pp.136–142

Asiatic Herpetological Research, Vol. 11

2008

An Assessment of Solitary and Arribada Nesting of
Olive Ridley Sea Turtles (Lepidochelys olivacea) at the
Rushikulya Rookery of Orissa, India
BASUDEV TRIPATHY1,2
1

Department of Environmental Sciences, Andhra University, Visakhapatnam – 530 003, India;
Wildlife Institute of India, PO Box 18, Chandrabani, Dehradun – 248 001, Uttraranchal, India.
Corresponding author E-mail: tripathyb@yahoo.co.uk

2

Abstract.- The solitary and arribada population of Olive Ridley Sea Turtles at the Rushikulya rookery of Orissa of
India was monitored for two nesting seasons (2003–04 and 2004–05). Mass nesting population census of turtles was
carried out using standard IUCN/SSC Marine Turtle Specialist Group recommended statistical technique (number ofturtles counted: n = 11024). Curved carapace measurements of egg laying females were recorded (67.16±3.65). There
was a reduction in the size class of nesting females as compare to the data available on turtle morphometry from
Orissa coast in the last decade. The sporadic nesting was documented at the rookery from December to April with apeak in March and with no major intermediate nesting activities in between. The mass nesting census differs greatly
as compare to the nesting figures projected by the state wildlife authority. While the state wildlife authority projects
a higher figure of nesting turtles, the actual number of turtles that nests during arribada is quite low. Continuous monitoring of the beach for assessment of solitary nesting activities along with accurate methods of mass nesting census
is required for proper assessment of the Olive Ridley Sea Turtle population at the Rushikulya rookery of Orissa.
Keywords.- Lepidochelys olivacea, solitary, arribada, estimation, technique, India.

Introduction
Nesting of Olive Ridley Sea Turtles (Lepidochelys olivacea) takes place either in solitary or in great simultaneous aggregations (mass nesting) where upto 100,000
females come onto the beach to lay their eggs also popularly known as arribada; a Spanish term meaning mass
arrival (Pritchard, 1997). Orissa, a state in India along
the easten coast, harbours three major arribada sites viz.
Gahirmatha, Devi and the Rushikulya rookery (Pandav
et al., 1994; see Fig. 1). Besides solitary nesting all
along the coast of Orissa, more than a hundred thousand
turtles are believed to nest annually at Gahirmatha (Dashand Kar, 1990) and tens of thousands nest at other two
locations, i.e. Devi and the Rushikulya rookery (Kar,
1982; Pandav et al., 1994). In spite of its biologicalimportance, solitary nesting has never been evaluatedadequately in many important nesting rookeries (Castro,1986). Although some information is available on solitary nesting of L. olivacea at Gahirmatha and Devi rookery (Pandav, 2000), there is little or no information on
solitary nesting activities at the Rushikulya rookery.
Similarly, the mass nesting events at the Rushikulya
rookery have not yet been monitored properly; current
data are from anecdotal accounts (Pandav et al., 1994)
and the imprecise census by the Orissa State Forest
Department due to improper statistical techniques(Pandav,
2000;
Shanker
et
al.,
2003;

© 2008 by Asiatic Herpetological Research

http://www.wildlifeorissa.org). The Orissa State Forest
Department have reported mass nesting at this rookery
every year since 2001, but accurate estimates of thenumber of nesting turtles in arribadas are not available
in the absence of a standard technique for mass nesting
census (Patnaik et al., 2001; Shanker et al., 2003). The
IUCN/SSC Marine Turtle Specialist Group (MTSG) has
recommended for use of strip transect method for estimating the arribada on mass nesting beaches, on thebasis of successful experiment by Valverde and Gates(1999).
The Olive Ridley Sea Turtle is an endangered
species according to the protection status of IUCN andas per CITES prohibited for trade of any kind and also is
included in the schedule I of Indian Wildlife (Protection)
Act (1972) and is legally protected. However, over the
past decade, more than 100,000 dead turtles have beenreported along the Orissa coast due incidental and accidental fishing related casualties in the sea. Whether thismortality has an impact on the population size of L. olivacea is yet to be known (Pandav and Choudhury,2000). In this paper, in light of its importance, the sporadic nesting and mass nesting census of L. olivacea at
the Rushikulya rookery was evaluated for two seasonfrom November to April (2003–04 and 2004–05) using
standard techniques recommended by the MTSG toascertain the actual arribada nesting population of turtles
at this rookery and compare this figure with estimatesfrom the Orissa State Forest Department.

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Figure 1. Map of Orissa coast in India with three arribada sites.

Figure 2. Map of Rushikulya sea turtle rookery, Orissa.

