Radio Telemetry of Hawaiian GreenTurtles at Their Breeding Colony

Andrew E. Dizon was with the HonoluluLaboratory. Southwest Fisheries Center, Na­tional Marine Fisheries Service. NOAA, Hono­lulu. HIlJ6812 and George H. Balazs is on anIntergovernmental Personnel Assignment fromthe Hawaii Institute of Marine Biology, Uni­versity of Hawaii, to the NMFS HonoluluLaboratory. Dizon is now with the SouthwestFisheries Center. NMFS, NOAA. P.O. Box 271 ,La Jolla. CA 92038.

ANDREW E. DIZON and GEORGE H. BALAZS

Introduction

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Figure I. - French Frigate Shoals,site of 90 percent of the breedingactivity of the green turtles in the

Hawaiian Archipelago.

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Midway Is.

More than 90 percent of the breedingactivity of the Hawaiian green turtle,Chelonia mydas, occurs at a small atollsituated about midway along the 2,450km length of the Hawaiian Archipelago(Fig. I). Here, principally during Mayand June, turtles gather to copulate andnest.

Because of the specificity of themarine turtle's choice of breeding sitesand times, any significant disturbanceby man during this period could haveprofound effects upon the population.Yet little is known about the marinehabitat of the animals during this period.Most of the work (Balazs, 1976, 1980)has involved hauled-out turtles when

Laysan I. GardnerPinnacles______________+- 25'

ABSTRACT-Little is known aboUl therange and movements ofgreen turtles, Chel­onia mydas, during the criticalperiod oftheirlife history when they gather on their breedinggrounds to copulate and nest. In order toinvestigate these behaviors, we developedradio telemetry techniques to determine posi­tion and environmental temperature. Accessto the turtles is facilitated because HawaiianChelonia have a unique behavior of landbasking For about] weeks in the middle ofthe breeding season, we plotted the move­ments offour males and four females.

This report concentrates primarily ontracking methods. but we also discuss the

FrenchItq I.. Frlg~.te

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distribution of the turtles and their fidelity tothe nesting beach. Although there are twonesting complexes of the breeding atoll andthey are separated by 9 km, no movementsbetween the two areas were observed. Bothmales and females remained in proximity towhat we believe is their natal beach.

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May /982. 44(5) IJ

they are readily visible to the investigator.Where the turtles go between the periodswhen they crawl out on the beach re­mains a mystery. Yet it is when theturtles are in the nearshore waters thatthe greatest potential for conflicts withhumans exists. Managers of the habitatmust be informed about the distributionof the turtles during the breeding periodin order to avoid potentially damaginginteractions.

The purpose of our study was todevelop radio telemetry techniques tolocate turtles throughout their breedinghabitat and to study their range andbehaviors during the breeding period.This report will concentrate primarilyon the tracking technique and brieflydescribe the breeding habitat range.SpecifIc details of their behaviors will bethe subject of a subsequent paper.

Green turtle at French Frigate Shoals.The Site

The breeding atoll is called FrenchFrigate Shoals (FFSI. It is a crescenl­shaped platform which rises 10 withinabout 40 m of the surface (Amerson.\9711. Extensive reef growth has oc­curred on the platform and now thereare about 12 permanent islands. 4 withwell-established vegetation.

Tern Island, the largest. was modifIedduring World War lito serve as a refuel­ing base for aircraft support of the Mid­way Campaign. It was later used by theU.S. Coast Guard which maintained aloran station there until 1979. The U.S.Fish and Wildlife Service now maintainsthe island with several resident biologists.French Frigate Shoals as well as most ofthe other islands of the northwesternsegment of the archipelago are units ofthe Hawaiian Islands National WildlifeRefuge and are designated officially as aResearch Natural Area. Tern Island wasthe base of our operation.

The Turtles

Work over the past K years on theturtles of FFS has revealed much abouttheir natural history. The turtles arriveat the breeding atoll during mid- April toearly June. Courtship and copulationtake place then. Nesting starts as early asmid-May, peaking in June. and has all

/4

but ceased by mid- August. Nesting takesplace over most of the larger stableislands with approximately 55 percentnesting at East Island and 35 percent atWhale-SkatelTrig Island complex (Fig.II. As many as six egg clutches may belaid by a single female during one seasonbut the mean is 1.8. The interval betweenoviposition in turtles that nest more thanonce averages 13 days. ranging from IIto 18 days. Females journey to thebreeding atoll once every 2 or moreyears: males every 1or more years. Theturtles come from and return to feedingpastures located in the rest of the archi­pelago. These long- range precise migra­tions to and from the breeding islandshave been documented by the markingand subsequent recapture of 52 turtles(Balazs, 1976, 19XOl.

