geological control of podocnemis expansa … · geological control of podocnemis expansa and...

445Geological control of turtles nesting... ACTA AMAZONICA 33(3): 445-468

GEOLOGICAL CONTROL OF Podocnemis expansa ANDPodocnemis unifilis NESTING AREAS IN RIO JAVAÉS,

BANANAL ISLAND, BRAZIL

Paulo Dias FERREIRA JÚNIOR1 & Paulo de Tarso Amorim CASTRO2

ABSTRACT - The distribution of the nests of Podocnemis expansa (Amazon turtle) andPodocnemis unifilis (yellow-spotted side neck turtle) along the point bars of the Javaés River inBananal Island, demonstrates a clear preference of these chelonians for differentiated geologicalenvironments, in respect to the morphology, grain size or height of the nests in relation to thelevel of the river. The topographical distribution and the differences in the grain size of the sedi-ments that compose the point bars of the river, originated from the multiple sedimentary pro-cesses, and make possible the creation and separation of different nesting environments. Eachturtle species takes advantage of the place that presents physiographic characteristics appropri-ate to the hatching success of their eggs. The superposition of the P. expansa and P. unifilis nestplacement areas is rare. The P. expansa nests are concentrated on the central portion of the beacheswhere successive depositional sedimentary events produced sandy banks more than 3.3 m abovethe river water level. The P. unifilis nests are distributed preferentially in the upstream and down-stream portions along the point bars where the sandy deposits rarely surpass 1.5 m at the momentof laying. P. expansa nests located on the beaches of fine to medium sized sand hatch in a meanof 68 days, while those incubated on beaches of medium to coarse sand size take a mean of 54days to hatch.Key-words: Podocnemis, turtle, sediment, nesting place, incubation duration

Controle geológico das áreas de nidificação de Podocnemis expansae Podocnemis unifilis no Rio Javaés, Ilha do Bananal, Brasil

RESUMO - A distribuição das covas de Podocnemis expansa (tartaruga-da-amazônia) e Podocnemisunifilis (tracajá) ao longo das barras em pontal do rio Javaés na Ilha do Bananal, mostra uma clarapreferência destes quelônios por ambientes geológicos diferenciados, seja em relação à morfologia,constituição granulométrica ou altura das covas em relação ao nível do rio. A compartimentaçãotopográfica e as diferenças no tamanho dos sedimentos que compõem as barras em pontal, oriundasde processos sedimentares múltiplos, possibilita a criação e separação de ambientes de nidificaçãodistintos. Cada espécie de quelônio se aproveita do local que apresenta características fisiográficasapropriadas à incubação de seus ovos, sendo rara a superposição das áreas de nidificação de P.expansa e P. unifilis. As covas de P. expansa concentram-se na porção central das praias ondesucessivos eventos de deposição produziram bancos arenosos com uma altura superior a 3,3 mem relação ao nível do rio. As covas de P. unifilis distribuem-se, preferencialmente, nas porçõesmontante e jusante das barras em pontal onde os depósitos arenosos raramente ultrapassam 1,5m de altura no momento da desova. Covas de P. expansa localizadas nas praias de areia fina amédia eclodem, em média, em 68 dias ao passo que aquelas incubadas em praias de areia médiaa grossa levam, em média, 54 dias para eclodirem.Palavras-chave: Podocnemis, nidificação, tartaruga, sedimento, duração da incubação

1,2 Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto -Campus Morro do Cruzeiro,Ouro Preto – MG (CEP: 35.400-000) -Telephone: (31) 3559-1600 -Fax (31) 3559-1605 -1e-mail: [email protected] -2e-mail: [email protected]

446 Ferreira Júnior & Castro

INTRODUCTION

The Amazon turtle (Podocnemisexpansa) and the “tracajá” (yellow-spotted sideneck turtle, Podocnemis unifilis) are the mostcommon fresh water chelonians of theTocantins-Araguaia basin. These species belongto the Pelomedusidae family, which has fivespecies distributed throughout the northern andcentral western regions in Brazil (Iverson,1992). In the Tocantins and Araguaia rivers, theAmazon turtle’s and the tracajá’s nesting sea-son extends from June to December.During this period the level of the main andtributary rivers fall drastically, exposing thesandy banks which are used for nest placement.The geological aspects of these sandy banks,commonly denominated beaches, varyalong the rivers being controlled by the charac-teristics of the substratum and hydrologicalregime.

The distribution of the P. expansa andP. unifilis nests along the sandy banks allowsthe characterization of environments appropri-ate to each of the species. In spite of the mor-phological differences of the sandy banks ofseveral places, it is possible to recognize geo-logical conditioning common to the turtle nest-ing areas (Ferreira Júnior 2003). In general, itis observed that the P. expansa prefersthe central part of the beaches, where theheight relative to the river water level surpasses3.3 m on the date of the laying. The P. unifilischooses upstream and downstream the areasof the beaches, where the sandy deposits usu-ally are located 1.5 m above the river level,on the day of the laying. The superposition ofthe oviposition areas between these speciesis rare.

As P. expansa and P. unifilis presentsexual determination dependent on the incuba-tion temperature (Alho et al., 1985; Souza& Vogt, 1994,;Valenzuela et al., 1997) it isimportant to know the nesting environmentthat, together with the variations of the me-teorological conditions (i.e. rainfall, exposure tosunlight and the temperature of the air) willdetermine the temperature to which the eggswill be submitted. The hydric and thermal sur-roundings of the turtle nests can be influencedby several environmental and ecological factors,such as the mineralogical composition (Miltonet al., 1997) and the sediments grain size (Souza

& Vogt, 1994; Ferreira Júnior, 2003), the al-bedo (Hays et al., 2001), the nestdepth (Burger, 1976; Wilhoft et al., 1983), thenest placement (Vogt & Bull, 1984; Whitmore& Dutton, 1985; Horrocks & Scott, 1991;Hays & Speakman, 1993), the vegetationalcover (Vogt & Bull, 1984; Janzen, 1994;Janzen & Morjan, 2001) and the date of lay-ing (Vogt & Bull, 1982; Mrosovsky et al.,1984).

In this work, the geological characteris-tics of the P. expansa and P. unifilis nesting areasin the Javaés River, right margin of the BananalIsland in the state of Tocantins will beanalyzed. From August 3 to December 15,2000, we collected information about sixbeaches in which had 339 P. expansa and 487P. unifilis nests were labeled. All of thesebeaches can be classified as point bars. Theirsediment grain size concentrates in the sand sizewith very low mud content. The mineralogicalcomposition is basically formed of quartz andfeldspar.

