nesting

grounds, that turtles occasionally refrain from nesting, but then re-

emerge on schedule at a later date, thus preserving the expected two

week cycles.

At Ascension, more nestings were recorded for the remigrants than

for the recruits in both 1976-77 and 1977-78 (Fig. 7). Schulz (1975)

in Surinam, and Carr et at. (1978) at Tortuguero, also found that

remigrant turtles laid more clutches than did the new recruits. Both

authors believe that many turtles probably nest only once during the

season. My data also suggest this (Table 1; Fig. 6). Carr et al.

(1978) postulated that recruits may begin their reproductive life with

a migration that culminates in only a single nesting.

Reproductive Homing

My data reveal three degrees of precision in re-emergent site

tenacity, depending on the time interval separating the emergences.

Emergences separated by fewer than seven days were probably separate

attempts to lay the same clutch of eggs, and were characterized by a

higher degree of site fidelity than were re-nestings separated by longer

time intervals. This is in accord with results of my tracking experiments

(see Chapter 3), which suggest that during the first 24 hours after

abandoning a nesting attempt turtles generally remain within the

vicinity of the nesting beach. Those which have deposited their eggs

travel greater distances. Obviously the chances that a turtle will

re-locate a site at which she previously emerged would be enhanced if

she does not leave the area between emergences.

Site fidelity would logically be expected to decrease with an

increase in time between emergences. A Pearson correlation demonstrated

no significant correlation between the time interval and the amount of

geographic displacement separating emergences that occurred during a

season (N = 601; r = -0.01; p = 0.80). This is consistent with the

findings of Carr and Ogren (1960) at Tortuguero, that there was no

decrease in site fixity over time.

Similarly, site fidelity would be expected to decline even more

sharply in returns after migratory intervals of two or more years. At

Tortuguero, however, Carr and Carr (1972) found a similarity between

nest-site intervals for the 12-day renesting returns and those for the

remigrant turtles. Because the tagging effort at Ascension has been

so uneven from year to year (Table 7), it is difficult to compare the

site tenacity in renestings within the same season, with that in

emergences separated by a remigration interval. Carr (1975) reported

a tendency for the precision of remigratory homing to exceed that of

the renesting returns, based on 24 remigrant returns at Ascension.

Today, the data base has increased to 68 remigrants, and the data now

suggest that there may be a very slight decline in site fidelity after

a remigratory interval (cf. Tables 2 and 5).

For emergences separated by less than seven days, site tenacity at

the level of the beach cluster is nearly perfect, but it is lessened

when longer time intervals separate the emergences (Table 3). To

determine whether the turtles showed stronger site fidelity to one beach

cluster than to another, I grouped the turtles according to the beach

cluster at which most of their nesting emergences occurred and compared

the performance of turtles within the group. A Chi-square test showed

there is no significant difference in site fidelity to a cluster between

turtles from the three major beach clusters--South West Bay, Long Beach

and North East Bay. Proportionally more individuals from the English

Bay cluster may have strayed to other beach clusters, but the results

are inconclusive (Table 3). It would be reasonable for English Bay

cluster turtles to stray more frequently, because the distance between

the extreme ends of the cluster is only 1,375 m; whereas the correspond-

ing distances along the South West Bay, Long Beach and North East Bay

clusters are respectively 2,690, 3,440 and 4,000 m. In cases in which

a turtle did stray between beach clusters during successive emergences,

she was more likely to go to an adjacent beach cluster than to one

farther away (Tables 4 and 5).

Besides their tendency to return to a particular cluster, the

Ascension turtles showed a tendency to nest repeatedly on the same

beach within a cluster, especially when the emergences were separated

by less than seven days (Table 6). Although the North East Bay cluster

turtles showed no greater tendency to emerge to nest on other beach

clusters than did those from either South West Bay or Long Beach, they

did show a greater tendency to re-emerge at different beaches within

that cluster (Table 6). This was true regardless of the number of days

between emergences. It seems likely that the number of beaches that

make up a beach cluster, and the lengths of those beaches, may be

influential in determining whether turtles return to the same beach.

There are eleven separate beaches in the North East Bay cluster, compared

to four in the South West Bay cluster and seven in the Long Beach cluster.

The average length of the North East Bay beaches is only 83 m (median

45); for South West Bay beaches 248 m (median 175), and for the Long Beach

beaches 349 m (median 290). These data support the assumption that it may

be easier for a turtle to home in on a longer beach than on a shorter one.

The weaker site fidelity for a specific beach at the North East Bay

cluster is consistent with the behavior of the individuals I tracked.

