•

~~~'fT OF Co

~'\ ••.., .4f 4f~

Q.~ ~~..;rr «'~

4.J .,;u. ('\ c) f"\

* A'~~{:f!~

~ c::. - ~

-t-

~ ~1t. I

- ~~

(l'C - +-~

S""lTES O~ ~

NOAA Technical Memorandum NMFS-SEFC-112

MOVEMENT AND SURFACING BEHAVIOR PATTERNS

OF LOGGERHEAD SEA TURTLES IN AND NEAR

CANAVERAL CHANNEL. FLORIDA

(SEPTEMBER AND OCTOBER 1981)

ANDREW J. KEMMERER. ROBERT E. TIMKO.

AND SAMUEL B. BURKETT

APRIL 1983

u. S. DEPARTMENT OF COMMERCE

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

NATIONAL MARINE FISHERIES SERVICE

MISSISSIPPI LABORATORIES

NATIONAL SPACE TECHNOLOGY LABORATORIES

NSTL STATION, MISSISSIPPI 39529
NOAA Technical Memorandum NMFS-SEFC-112

Technical Memorandums are used for documentation

and timely communication of preliminary results,

interim reports, or special-purpose information,

and have not received complete formal review,

editorial control, or detailed editing.

MOVEMENT AND SURFACING BEHAVIOR PATTERNS

OF LOGGERHEAD SEA TURTLES IN AND NEAR

CANAVERAL CHANNEL, FLORIDA

(SEPTEMBER AND OCTOBER 1981)

ANDREW J. KEMMERER, ROBERT E. TIMKO

AND SAMUEL B. BURKETT

APRIL 1983

U.S. DEPARTMENT OF COMMERCE

Malcolm Ba1drige, Secretary

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

John V. Byrne, Administrator

NATIONAL MARINE FISHERIES SERVICE

William G. Gordon, Assistant Administrator for

Fisheries
ACKNOWLEDGEMENTS

A significant portion of this study was funded by the Corps of Engineers.

Special thanks are due the Corps for their vessel support, the Kennedy Space

Flight Center of the National Aeronautics and Space Administration for technical

assistance and support of the continuous radio monitoring activity, personnel

from the Southeast Fisheries Center's Pascagoula Laboratory of the Mississippi

Laboratories for capture and handling of the sea turtles, and to the numerous

other Federal employees and contractors who helped with the study.
MOVEMENT AND SURFACING BEHAVIOR PATTERNS

OF LOGGERHEAD SEA TURTLES IN AND NEAR

CANAVERAL CHANNEL, FLORIDA

(SEPTEMBER AND OCTOBER 1981)

INTRODUCTION

As part of a larger effort involving trawling and aerial surveys of loggerhead

sea turtles (Caretta caretta) in the Canaveral Channel and vicinity, a radio

and acoustic tracking study of these animals was conducted over a 20-day

period (September 19 to October 8, 1981). Primary emphasis was to determine

if tracking approaches would provide information relevant to tactical management of dredging and sea turtle recovery programs for the channel. Loggerhead

sea turtles are listed as threatened species under the Endangered Species

Act of 1973.

Little information exists on tracking techniques for sea turtles (summarized

by Timko and DeBlanc, 1981). This meant a major portion of the tracking study

had to be directed at development and evaluation of approaches and procedures

for monitoring movement patterns of these animals. Recent successes with radio

tracking studies of juvenile turtles (Timko and DeBlanc, 1981) provided most

of the initial guidance augmented by information from satellite tracking studies

in the northern Gulf of Mexico (Timko and Ko1z, 1982). Besides radio and

acoustical tracking, an experimental effort was conducted to continuously

monitor surfacing behavior patterns of the turtles to provide information

both for guiding future tracking studies and for extrapolating aerial sea

turtle counts to estimates of population size.

METHODS AND MATERIALS

The tracking study was divided into three portions: radio tracking, acoustic

tracking, and continuous radio monitoring. An overview of the experimental

design is shown in Figure 1 and of the study area in Figure 2.

RADIO TRACKING

Small, battery-powered transmitters encased in 6.35 by 20.32 cm plastic pipes

were attached to 20 turtles with nylon 1andyards approximately two-thirds the

length of their carapaces. The transmitters operated at frequencies ranging

from 165.55 to 165.75 MHz with a design output power of 10 mw. Center frequencies and relative powers for each transmitter are given in Table 1.

Sufficient battery power was provided for three months of continuous operation.

The plastic pipes were internally ballasted to be slightly positively buoyant

and to float with the longitudinal axis vertical. This permitted a 25.4 cm

transmitter antenna, which projected from the upper end of the pipe, to extend

above the water when the turtle surfaced. A steel eyebolt mounted on the

bottom of each of the pipes served as the attachment point for a 136 kgm monofilament nylon attaching lanyard. The opposite end of the landyard was attached

to the trailing edge of the turtle's carapace by a stainless steel tab secured

with two stainless steel screws.

1
N

DIRECTIONAL RADIO RECIEVER /

CORPS OF ENGINEERS

DIRECTIONAL

HYDROPHONES

VISUAL TURTLE COUNTS

CONTINUOUS

RADIO

MONITOR

Figure 1. Conceptual Overview of Canaveral Channel Tracking Study.
NASA

PAD 29.

~

;:,"'" R~

~

• SPOIL SITE

• WRECK

••

1 KILOMETER

14

Figure 2. Cape Canaveral study area. Numbers along the channel

represent permanently located NMFS sea turtle

trawling stations.

3
Table 1. Center frequencies and relative output powers for the tracking

transmitters. Output powers are relative to the strongest

transmitter serial number 9300.

Transmitter Serial

Number

9299

9300

9301 (not used)

9302

9303

9304

9505

9306

9307

9308

9309

9310

9311

9312

9313

9314

9315

9316

9317

9318

9319

Center

Frequency (MHz)*

165.5508

165.5607

165.5710

165.5807

165.5903

165.6002

165.6097

165.6202

165.6305

165.6402

165.6503

165.6598

165.6699

165.6800

165.6897

165.7004

165.7099

165.7200

165.7301

165.7391

165.7499

Relative Output

Power (dBM)*

-11.70

0.00

-18.30

-14.40

- 4.40

- 5.00

-11. 20

- 3.40

- 4.60

-13.80

- 3.90

- 1.60

-17.70

- 7.40

-15.60

- 6.50

4.30

- 4.20

- 3.50

- 4.20

- 5.20

*Measured with a HP 8582 Automatic Spectrum Analyzer.