137

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Table 1. Sporadic and intermediate nesting of L. olivacea
at the Rushikulya rookery of the Orissa coast.
2003–04

Month

November

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Asiatic Herpetological Research, Vol. 11

Parameters

2004–05

No. of No. of inter- No. of
No. ofsporadic mediate sporadic intermedinestingnesting
nesting ate nesting(No. of(No. of(No. of(No. ofnights)nights)nights)nights)
5 (5)

0

0

Table 2. Sea turtle (L. olivacea) mass nesting census at
the Rushikulya rookery.
Year
2004
No. of days sampled
Total area of nesting (m2)

2005

4
2
150,000 200,000

Duration of arribada (in minutes)

780

780

0

Total number of egg laying turtles

1,144

3,908

20

20

December

6 (5)

0

2 (2)

0

Width of transect (m)January17 (8)0

12 (3)

013

13

February30 (22)031 (6)

119 (6)

Number of sampling period(one hour sampling)March

166 (21)258 (9)170 (29)0

Total length of transect (m2)(100 x 100 x No. of transect)

1,500

2,000

April

86 (14)0

23 (10)0

Average duration of oviposition(in minutes)

14.5

13.5

Estimated number of turtles
nested during arribada

23,461

86,688Estimated variance of the total
number of egg laying females

1,138.571 4,599.4

Being a migratory species L. olivacea are known toarrive in the Orissa coast during late October and remainin the coastal waters until May and thereafter migrateback to the southern Bay of Bengal and Indian Oceanarea. There are no turtle activities after April/May until
October in Orissa. Therefore, the field work was concentrated at Rushikulya between November and May.
The mass nesting beach at the Rushikulya rookery is
located on the sand spit along the northern end of the
Rushikulya River mouth. Rushikulya is situated 320 km
south of Gahirmatha mass nesting beach (Lat. 19° 22′ N
and Lon. 85° 02′ E). Turtle nesting at Rushikulya takes
place along a stretch of ~5 km immediately north of the
Rushikulya River mouth from the village Purunabandha(1 km north of the Rushikulya River mouth) to
Kantiagada village (Fig. 2).
For systematic coverage, the entire stretch of nesting beach was divided into 100 m segments and wasmarked with wooden poles. To monitor nesting activities, patrolling was done by foot every night between
1700 and 0700 hr from November to April of 2004 and2005 (1st November to 30th April for both years). Sea turtles are known to nest along the Rushikulya rookery
towards the end of December (Basudev Tripathy, personal observation) and therefore the chance of missingout of some crawls during the nesting season was minimal. Turtle crawls onto the beach were classified into
nesting and non-nesting types based on crawl mark pattern and sign of nest (Schroeder and Murphy, 1999).
There is no standard classification of solitary nesting or
arribada nesting based on the number of nests per night.
However, keeping the beach length of the study area (~5km) in mind, the author classified night with less than 20
nesters (~4 nests/km) as solitary nesting, nesting densities of 20 to 99 turtles (<20 nests/km) were consideredintermediate nesting, while those with >100 (>100/km)
or above turtles as arribada nesting. A modified strip

transect method was used to estimate the mass nesting at
the Rushikulya rookery (Valverde and Gates, 1999).
This method was effective in arriving at an estimate of
the number of nesting females, with a mean, varianceand confidence intervals that provide rigorous statisticalsupport for the results. A 20 m strip transect was laid atevery 100 m segment of the nesting beach. Only egglaying females (turtles in oviposition) within the strip
were counted on hourly intervals starting with the firstindividual ascending the beach in the evening until
morning when there were no nesting activities.
The formula below was used for computation of
the mass nesting data (see Valvarde and Gates, 1999):

Estimate of nesting =AxHxN
WxtxLxh

Where:
A
H
N
W
t
L
h

=
=
=
=
=
=
=

Total available nesting area (in m2)
Duration of arribada (in minutes)
Total of number of egg laying turtles
Width of the transect (in m)
Number of sampling period (in days)
Total of length of all transects (in m)
Average time spent by turtles for egg
laying (in minutes)

Size of female L. olivacea was determined by themeasurement of curved carapace length (CCL) at thetime of egg lying. Each turtle was measured down the
midline from the nuchal notch to the posterior carapace

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No. of sporadic nesting individuals

450
400
350
300

2003-04
2004-05

250
200
150
100
50
0
December January February

March

April

MonthsFigure 3. Monthly turtle nesting at Rushikulya for L. olivacea (2003–04 and 2004–05).