Although the two turtles tracked after they abandoned a nesting attempt

at North East Bay beach remained within the offshore waters of the North

East Bay beach cluster, they travelled away from North East Bay beach

itself, and even briefly crawled ashore on other beaches within the

cluster (Fig. 18 and 19). In comparison, all six turtles tracked after

abandoning a nesting attempt at South West Bay beach (Figs. 16, 20-24)

remained in the vicinity of South West Bay beach itself, and any brief

emergence occurred on that beach (Figs. 20-21).

To determine whether individual turtles homed to a location within

the boundaries of a single beach, I used an index of site fixity. The

index is a measure of the average distance the collective emergences of

each turtle strayed from a point midway between her two most extreme

emergences. Using these calculations, Figure 8 compares the site

fixity of turtles nesting at the three most important beaches--North

East Bay beach, Long Beach and South West Bay beach. The lengths of

the beaches are, respectively, 350 m, 915 m, and 480 m. A Kruskal Wallis

test (Siegel, 1956) showed no significant difference (p < 0.05) between

the average distances calculated at the three beaches. There were only

small increases in the mean distances. This suggests that at Ascension,

once a turtle locates a beach at which she nested previously, her ability

to locate a particular point within the boundaries of that beach is not

substantially hindered by the overall length of the beach.

My site fixity index only considered those emergences occurring

within the boundaries of a given beach. Because the nesting ground at

Ascension is broken into short segments of beach, it would have been

unrealistic to use an index that would incorporate all the emergences

of a turtle. Re-emergences occurring on different beaches which were

separated by expanses of rock shoreline would have distorted the values


Clutch Size

Hirth (1980) published a regression of the mean clutch sizes and

mean carapace lengths in eleven green turtle populations. The average

clutch size for Ascension turtles, 120.9 eggs (N = 548), fits Hirth's

regression line better than the figure of 115.5 eggs (N = 140) (Hirth

and Carr, 1962) which he plotted on his graph.

My analysis of the data gathered by Hirth during his visit to

Ascension clearly demonstrates that within a season, the number of eggs

laid by individual turtles tends to decrease with each successive nest-

ing. However, the trend does not manifest itself as an overall decrease

in the average size of clutches laid from month to month as the season

progresses. Schulz (1975) also found no significant differences in clutch

sizes for different periods during the nesting season. This is probably

because new turtles arrive at the nesting beach throughout the season,

and their larger clutches compensate for the smaller clutches being

laid by turtles that had already deposited clutches earlier in the

season. Hirth's 1960 data (Carr and Hirth, 1962) suggests that a turtle's

first clutch of the season is large regardless of whether it is laid near

the beginning or the end of the season.

Remigration Intervals

Three and four years are more clearly dominant among remigration

intervals recorded for 68 Ascension turtles between 1960 and the present

(Figure 10), than they were in 1973 when only 24 remigrants had been

recorded (Carr, 1975). The tagging effort at Ascension has been erratic

over the years (Table 7) so the question arises whether the observed

proportions of their cycles reflect the true situation or are artifacts

of the sampling procedure.

Tag loss also influences observed remigratory intervals. The

percentage of remigrants in my study that had lost their tags, 78%, is

high compared with the 23% recorded among 462 remigrants to Tortuguero

in 1976 (A. Carr, pers. comm.); but is comparable to that observed in

populations elsewhere (Mrosovsky, 1977). There was correlation between

Table 7. Number of turtles tagged at Ascension Island
each year. Numbers indicate tagging effort
and do not reflect levels of nesting

Year Number of Turtles Tagged'

1960 203
1961 0
1962 0
1963 0
1964 159
1965 83
1966 122
1967 145
1968 0
1969 124
1970 100
1971 36
1972 96
1973 567
1974 511
1975 25
1976 65
1977 564
1978 457
1979 127

Total 3,384

numbers of turtles recaptured on the coast of Brazil and numbers of

years elapsed since the last observed nesting emergence; all the

recaptures of turtles in Brazil occurred within six years after tags

had been applied (Fig. 11). This trend probably reflects rates of tag

loss. Although mortality on the feeding grounds is an alternate

explanation for this trend, the implications are the same with respect

to remigration intervals. The largest number of observed remigrations

would be expected after shorter time intervals, especially after one

year. Remigrations by green turtles after intervals of one year, have

rarely been observed anywhere, however, and no one-year remigrants

were reported at Ascension (Fig. 10). Thus, we can assume that the

observed numbers of turtles returning to nest after intervals of two

and three years do not include one-year remigrants overlooked during a

previous nesting season, and our observation that three-year remigrants

outnumber two-year remigrants by at least seven to one (Fig. 10) is

probably valid.