4
All radio tracking was done from a leased Cessna Model 172 aircraft. This

aircraft was selected because of its high wing design and supporting struts

which provided an excellent location for mounting tracking antennas. Tracking

equipment consisted of directional receiving antennas mounted on each side

of the aircraft, an antenna switchbox, a portable battery-powered transmitter

receiver, and a Loran-C navigation receiver. Tracking flights were flown

every other day during the 20-day experimental period, normally beginrting

at 8:00 a.m. and lasting 3-4 hours. Normally, the aircraft was flown at an

altitude of about 760 meters along lines parallel to the coast. During flights,

the transmitter receiver was manually tuned to individual transmitter frequencies.

When a signal was detected, the antenna switchbox was used to switch between the

antennas on both sides of the aircraft to determine the most probable direction

of the transmitter based on relative signal strength. Once this direction was

determined, the aircraft was turned toward the transmitter in a circling manner

to pinpoint the location of the transmitter similar to the procedure described

by Timko and DeBlanc (1981). Unfortunately, few transmitters were on the

surface long enough to obtain an accurate location which meant that the majority

had to be positioned based only on relative signal strengths between the antennas.

Generally it requires about 5 minutes to obtain a rough location with this

tracking method and about 10 minutes to insure reasonably good accuracy.

ACOUSTIC TRACKING

Acoustic pingers were attached to each of the turtles equipped with radio

transmitters. The pingers were a standard commercial variety enclosed in

brass cylinders 4.5 cm in diameter by 16.0 cm in length. They weighed approximately 450 gms in seawater and contained sufficient batteries for 30 days of

continuous operation. The pingers operated at 10 frequencies ranging between

30 and 45 KHz with ping rates ranging between 0.5 and 5.0 pings per second.

The frequencies and ping rates were selected to identify individual animals

acoustically. The pingers were attached to the left rear of each turtle's

carapace, opposite the attachment point of the radio transmitter, with two

bolts. Figure 3 shows a turtle with both transmitting devices attached and

marked with a painted number for identification during aircraft overflights.

All acoustic tracking was done from a Corps of Engineers 12.2 m steel hull

cre~boat. The acoustical receiving system consisted of a portable tunable

receiver and directional narrow-beam hydrophone. The hydrophone was mounted

on a vertical movable shaft to permit it to be manually swung in and out of

the water, lowered to beneath the keel of the vessel, and rotated 360 degrees.

A compass mounted on top of the shaft provided true bearings of the sensitive

axis of the hydrophone (Figure 4).

Acoustic tracking was done every other day of the experiment period. A series

of listening stations were established initially (Figure 5) to provide complete

coverage of the study area based on preliminary test results off Mississippi

with the hydrophone and several pingers. These tests indicated a detection

range between 1.6 and 3.2 km. However. subsequent tests in the Canaveral

Channel indicated detection ranges of only about 0.5 km, presumably due to

vessel traffic noise and high turbidities. This resulted in the coverage

5
-

\

Figure 3. Loggerhead sea turtle with radio and acoustic tags. The number

painted on the turtle's carapace was for aerial identification.

6
Figure 4. Configuration and operation of the acoustic tracking system from

the Corps of Engineer's crew boat.

7
....,~

• ~

~ •

"y'b .. ~

~~,2 ,. •

...., ~'~~ 3

•

~

"''i- ~,

4

....,.

~'

....,

SPOIL SITE

e

-v

•

"yfo • WRECK

. ~

5 ."v

"y">.

•

"y"'"

to·

•

~"y

")

•

". "y'

....,

9;).

•

"y~

'?

0,. • ,OJ

...., ~. •

,'0

'\Ii ,. • ,'\

">.

':',.. •

,to

">.

....,. •

">.

">.. 15

'\Ii

">.~.

Figure 5. Location of acoustic stations for acoustic positioning of

loggerhead sea turtles.

8
area being reduced to include only the channel and the area around a wrecked

vessel. The general procedure used to locate turtles was to stop at each

station and manually tune the receiver through the pinger frequencies. Individual pingers could be recognized by their frequency and ping rate. When

a pinger was detected, the bearing of the hydrophone and location of the vessel

(Loran-C) were recorded and the vessel was run toward the turtle to obtain a

second bearing approximately 0.4 km from the original detection point. Triangulation was used to locate the pingers based on bearing and vessel location data.

CONTINUOUS RADIO MONITORING

A basic assumption for this portion of the study was that continuous monitoring

of the radio transmitters attached to the turtles would provide data representing

surfacing behavior of the animals.

Essentially, transmitted signals are completely attenuated when the transmitter

antenna is beneath the water. Conversely, signals from a transmitter can be

detected when the antenna is out of the water. The absence or presence of a

radio signal thus was assumed to correspond to periods when a turtle was beneath

or at the surface of the water.

The receiver used to continuously monitor the radio frequencies corresponding

to the 20 radio-tagged turtles was a Hewlett-Packard (HP) Model 6566 Spectrum

Analyzer which operated in an automatic mode under the control of a HP Model

9825 desk top computer. Data were recorded on a HP Model 9825 plotter. Figure

6 shows the configuration of the equipment. The spectrum analyzer was programmed

to scan the frequency spectrum containing the 20 turtle transmitters every 100 ms.

On each scan, the maximum signal level for each transmitter frequency was

recorded and the data were accumulated over a 30-sec time interval. The data

were then digitally filtered to remove extraneous noise and compared to empirically derived threshold criteria developed during a test phase prior to the

experimental period. If the data satisfied these criteria. a point was printed

by the printer on the data record. Each printed point thus represented one

or more signals assumed to be from a given transmitter.