Location and physiographicaspects of the area

The studied area is located at the mar-gins of the Javaés River, which is the easternborder of Bananal Island, the largest fluvial is-land of the world. The northern partof the Bananal island forms the NationalPark of Araguaia, where the Center of Conser-vation and Management of Reptiles and Am-phibians (RAN), an organ linked to theBrazilian Institute of Renewable Natural Re-sources (IBAMA), has a field base that sup-ports management, research and protectionactivities for P. expansa and P. unifilis.(Figure 1) during the laying, incubation andhatching season.

The climatic seasonality is remarkable,with a rainy season going from September toMarch and a dry season from April to Sep-tember. The total annual rain is around 1750mm (IBAMA, 1995). Due to this rainfall dis-tribution, the level of the Javaés River has ex-treme oscillations. During the dry season, thepoint bars emerge and they are used by turtlesand birds (black skimmer Rynchops nigra andlarged-billed tern Phaetusa simplex) as nestingsites. Rainfall close to the riverhead can causesmall and fast rises (“repiquetes”) in the levelof the Javaés and Araguaia rivers.

447Geological control of turtles nesting...

Comprida Beach

Jaburu Beach

Canguçu Beach

Murici Beach

Javaés River

Goiaba Beach

Pombas Lake

Cocal Channel

6005968896

9000

9004

0 2000 m500 500

Lagoa Beach

Alta Beach

Marreca Beach

N

Brasília

9008

9 55'O

50 10'O 50 05'O10 00'O

Bonita Beach

Tocantins State

Arag

uaia

Ri v

e r

Palmas

Toca

ntin

s Ri

ver

Java

és R

iver

Study Area

Brazil

Figure 1 - Map showing the location of the studied areas.


Because the extensive sandy banks usedby the turtles are located inside the channel,there is no vegetational cover. The riparianforest that surrounds the Javaés Riverinterferes very little in the environment of thebeach. During the hottest part of the day, mostof the nests receive direct sunlight. Fewof them which are located at the limit of thebeach and forest are shaded at the end of theafternoon.

MATERIALS AND METHODS

Six beaches have been chosen, namelyCanguçu, Jaburu, Comprida, Marreca, Cocoand Murici are located close to the RAN/IBAMA field base. These beaches have thelargest concentration of P. expansa and P. unifilisnests in the Araguaia National Park. Searchingfor nests is done by members of the researchteams and by the agents of IBAMA. Everymorning the beaches are spanned, looking fortracks left by the turtles in previous night. Thetracks are followed until the nests are locatedand labeled with numbered sticks.

During the monitoring of the laying sea-son, it was decided not to label the nests of P.unifilis in the Marreca and Murici beaches.Both of them have fine sand and it is hard tolocate nests there, since wind action frequentlyobscures the turtle tracks. However, theJaburu and Comprida beaches that are alsoformed by fine sand were monitored becausethey are located close to the IBAMA fieldbase. In this case, the travel time to the beachesis so short to permit the observation of someP. unifilis tracks before the windobliterates them.

The mapping of the beaches was doneon a scale of 1:1000 using theodolite, compassand tape measure. This scale allowed the rep-resentation of the main beach morphology andchannel features, as well as the plotting of allthe turtle nests. The mapping was accom-plished in the month of October, when the ovi-position had been finished, in order not to in-terfere in the laying process. The height of thenests was measured with the aid of a Kernlevel with a precision of 5 mm. The measure-ments were made in order to define two heighttypes:

The height on the laying date, whichreflects the topographical conditions found bythe turtles during the oviposition.

The maximum height of the nests, aim-ing the establishment of a common patternamong the several beaches, with respect to thetopographical conditions.

The maximum height of the nests wasregistered on November 1st, when the JavaésRiver reached its lowest depth. On this day,the Javaés River depth was taken and it al-lowed comparisons among the heights of thenests in all the beaches. The level of the JavaésRiver was taken daily close to the IBAMAbase from August to December, during the nestmonitoring period.

As the beaches are composed of sedi-ments, generally poorly selected and disposedin layers, samples were collected close to thematerial that recovers the nests and which washomogenized during the closing of the nests bythe turtle females. Three hundred and twelvesamples of sediments were submitted to thegranular analysis according to the scale of Folk/Wentworth (Table 1).

Table 1 – Granulometric fractions used in the analyses of 312 samples of sediments collected inthe nests of P. expansa and P. unifilis. Dimensions are given in mm.

Student’s t-test was used in the analy-sis of the variations of the height, incubationduration and depth of the nests between P.expansa and P. unifilis. Variance analysis(ANOVA) has been used for determination ofthe variations of the incubation duration alongthe beaches. Linear regression has been used in

the determination of the grain size influence ofthe sediments on the incubation duration.All statistical analysis was performed accord-ing to Zar (1998). Significance has been ac-cepted at a level of 5%. The data of the meanwill be presented followed ± SD (standarddeviation).

dnaS

noitcarF elbbeP levarGesraocyreV esraoC muideM eniF enifyreV

duM

noisnemiD 4> 2-4 1-2 5.0-1 52.0-5.0 521.0-52.0 560.0-521.0 560.0<


Figure 2 gives the terminology of thebeaches used in this work. Here geomorpho-logic and topographic criteria were used. Thelength of the point bars is measured in its larg-est extension, parallel to the channel.

The width of the point bars is the maximumwidth taken perpendicularly to the channel.The analysis of the height of the dunes followsthe recommendations of Ashley (1990)(Table 2).

Figure 2 – Terminology used and features collected in mapping of the Javaés River point bars.A: Margin or internal part of the point bar, close to the forest. B: External margin of the pointbar in contact with the river. C: The hatched part indicates the high beach points, generated bythe migration and amalgamation of several sandy deposits. There are dunes of small and me-dium size. The main nesting is by P. expansa. D: Low part of the beach with heights under 1.5m and normally used as nesting site by the P. unifilis. E: “Boiadouro”, representing the deepestpoints of the rivers where the turtles float and wait for the adequate moment to exit for thenesting. 1: Channel chute bars – sandy deposits with a lobete form. They generally develop inthe downstream portion of the point bar and they constitute one of the highest sites of thebeach. They are used as nesting sites by P. expansa. 2: Abrupt front part constituted by theamalgamation of several large-sized dunes. This feature is named accretionary dune front byAshworth et al. (2000). It divides the beach in two distinct topographical regions. 3: Crest ofa large-sized dune. 4: Crest of a small and medium sized-dune. 5: Temporary ponds generatedin front of the dunes. 6: Trough located in front of the large-sized dunes that connect the deep-est points of the river to the nesting sites. They are used as access way by P. expansa. 7: Pathcovered by P. expansa during the nesting.