It is more difficult to estimate the relative number of four-year

remigrants reliably. The figure for this group is probably inflated

by the inclusion of two-year remigrants whose previous remigration had

been overlooked. Since tag loss is greater after four years (Fig. 11),

than after two, however, the data in Figure 10 probably under-represent

the number of four-year remigrants. In actuality, the four-year

remigratory interval is probably dominant, and the three-year interval

the next in frequency. A long remigratory interval seems reasonable in

view of the great distance between the nesting and feeding grounds of

the population.

Only one Ascension turtle was recorded as a double remigrant. She

nested after three years, and then again two years later. Such modulated

periodicity has also been observed in other populations (Carr and Carr,

1970; Schulz, 1975; Carr et at., 1980; Balazs, 1980).

Long Distance Recoveries

There is no correlation between the sites where turtles nested on

Ascension and sections of the coast on which they were later intercepted

off Brazil (Fig. 12). Neither was any correlation observed between

places on the beach at Tortuguero where the turtles nested, and the

areas where they were later recaptured (Carr et at., 1978).

All the Brazilian recoveries of Ascension turtles were made within

six years of the time they were tagged on the nesting beach (Fig. 11).

The four Brazilian recaptures that occurred within 100 days of a last-

observed nesting clustered around the easternmost part of the bulge of

the continent (Fig. 12). However, there was no correlation between the

point along the Brazilian coastline and the period of time that had

elapsed since it was last sighted on the Ascension beaches (Carr, 1975).

This suggests that the first landfall of a migrating turtle after it

has left Ascension is the bulge of Brazil, and that the turtles

subsequently disperse northward and southward along the coast.

The quickest recovery of an Ascension turtle was made 56 days after

it had been observed nesting on March 22, 1977. This rapid crossing

suggested oriented travel. To swim the straightline distance of 2,300

kms, this turtle travelled at an average rate of 41.1 km per day.

During the months of February, March and April the mid-equatorial

current from Ascension to the bulge of Brazil flows at speeds of 0.4 to

0.9 knots (Anon., 1975). At this rate an object drifting with the

current would take from 58 to 129 days to reach Brazil. Thus, the

turtle which took a maximum of 56 days probably did not travel passively

in the current. The speeds of travel of turtles captured shortly after

leaving nesting beaches have been calculated for other populations

(literature reviewed by Carr et al., 1978). Schulz (1975) estimated

an average travel speed of 35-80 km per day (or 0.8-1.8 knots) for

green turtles travelling against the current from the Surinam nesting

grounds to the feeding grounds of Brazil. Thus, it seems likely that

turtles travelling from Ascension with the current can easily reach

Brazil in less than 56 days.



Female green turtles spend most of their adult lives at their

foraging pastures, migrating to the nesting grounds once every two,

three or four years, or even less frequently (Carr, 1975; Carr et at.,

1978). During a season, a female usually lays from one to seven egg

clutches (literature reviewed by Ehrhart, in press). Since consecutive

layings are separated by intervals of about two weeks, a turtle may

spend as much as four months at the nesting grounds. Little is known

about the behavioral ecology of female green turtles during that time.

Most of what we know about interesting ecology has come from the visual

tracking experiments performed by Carr at Tortuguero (Carr, 1967a;

Carr, 1972) and at Ascension (Carr, 1972; Carr et aZ., 1974) and by

Meylan (1977; in press a) at Tortuguero. Julie Booth made underwater

observations of interesting females in Australia (Booth and Peters,


Tracking does not only provide information about the occupancy

of the interesting habitat. It can also be a tool with which to

evaluate how a turtle reacts to features within its environment (topog-

raphy of the seabed, water depth, etc.), which may in turn lend clues

to the mechanism of sea turtle orientation. Sea turtles guide them-

selves through long distances between their foraging and breeding

grounds, and also show clear, though variably precise site fixity in

returning to the nesting beach (Carr et al., 1978). Ascension Island

turtles usually return to the same beach for repeated nestings--often

close to the same point on that beach (Chapter 2). The sensory cues

that mediate this behavior are unknown. Investigation is handi-

capped by the fact that data can usually only be obtained when a tagged

female is up on the nesting beach, or when her tag is returned after she

has been killed at the feeding grounds. It has generally not been

possible to plot the exact routes taken by turtles during their goal-

finding activities.