The spectrum analyzer and supporting equipment were located in a mobile instrument van adjacent to the channel study area. A vertically polarized yagi

antenna to receive the signals was mounted on an existing NASA tower (Pad 29)

located at 80°35' and 28°5'. The major antenna sensitivity lobe was approximately 60 degrees in beam width and was directed south-southwest at approximately

150° to cover both the Canaveral Channel and spoil site. Verification of

antenna coverage and system performance was obtained during the test phase

where a maximum detection range of about 10 km along the major axis was determined. This range dropped to about 6 km 30° off-axis.

All data were initially recorded on the HP plotter record and then manually

transcribed onto computer load forms. Data transcribed included transmitter

number and start and stop times of each transmission period for a given transmitter. A certain amount of editing was performed during the transcription

including elimination of obvious noise (e.g. point occurs at the same time

in all data channels) and identification of time periods the spectrum analyzer

was not operating due to power failures or similar problems.

9
YAGI (Y53 (130-190)

VERTICAL POLARIZATION

r ------------------------------------- ----------- -,

RF

IN

DIRECTIONAL

COUPLER

-20dB

TELONIC

BP FILTER

CF 165.651

0.5';,

KMC

PRE AMP

ENVIRONMENTAL

ENCLOSURE

'------ --- -- ------ ---- --.- -.-- ---- ----- --- -- -- ----

TEST

IN

RF

OUT

•••• VERTICAL

ELEVATION

15.5 METERS

RG-214

30.5 METERS

---.----- ----.----------. 1 - - - - ....-.--------.

15V DC

SIGNAL

SYNTH.

HP 8660A

POWER

SUPPLY

ANALYZER

HP 8566

HP 9825

&

PLOTTER

VAN

1_- ~

POWER

PLUG

Figure 6. Block diagram of continuous monitoring system for

radio transmitter equipped sea turtles.
CAPTURE AND RELEASE OF TURTLES

The loggerhead sea turtles were captured in two groups on September 19 and

20, 1981, from the Canaveral Channel with a NMFS chartered shrimp trawler.

Size and weight measurements were taken from the captured turtles and sex

was determined when possible. The turtles were either released in the channel

or at a dredge spoil site located approximately 8 km south of the channel.

Turtles released at the spoil site were selectively tagged with the most

powerful radio transmitters; no selection was made with the acoustic pingers.

The turtles captured on September 19 were tagged and released the same day

into the channel and the ones captured on the second day were all tagged and

released at the spoil site. A summary of biological measurements and tagging

data is given in Table 2. The operation of each acoustic pinger and radio

transmitter was verified prior to release of a turtle.

RESULTS AND DISCUSSION

RADIO AND ACOUSTIC TRACKING

Results from radio and acoustic tracking portion of the study were disappointing.

Figure 7 summarizes the radio tracking data. The tracking of six turtles was

terminated before the end of the experimental period due to the transmitters

breaking off the turtles. Normally, a detached transmitter is easy to identify

because it transmits continuously. Three of the detached transmitters were

recovered; the remaining three drifted too far from the study area for practical

recovery. The reason why most of the turtles detected were from the release

made at the spoil site is probably because they had the most powerful transmitters (Table 1). Unfortunately, few of the detections resulted in positions

due to very brief and infrequent surfacing periods. These periods were found

to average less than 3 min which is significantly less than the 5 min required

for a rough estimate of location.

Movement patterns of four turtles determined from radio tracking data are

shown in Figure 8. All four of these turtles were released at the spoil site

on September 20, 1981. All returned to the channel within a few days after

release and at least two of the turtles apparently remained in or near the

channel for most of the experimental period.

The acoustic tracking data are summarized in Figure 9. Only 10 of the 20

released turtles were detected at least once acoustically during the 20-day

study period. Of these, 4 were released in the channel and 6 at the dump

site. Difficulty was reported in detecting the slower ping rates, but this

difficulty was not reflected in the data. Of the 26 detections reported,

12% were from pingers with 0.5 pings/see transmission rates, 35% from pingers

with 1.0/sec rates, 0% from pingers with 2.0/sec rates, 35% from pingers

with 3.0/sec rates, and 19% from pingers with 5.0/sec rates.

11
•.....•

N

Table 2. Summary of turtles receiving radio and acoustic transmitters

Turtle Carapace (em) Radio Tag Acoustic Ta! Release Data

Number Sex* Length Width Number Freq. (MHz) Number Freq. (KHz) Pings/See Date Location

0 M 91.2 68.2 9299 165.55 1324 30 2.0 9/19 28°23'04 80°31'96

1 M 91.9 68.6 9300 165.66 1341 41 0.5 9/20 28°19'52 80°33'52

2 I 69.6 56.6 9302 165.58 1329 33 2.0 9/19 28°23'50 80°32 '90

3 I 64.0 52.8 9303 165.59 1338 41 2.0 9/20 28°19'52 80°33'52

4 I 70.6 55.9 9304 165.60 1321 41 3.0 9/20 28°19'52 80°33'52

5 I 69.3 56.6 9305 165.61 1330 33 3.0 9/19 Station 10

6 F 88.6 67.6 9306 165.62 1340 42 5.0 9/20 28°19'52 80°33'52

7 I 79.0 59.7 9307 165.63 1342 43 1.0 9/20 28°19'52 80°33'52

8 I 65.0 54.9 9308 165.64 1325 33 3.0 9/19 Station 10

9 I 64.5 53.8 9309 165.65 1336 43 0.5 9/20 28°19'52 80°33'52

10 I 81.0 61.2 9310 165.66 1344 43 5.0 9/20 28°19'52 80°33'52

11 I 76.7 60.5 9311 165.67 1331 33 5.0 9/19 Station 11

12 I 73.9 61. 7 9312 165.68 1326 35 5.0 9/19 Station 10

13 I 93.6 60.2 9313 165.69 1327 36 0.5 9/19 Station 10

14 I 73.2 58.2 9314 165.70 1334 38 2.0 9/19 28°23'04 80°31 '96

15 M 88.6 69.9 9315 165.71 1332 38 0.5 9/19 28°23'50 80°32'90

16 I 73.7 61.2 9316 165.72 1333 40 1.0 9/19 28°23'50 80°32'90

17 I 66.3 57.4 9317 165.73 1339 43 3.0 9/20 28°19'52 80°33'52

18 I 65.0 54.1 9318 165.74 1337 45 1.0 9/20 28°19'52 80°33'52

19 F 91.9 73.9 9319 165.75 1343 45 3.0 9/20 28°19'52 80°33'52

*M = Male; F = Female; I = Immature (not possible to determine sex)
•......