Table 2 – Classification of the dimensions of the dunes, recommended by Ashley (1990) andused in this work. The spacing is measured between the crests of the dunes.

)D3eD2(senuD

)m(noisnemiD elppiR llamS muideM egraL egralyreV

gnicapS 5-6.0< 5-6.0 01-5 001-01 001>

thgieH 4.0-570.0< 4.0-570.0 57.0-4.0 5-57.0 5>

RESULTS

All the beaches that were studied in theJavaés River can be classified as pointbars that, according to Levey (1978) are sedi-ments deposited along the internal part of themeander occupying the area of thechannel between the thalweg and the inferiorlimit of the floodplain. The dimensions ofthe point bars depend on their positioning,

with the dimensions on the left marginbeing smaller than those on the rightmargin (Table 3). The height of the nests ofP. expansa approximately indicates the heightof the beaches. According to the average val-ues it can be observed that, in the placechosen for nesting by P. expansa, thebeaches of the left margin are higherthan the ones of the right margin(Table 4).

Table 3 – Dimensions of the point bars of the Javaés River used for nesting by P. expansa in thestudied area. The length of the point bar is measured in its largest extension, parallel to thechannel, and the width is taken in the maximum point perpendicularly to the channel (seeFigure 2). The width refers to the extreme point of the beach

hcaeB )m(htgneL )m(htdiWnigramthgiR

uçugnaC 0792 074adirpmoC 0532 052

ocoC 0543 062nigramtfeL

urubaJ 0611 091iciruM 028 061

acerraM 008 561

Table 4 – Mean ± SD of the maximum height of the nests of P. expansa and P. unifilis along thepoint bars of the Javaés River in 2000. The date of November 1st was taken as reference, be-cause it was when the Javaés River reached its lowest depth. The nests of P. unifilis were notmarked in Marreca and Murici beaches. The numbers between parentheses are the sample size.

asnapxesimencodoP silifinusimencodoP

hcaeB )mc(thgiehmumixaM egnaR )mc(thgiehmumixaM egnaR

uçugnaC )05(71.85±0.313 724-711 )331(50.87±2.281 274-66

urubaJ )6(77.84±0.504 654-813 )73(73.88±8.451 444-33

adirpmoC )61(97.36±6.363 625-762 )35(77.29±1.791 014-55

iciruM )32(54.85±1.935 174-342

acerraM )02(54.85±7.983 174-342

ocoC )361(20.15±4.692 844-201 )081(17.23±7.701 573-54

sehcaebehtllA )872(84.88±4.233 646-201 )304(56.57±4.841 274-33

There is a minimum required height forthe nesting (Figure 3a). Each species choosesan area with a suitable height range relative tothe level of the Javaés River in the date of thelaying (t = 25.74, df = 520, p < 0.001). Thedata suggest that 50% of the nests of P. expansa

are between 250 and 329 cm high at thedate of the laying. This condition excludes theareas upstream, downstream and close tothe margin of the river. The P. unifilis behavioris different and the height of 50% of thenests varies from 48 to 126 cm at the


date of the laying. This situation is foundupstream and downstream parts of the beachesand also in the external portions of thepoint bars.

The depth of the nests varies betweenthe species (t = 77.13, df = 483, p <0.001). The nests of P. unifilis being shallower(x = 15.6 ± 1.95 cm, n = 207) than the

ones of P. expansa (x = 60.4 ± 8.17 cm, n =278) (Figure 3b).

The incubation duration – consideredhere as the period between the layingand the hatchling emergence from thenest – varies significantly among thespecies (t = 25.19, df = 331, p < 0.001)(Figure 3c).

0

100

200

300

400

500

600

P. expansa P. unifilis

Min-Max25%-75%Median value

Hei

ght o

f the

nes

t at t

he d

ate

of la

ying

(cm

)

a

0

20

40

60

80

100


Dep

th to

the

botto

m o

f the

nes

t (cm

)

b

30

50

60

80

100

110


Incu

batio

n du

ratio

n (d

ay)

c

90

70

40

Figure 3 - Reproductive and biological parameters of P. expansa and P. unifilis in the nestingseason of 2000 in the Javaés River. a) Height of the nests of P. expansa and P. unifilis in thedate of laying. Sample size: 278 P. expansa nests and 244 P. unifilis nests. b) Depth of P. expansaand P. unifilis nests. Sample size: 278 P. expansa nests and 207 P. unifilis nests. c) Incubationduration of P. expansa and P. unifilis nests. Sample size: 271 P. expansa nests and 62 P. unifilisnests.


For P. expansa there is an outstandingdifference between the incubationduration along the beaches (F5,265 = 26.94, p <0.001) (Table 5, Figure 4a). The beachesof fine to medium sand size like Jaburu,Comprida, Marreca and Murici presentan average incubation duration of 63.5 ± 7.38days, while in those of medium to coarse

sand such as Canguçu and Coco theincubation duration is of 54.4 ± 5.05days.

The incubation duration of P. unifilisdoes not vary significantly along thebeaches (F3,58 = 0.92, p = 0,4351) and it hasan average of 79.8 ± 6.43 days (Table 6,Figure 6).

Figure 4 – Incubation duration along the beaches of Javaés River during the nesting season of2000. a) P. expansa, b) P. unifilis.

80

60

105

100

95

90

85

75

70

65

55

Canguçu Jaburu Comprida Murici Marreca Coco

Min-Max25%-75%Median value

35

80

Incu

batio

n du

ratio

n (d

ay)

a

75

70

65

60

50

45

40

Incu

batio

n du

ratio

n (d

ay)

b

Possible sources of influence on theincubation duration show significant differencesbetween the species. The nest grain size(F5,265 = 9.05, R2 = 0.2009, p < 0.001) andthe nests height, in the date of the laying(F1,238 = 84,10, R2 = 0.2611, p < 0.001), aswell as the maximum height registered inNovember 1st (F1.238 = 103.82, R2 = 0.2755,

p < 0.001), affected the incubation durationof P. expansa. They did not show an influenceon P. unifilis incubation time (Table 6).The depth of the nest affects the incubationduration of P. unifilis (F1.54 = 5.30, R2 = 0.0895,p = 0.0251) and it does not interfere in P.expansa (F1.257 = 0.89, R2 = 0.0025, p =0.3451).