tip using a flexible measuring tape. Values were rounded
to the nearest 0.5 cm.
Of the 568 nests observed during the 2003–04 nesting season between December 2003 and April 2004,
45.2% of the nesters were intermediate nesters, with rest
being sporadic nesters (Table 1). Similarly, during the
2004–05 nesting season, intermediate nesting was calculated to be 33.3% (Table 1). There was a distinct patternof solitary nesting observed at Rushikulya rookery, witha peak in activity during March for both the season (Fig.
3).
A total of 15 and 20 transects with 20 m width and100 m length were established for counting turtles inarribadas during 2004 and 2005 respectively (Table 2).
During 2005, the topography of the beach changed drastically and mass nesting was extended from the estuarine
mouth and 2 km northward, and therefore, five moretransects were laid. Although arribada took place twice
during 2004 (February 9–10 and March 10–13), theFebruary arribada could not monitored due to logistic
constraint and hence the census was done only for the
March 2004 arribada. During four days of peak nestingin March, a total of 23,461 turtles were estimated tohave nested in arribada. However, the 2005 arribada waslarger and was estimated to be 86,688 nesting individuals in two nights when censuses were carried out (Table
3).
Nesting females in arribadas at the Rushikulya
rookery had an average CCL of 67.163.65 cm (n = 515;
min: 60.8, max: 73.61), a value slightly greater than thatof the solitary nesters at 66.024.34 cm (n = 335; MannWhitney = 505, p = 0.0004). No significant differencesin CCL existed for arribada of February and March 2004
(Kruskal-Wallis χ2 = 6.9, p = 0.2412) and also between
2004 and 2005 season (Kruskal-Wallis, χ2= 5.80, p =0.1225).
Solitary nesting emergence of L. olivacea is known139

to occur almost every month along rest the Orissa coast(Dash and Kar, 1990). However, solitary nesting isfound in greater numbers during January to May, indicating that this is the main nesting season for this species(Pandav and Choudhury, 2000). Although year roundsporadic nesting is not known from the Rushikulya
rookery, this study confirms sporadic nesting of olive
ridley turtles at the rookery between December andApril, with a peak in March and is identical to other sea
turtle rookeries along the Orissa coast. Temperature,
weather condition, physiography of nesting beaches andthe adjacent sea, conditions of tide, temperature and surface current circulation all play an important role indetermining female nest selection (Pandav andChoudhury, 2000). However, this study could not incorporate the above variables at the Rushikulya rookery due
to logistic constraints. Unlike Gahirmatha and Devi
(Basudev Tripathy, personal observation) where sporadic nesting is almost continuous for the entire season(>10 turtles/night), at Rushikulya rookery, sporadic nesting is irregular, with nesting intensity increasing before
the commencement of the arribada. During the othernights, there is either no nesting or low sporadic nesting(<5 turtles/night). However, it is likely that the females
emerging on nights with intermediate levels of nesting
are responding to arribada cues (cue such as southerly
strong wind, cloudy weather and strong wave action in
the sea) and are truly arribada nesters. What actuallycomprises solitary or arribada nesting must also be evaluated in light of the total population for a given beach(Dash and Kar, 1990). During the present study, there
was no major intermediate nesting events observed at
the Rushikulya rookery except for nine nights in 2004
February and six nights during 2005 March, when nesting per night was over 100. However, it is likely thatthese turtles were early arribada nesters, since the arribada commenced in the rookery few days later.
At the Rushikulya rookery, although arribadas werereported for many years, precise mass-nesting censuseshave not been carried out. The Orissa Forest Department
report estimates the number of turtles during the arribada every year, but the methods used are unpublished andunavailable (estimated by Orissa State Forest
Department; Table 4). Furthermore, it is not clear thatmethods are standardized, unbiased and therefore comparable. The State Forest Department staff counts all
female turtles that remain on the beach during arribada.
However, during arribada emergence, many turtles do
not deposit their eggs (~30–40%) and hence are not partof true nesting population. While estimating nestingarribada population, this factor greatly affects the population size estimation and leads to bias. In the past 25
years, a variety of approaches and methods have beenused to estimate female populations at arribada beaches

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Table 3. Estimates of arribada (nesting number) for the2004 and 2005 nesting season.

Date

2004
10th March
2004
11th March
2004
12th March
2004
13th March
2004
Total
(4 nights)
2005
14th March2005
15th March
2005
Total
(2 nights)

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Number ofUppernesting
Lower
confiturtle
confidence dence(x)intervalinterval(95%)