w

TURTLE RELEASE DAY FROM START

NUMBER LOCATION 1 2 3 4 S 6 7 8 9 10 11 12 13 14 lS 16 17 18 19 20

0 CHAN NONE

1 DUMP I I X

2 CHAN X X X TERMeD

3 DUMP X X X X X X

4

" X X X X TERM 1

S CHAN X X

6 DUMP X X X

7 " X X X X X X

8 CHAN X X TERMeD

9 DUMP X X X TERM 2

10 "

NONE

11 CHAN I I

X X

12 "

X X X X X TERMQ)

13 " NONE

14 II NONE

lS "

I

IX 16 II X X X TERM@

17 DUMP NONE

18 " I I X X X X

19 II NONE

CD RECOVERED

Q) TRANSMITTING CONTINUOUSLY; NOT RECOVERED

Figure 7. Sunnnaryof Aircraft Tracking Results (X' s indicate that a signal was

received on that day. TERMindicates that tracking was terminated for

this animal. I
10-1,3,5,&7

II

-,

...... .. .••. ,....

.... ,

,.

9-23.•. ,

,,

'",....

".... ,

"

".... ,

".... ,

.••. ,

'""

"

80°30'

9·27

10-1&7

#3 .••••••••.

• 71-:~1

.9 I

Figure 8. Movement patterns of four turtles determined from aircraft tracking

of their radio transmitters. Dates of each positioning (1981) are

given next to the estimated location.

14
•......

(J'1

TURTLE RELEASE DAY FROM START

NUMBER LOCATION 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

0 CHAN NbNJ

1 DUMP I I X

2 CHAN NONE

3 DUMP NONE

4 II NONE

5 CHAN NONE

6 DUMP NONE

7

il X

8 CHAN X X X X X

9 DUMP X X

10 II NONE

11 CHAN I~I X

12 II X X

13 II NONE

14 II NONE

15 II NONE

16 II X X X X X

17 DUMP X

18 II X X X

19 II X X X

Figure 9. Summary of acoustic tracking data. (X's indicate that the animal was detected

by the survey vessel on that day.)
Nine of the 10 turtles detected acoustically were located with sufficient

accuracy for tracking (Figure 10). All of the positions were outside but

near the channel and, with one exception, were north of the channel. The

lack of very many locations for most of the detected turtles makes inter~

pretation of the data questionable, but there was an indication that most

movement was generally parallel to tbe channel. There also was an indication

of a reaction of several turtles to vessel traffic as some of the turtles

appeared to move when approached by the tracking vessel.

The disappointing results from the acoustic tracking were due to high ambient

noise levels and signal attenuation by turbid waters in the study area. Future

studies should attempt to increase transmitter range by reducing signal frequency,

increasing transmitter power, or a combination of these factors. Additionally,

future studies should consider a change in tracking procedures from the general

survey approach attempted in this study to tracking of individual animals

over extended time periods.

A comparison of radio and acoustic tracking data failed to produce anything

of significance except to show that 8 of the 10 turtles released at the spoil

site returned to the channel within 13 days after release. This return has

been documented in other NMFS studies based on traditional tagging approaches.

The rate of return apparently is rapid. The minimum period shown by this

study was 3 days, the maximum 13 days, and the mean 7 days. This rate of

return, however. should be used with caution as it probably reflects maximum

time periods; i.e. the turtles could have arrived back at the channel much

sooner than indicated from the tracking data.

CONTINUOUS RADIO MONITORING

A summary of results from the continuous radio monitoring portion of the study

is presented in Figure 11. As noted for the radio tracking, six of the transmitters became detached from the turtles prematurely. This was determined

almost immediately from the continuous monitoring data due to the characteristic

consistent and continuous signals from the detached transmitters.

The continuous radio monitoring data were subjected to an initial and final

series of edits to account for detached transmitters, background and periodic

radio noise and interference, periods of receiver inoperation, and periods

when the turtles were out of the range of the receiver. The first initial

edit was performed automatically in the frequency domain based on frequency

characteristics of the transmitted signals. A second initial edit also was

performed automatically to threshold all returns to a pre-established level.

Even with these two edits, however, a considerable amount of radio noise was

noted in the data record and an attempt was made by the system operators to

manually edit the data to eliminate the noise. This may have introduced some

operator bias into the data in the initial edit as it was based to some degree

on the relatively consistent surfacing behavior patterns of the turtles during

periods of relatively little ambient noise. And finally, the entire data

record for transmitter 9310 was omitted in the initial edit due to transmissions

in this channel from an unknown source.

16
80"35'

28"25'

80"32' 80"31'

28"24'

® (9-201

-l\,

"

~

"- "-

..

-' ..® (9-301

-, ~-

@(9-301

TURTLE NO.11 --- ---

TURTLE NO. 12 - - --

---~ .••...

...

28"22'

28"23'

Figure lOa. Acoustic tracks of turtles 11 and 12.
80"35'

28"25'

80"34' 80"33' 80"32' 80"31'

•....•

CO

-- -~..•..

....

28"24'

28"23'

TURTLE NO. 0

TURTLE NO.9 __ ._._._.

TURTLE NO. 17

TURTLE NO. 18

TURTLE NO. 19 - _

28"22'

Figure lOb. Acoustic tracks of turtles 0, 9, 17, 18, and 19.

@C9-24) t@ (9-28)
80"35'

28"25'

--...•.....••

.••..

28"24'

28"23'

TURTLE NO. 7

TURTLE NO. 8

28"22'

80"34' 80"33' 80"32' 80"31'

Figure lOco Acoustic tracks of turtles 7 and 8.
