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Revista de Biología Tropical, ISSN: 2215-2075 Vol. 69(3): 1124-1137, July-September 2021 (Published Set. 30, 2021)

Nesting trends of olive ridley sea turtles Lepidochelys olivacea

(Testudinata: Cheloniidae) on two beaches in Northwestern Mexico

after 30 and 40 years of conservation

Ingmar Sosa-Cornejo

1,2

; https://orcid.org/0000-0003-0465-9956

Rodolfo Martín-del-Campo

; https://orcid.org/0000-0002-7280-3932

Héctor R. Contreras-Aguilar

; https://orcid.org/0000-0003-3879-3643

Fernando Enciso-Saracho

; https://orcid.org/0000-0002-2847-9055

Zuleika Beatriz González-Camacho

; https://orcid.org/0000-0003-3110-2918

Jesus I. Guardado-González

; https://orcid.org/0000-0002-0257-6826

Samuel Campista-Leon

; https://orcid.org/0000-0001-7552-2303

Luz I. Peinado-Guevara

; https://orcid.org/0000-0001-5881-4558

1. Posgrado en Ciencias Biológicas, Facultad de Biología, Universidad Autónoma de Sinaloa, Culiacán, Sinaloa,

México; parlama_michin@uas.edu.mx

2. Laboratorio de Tortugas Marinas, Facultad de Biología, Universidad Autónoma de Sinaloa, Culiacán, Sinaloa,

México; zulegoncam@gmail.com

3. Department of Oral Health Sciences, Faculty of Dentistry, Life Sciences Institute, University of British Columbia,

Vancouver, BC V6T 1Z3, Canada; rodolfo@dentistry.ubc.ca

4. Programa de Tortugas Marinas de la Unidad Académica Preparatoria “Comandante Víctor Manuel Tirado López”,

Universidad Autónoma de Sinaloa, Rosario, Sinaloa, México; contrerasaguilarhector@gmail.com (*Correspondence)

5. Programa de Tortugas Marinas de la Facultad de Ciencias del Mar, Universidad Autónoma de Sinaloa, Mazatlán,

Sinaloa, México; mano24@live.com

6. Departamento de Turismo, H. Ayuntamiento de Elota, Sinaloa, México; ivantortugasceuta1@gmail.com

7. Laboratorio de Microbiología y Biología aplicada, Facultad de Biología, Universidad Autónoma de Sinaloa, Culiacán,

México; samcl@uas.edu.mx, luzipg@uas.edu.mx

Received 31-III-2021. Corrected 07-VI-2021. Accepted 19-IX-2021.

ABSTRACT

Introduction: Although olive ridley sea turtle (Lepidochelys olivacea) are the most abundant sea turtles in the

world, quantitative information is scarce and unevenly distributed among regions. There are many management

and conservation programs for this species, and assessments are necessary to identify nesting trends and effec-

tively manage current conservation programs. PROTORMAR-UAS is a Research and Conservation program

for the olive ridley turtle created by the Autonomous University of Sinaloa, Mexico. The program utilizes two

biological stations: Santuario Playa Ceuta (SPC) and Playa Caimanero (PC).

Objective: To evaluate the nesting trend of olive ridley turtles on two beaches in Northwestern Mexico and to

predict prospective nesting trends for the next 30 years.

Methods: Using annual nesting data collected over 40 years at SPC (1976-2016) and 30 years at PC (1986-

2016), we evaluated nesting trends, hatching success, predation and poaching of olive ridley turtles on the two

beaches in Northwestern Mexico. Then, prospective nesting estimates for the next 30 years were calculated

predictive time series model.

Sosa-Cornejo, I., Martín-del-Campo, R., Contreras-Aguilar,

H. R., Enciso-Saracho, F., González-Camacho, Z. B.,

Guardado-González, J. I., Campista-Leon, S., & Peinado-

Guevara, L. I. (2021). Nesting trends of olive ridley sea

turtles Lepidochelys olivacea (Testudinata: Cheloniidae) on

two beaches in Northwestern Mexico after 30 and 40 years

of conservation. Revista de Biología Tropical, 69(3), 1124-

1137. https://doi.org/10.15517/rbt.v69i3.46490

https://doi.org/10.15517/rbt.v69i3.46490

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Nesting and feeding habitats of six of the

seven species of sea turtles in the world are

distributed in Mexico, and sea turtle migra-

tory corridors include coastlines with national

jurisdiction (Márquez, 1990). Sea turtles and

humans have interacted for thousands of years,

and sea turtles have been a source of food since

the beginning of the first civilizations, includ-

ing in ancient Mesopotamia (Frazier, 2003). In

Mexico, sea turtle harvesting started in the late

1950s and early 1960s, and it is estimated that

between 1965 and 1970, more than 2 million

sea turtles (mostly olive ridleys) were captured

(Márquez, 1996; Peñaflores et al., 2000). This

practice, together with other human activities

such as egg extraction, destruction of habitats

in nesting areas, and bycatch, has had an impact

on the decline in sea turtle populations (Behera

et al., 2016; Pandav et al., 1998; Pritchard,

1996; Spotila, 2004); therefore, in 1966, the

first turtle camps for study and conservation

were established, and in 1990, a total and per-

manent ban of the capture of all species of sea

turtles in Mexico was declared (DOF, 1990).