Hawaiian Chelonia exhibit a uniquebehavior which make them quite amen­able to biological study. The turtles baskon land for extended periods both dayand night. and while hasking they arerelatively easy to capture and tag. FrenchFrigate Shoals is one of eight hreedingcolonies designated for high priority bythe World Conference on Sea TurtleConservation (1979) by reason of unique

ecology and isolation. Balazs (19801 in aslUdy period extending over 8 years hastagged over 140 adult male and 528 adultfemale turtles. Yet mark- and- recapturestudies are not well suited for delimitingthe critical habitat of the turtles duringtheir sojourns within the nearshorewaters between nesting or basking periodon land. Extensive trapping in the waterto recapture the marked animals isimpractical. IdentifIcation marks paintedon the shells allow for visualization oflimited movements, hut most turtles arequickly lost to the observer when theyare not basking or nesting.

We felt that radio telemetry to deter­mine movements was the least intrusivemethod of determining positions duringtrips away from the beach. We attachedsmall transmitters to the turtle's carapaceand fIxed their positions by triangulationfrom two distant receiving stations. Withthis technique we were able to determinepositions of the turtles during basking orswimming on the surface. As a result wewere also able to ascertain the fractionof time the animals spent on the surfaceor on land and how much time sub­merged. These data are necessary tocorrect past and future census informa-

Marine Fisheries Review

tion since. at anyone time. only a fractionof the turtles are visibk to an observer.Our transmitters were sensitive to theenvironmental temperature so that wecould determine whether turtles werebasking on land or swimming at thesurface. This information as well as otherperformance parameters of the turtleswill be the subject of a subsequent paper.For now. we are interested in the tech­niques and range.

Green turtle basking at French Frigate Shoals.

Past Telemetry WorkWithin Breeding Colonies

"One of the conspicuous gaps in thebehavioral ecology of the green turtle... is the lack of data on the movementsof females during the 12-14 day periodsbetween their emergences at the nestingbeach" (Carr et al.. 1974). Actually. anumber of studies have been conductedbut more data still need to be generated(Carr, 1967a. 1967b. 1972: Baldwin.1972: Meylan. 1978. in press: Standoraet al.. 1979: Feazel. 1980: Mortimer.1981). The internesting movements oftwo other species have also been investi­gated (loggerheads. Caretta carella.Murphy, 1979: Stoneburner. 1979: andKemp's ridley. Lepidoche(vs kempi.Pritchard. 1980). All of these data arecharacterized by few subjects. no males.and short tracking periods. Most utilizeda towed drogue usually equipped with apennant and light. Sometimes sophis­ticated satellite transmitters were em­ployed (Stoneburner, 1979; Daniel,1980). Thus technical equipment is notcause for the information gap. Nor issize a problem since in fact telemetrydevices (both radio and acoustic) areavailable for use on juveniles and hatch­lings (Ireland, 1979a, 1979b; Garmon,1981 ; Timko and DeBlanc, 1981; Stinsonand Fritts\ Our goal was to deploy radiotransmitters on both male and femaleturtles, track them throughout a signifJ­cant portion of the reproductive period,and collect as many distributional,behavioral. and physiological data aspossible.

'M. L. Stinson. 1553 Avocado Drive, Vista, CA92083; T. Fritts. National Fish and WildlifeLaboratory, Tulane University, Belle Chasse.LA 70037, pers. commun.

May /982. 44(5)

The Transmitters and TheirDeployment on the Turtle

The 2 m (149 mHz) transmitters weemployed were purchased as "off-the­shelf' items from Telonics, Inc.' Mesa,Ariz., (Fig. 2). These were hermetically

encapsulated 7.5 X 4 x 3 em, round­edged boxes with a mounting flange

'Reference to trade names does not implyendorsement by the ational Marine FisheriesService. NOAA.