Table 5 – Mean ± SD of the incubation duration of P. expansa and P. unifilis along the beachesin the nesting season of 2000. The incubation duration is the period that goes from the layingto the hatchling emergence, and it is given in days. The numbers between parentheses are thesample size.

*The beaches of finer to medium sand compose Murici, Marreca, Jaburu and Comprida beaches.**The beaches with medium to coarse sand compose Coco and Canguçu beaches.

asnapxesimencodoP silifinusimencodoP

hcaeB )syad(noitarudnoitabucnI egnaR )syad(noitarudnoitabucnI egnaR

uçugnaC )55(40.6±9.45 07-54 )83(88.4±7.87 29-17

urubaJ )6(65.7±0.56 57-75 )41(89.9±9.08 99-46

adirpmoC )71(49.6±3.66 47-55 )03(59.4±7.08 98-37

iciruM )03(69.6±6.16 57-45

acerraM )02(95.6±4.26 57-54

ocoC )681(94.4±2.45 26-63 )83(56.4±0.08 98-07

*sehcaebdnasenifotmuideM )37(30.7±2.36 57-54 )43(56.4±9.08 99-46

**sehcaebdnasmuidemotesraoC )142(09.4±4.45 07-83 )67(58.4±5.97 29-07

sehcaebehtllA )413(95.6±4.65 57-83 )021(36.5±8.97 99-46

Table 6 – Linear regression analysis of variables that can affect the incubation duration ofP. expansa and P. unifilis. The grain size refers to the granulometric fractions of medium andfine sand.

It was possible to delineate two groupsof beaches with different characteristics fromthe grain size analysis of samples collected inthe nests of P. expansa (221 samples) andP. unifilis (92 samples). The Jaburu, Marreca,Murici, and Comprida beaches presentfiner sediments, well selected and concentratedin the fine and medium sand fractions.The other group is formed by Canguçuand Coco beaches where the sedimentsare coarse, poorly selected, and they aredistributed in the very coarse, coarse, medium,and fine sand fractions (Table 7). The contentof mud in all the six beaches is small andrestricted to temporary ponds at thetrough of the dunes. The maximum volume ofclay registered was 6.08%, the mean being0.12% ± 0.38.

Data on the monitoring providedby IBAMA show the distribution of thenests of P. expansa since the implementationof the project in 1990. The P. expansa usuallychose the beaches of the right margin(Figure 5).

The point bars differ not only for theirdimensions and grain size, but each marginpresents its own geological characteristics.The point bars of the left margin are shorterand higher than those of the right margin(Tables 3 and 4). In general, the grain size ofthe sediments that compose the beaches of theright margin is coarse than those of the leftmargin. The other geological parameters, mainlythose related to the morphology of the beachesare not measurable, will be described indetail.

asnapxe.P silifinu.P

fd R2 F p fd R2 F p

ezisniarG 712,2 5872.0 98.14 100.0< 78,2 3400.0 6191.0 9528.0

htpedtseN 462,1 200.0 1366.0 1614.0 45,1 5980.0 03.5 1520.0

gniyalfoetadehttatsenehtfothgieH 372,1 9352.0 19.29 100.0< 311,1 2500.0 95.0 1244.0

tsenehtfothgiehmumixaM 372,1 5572.0 28.301 100.0< 311,1 9610.0 59.1 2561.0


Table 7 – Average grain size constitution of the nests of P. expansa and P. unifilis in the JavaésRiver in the nesting season of 2000.

dnaShcaeB eziselpmaS elbbeP levarG esraocyreV esraoC muideM eniF enifyreV duM

uçugnaCstsenllA 46 32.0 41.1 29.4 74.52 10.84 63.81 94.1 52.0

asnapxe.P 63 32.0 85.1 43.6 78.03 67.44 12.41 27.1 62.0

silifinu.P 82 22.0 38.0 90.3 35.81 91.25 86.32 12.1 32.0

urubaJstsenllA 21 97.0 88.1 50.4 74.02 12.84 93.22 10.2 91.0

asnapxe.P 2 0 0 80.0 95.2 74.34 74.25 13.1 70.0

silifinu.P 01 49.0 72.2 48.4 50.42 51.94 83.61 51.2 12.0

adirpmoCstsenllA 03 81.0 78.0 37.2 44.51 73.14 50.63 61.3 02.0

asnapxe.P 9 0 71.0 86.0 65.6 15.53 89.35 59.2 41.0

silifinu.P 12 62.0 71.1 16.3 52.1 88.34 63.82 42.3 12.0

ocoCstsenllA 481 46.0 72.2 26.8 97.82 59.83 36.91 20.1 70.0

asnapxe.P 251 16.0 73.2 64.9 70.13 97.73 97.71 58.0 40.0

silifinu.P 23 57.0 48.1 46.4 29.71 74.44 23.82 58.1 12.0

iciruMasnapxe.P 51 0 10.0 31.0 14.4 84.65 55.73 93.1 30.0

acerraMasnapxe.P 7 80.0 80.0 25.0 14.7 16.47 55.61 07.0 50.0

CanguçuComprida

JaburuMuriciCocoMarrecaGoiabaAltaBonita

Others Beach

2000

200019

98199619

94199219

90

Year

100

200

300

400

500

Num

ber o

f nes

ts

Figure 5 – Number of P. expansa nests per year of each studied beach from 1999 to 2001.


Beaches of the left margin

Jaburu Beach

The Jaburu beach historically presentsthe smallest number of nesting of P. expansa(Figure 5); in 2000 only eight nests were regis-tered. The P. expansa chooses the highest pointsin the center of the beach close to the internallimit of the point bars (Figure 6). The highestnest is placed on a channel chute bar in thedownstream portion of the beach.

The nests of P. unifilis are predomi-nantly found in the upstream and downstreamparts of the Jaburu beach. The nests are lo-cated mainly close to the base of the dunes.On the nesting date the nests are usually lo-cated in sand lower than 1.5 m in height (x =132 ± 100.2 cm). In the center of the beach,close to the external margin (close to the waterline), the nests of P. unifilis are located wherethe height is lower.