N

a

TURTLE RELEASE DAY FROM START

NUMBER LOCATION 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

I

0 CHAN NONE

1 DUMP NONE

2 CHAN X X X X X X X TERM CD

3 DUMP X X X X X X X X X X X X X X X X X X

4

II X X X TERM 1

5 CHAN X X X

6 DUMP X X X X X X X X X X X X X X X X

7

II X X X X X X X X X X X X X X

8 CHAN X X X X X TERM CD

9 DUMP X X X X X X X X X X X TERM 2

10 II X

11 CHAN X X

12 II X X X X X TERM 2

13 II X X X X

14 II X X X X X X

15 II X X X X X X X

16 II X X X TERM@

17 DUMP X X X X X X X X X X X

18 II X

19 II X X

CD RECOVERED

(])TRANSMITTING CONTINUOUSLY

Figure 11. Summary of continuous radio monitoring data.(X's indicate that a

signal was received on that day. TERM indicates that tracking of

this animal was terminated.)
The final edit was performed after the data had been transcribed onto computer

tape. An example of a 24-hour data record is given in Figure 12. This edit

consisted first of eliminating from the data record all signals from detached

transmitters, all time periods when the receiver was not operating and all

hours with simultaneous noise across the 20 channels. The last edit was a

subjective attempt to eliminate time periods for individual turtles when

obstensively they were out of the range of the receiver. The criterion used

to edit the data was that if fewer than 3 or 4 surfacings were recorded during

a l2-hour period, the entire l2-hour period was eliminated. In all instances,

if there was any uncertainty about a record, either due to frequent noise or

the lack of many turtle surfac.ings, the entire record was omitted.

Summaries of the continuous monitoring data are presented by day of experiment

in Figure 13, by turtle number in Figure 14, and by time of day in Figure 15.

Results are presented in I-hour periods with each hour representing a 60-minute

period in the edited data record for an individual turtle. A total of 848 hours

was recorded with the majority of the hours recorded during the first half of

the experiment (Figure 13). The first three days of the monitoring period were

omitted from any statistical analysis, however, because of differences noted in

the surfacing behavior of the turtles during this period, presumably due to

effects of handling and adjustment by the turtles to the radio and acoustic

tags. Only records from six turtles were judged to be reliable indicators

of behavior after the data edits (and elimination of the first 3 days), and

of these six animals, only four contributed significantly to the data base

(Figure 14). There was a pronounced diurnal periodicity in the data records

due primarily to increased radio frequency noise in the Cape Canaveral area

during daylight periods (Figure 15).

The three behavior parameters examined from the continuous monitoring data

records were time duration of each surfacing, number of sur facings per hour.

and the percent surface time per hour. An hour was considered to represent

an individual sample for the latter two parameters. If a surfacing occurred

during any given hour and extended into the next, it was assigned to the initial

hour. Graphical summaries of the three parameters are presented by time of

day and day of experiment in Figures 16 through 21. Tables 3, 4, and 5 provide

numerical summaries of the data by time of day. day of experiment, and turtle.

respectively. In computing the summary data, hourly statistics were derived

by summing through day and turtle, daily statistics by summing through hour

and turtle. and individual turtle statistics by summing through day and hour.

The entire edited data set, with the exception of the first three days, was

used for each summary.

The first three days of the experimental period were omitted from all analyses

to allow for a presumed behavioral adjustment period for the turtles. All

three parameters were much higher during the first three days than for the

remaining days (Table 4). This division was somewhat arbitrary although

apparently reasonable based on means and standard deviations from the daily

measurements.

21
N

N

20

15

10

5

o

o 5 10 15

24 HOUR CLOCK

9/22 TUESDAY (265)

20 .25

Figure 12. Example of a continuous monitoring data record for 24 hrs from September 22, 1981. Each

horizontal line represents an individual turtle record. Widths of the bars perpendicular

to the horizontal lines correspond to reception periods for the respective turtles. The

narrow vertical lines represent noise spikes and the wide vertical bar is a period when

the receiver was not operating.
- ~

-

-

~

-

1-

,.---

,-

~

- -

-

-

-~

.---

-

-

-

<:

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0

0

Z

40

30

50

60

70

10

80

20

90

Vl

a::

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0

J:

u.

0

a::

w

m

N

~

W :::>

z

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

DAY OF EXPER IMENT

Figure 13. Number of data hours by day of experiment after edit. Includes all turtles

and times (N = 848 hours).
...-

-

1-

-

-

- - -

-

-

-

-

- -

-

I - I I I

I

20

220

60

180

Vl

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0 140

:r:

u.

0

a::: w

CO

:;:;: 100

::>

z

N

~

o 2 3 4 S 6 7 8 9 10 11 12 13 14 1S 16 17 18 19

TURTLE NUMBER

Figure 14. Number of data hours for each turtle after data edit and elimination of first 3 days of

experiment. Includes all days and hours (Total N = 712 hours~
-

-

~ -

...-- -

~

i--

~ -

--- -

-

-

- -

- -

-

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30

50

40

20

10

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III

a:::

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0

a:::

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CO

~

=>Z

N

U1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

T (ME (LOCAL)

Figure 15. Number of data hours by time of day after edit and elimination of first 3 days of experiment.

Includes all turtles and days (N = 712 hours).
4.0 MEAN -- 2.20 ± 0.13 (95~ C.L.)

-

N =: 732 SURFACINGS

- -

~

..--

MEAN

I-- \ -

- - ----- ~-~-------------- --

-

- ~ .....-

-

- I--- -

-

~

,.....-

-

3.0

Vl

UJ

r-

:J

Z

~

UJ

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rUJ

u

<{

N U.

0'\ a:

:J

Vl

1.0

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

TIME (LOCAL)

20 21 22 23 211

Figure 16. Mean surface time per turtle surfacing by time of day. First 3 days of experiment omitted.
MEAN = 2.20 ± 0.13 (95% C.L.)