/5

..

turtle was propped up at about a 45°angle (head up) while still on its back.Sand was removed to allow room towork under it. A battery-driven drill.equipped with a counterbore bit and apositive stop to limit the depth of thehole was used to make four pilot holes inthe carapace. The plastic plate. alreadyequipped with the transmitter, was thenscrewed into place. The magnet holdingthe transmitter turned off was removedand a radio check back to the receivingstations was made to ascertain that every­thing was working. Cold- process roofingtar was applied to the transmitter. plate.and screws and then covered with sandand the turtle righted. The bionic Che­lonia immediately scrambled to theocean and swam off and the trackingbegan (Fig. 3).

Figure 2. - The transmitter and its mounting plate. Note the thread design onthe bone screws and the magnet which is used to turn the transmitter off.

attached to the bottom. A flexiblequarter- wavelength stub antennaemerged from the front and extended46 cm. The transmitters were tempera­ture-sensitive: as the package warmed,the pulse rate increased. We observedan effective range of over 10 km whenthe transmitter package was awash atthe sea surface and the receiving antennawas elevated about 9 m.

Since we were interested in followingthe animals for a long period, a reliableattachment method for the transmitterwas critical to the success of the project.Hawaiian Chelonia have a habit of restingwithin coral caves and under outcrop­pings. A tethered transmitter would beuseless and unless provided with a break­away link. would pose a danger to theanimals.

The study areas of the other workersreported earlier were generally free fromsuch obstructions. Thus we had to attachthe transmitter directly to the shell. Toconform to the curvature of the shelland yet provide a wide mounting base,the transmitter was secured to a 15 X IScm, 0.6 cm thick piece of high molecular

/6

weight polyethylene (Fig. 2). This verytough but flexible plastic easily con­formed to the carapace.

The plastic was attached to the shellwith surgical bone screws fabricated fororthopedic repairs (mallolar style. Zim­mer Inc.). The screws were made of aproprietary alloy which made themunreactive within the tissues of the shelland impervious to the seawater. Thethread of the screw was designed toprovide great holding power with thevery shallow penetration which we re­quired. Experiments with captive turtlesdemonstrated that the attachment tech­nique was sound but the silvery coatingof the transmitters was particularlyappealing to fellow tank- mates andnumerous biting attacks were made onthe units. This problem was eliminatedby camouflaging the transmitters withroofing tar and sand.

The actual attachment was choreo­graphed and refined until it took lessthan 45 seconds. At dusk. the baskingturtle was stealthily approached by oneof us and turned over on its back. A shorttime later. after nightfall, the chosen

The Receivers

We employed two separate receivingstations in order to fix positions of thetransmitter-carrying turtles. One waslocated in the old Coast Guard facilityon Tern Island: the other. 13 km away atEast Island. Tern Island was the primaryreceiving station which monitored con­tinuously. The East Island station wasonly active at 6- hour intervals: 0300.0900,1500. and 2100. During that timeperiod bearings were obtained on eachof the turtles and their positions plotted.

The receiving equipment at TernIsland consisted of two receiver systems:An omnidirectional antenna connectedto a receiver with a frequency scannerand a highly directional antenna con­nected to a receiver with a signal pro­cessor for digital measurements of periodand signal strength. The East Islandstation had a highly directional antennaand a receiver equipped with a processor.The directional antenna at Tern Island(mounted about 9 m off the ground) waspositioned with a motorized antennarotor while the one at East Island (5 moff the ground) was rotated by hand.Bearings were determined from theantenna rotor control box at Tern Islandand a compass mounted on the mast atEast Island. Under all but the weakestsignal conditions, our accuracy of bear­ing was about ±5°.

In addition to bearing fixes every 6hours, the station at Tern Island sampled

Marine Fisheries Review

Figure 3.- Transmitter-equipped female 200 relurning to the ocean after gearattachment.

Female 530Date No previous record 6/09 8/10 63Location TRIG

'Soulheast Island. Pearl and Hermes R'e-ef,.-(F=ig-.-'-)-------

while the animal was basking on TrigIsland 9 June 1980.

Table 1. - Tagging and tracking data. Tagging data are from Balazs' long-termstudy of the green turtles of Hawaii (Balazs. 1980). The "0"" date refers tothe date when the last signal was received from the transmitter. WS = Whale-Skate Island. TRIG = Trig Island. and EAST = East Island.