The olive ridley sea turtle (Lepidochelys

olivacea) is considered the most abundant sea

turtle in the world, and its main nesting sites

occur on the East coast of India and the coasts

in the Eastern Pacific, mainly in Costa Rica

and Mexico (Abreu-Grobois & Plotkin, 2008).

This species nests between July and January,

with two nesting strategies: solitary and “arrib-

ada”; the latter is a unique nesting strategy of

the genus Lepidochelys in which thousands

of females arrive to nest synchronously on

specific beaches for several days (Márquez,

1990; Pritchard, 2007). In Mexico, solitary

nesting areas extend from the coast of Baja Cal-

ifornia Sur to the coast of Chiapas (CONANP,

2011). Currently, Mexican legislation consid-

ers this species “endangered” (DOF, 2010); it

remains “vulnerable” according to the red list

of threatened species of the International Union

for the Conservation of Nature (IUCN) (Abreu-

Grobois & Plotkin, 2008) and is included in

Appendix I of the Convention on International

Trade in Endangered Species (CITES, 2014).

Because olive ridley sea turtles do not

reach sexual maturity until approximately 13

years (8-18 years) of age (Márquez, 1996; Zug

et al., 2006), assessments of nesting trends

over time are necessary to implement actions

and effectively manage current conservation

programs (Richardson, 2000). At Playa Esco-

billa, the most important arribada beach in

Mexico, sustained recovery has been report-

ed, with an increase from 200 000 nests in

1990 to more than one million nests in 2010

(CONANP, 2011); however, evaluations on

solitary beaches are rare (Ariano-Sánchez et al,

2020; da Silva et al., 2007; Hart et al., 2018;

James & Melero 2015; Viejobueno Muñoz &

Arauz, 2015). Evaluations at nesting beaches

are necessary to identify current nest trends,

predict future outlooks and make appropriate

management and conservation decisions for

the benefit of the population of sea turtle under

study (Balazs & Chaloupka, 2006; Ceriani et

al., 2019; Honarvar et al., 2016).

Results: A positive and significant correlation was identified between the number of annual nests and time for

both beaches (rho = 0.850, P ≤ 0.01 for SPC; rho = 0.677, P ≤ 0.01 for PC); the average hatching success rates

were 65.09 at SPC and 60.72 % at PC. The predictive time-series model indicated that the numbers of nests will

continue to increase through 2045, increasing three-fold at SPC and six-fold at PC with respect to the last year

of monitoring.

Conclusions: There was a clear positive trend in the number of olive ridley sea turtle nests at both sites, which is

consistent with trends found in other recent studies from the region. Therefore, we suggest that PC be designated

a legally protected nesting area since it is located within the latitudinal limits of olive ridley nesting and given

the need for resources for camp operation considering increased nesting and current problems with predation

and poaching. Because in Mexico operating a nesting beach without any protection status implies not having a

budget for its management.

Key words: nests; sea turtle conservation; olive ridley turtle; hatching success; poaching and predation.

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The Autonomous University of Sinaloa

(UAS) began efforts to conserve and conduct

research on sea turtles, and in 1976, it imple-

mented the Sea Turtle Program (PROTOR-

MAR-UAS), with the commitment to protect,

conserve and research these species as well as

their habitats. The program utilizes two biolog-

ical stations, Santuario Playa Ceuta (SPC) and

Playa Caimanero (PC), and continuous annual

data on nest abundance and hatching success

(HS) as well as problems such as poaching and

nest predation have been collected. The objec-

tive of this study was to evaluate the nesting

trends of olive ridley turtles at two beaches in

Northwestern Mexico (40 years for SPC and

30 for PC) and to predict prospective nesting

success over the next 30 years.

MATERIALS AND METHODS

Study site: The study was conducted

on two nesting beaches: SPC and PC. SPC

is 37 km long and is located between the

Cospita Estuary to the North (23°05’40” N

& 107°11’42” W) and the Elota River to the

South (23°52’43” N & 106°55’51” W); it is

in the central region of the state of Sinaloa,

Mexico, in the municipality of Elota (Fig. 1).