The present study is an attempt to learn more about the behavioral

ecology of female turtles during their interesting intervals. I

visually tracked the movements of turtles after they left their nesting

beaches, using polyurethane foam tow-floats. From shore, the positions

of the floats at sea were recorded. Although the use of a tow-float

has drawbacks, and may seem a primitive technique, it is virtually the

only way to get detailed information about the movements of turtles at

Ascension. Sophisticated radio tracking devices using either surface to

surface, or satellite transmission would also require that the trans-

mitter be elevated above the surface of the water. Ireland (1980)

successfully followed the movements of turtles on their feeding grounds

in Bermuda by using sonic devices attached directly to the carapace of

the turtles. At Ascension, this method would not be practical because

the turtles often swim close to shorelines pounded by heavy surf, and

the air bubbles in the water would reflect sonic signals.

Most previous tracking experiments with interesting females have

focused on movements after egg laying (Carr, 1967a; Carr, 1972; Carr

et at., 1974; Meylan, 1977 and in press a). In the present study, two

types of experiments were conducted. Turtles were tracked after

successful nesting, and also after abandoned nesting attempts. By

tracking the turtles after abandoned nesting attempts, I was able to

examine the manner in which the nesting beach was reapproached, and to

gather clues that might suggest the sensory basis of nest site selection.

The turtles in my experiments abandoned their nests because they were

frightened by me. On Ascension, however, even when there is no human

interference, nesting females often return to the sea without having

laid their eggs. This is probably because of the difficulty they

have excavating a satisfactory egg chamber in the coarse, dry sand

(Chapter 2).

An understanding of sea turtle behavior after abandoned nesting

attempts will help in evaluating what level of disturbance is tolerable

on the nesting beach. Moreover, to help protect the breeding turtles

from such hazards as incidental catch, trawling, and pollution, it is

necessary to define the interesting habitat and to determine the

activities of the animals within it.

Materials and Methods

The travel of each turtle in the interesting habitat was recorded

by visually tracking a float attached by a 20 m nylon line to the

posterior margin of the carapace. Simultaneous compass bearings were

taken at intervals of about 3 minutes, from two points on the shore.

The positions of the float were determined by triangulation.

The floats, made of polyurethane foam, were elliptical in shape,

and measured 19 x 12 x 7 cm. A fiberglass fishing rod served as a mast,

and to the middle of this a small piece of foam was affixed, to prevent

the float from turning over. At the top of the mast there was a 3 volt

light bulb, wired to a flasher circuit. As a back-up in case of light

failure a chemical light stick (Cyalume) was taped to the mast. Ballast

was provided by a lead disc and a 6 volt battery. The body of the float

was waterproofed with bright yellow epoxy (Boat Renu) paint. Daytime

visibility was enhanced by fluorescent orange spray paint and by yellow-

and-orange flagging attached to the mast.

The float line was fastened to the shell of the turtle by 1.5 mm

ungalvanized baling wire, threaded through a hole drilled in one of the

posterior marginals. Because jagged rock reefs are abundant around the

perimeter of the island, I chose wire weak enough to break and free the

turtle if the float became snagged.

Compass bearings were taken with an Embeeco compass-bearing

monocular from promentories around the island perimeter. For maximum

accuracy, care was taken to choose positions from which lines of sight

would be approximately perpendicular to each other. In a few cases, it

was necessary to estimate the position of the turtle using only a single

compass bearing. Turtles that had nested at the English Bay beaches

were not tracked. The difficult terrain and lack of suitable promentories

would have made continuous observation impossible. Likewise, at Long

Beach an offshore fuel line that would have entangled the tracking

device made tracking impracticable. Only turtles found nesting at

either South West Bay or North East Bay beaches (Fig. 1) were tracked.

These included four that had successfully nested, and eight others that

had not been permitted to lay eggs before returning to the sea. One

individual of the latter group was continuously tracked from the time

it abandoned its nest, until two days after it had successfully laid

eggs the following night (a total of 60 hours).

Results and Discussion

The movements of four turtles after successful nesting are shown

in Figures 13-15, 17. Movements of eight turtles that were frightened

at uncompleted nest holes before laying are shown in Figures 16, 18-24.

Figures 16 and 17 are consecutive tracks of the same individual, the

first after abandoning a nesting attempt, and the second after laying

eggs the following night. All compass bearings taken on the tracking

floats were incorporated into the tracks in Figures 13-24. Times are

indicated at fifteen minute intervals, unless otherwise specified. Table

8 gives the nesting history of turtles before and after they were


The travel-patterns of turtles that had laid eggs were consistently

different from those of turtles that had abandoned a nesting attempt.