First First SecondTransmitter deployment

Tagging tagging recovery recovery On Off Days

Male 350Date 7/31/75 4/12/76 9/25/77 6/08 9/04 73Location WS WS WS WS

Male 360Date No previous record 6/08 6/27 19Location WS

Male 510Date No previous record 6/09 6/14 5Location WS

Male 540Date 5/03/70 5/04/79 6/09 8/12 49Location TRIG TRIG TRIG

Female 200Date 6/09 6/30 21Location 3/22/68 TRIG

Female 450Date 7/10170 7/05/74 6/08 11/13 143Location EAST EAST WS

Female 490Date 6/19/79 6/29/79 6/09 8/07 60Location WS WS WS

east Island. Pearl and Hermes Reef{Fig. J l. The transmitter was attached

every \0 minutes throughout the wholestudy period and continuously duringthree 24- hour periods. The frequencyscanner was programmed to scanthrough the transmitter frequencies.When a signal was detected, the pulserate was read to determine temperatureof the transmitter. These data will bepresented in a subsequent paper but itshould be mentioned that the amountof time spent on the ocean surfacewhen the signal could be detected wasusually less than I minute. Thus notmuch time was available for us to mea­sure pulse rate and fix position.

Every 6 hours the receiving equipmentat East Island was turned on. When aturtle signal was detected at Tern Islandby the scanner-equipped receiver, theinformation was relayed to East Islandand both stations attempted to fIx thebearing of the signal with the directionalantennas. Sometimes it was impossibleto obtain fIxes on all of the turtles. Wewould hear the signal from a given turtle.but it would not stay on the surface longenough to get an accurate fIx.

Residence Times

Four males and four females wereequipped with transmitters. For con­venience, the turtles were identified bythe last three digits of the frequency oftheir transmitters. For instance. the maleequipped with a 149.350 mHz trans­mitter was known as male 350 (Table 1).This animal was originally tagged with aflipper tag on 31 July 1975 while baskingon Whale-Skate Island and recoveredon 12 April 1976 and 25 September1977 while again basking on the sameisland. The turtle was captured again onWhale-Skate Island and the transmitterattached on 8 June 1980.

Male 540 (\49.540 mHz) was originallytagged on 3 May 1979 while basking onTrig Island and found again a day laterin the same place. Copulation injurieswere noted at the time. The transmitterwas attached on 9 June 1980 while onWhale-Skate Island.

Males 360 and 510 had no previoustagging history and had transmittersattached on 8 and 9 June, respectively,while they were on Whale-Skate Island.

Female 200 was originally tagged on22 March 1968 while basking on South-

May /982. 44(5) /7

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Figure 4. - Distribution of position fixes of the male turtles. Male 510 left the breeding colony about midway into thetracking period.

Female 450 was tagged first on 10 July1970 and recovered again 5 July 1974while nesting on East Island. The trans­mitter was attached on 8 June 1980 whileit was basking on Whale-Skate.

Female 490 was first tagged on 19June 1979 while it was on Whale-Skateand recovered again in the same place\0 days later. The transmitter wasattached on 9 June 1980 while it wason Whale-Skate Island.

Female 530 was equipped with thetransmitter on 9 June 1980. It had noprevious history of tagging.

Our monitoring program was con­tinued until 30 June 1980. Then thestation at Tern Island was manned spor­adically after our departure by caretakerpersonnel in order to see how long it waspossible to maintain contact with thetransmitter-equipped turtles. Of course.when a signal disappeared. it could eithermean the turtle departed the colony orhad shed the equipment. One transmitter(from female 490) was discovered offWhale-Skate Island in about 2 m of waterin June of 1981. The screws were still inthe plate and evidenced no sign of cor-

rosion. Female 450 was found nestingon East Island in June \981 without atransmitter; the small screw holes in thecarapace were clean and without anysign of infection. So the attachmentmethod is safe for the turtles and theequipment is eventually shed.