Marreca Beach

Channel chute bars with its typicallobed geometry occur in the downstream por-tion of the Jaburu and Marreca beaches. Thesubsequent part of these bars has bushes, whichhelps its fixation. Marreca beach (Figure 7), likethe other point bars of the Javaés River, hasits downstream internal limit formed by ascarp which is formed by erosion due to sec-ondary channels flow during the flood period.Inside these channels the chute bars are de-velop. It is common to find nests ofP. expansa in the top of the chute bars thatfrequently constitute the highest portion of thepoint bars. In the Marreca beach four nests ofP. expansa were found in the top of the chutebars while in the Jaburu beach only two nestswere found.

Murici Beach

Murici beach has a concentration of 26nests in a small area of about 1 ha (Figure 8).The upstream and downstream portion of theMurici beach and the places close to the exter-

nal margin are avoided by the P. expansa, be-cause the height in these places is very low,under 1.5 m.

Murici beach presents a pattern of dis-tribution of chelonian nests similar to Jaburuand Marreca beaches. There is a continuous in-crease in the height of the beach towards thecenter portion of the point bar in a “slope”pattern.

In Jaburu, Marreca and Murici beachesthe exit of the P. expansa happens always inspecific points in the troughs of the dunes,which act as a connection between the deepestparts of the river and the beaches. The pathfollowed by the turtles, marked by their tracks,describes a path upstream as well as down-stream, with no apparent preferential direction.P. expansa tracks are not found on the abruptmargins of the beach, where the declivity ishigh.

Beaches of the right margin

Canguçu Beach

Canguçu beach marks the upstream limitwhere the nesting of P. expansa in significantnumbers. Above this beach the Javaés Riverbecomes shallower, frequently less than 30 cmdeep, and the beaches become lower with rarehigh elevations points. This fact precludeP. expansa nestsing. On the other hand, theP. unifilis is common upstream Canguçu beach,in spite of being not as abundant as in thestudy area.

When the water level of the Javaés Riverlowered during the dry season extensive sandybanks in the center portion of Canguçu beachemerged. These deposits subdivide the“boiadouro” (popular denomination of thedeepest points of the rivers where the chelo-nian await for the adequate moment to exit forthe nesting – Figure 2) in two parts. Theseparts are linked by a narrow channel. P. expansaemerge from “boiadouro” through this channelto the beach. P. expansa do not nest on the partof the beach in front of the sandbanks portionnear the “boiadouro”.


Figure 6 – Distribution of P. expansa and P. unifilis nests along the Jaburu Beach.


Figure 7 – Distribution of P. expansa nests along the Marreca Beach.

P. expansa exit

Amazon turtle return

P. expansa return

Pat

h fo

llowe

d by t

he A

mazon

turtle

during th

e nesti

ng

Downstream: low part of the point bar constituted of small dunes oriented in high angle with respect to Javaés River direction.

Channel chute bar: deposits generated in the period of flooding. They are formed by a topographical hight that are used as nesting place by some .P. expansa

Center: high part of the point bar. Nests of spread on this area. There is not a specific point that concentrates some of 17 nests.

In the external part of the beach there are small and spaced dunes. The internal part is plain without dunes. To the internal portion a fast increase of the height of the beach takes place

P. expansa

.

Front part of a large dune that limits the high part of the beach. Nests of are frequent.P. expansa

Upstream: small and spaced dunes. Since the dune are spaced there is no sufficient increase of the height in order to permit the nesting of . Only nests of

are found at this place.P. expansa

P. unifilis

Marreca Beach

0 100 m20 20

Legend

Java

és R

iver

nestP. expansa

Crest of large size duneCrest of small and medium size dunesPath cover by during the nestingP. expansaBushes


Java

és R

iver

Center: accretionary dune front marks the boundary between center and downstream portion. Its position near a large and deep trough turn the clibing of the to the highest point possible.

P. expansa

At this area is plain and the nests are more spreadout.

The nests are dispersed in a large and relatively plain area in the stoss side of the large-sized dunes that are set at large intervals.

Area with high concentration of nests. The place chosen for the nesting is relatively plain.

P. expansa

Downstream: small dunes that migrate orientated with high angle with respect to the Javaés River direction.

Upstream: the dunes are medium sized and they migrate oriented with high angle with respect to the Javaés River direction. As the dunes are spaced, they do not form deposits with high points.

Murici Beach

In the external part, there are dunes of small and medium sizes that migrate with crests oriented with high angle with respect to the Javaés River direction.

P. expansa nestCrest of large size duneCrest of small and medium size dunes

Legend

Path cover by during the nesting

P. expansa

Bushes

P. expansa exit

P. expansa return

Figure 8 – Distribution of P. expansa nests along the Murici Beach.


Canguçu beach can be divided in twoparts (Figure 9). a) Upstream – it is formedby an extensive area characterized by the curvedline of the point bar. The accretionary dune frontis oriented at a low angle in respect to the chan-nel direction. It is separated from the down-stream part by a topographical high area whichhad 23 nests of P. expansa, along 32 ha. Dur-ing the dry season, erosive processes occur inthe upstream portion of the beach where thecurvature of the channel is more pronounced.As a result of the erosive processes a 1m highscarp at the external margin of the beach isformed. This scarp acts as a barrier for the P.expansa and P. unifilis to exit from water tobeach in this area. b) Downstream – there is anarrow, long part of the beach, without pro-nounced topographical high, where the dunescrests is in high angle with respect to the chan-nel direction. The height of the beach increasesslowly and gradually towards the internal partof the point bar. The arrangement of the dunesin high angle favors the development of sev-eral access channels in their trough. The nest-ing of P. expansa take place in the internalmargin of the beach close to the forest. Cocalchannel has the largest number of nests of P.expansa. It has water only during the high waterseason, when the Javaés River winds its waythrough its extensive floodplain and createsalternative paths for water flow (Figure 1). Inthis place of about 4 ha, 33 nests of P. expansawere found. The nests of P. unifilis are distrib-uted throughout the nesting area and concen-trate close to the base of the dunes.