Standard
error

4,262

3,534.1

4,990.03

364.36

12,434

11,270.86 13,598.1

507.45

4,362

4,227.1

4,297.1

273.252,503

2,204.03 2,802.86

149.8

23,561

21,236.09 25,688.09

44,46642,017.33 46,915.99 7,379.48

42,22240,444.45 44,001.99 6,129.67

86,68882,461.78 90,917.98

of Orissa (reviewed by Shanker et al., 2003). The present study estimated very low nesting populations during
arribadas (using the standard technique as suggested by
the IUCN/MTSG (Valvarde and Gates, 1999) comparedto the figures projected by the Orissa state forest department (Tables 3 and 4). While projection of a large nesting figure attracts attention, particularly to the national
and international media and conservation communities

at large, it may results in the downgrading of this species
in the Indian Wildlife (Protection) Act and IUCN’s Red
List.
In recent years (at least between 1996 and 2000), a
small but significant decrease in curved carapace length(CCL) of female Olive Ridley Sea Turtles has been documented (Pandav et al., 1994; Kalb, 1999). Similarly,
the average CCL of females at Gahirmatha from 1978 to1985 were larger than those measured during
1996–2000 (Dash and Kar, 1990; Pandav andChoudhury, 2000). The present study found that arribada
nesters are significantly larger than the solitary nesters,with a mean CCL being 1.14 cm greater, but was within
the range. The decrease in size class (as compare to
1996–2000) was not detected during the current study,
but this could be due to a small sample size, the lack ofsufficient data, and a less accurate measuring technique(measuring tape for CCL Vs metallic calipers for SCL).
In conclusion, it is apparent that the solitary andarribada nesters are not different, but from the same population stock. The genetic study on Olive Ridley Sea
Turtles from Orissa also supports this view (Shanker etal., 2004). Also, sporadic nests contribute equally to the
population recruitment as that of arribada nesters being
hatching success is higher for the later (Castro, 1986,
also see Tripathy et al., 2003). Olive Ridleys along theOrissa coast are known to exhibit fidelity to their breeding as well as nesting ground (Dash and Kar 1990,
Pandav et al., 2000). Nesting females are known to
exhibit movement between rookeries in Orissa bothwithin and between seasons (Tripathy and Pandav, inpress; Pandav and Choudhury 2000). Migration andinter-rookery movement by females during the breeding
and nesting season along Orissa coast has also been documented (Pandav and Choudhury, 2006). Hence, knowl-

Table 4. Estimates of arribada at the Rushikulya rookery by the Orissa Forest Department and other researchers(1994-2005).
Year

Nesting estimate

Date of arribada

Reference

1994–1995

2,000,000

14–16 March 1995

Pandav et al., (1994)

1995–1996?

06–08 March 1996

- do -??

1996–1997?

31 January–3 February 1997

1997–1998?

20–23 March 1998

B. Pandav (Personal
Observation)—

1998–1999—

No arribada—

1999–2000—

No arribada—

2000–2001

1,59,000

26 February–4 March 2001—

2001–2002—

No arribada—

2002–2003

2,08,000

09–14 March 2003

2003–2004

2,01,000

10–15 March 2004

Orissa State Forest
Department—

2004–2005?

15–18 February 2005

—

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Asiatic Herpetological Research, Vol. 11edge of the location and temporal use of nesting groundsof Olive Ridley Sea Turtles in Orissa is important inview of the habitat loss and large-scale mortality of turtles in the offshore waters. Therefore, along with protection of arribada nesters, it is necessary to monitor thebeach and safeguard the sporadic nesters and their habitat as well.
Prior to this study, there were no proper estimates of
the number of turtles that nest during arribada at the
Rushikulya rookery. Our estimates show that the number of turtles could be much less than what is projectedby various governmental agencies. Thus, declaration ofa mass nesting population in broad terms (e.g. hundredsof thousands) without a proper assessment may result in
the reduction of protection required for L. olivacea in
their breeding ground, which is already meager. Hence,standard and accurate techniques for mass nesting census are urgently required for additional years for monitoring the status and nesting trends of L. olivacea at thein Rushikulya rookery of Orissa. As evidence from thelast decade of sea turtle mortality data from Orissa(Pandav and Choudhury, 2000), reduction of the sizeclass of individuals participating in arribadas (Shanker
et al., 2004; Tripathy, 2005), and elimination of the older
females from the breeding stock over a period of time.
However, to confirm this, extensive and accurate measurements of the nesting females and clutch sizes need tobe performed to determine if there is a difference/reduction in size of L. olivacea over the years at rookeries inOrissa, and thereby a declining of the Olive Ridley Sea
Turtle population of the Indian Ocean area and or the
rest of the world.

Acknowledgments
This study was part of the author’s doctoral work and heis thankful to Dr. P. S. Raja Sekhar and the Head of the
Department of Environmental Sciences, Andhra
University, Visakhapatnam for approving the work andsupport as well as the Orissa Forest Department for permission to conduct field work. The author is thankful tofield assistants and volunteers of Purunabandha village,
Ganjam for their help in data collection during arribadas.

141

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Submitted: 19 October 2006
Accepted: 23 September 20072008