N = 732 SURFACINGS

-

-

-

~

-- MEAN r

-

\

-."""- -

--~- ..-- - -'"'- ___ I

-- ----

~ -

1- ~

--

~

-

- «

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c

0

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LL

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-V)

w 3.0

~

::::>

z

:E

N

.......•

1 2 3 4 5 6 7 8 9 10 11 12 13

DAY OF EXPERIMENT

14 15 16 17 18 19 20

Figure 17. Mean surface time per turtle surfacing by day of experiment. First 3 days of experiment are

not included in computation' of mean.
1.5

a::

:::::>

0

:x: ~

Vl

lJ 1.0 z

U

«

u.

a::

:::::>

Vl

N

ex>

0.5

MEAN = 1. 03 ± 0.04 (95'b C.L.)

N = 712 HOURS

-

...--

.--- ..--

MEAN

.---

I-- - -

- ----- -~--- ---- -I- -

- -

-

2 3 4 5 6 7 8 9 10 11 12 13 14

TIME (LOCAL)

15 16 17 18 19 20 21 22 23 24

Figure 18. Mean number of turtle surfacings per hour by time of day. First 3 days of experiment

omitted.
N

1.0

2.0

1.5

a::

:J

o

J:

--Vl

lJ

z

U

< 1.0

u.

a::

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0.5

MEAN = 1.03 ± 0.04 (95% C.L.)

N = 712 HOURS

-~

fo--,

-

--

MEAN

I---

' \_- .~--- - - -I- - ------

--- f--

~

.

<

I-

<

£:)

0

•

z

2 3 4 5 6 7 8 9 10 11 12 13

DAY OF EXPERIMENT

14 15 16 17 18 19 20

Figure 19. Mean number of turtle surfacings per hour by day of experiment. First 3 days of experiment

are not included in computation of mean.
7.0

6.0

MEAN 3.78 ± 0.27 (95';, C.L.)

N 712 HOURS

5.0

UJ

:2:

I- MEAN

UJ

---~-

U 4.0

<t: ---

u.

a:::

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II)

I- 3.0

z

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w U

0

a:::

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Cl.

2.0

1.0

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

TIME (LOCAL)

Figure 20. Mean percent surface time per turtle by time of day. First 3 days of experiment omitted.
9

MEAN = 3.78 ± 0.27 (95% C. L.)

N = 712 HOURS

1-

-

~

-

-

-

- -- MEAN

----=-- ----_\- -

- -

-- -- ----- ---- --~--- -

- ~

-

-

- e(

le(

C

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8

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IZ

w w

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0:::

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3

2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

DAY OF EXPERIMENT

16 17 18 19 20

Figure 21. Mean percent surface time per turtle by day of experiment. First 3 days of experiment are

not included in computation of mean.
Table 3. Summary of turtle surfacing measurements after omission of first 3 days

of experiment. Measurements include six turtles over 17 days.

Hour Surface Time (min) Surfacings/Hour Percent Surfacing Time

n x s n x s n x s

1 42 2.3 1.6 42 1.0 0.4 42 3.9 2.9

2 40 2.3 1.0 44 0.9 0.6 44 3.4 2.6

3 40 2.2 1.1 39 1.0 0.4 39 3.7 2.4

4 35 2.7 3.8 38 0.9 0.4 38 4.2 6.2

5 37 2.3 1.9 39 0.9 0.6 39 3.6 4.3

6 37 3.0 3.2 36 1.0 0.6 36 5.2 6.7

7 29 3.7 3.9 30 1.0 0.4 30 5.9 6.7

8 10 1.8 1.0 8 1.3 0.9 8 3.7 3.3

9 11 1.1 0.3 8 1.4 0.5 8 2.5 1.3

10 26 2.6 2.5 24 1.1 0.6 24 4.7 4.7

11 24 2.0 0.9 22 1.1 0.6 22 3.6 2.4

12 20 1.7 0.7 22 0.9 0.8 22 2.5 2.3

13 16 1.9 0.9 12 1.3 0.7 12 4.3 2.2

14 11 1.6 0.7 10 1.1 0.6 10 3.0 1.7

15 13 1.7 0.9 14 0.9 0.5 14 2.6 1.8

16 17 2.0 1.0 18 0.9 0.6 18 3.1 2.7

17 23 1.8 0.8 25 0.9 0.6 25 2.8 2.2

18 40 2.1 1.9 35 1.1 0.5 35 4.0 3.5

19 41 2.0 1.2 39 1.1 0.6 39 3.6 3.0

20 54 1.9 0.8 44 1.2 0.8 44 3.9 2.4

21 42 1.9 1.0 42 1.0 0.5 42 3.1 2.1

22 36 2.3 0.8 37 1.0 0.6 37 3.7 2.7

23 48 2.1 0.9 44 1.1 0.6 44 3.8 2.2

24 40 2.1 1.6 40 1.0 0.8 40 3.5 3.2

TOTAL 732 2.2 1.8 712 1.0 0.6 712 3.8 3.7

32
Table 4. Summary of turtle surfacing behavior by day after start of experiment.

All days included but first 3 days of the experiment are not included

in totals

Day

Surface Time (Min) Surfacings/Hour Percent Surfacing Time

- - -

n x s n x s n x s

1 61 2.4 1.1 30 2.0 1.0 30 8.1 4.4

2 73 2.7 2.0 38 1.9 0.7 38 8.6 6.3

3 83 3.2 4.3 68 1.3 0.9 6.3 7.0 9.6

------- ----- -------- -------- -------- ---------- -------- ------- ---------- ---------

4 45 2.1 1.2 44 1.0 0.7 44 3.6 2.8

5 88 2.0 0.9 80 1.1 0.5 80 3.6 2.2

6 33 2.2 1.1 32 1.0 0.6 32 3.7 2.9

7 61 2.5 2.0 52 1.2 0.7 52 4.8 3.9

8 82 2.8 3.5 78 1.1 0.5 78 4.9 6.6

9 57 2.1 0.9 72 0.8 0.5 72 2.8 2.0

10 85 2.2 1.4 92 0.9 0.6 92 3.5 3.0

11 74 2.3 2.3 68 1.1 0.6 68 4.2 4.7

12 64 1.9 1.7 60 1.1 0.5 60 3.4 3.1

13 21 2.2 2.0 20 1.0 0.7 20 3.9 4.1

14 45 1.8 0.9 41 1.1 0.7 41 3.4 2.5

15 15 2.0 0.8 15 1.0 0.5 15 3.3 2.0

16 0 - - 0 - - 0 - -

17 15 2.6 1.2 16 0.9 0.6 16 4.1 3.1

18 15 1.7 1.3 10 1.5 1.0 10 4.3 3.1

19 25 1.9 0.9 24 1.0 0.6 24 3.3 1.9

20 7 1.4 0.5 8 0.9 0.4 8 2.1 1.2

TOTAL* 732 I2.2 1.8 712 1.0 0.6 712 3.8 3.7

*Measurements from first three days omitted from totals.