Comprida Beach

It can be divided in two parts, due tothe complexity of the deposits and the con-centration of the nests. A narrow sandy strip,up to 10 m wide and 250 m long, makes theconnection between the upstream and down-stream domains, submerged after the beginningof November (Figure 10). a) Upstream – it ismarked by channel chute bars that apparentlyhave been deposited through the interaction ofthe flow of the Javaés and Riozinho rivers.Shrub growth stabilizes the sand deposits ofthe channel chute bars. There were four P.expansa nests and only one P. unifilis nest found

in this habitat. b) Downstream – it is a shelfformed by the migration and overposition ofseveral dunes with crests in a high angle withrespect to the channel direction. It is a wellmarked topographical unevenness. In this place,in 1999, a large nesting of P. expansa was reg-istered, with about 120 nests. At the end ofthe point bar there are several channel chutebars that are responsible for the largest heightsregistered on the beach.

The P. expansa took advantage of thecountless existing access channels in the troughof the dunes in order to reach the beach. Fifty-five nests of P. unifilis are distributed in theupstream part of this domain, where the heightof the point bar is up to 2 m high. The nestsconcentrate mainly at the base of the dunes.The access to the nesting place is done, fre-quently, from the channels located in the troughof these dunes. There is not a specific pointthrough which a great number of turtles ascendto the beach.

Coco Beach

It is a large point bar developed in ameander on the right margin of the Javaés River(Table 3). It had the largest number of P.expansa and P. unifilis nests in 2000 (Figure11). The upstream portion shows evidence ofrecent deposition, emerging for the first timein 2000. The amalgamation of the deposits isnot verified and as a consequence, the heightof the nests of P. unifilis registered is below 46± 5.94 cm at the time of the laying (n = 22)and 108 ± 8.52 cm in November 1st, when theJavaés River was at its smallest level. Most ofthe nests of P. unifilis are located on crest ofthe dunes in this area. There are nests close tothe base of the dunes, and not just on the crestof the dunes in places where the height of thebeach is higher.

The downstream part is plain, includ-ing dunes of small size spaced in a high anglewith respect to the direction of the river. Sinceamalgamation of the deposits generated by themigration of the dunes does not happen, theheights are modest. In this case there is onlyone P. unifilis nest. In November the rising ofthe Javaés River caused the fast inundation ofalmost all the nesting area.


Figure 9 – Distribution of P. expansa and P. unifilis nests along the Canguçu Beach.


Java

és R

iver

The dunes have the crests oriented obliquely with respect to the Javaés River direction. The amalgamation of the deposits takes place and, consequently, the height of the beach increases, making the nesting of possible close to the internal margin of the bar in the small point of land.

P. expansa

0 100 m20 20

Upstream: it is marked by nests of located on the top of channel

chute bars. One nest of was found close to the river

P. expansa

P. unifilis

Narrow strip of transition between the upstream and downstream portions.

Low part, formed by small and medium sized spaced dunes, with no amalgamation of the sandy deposits. There are only nests of .P. unifilis

P. expansa nests in the internal and higher part of the bar. The few dunes of this area are small-sized and spaced.

In this area the nesting of about 120 nests of was registered in 1999.

P. expansa

P. unifilis chose the external part of the bar, close to the river, and it preferentially nested in front of the dunes.

The amalgamation of several large-sized dunes generates an outstanding topographical feature that limits the area appropriate for the nesting of .P. expansa

Comprida Beach

P. expansa nestP. unifilis hatched nestP. unifilis predated nest

Crest of large size duneCrest of small and medium size dunes

Legend

Path cover by during the nestingP. expansaBushes

Figure 10 – Distribution of P. expansa and P. unifilis nests along the Comprida Beach.


Figure 11 – Distribution of P. expansa and P. unifilis nests along the Coco Beach. a) down-stream, b) center, c) upstream.


In the central part, where the largestnumber of nesting of P. expansa happened, theheight of the beach increases gradually down-stream, without significant steeps. The dunesare of medium to large size, spaced, with crestsat a high angle with respect to the channel di-rection, and frequently they cross the beach en-tirely. The spacing between the dunes is re-duced in the downstream direction and theystart to migrate one over the other, amalgamat-ing and increasing the height of the point bar.A small-vegetated area serves as an obstacle tothe migration of the dunes in the middle of thebeach. The beach is flat in this area. The endof the area of nesting of P. expansa is markedby an accretionary dune front, about 200 cmhigh. The amalgamation of the deposits hascreated a great elevation in this area, whosecrest is almost parallel to the direction of thechannel.

The location of the tracks of P. expansaindicates that exist is at specific point, closeto the trough of a great dune. The path of theturtles had a paraboloid shape not only up-stream but downstream as well. The return didnot occur in a specific point of the channel.The concentration of exits of the turtle at agiven point can be explained based in the mor-phology of the beach and in the existing rela-tionships between the sandy deposits and the“boiadouro”. Sandy upstream bars, althoughimmersed to small depths, made the locomo-tion of P. expansa difficult. The points thatallow the connection between the “boiadouro”and the beach are restricted and concentratedin the trough of the dunes, way ahead of thehighest parts of the point bar.

DISCUSSION

Temperature-dependent sex determina-tion in most species of turtle studied raised at-tention to the conditions that govern or inter-act with the substratum, determining the tem-perature which the eggs undergo during the em-bryogenesis. According to Charnov & Bull(1977), Bull (1980), Bulmer & Bull (1982), andJanzen & Morjan (2001) the sex ratio of theoffspring is governed by two factors: a) ther-mal sensitivity of the embryo to the sexual de-termination, b) maternal choice of the thermal

qualities of the nesting place. Janzen & Morjan(2001) showed that Chrysemys picta use thesame microenvironment in successive nesting,which is in agreement the theory that the fe-males can “control” the sex ratio of the off-spring by the choice of the thermal environ-mental of the nests.

Several examples show the importanceof the nesting place in the survival and in theembryonic development of several lizard spe-cies and turtles. In all cases it seems clear thatthe choice of the nesting places is not randomand seeks to match the physiologic character-istics of the adult females (i.e. size and terres-trial locomotion agility) and characteristics ofthe clutches (i.e. clutch size) to the character-istics of the environment (hydric and thermal)that will control the embryogenesis.

For Ewert et al. (1994) the pivotal tem-perature will have a decisive influence on theplace chosen for the nesting of four fresh wa-ter species in a same region. Therefore the sexratio of the offspring stays balanced, since thefemales use places with different thermal char-acteristics. This would compensate the differ-ences of the pivotal temperature among thespecies.