Table 1 also provides information onthe length of time signals were heardfrom the turtles. The signal from male5\ 0 disappeared first. We think it left thebreeding colony because its last positionwas fixed on 14 June far outside theeastern fringing reef. Male 360 was last

/8 Marine Fisheries Review

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Figure 5, - Distribution of position fixes of the female turtles, Female 200 regularly came to Tern Island to nest.

heard from on 27 June. Female 200 cameto Tern Island to nest twice. At thesecond nesting we decided to removethe transmitter and evaluate its conditionand take a close look at the screwwounds. Both the turtle and the trans­mitter were fine. Our last transmissionfrom her was on 30 June. She was laterspolled again nesting on Tern Islandon 17 July.

The other bve turtles (350. 450. 490.530. and 540) were all still transmittingwhen the field party left Tern Island onJO June.

Females 490 and 5JO remained in thecolony until the middle of August, leav­ing on the 7th and 10th. Male 540 lefton the 12th of the same month. MaleJ50 remained another month and waslast heard from on 4 September. Female450 remained the longest in the breedingcolony (signals were heard until 13

ovember). She is likely a permanentresident of FFS.

Habitat Utilized

Our results show that the nearshorehabitat of males and females at the

breeding colony is in proximity to thebasking and nesting islands near wherethey were captured (Fig. 4. 5). Whileunderstandable perhaps for the females.it is curious that the males adhere soclosely to the nesting beaches. EastIsland remains the nesting site for 55percent of the FFS- breeding turtles.

evertheless we never observed ourturtles traveling the 9 km south to theEast Island area. Clearly. there is astrongevolutionary bias for a female to returnto the same nesting beach year afteryear. Since the beach was adequate for

Mal' IIN!2, 44(5) 19

Table 2.-Specificity of returns by male and female turtles to listed areas with­in the French Frigate Shoals breeding grounds (Balazs, 1980). Data are basedupon a tagging and subsequent recoveries from 1970 to 1980. TRIG-WS =Trig Island and Whale-Skate Island complex. EAST = East Island, and GIN =Gin Island complex (Fig. 1).

TRIG-WS EAST GIN TotalItem same/stray same/stray same/stray same/stray

MalesNumber 33/8 16/2 0/0 49/10Percent stray 24 12 20

FemalesNumber 15/5 68/3 0/3 83/11Percent stray 33 4 100 13

her mother and for her as a hatchling. itis highly probable it will be adequate forher and for her hatchlings. But the maleshave no such stake. The best strategywould be to impregnate as many femalesas possible regardless of which nestingbeach they will eventually employ. Thusit is curious that the ranges of the maleswere so tightly coupled to the place theywere tagged. This specillcity apparentlyextends over the years. Male 350 wasoriginally tagged on Whale-Skate Islandin 1')75 and male 540 was tagged in 1979on Trig Island. Table 2 details previousrecords of year-to-year visits by malesand females to the various islands. Theapproximately 13- 20 percent strayingcould be due at least in part to thepermanent residents. They seem. asfemale 450 shows. to make use of moreof the reefs and beaches of FFS. She washeard from well into November and wasspotted several times on the beach atEast Island during the summer of 19~1.

Thus. our results strongly infer thatimprinting to the nesting beach and itsenvirons occurs in both males andfemales and that this response seemspermanent at least over several years.These results also emphasize the impor­tance of maintaining the utilized marinehabitat and the nesting beach as freefrom disturbing influences as possible. Itis imperative for the well- being of thepopulation that no alterations in thehabitat be made since once imprintedthe green turtle is unlikely to switch itsbreeding habitat.

Acknowledgments

Our telemetry field team also includedCausey Whitlow. Howard A. JemisonIll, Steven Kramer, Susan and RobertSchulmeister. Ruth Ittner. and ElizabethFlint. Each of these individuals madevaluable contributions to the project.We also want to express our appreciationto the U.S. Fish and Wildlife Service for

20

the use of support facilities on TernIsland. and for permitting the researchto be conducted within the HawaiianIslands National Wildlife Refuge.

Literature Cited

Amerson. A. B., Jr. 1971. The natural historyof French Frigate Shoals. NorthwesternHawaiian Islands. Atoll Res. Bull. 150.383 p.

Balazs. G. H. 1976. Green turtle migrations In

the Hawaiian Archipelago. BioI. Conserv.9:125-140.