33
Table 5. Summary of surfacing behavior measurements for individual turtles. Measurements from first 3 days

of experiment omitted.

Turtle Carapace

Surface Time (min) Surfacings/Hour Percent Surface Time

Number Length (em) - - - n x s n x s n x s

3 64.0 255 2.2 2.1 213 1.2 0.7 213 4.3 4.5

6 88.6 142 2.2 1.2 179 0.8 0.5 179 3.0 2.5

7 79.0 49 2.2 1.8 40 1.2 0.4 40 4.5 3.2

8 65.0 3 3.3 1.5 4 0.8 0.5 4 4.2 3.5

9 64.5 151 2.2 1.9 138 1.1 0.5 138 4.0 3.8

18 65.0 132 2.2 1.7 138 1.0 0.6 138 3.5 3.3

TOTAL - 732 2.2 1.8 712 1.0 0.6 712 3.8 3.7
Mean surfacing time by time of day ranged from a low of 1.1 min to a high

of 3.7 min with an overall mean of 2.20 ±0.13 min at a 95% confidence level

(Figure 16 and Table 3). From the fourth to the last day of the experiment,

mean surfacing time by day ranged from 1.4 min to 2.8 min (Figure 17 and Table

4). By individual turtle~ mean surface time ranged from 2.2 min to 3.3 min

with all but one of the means equaling the overall mean of 2.2 min (Table

5). A one-way analysis of variance was applied to the data to test for effects

of turtle, time of day~ and day of experiment on surface times (Figure 22).

Only time of day was significant (99% confidence level) suggesting that surface

time per surfacing varied with time.

The mean number of turtle surfacings per hour was relatively consistent over

time averaging 1.03 ±O .04 (95% confidence limits) with a range of 0.9 to 1.4

mean sur facings per hour (Figure 18 and Table 3). The parameter also was

relatively consistent by day of experiment with daily means ranging from 0.8

to 1.5 sur facings per hour (Figure 19 and Table 4). The range in mean number

of surfacings by turtle was relatively small with a low of 0.8 and a high

of 1.2. Significant differences, however, were found with this parameter

between turtles and day of experiment (Figure 23).

Percent surface time was a key parameter for the experiment and it was found

to average 3.78 ±0.27% (95% confidence limits). The range in hourly means

was 2.5 to 5.9% (Figure 20 and Table 3) and in daily means from 2.1 to 4.9%

(Figure 21 and Table 4). For the six turtles, the mean percent surface time

ranged from 3.0 to 4.5%. A one-way analysis of variance applied to the percent

surface times showed significant differences between turtles (99% confidence

limits) with no significant differences by time of day or by day of experiment

(Figure 24).

To determine if diurnal trends in the surfacing behavior of the turtles existed,

time averaging was applied to hourly values for each of the three parameters.

Two averages were used to minimize data variability. Mean surface time per

surfacing demonstrated a definite trend with the surfacing periods increasing

just before dawn to a peak shortly after dawn and then dropping rapidly off

to the shortest period about mid-day (Figure 25). After mid-day, surfacing

periods gradually increased to about the overall mean value by the beginning

of the next day. Less of a trend was indicated by time-averaged surfacingsjhour,

but some trending was suggested (Figure 26). The number of surfacingsjhour

were lowest just before dawn increasing to a maximum about mid-·morning.

Following the mid-morning high, the averaged values decreased to a low in

mid-afternoon followed by another peak just before sunset.

A well-defined trend occurred with the time-averaged percent surface time

values (Figure 27). The maximum period on the surface was shortly after dawn

(i.e. 7:00 a.m.) after which percent surface time dropped rapidly to a low

about mid-afternoon. This apparent rapid change in the amount of time spent

on the surface by a turtle as a function of time of day could have significant

implication for any investigation dependent on surface observations of turtles.

One should recognize, however, that this particular trend was not supported

statistically (Figure 24).

35
A. Turtle

Source of Degrees of Sum of Mean

Variation Freedom Squares Square F

Turtles 5 4.4296 0.8859 0.2633

Error 726 2442.8327 3.3648

TOTAL 731 2447.2623

B. Time of Day

Source of Degrees of Sum of Mean

Variation Freedom Squares Square F

Hours 23 152.7163 6.6398 2.0487**

Error 708 2294.5460 3.2409

TOTAL

I

731 2447.2623

** Significant 99% Confidence

C. Day of Experiment

Source of Degrees of Sum of Mean

Variation Freedom Square Square F

Days 15 65.3281 4.3552 1.3092

Error 716 2381.9342 3.3267

TOTAL 731 2447.2623

Figure 22. Analysis of variance of the effect of turtle, time of day, and

day of experiment on amount of surface time per surfacing.

Excludes first 3 days of experiment.

36
A. Turtle

Source of Degrees of Sum of Mean

Variation Freedom Squares Square F

Turtles 5 19.1284 3.8257 11.7281**

Error 706 230.3098 0.3262

.

TOTAL 711 249.4382

** Significant at 99% Confidence

B. Time of Day

Source of Degrees of Sum of Mean

Variation Freedom Squares Square F

Hours 23 7.5839 0.3297 0.9380

Error 688 241.8543 0.3515

TOTAL 711 249.4382

C. Day of Experiment

Source of Degrees of Sum of Mean

Variation Freedom Squares Square F

Pays 15 9.6781 0.6452 1.8729*

Error 696 239.7601 0.3445

TOTAL 711 249.4382

*Significant at 95% Confidence

Figure 23. Analysis of variance of the effect of turtle, time of day, and

day of experiment on number of surfacings per hour. Excludes

first 3 days of experiment.