All the turtles that laid eggs initially moved into water 12-16 m deep,

and then travelled parallel to the shoreline for distances of up to 7 km,

and did not venture into water less than 8 m deep during the first 3

to 11 hours (Figs. 13-15, 17). The frustrated nesters on the other

hand, stayed in the vicinity of the beach from which they had been

frightened, and travelled back and forth in near-shore waters (Figs.

16, 18-24). Both patterns of behavior were clearly shown by the

Figure 13. Movements of turtle 15426 during the first 5.6 hours
after laying eggs at North East Bay beach in the second
egg chamber that she dug. Tracking ended when the float
could no longer be seen in the glare of the morning sun.
The mast from the float was later found wash d up on the
shore at the point indicated by the symbol T. There
were no other observed nesting emergences by 15426.

TURTLE NO. 15426
23 APRIL 1977


500 -N-

* 1JI



0 500


PPt I1

PPt 3

Figure 14. Movements of turtle 15139 during the first six hours
after laying on South West Bay beach. Tracking
terminated when she freed herself after the tow-line
snagged on submerged rocks. All earlier and later nest-
ing emergences recorded during 1977 occurred at South
West Bay beach (Table 8).



0 1000




18Mm 9-m 5m '. f
0645 BEACH
t 1 0.6 45

S 0600 ,; :;

S.TURTLE NO. 15159
:" 5 MAY 1977


0400 /., BEACH
I i. ."
1 .i


Figure 15. Movements of turtle 15153 during the first 38 hours
after laying eggs at South West Bay beach. Tracking
terminated when the turtle was cut free after the float
tangled on the fuel line near Long Beach. There were
no other recorded nesting emergences.

TURTLE NO. 15153
25- 26 FEB. 1977

0 '-t 1000




Figure 16. Movements of turtle 15206 during the first 17.3 hours
after she abandoned a nesting attempt at South West Bay
beach. Eggs were not laid. Tracking ended at sundown
(1930 hours), because the light on the float had been
smashed. At 2115 hours, 1.8 hours later, the turtle
emerged from the surf towing the float, and nested at
approximately the same point on South West Bay beach
where she came out the previous night (see symbol in
Fig. 17). Figure legend 17 describes the rest of her
nesting history.

TURTLE NO. 15206
12 MARCH 1977


i8m 5m BAY BEACH


0 500


4. u

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Figure 20. Movements of turtle 15516 during the first 10.3 hours
after having been frightened away from her third nest
hole on South West Bay beach. She was reluctant to leave
the beach and even began to dig a fourth body pit on her
way to the water. Tracking was terminated when the float
could no longer be seen in the glare of the morning sun.
She was not observed nesting on the second night, although
I checked the beaches in the vicinity of South West Bay
throughout the night. All recorded earlier and later
nesting emergences during 1978, except one, occurred at
South West Bay beach (Table 8).



18m TURTLE NO. 15516

5 20-21 FEBRUARY 1978
S MET 50

Figure 21. Movements of turtle 15923 during the first two hours
after having been frightened away from her second egg
chamber at South West Bay beach. Eggs were not laid.
Tracking terminated when the tow-line snagged on sub-
merged rocks, allowing the turtle to pull free. She
was not seen nesting again. All her recorded nestings
during 1977 were on South West Bay beach (Table 8).

TURTLE NO. 15923
1-2 JUNE 1978












'~' '

.. V :..: *,


r) u D)Q
4- 0 COe
D0 4-0 4- '
on ( -o0o
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mcm ar
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4- O 0 E) +-
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o cenOrene

0 Co) C -

E -D N -C L-
en c en N U .4 en







r< i



Figure 23. Movements of turtle 16019 during the first 3.3 hours
after having been frightened away from her first egg
chamber at South West Bay beach. Eggs were not laid.
Tracking ended when heavy surf broke off the float as
she approached shore. She emerged to nest the follow-
ing night, 27 May at 2230 hours, on South West Bay
beach (symbol (). She dug at least three egg chambers
before laying. No other nesting emergences were observed.






.* ,



TURTLE NO. 16019
26-27 MAY 1978





Figure 24. Movements of turtle 15415 during the first two hours
after having been frightened away from her fifth nest
hole at South West Bay beach. Eggs were not laid.
Tracking terminated when the float became snagged on
submerged rocks. Turtle 15415 was not recorded nesting
again. She had been observed nesting at approximately
the same point on South West Bay beach one month earlier,
on 21 April.

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