____ . 19~0. Synopsis of biological data onthe green turtle in the Hawaiian Islands.

.S. Dep. Commer.. NOAA Tech. Memo.NMFS SWFC-7. 141 p.

Baldwin. H. A. 1972. Long-range radio trackingof sea turtles and polar hear-instrumentationand preliminary results. In S. R. Galler. K.Schmidt-Koenig. G. J. Jacobs. and R. E. Belle­ville (editors). Animal orientation and naviga­tion. p. 19-37. Nat. Aeronaut. Space Admin ..Wash .. D.C.. SP-262.

Carr. A. 1967a. Adaptive aspects of the sched­uled travel of Chelonia. In R. M. Storm(editor), Animal orientation and navigation.p. 35- 55. Proc. 27th Annu. BioI. Colloq. Oreg.State Univ. Press. Corvallis.

____ . 1967b. Caribbean green turtle. im­periled gift of the sea. Natl. Geogr. 131 :876­890.

---:-:-:-__.' 1967c. So excellent a tishe. NaturalHistory Press. Garden City. .Y., 248 p.

____ . 1972. The case for long- rangechemoreceptive piloting in Chelonia. In S. R.Galler. K. Schmidt- Koenig. G. J. Jacobs, andR. E. Belleville (editors), Animal orientationand navigation. p. 469-483. Nat. Aeronaut.Space Admin .. Wash .. D.C.. SP-262.

Carr, A.. P. Ross. and S. Carr. 1974. Internest­ing behavior of the green turtle. Cheloniamydas. at a mid-ocean island hreedingground.Copeia 1974:703- 706.

Daniel. H. 1980. Dianne. the turtle. is trackedby satellite. NOAA ews 5(16):5, 8.

Feazel, C. T. 1980. The turtle run. Sea Front.

26:240- 243.Garmon. L. J9~ I. Tortoise marsh wallow'! Sci.

News IJ9:217.Ireland. L.c. 1979a. Homing behavior of juve­

nile green turtles. Chelonia mydas. In c.J.Amlaner. Jr.. and D. W. MacDonald (editors),A handbook on biotelemetry and radio track­ing. p. 761- 764. Pergamon Press. Oxford.

____ . J979b. Homing behavior of imma­ture green turtles (Chelonia mvdas). (Abstr.)Am. Zool. 19:952.

Meylan. A. B. 1978. The behavioral ecology ofthe west Caribbean green turtle (Cheloniamvdas) in the internesting habitat. Master'sThesis. Univ. Fla.. 131 p.

_-,--__ . In press. The behavioral ecology ofthe west Caribbean green turtle (Cheloniamydas) in the internesting habitat. In K. A.Bjorndal (editor). The conservation and biol­ogy of sea turtles. Smithson. Press.

Mortimer. J.A. 1981. Reproductive ecology ofthe green turtle. Chelonia mydas. at Ascen­sion Island. Ph.D. Diss.. Univ. Fla.. 162 p.

Murphy. T. M.. Jr. 1979. Sonic and radio track­ing of loggerhead turtles. Mar. Turtle Newsl.II :5.

Pritchard. P.C.H. 1980. Report on UnitedStates/Mexico conservation of Kemp's ridleysea turtle at Rancho Nuevo. Tamaulipas,Mexico in 1979. Final rep.. U.S. Fish Wildl.Contract 14-16-0002-80-2. U.S. Fish Wildl.Serv.. Albuquerque. .M.. 27 p.

Standora, E.A .. l.R. Spotila. and R.E. Foley.1979. Telemetry of movement and body tem­perature data from green turtles. Cheloniamydas. at Tortuguero. Costa Rica. (Abstr.)Am. Zool. 19:981.

Stoneburner. D. L. J979. Satellite telemetry ofinternesting movements of loggerhead seaturtles at Cumberland Island national sea­shore. U.S. Dep. Inter., Natl. Park Serv.,Southeast Reg. Off.. Atlanta, Ga., 7 p.

Timko. R. E., and D. DeBlanc. 1981. Radiotracking juvenile marine turtles. Mar. Fish.Rev. 43(3):20-24.

World Conference on Sea Turtle Conservation.1979. Sea turtle conservation strategy. WorldConference on Sea Turtle Conservation. 26­30 November. 1979. Wash., D.C.. 38 p.

Marine Fisheries Review