37
A. Turtle

Source of Degrees of Sum of Mean

Variation Freedom Squares Square F

Turtles 5 222.9605 44.5921 3.3222**

Error 706 9475.9775 13.4221

TOTAL 711 9498.9380

** Significant at 99% Confidence

B. Time of Day

Source of Degrees of Sum of Mean

Variation Freedom Squares Square

Hours 23 380.0375 16.5234 1.2466

Error 688 9118.9005 13.2542

TOTAL 711 9498.9380

C. Day of Experiment

Source of Degrees of Sum of Mean

Variation Freedom Squares Square F

Days 15 298.8417 19.9228 1.5072

Error 696 9200.0963 13.2185

TOTAL 711 9498.9380

Figure 24. Analysis of variance of the effect of turtle, time of day, and

day of experiment on percent surface time. Excludes first 3

days of experiment.

38
- - - FIRST AVERAGE

SECON 0 AVERAGE

3.0

V)

UJ

I-

:J

z

- 2.5

~

UJ

~

IUJ

U

«

LIc::: 2.0

:J

V)

1.5

MEAN 2.20 MINUTES

/

2 4 6 8 10 12 14

TIME (LOCAL)

16 18 20 22

Figure 25. Time averaged diurnal surfacing periods (surface time per surfacing)

of loggerhead sea turtles. Averaging done by combining data from

adjacent hours on either side of a given hour with data from that

hour. Second averaging done in a similar way, but with averaged

results from the first averaging. (N = 732; data from first 3 days

of the experiment omitted).

39
---- FIRST AVERAGE

SECOND AVERAGE

1.2

R

I \

I \

ct: I ~ \

0

:I: ~

--(/) 1.1

l.J MEAN 1.03 z

_1_- -

u

-<

u..

ct:

~

(/) \

1.0 \

, I

\ I

\ I

'g

0.9

2 4 6 8 10 12 14

TIME (LOCAL)

16 18 20 22

Figure 26. Time averaged diurnal surfacing patters (surfacings/hour) of

loggerhead sea turtles. Averaging done by combining data from

hours on either side of a given hour with data from that hour.

Second averaging done similar to the first, but with averaged

results from the first averaging. Data from first 3 days of

experiment omitted.

40
MEAN 3. 7890

I -~----+--

/ \

~

5.0

--- FIRST AVERAGE

SECOND AVERAGE

3.0

3.5

4.5

UJ

~

IUJ

U

«

~ 4.0

::J

Vl

IZ

UJ

U

~

UJ

Q.

2 6 8 10 12 14

TIME (LOCAL)

16 18 20 22

Figure 27. Time averaged diurnal surfacing pattern (percent surface time)

of loggerhead sea turtles. Averaging done by combining data

from adjoining hours of an hour with data from that hour.

Second average done similar to first, but with average values

from the first averaging (N = 712; first 3 days omitted).

41
SUMMARY AND CONCLUSIONS

A 20-day experiment was conducted in and near Canaveral Channel. Florida.

beginning on September 19. 1981. to monitor movement and surfacing behavior

patterns of loggerhead sea turtles. Movements were determined by radio and

acoustic tracking with neither of the approaches giving very satisfactory

results. Radio tracking was limited by very short and infrequent periods

spent by the turtles on the surface. Acoustic tracking was limited by the

relatively short detection range of the transmitters (approximately 0.5 km)

due presumably to high ambient noise levels and excessive turbidities. Studies

to monitor and characterize surfacing patterns of the turtles were much more

successful with six turtles being monitored periodically during the experimental

period. These studies depended on a continuous monitoring radio receiver

positioned adjacent to the study area.

Probably the most significant finding from the radio and acoustic tracking

studies was that at least 8 of the 10 turtles captured in the Canaveral Channel

and released at a spoil site approximately 8 km south of the channel returned

to the channel. All 8 of the turtles returned within 13 days with an average

minimum return time of 7 days. Additionally, observations during the acoustic

tracking portion of the studies indicated that at least some of the turtles

appeared to react to the approach of the tracking vessel.

Results from the continuous monitoring portion of the experiment suggested

a period of about 3 days was needed for captured, tagged, and released turtles

to normalize their surfacing behavior patterns. The mean time spent by a

turtle during a surfacing was 2.20 ±0.13 min (95% confidence limits). The

turtles surfaced an average of 1.03 ±0.04 (95% confidence limits) times an

hour and spent an average of 3.78 ±0.27% (95% confidence limits) of their

time at the surface. A trend analysis suggested a diurnal periodicity in

all three of the behavior parameters with pronounced peaks in surfacing activity

occurring near and shortly after dawn. The lows in surfacing behavior activi.ty

normally appeared to occur near mid-afternoon.

Recommendations from the experiment are that future radio tracking studies

should consider development of a receiver system capable of detecting and

locating a surfacing turtle within 2 minutes. Ideally, this system should

be usable from an aircraft. Future acoustic tracking studies need to consider

approaches to increase detection range such as lower frequencies and greater

transmitter power, as well as a change in tracking tactics. The continuous

monitoring portion of the experiment was relatively successful, but significantly

greater success probably could be achieved if additional methods to reduce

effects on ambient noise and provide an indication of transmitter location

had been applied. Examples of these methods include greater and stabilized

transmitter power, the use of reference transmitters, monitoring of signal

amplitude as an indicator of range, and multiple directional antennas to gain

estimates of transmitter bearings.

42
LITERATURE CITED

TIMKO, R. E. and D. DeBlanc

1981. Radio Tracking Juvenile Marine Turtles. Marine Fisheries Review

43(3):20 .•.24.

TIMKO, R. E. and A. L. Kolz

1982. Satellite Sea Turtle Tracking. Marine Fisheries Review

44(4):19-24.

43