Burger (1976) has observed that thetemperature of the nests of Malaclemys terra-pin terrapin depends on the position of the neston a sandy dune. Hays et al. (2001) had at-tributed the thermal variations in the severalenvironments of the beaches to the albedo dif-ference. Bodie (2001), in a compilation work,pointed out that most of the species of freshwater turtle prefer open and sandy beaches forthe nesting and that they can seek alternativehabitats, such as levees, when their traditionalnesting places are not available. Raising of theriver could put the eggs at risk, as pointed byAlho & Pádua (1982), for P. expansa and byStanding et al. (1999), for Emydoideablandingi.

Souza & Vogt (1994), while analyzingP. unifilis in Costa Marques (RO), had indicatedthat nests located in sunny places and in sedi-ments in the coarse size sands (1 to 0.5 mm,according to these authors’ classification) ex-periment larger daily temperature fluctuation.The average temperature of the nests locatedin sediments in the coarse size sand is larger


than that of the nests in fine sand. These au-thors did not associate the sex ratio of the off-spring with the grain size of the substratum;they just suggested that the nests located incoarse sediments would bias female sex ratiomore than those placed in finer sediments.

The grain size of the substratum wherethe nests are placed does not have influenceonly on the temperature. For the sea turtle Che-lonia mydas to makes a nest cavity it is neces-sary that the place presents humidity or smallroots that give enough cohesion to the substra-tum in order to prevent the walls from tum-bling (Bustard & Greenham, 1968). Cheloniamydas constructs a nest more easily in finersand (Mortimer & Carr, 1987). The coarse anddry sand makes the opening of the nests diffi-cult, forcing the females to dig several placesbefore finding an appropriate local.

Hatchling success is influenced stronglyby the nest site for fresh water turtle speciesas P. expansa (Alho & Pádua, 1982; FerreiraJúnior 2003), Emys orbicularis (Servan et al.,1989), E. blandingii (Standing et al., 1999), andsea turtle species such as Dermochelyscoriacea (Whitmore & Dutton, 1985),Eretmochelys imbricata (Horrocks & Scott,1991) and Caretta caretta (Hays & Speakman,1993). Beaches with different hatchling successpresent larger concentration of nests in thepoints where the survival of the offspring islarger (Horrocks & Scott, 1991; Hays &Speakman, 1993).

Bragg et al. (2000) compared the nest-ing locals of different lizards, and the specieswith temperature-dependent sex determinationon the (Eublepharis macularius andHemitheconyx caudicinctus) preferred placeswith intermediate temperatures. On the otherhand, the species Coleonyx mitratus, whichpossesses genetic sexual determination, did nothave a preferred place.

In the Javaés River the nesting areas ofP. expansa and P. unifilis show different mor-phologic aspects. Although both species canuse the same point bar each species choosesmorphologically different places to nest. Themineralogical constitution is relatively homo-geneous in all the six beaches and it does notinfluence the nest site chosen by individualsof either the both species, nor does it affectduration incubation.

The data suggest that the grain size dis-tribution in and among different beaches affectssignificantly the incubation duration of P.expansa. The P. expansa is selective in thechoice of the nesting places, preferring histori-cally the beaches constituted by coarse sedi-ments. Since 1990 (Figure 5) the largest con-centrations of nests always took place in thepoint bars of the right margin. Besides the largercomplexity of the beaches, the grain size sedi-ments of the right margin are coarse. This factindicate a primary control of the geologicalaspects on the reproductive biology of P.expansa.

The incubation duration varies signifi-cantly among the beaches for P. expansa duein part to the influenced of grain size of thesediments (Table 6 and Figure 4a). There aredifferences of incubation duration between theCoco beach, with a mean of 54.2 ± 4.48 days,and Comprida beach, with a mean of 68.3 ±7.70 days. The longer incubation duration forComprida beach is associated to its finer grainsize sediments. Grain size of the sedimentsinfluences on the incubation time for P. expansa,but not for P. unifilis (Table 6). Other elementsshould be interacting and affecting the embryo-genesis of P. unifilis.

It is worth highlighting two characteris-tics that are different for the two species stud-ied: the height of the nests and the eggshelltype. In accordance with Pritchard & Trebbau(1984) the eggshell of P. expansa is flexible andthe one of P. unifilis is rigid. For Packard et al.(1982) eggs with flexible eggshells are moresensitive to the variations of the hydric envi-ronment, absorbing water in humid conditionsand becoming dehydrated in dry ones. Thewater exchange with the environment is relatedto the metabolic rate, affecting the incubationduration. Eggs with rigid eggshells, as P. unifilis,present low porosity and little exchange ofwater with the environment, being less depen-dent from the hydric environment. Thus, itseems that for P. unifilis the rate of embryonicdevelopment and the incubation duration arenot affected by the hydric conditions of thenests.

The difference in the constitution of theeggshells of the P. expansa and P. unifilis eggs(Pritchard & Trebbau, 1984) helps to under-


stand the differences found in the microenvi-ronment in the nests. The rigid eggshell of P.unifilis makes possible incubation at smallerdepths. Perhaps, this would be possible evenin drier places, because the dehydration of theeggs is minimized by the small porosity of theeggshell (Packard et al., 1982). On the otherhand the eggs of P. expansa demand a greaterdepth (Figure 3b), since the eggshell does notsupply an adequate protection against the de-hydration.

The height and the depth of the nestsof P. unifilis and P. expansa should also affectthe microenvironment of the nests (Figure 3aand 3b). The P. expansa nests are deeper thanthe P. unifilis nests (Figure 3b), which in part,control the distribution of the nests along thebeaches. Wilson (1998) suggests that mediumand large sized turtles, such as P. expansa (Alhoet al., 1985) and Apalone mutica (Plummer etal. 1994), nesting in open areas to maximizethe exhibition of the nests to the sun, and smallturtles as Kinosternon baurii need the protec-tion of the vegetation and of the humidity sincethey can not dig deep nests and avoid very hightemperatures. Shallow nests are submitted tolarge daily oscillations of temperature (Burger,1976; Thompson, 1988; Wilson, 1998). Thelower depth of the water table and the stem-ming increase of humidity could minimize thedaily variations of the temperature. The greaterhumidity would minimize the influence of theheat exchange, which is more effective in coarseand dry sediments than in fine and humid sedi-ments (Harrison, 1985; Novak & Black, 1985;Harrison & Morrison, 1993).

The bottom of the clutch of P. expansais located at an mean depth of 61 cm (Figure3b). Algo in oceanic beaches there are not sig-nificant differences of the sand temperature ata depth of 60 cm (Mrosovsky et al., 1984). Inspite of the difference between the sea and flu-vial environments, it is believed that the pro-file of heat transmission in large depths has asimilar behavior, with daily variations of tem-perature being small at such depths. A greaterheight of the beach is required so that the hu-midity originated from the water table is in arange appropriate to the incubation.

Another fact that can be related to thegreater height required by the eggs is the syn-

chronism between the drought of the river andthe nesting behavior of P. expansa. The begin-ning of the nesting season is associated withthe stabilization of the river in its lowest level(Alho & Pádua, 1982). The survivorship of latehatching of some clutches would be influencedif the rise of the river water level were antici-pated. In this case, higher areas nesting posi-tion allows the hatching of most of the nests,even if the level of the river rises faster(“repiquetes”). The eggs of P. unifilis, in the2000 nesting season, begin hatching in the sec-ond half of October, before water levelbegan to rise.

The choice of the nest sites is related tosome habitat requirements, such as, the pres-ence of “boiadouros”, access channels and to-pographical levels. The morphology of thebeach will bring direct consequences to the dis-tribution of the nests. Wide and relativelyplain and uniform areas such as the central partof the Marreca beach (Figure 7) and the up-stream part of the Canguçu beach present nestsof P. expansa uniformly distributed. The ap-propriate height for P. expansa is only reachedwhen the river water flow makes successiveevents of migration of the dunes and amalgam-ation of the dunes. The choice of the centralpart of the beaches of the right margin (Figure9 and 11) explains this aspect. The separationamong the high areas, chosen by P. expansa andthe low parts, selected by P. unifilis in Coco,Canguçu, Comprida and Murici beaches is clear.

The dimensions and morphology of thepoint bars will depend on their positioning andinteraction with the water flow of the channel.In spite of being smaller, the point bars of theleft margin are higher and its external marginsare more abrupt, which sometimes hinders theaccess of the females to the nesting places. Agreat elevation of a place alone is not enoughto define the best area for nesting of P. expansa(Tables 3 and 4). In spite of the smaller heights,the beaches of the right margin are, historically,the most used by P. expansa (Figure 1 and 5).

The Javaés River is deep and calmenough to allow the turtles to rest in the vicin-ity of the beaches. The Canguçu beach clearlyexemplifies the importance of the“boiadouros”. The greater concentration ofnests in 1990, 1993, 1994, 1996, 1997 (Figure


5) happened at the Canguçu beach. Nowadays,the Canguçu beach importance has been reducedin comparison to Coco and Comprida beaches.Reports of the field agents that work in theproject since its implantation in 1990 describethe decrease of the “boiadouro” as a result ofthe formation of sandy banks that, even whensubmerged, make the navigation in the area dif-ficult. The smaller nesting of P. expansa inCanguçu beach is partially attributed to thedecrease of the “boiadouro” area.

The nesting decrease of P. expansa inComprida beach in 2000 is not well understood,since the “boiadouro” is still deep and there iseasy access to the beach without the presenceof sandy banks to difficult the turtles exit. Thebeach height remained similar up until last year.The decrease of more than 120 nests, in 1999,to only 18 nests in 2000, will only be explainedwith the monitoring for couples of years more.

Due to its smaller size and larger mobil-ity, P. unifilis reach the beaches more easily, fre-quently using the channels in the trough ofsmall dunes, which are common along the up-stream and downstream parts of the point bars(Figures 9, 10 and 11). Channels of access thatexist in the trough of the dunes make the con-nection of the “boiadouro” to the highest pointsof the beach. Its importance can be verified atCoco beach, where the exit of P. expansa is con-centrated at one only point. This fact helps tounderstand the high nesting rate in that por-tion of the point bar. In the other beaches, wherethere are several access channels or the mor-phology of the beach is a ramp-like, there wasnot a high concentration of nests at only onepoint. The exit of P. expansa happens in onlyone point of in the upstream portion ofCanguçu beach close to a submerged sandy bankthat marks the upstream limit of the“boiadouro”.

Souza & Vogt (1994) attribute the dif-ferentiation of the nesting areas of these spe-cies in the beaches, to the fact that the destruc-tion of the nests of P. unifilis by P. expansathat nested later. This hypothesis is rejectedfor the beaches monitored in the Javaés River,because besides being very wide, there is not asuperposition of the nesting areas. The distri-bution of the nests of P. expansa and P. unifilisshows the influence of the fluvial environment

on the choice of the nesting area. This distri-bution in separated morphological placesshould be considered in the managementprojects that frequently use to transfer of nests.As we could observe, it is not only sufficientto transfer the nests to high places, abovethe earlier rise of the level of therivers (“repiquetes”) because at least for theP. unifilis, proximity with the water tableis required by the turtles at the momentof the nesting. If we change the environmentalconditions (which means change in thermaland hydric conditions), we can somehowinduce unforeseen or poorly understoodmodifications on the reproductive biology ofturtles.

ACKNOWLEDGMENTS

This work is part of the PhD researchof Paulo Dias Ferreira Júnior accomplished inthe Departamento de Geologia of theUniversidade Federal de Ouro Preto, with ascholarship by CAPES. The support in thefield work was given by RAN/IBAMA and bythe Instituto Ecológica. We would like to thankDivaldo Rezende and Mariluce Messias of theInstituto Ecológica and Antônia Lúcia and YedaBataus of RAN/IBAMA. Special thanks toAdriana Malvasio from Universidade Federaldo Tocantins for critical reading of the manu-script and presentation to the world of turtles.We thank Paulo de Marco Júnior fromUniversidade Federal de Viçosa for the help inthe statistical analysis. The collection of thedata was only possible with the help of the ofRAN/IBAMA agents, Gonzaga and Alfreu andthe undergraduate students of the UniversidadeFederal do Tocantins, Giovanni, Eliene, Odimar,Fernando, Jackson, Edileila, Marcos, Valderico,and undergraduate students of the UniversidadeFederal de Ouro Preto, Ariadne and LuísGustavo. Our thanks to the friends Marcos andRossana for the hospitable welcome at theCentro de Pesquisas Canguçu.

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Aceito: 20/03/2003

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