SPC was declared a Reserve and Refuge Zone

for the Protection, Conservation, Repopulation,

Development and Control of Various Species

of Sea Turtles (DOF, 1986) and as a sanctuary

for olive ridley turtle nesting (CONANP, 2018;

DOF, 2002). PC was designated a biological

station in 1986; it is approximately 39 km

long and is located between the mouth of the

Presidio River to the North (23°05’29” N &

106°17’19” W) and the mouth of the Baluarte

River to the South (22°50’15” N & 106°02’26”

W); it is in the Southern region of the state of

Sinaloa, Mexico, in the municipality of Rosario

(Fig. 1). PC is not yet legally designated as a

protected beach.

Nesting data: During the nesting season

(July-December) from 1976 to 1991 at SPC and

from 1986 to 1991 at PC, night tours were car-

ried out by university staff and field volunteers

to collect eggs and conduct a census of nests

(collected, poached and predated); however,

Fig. 1. Location of the nesting beaches of Lepidochelys olivacea in Northwestern Mexico managed by PROTORMAR-UAS.

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during this period, it was not possible to cover

the entire beach on a daily basis due to logisti-

cal and budget reasons. In 1992, more person-

nel and transport equipment were obtained, and

the tours were carried out systematically. The

tours 1) followed daily routes and 2) covered

the entire study area, ensuring the counting

of all nests in each season (Schoreder & Mur-

phy, 2000). The collected eggs were incubated

in hatchery or polyurethane boxes that were

numbered consecutively to facilitate analysis

(Mortimer, 1999). At the end of the incubation

period, nest exploration was performed (45 ±

3 days) to estimate hatching success (HS) by

dividing the number of eggs hatched (NEH) by

the total number of eggs (TNE) incubated for

each nest, with the formula HS = (NEH/TNE)

× 100 (Caut et al., 2006). Later, the hatchlings

were released into the sea during the night or at

dawn during low tide when the waves were not

very strong so the hatchlings could enter the

sea easily and quickly, preventing predation.

This research was carried out under agreements

with and permits granted by the Subsecre-

taria de Gestión para la Protección Ambiental,

Dirección General de Vida Silvestre (SGPA/

DGVS/06306), which are renewed annually.

Data analysis: The total number of nests

for each season, including collected, predated

and poached nests, the HS for each beach

each year were collected. The averages (with

their standard deviations) of each of these

parameters for the entire period were calcu-

lated, and a Mann-Whitney U test (P < 0.05)

was performed to identify differences between

the beaches with respect to the monitoring

data. Spearman correlation analysis was used

to assess correlations between the total nests

registered (which included collected, predated

and poached nests) and the study period. All

statistical analyses were performed with Sig-

maPlot v11 software. Nest abundance in 2045

was predicted by a predictive time series model

using IBM SPSS Statistics 23 software (Brown

et al., 1975; Gil & Lobo, 2012). The prospec-

tive analysis was performed for the next 30

years (more than two generations) considering

the average age at sexual maturity (13 years) of

the olive ridley turtle (Márquez, 1996; Zug et

al., 2006), with the assumption that mortality

will remain constant due to the standardization

of the years that PROTORMAR-UAS has per-

formed work on the beaches.

RESULTS

Registered and collected nests and pre-

dation and poaching: At SPC from 1976 to

2016, a total of 11 238 nests were registered,

of which 9 755 were collected, 848 were pre-

dated, and 635 were poached (Table 1); at this

beach, before 1992, the collection of nests was

variable (mean= 99.4 ± 75.4 nests per year).

This was because the same effort was not made

for technical reasons, but in 1992, the effort

was standardized, and since then, the number

of nests was approximately 340.2 ± 164 nests/

year, although there were nesting seasons with

less than 200 nests/year (1995= 187, 1998=

186, 2001= 169, 2002= 157 and 2003= 188). In

2004, it was not possible to work due to budget

constraints. At PC, only data from 1989 to 2016

were considered event though protection began

in 1986; before 1989, there were technical and

operational difficulties preventing consistent

monitoring, and some data were lost. During

the study period a total of 29 001 nests were

registered, of which 24 379 were collected,

1 878 were predated and 2 744 were poached.

The average number of registered nests before

2005 was 176.9 ± 110.1 nests/year, and after

2005, the abundance of nests increased to

2 180.9 ± 1 144.6 nests/year. The 2015 season

had the highest nesting record (4 859 nests)

(Table 1). When comparing the parameters

between nesting beaches, no significant differ-

ences were identified (P > 0.05).

Nesting, predation, and poaching

trends: For both nesting beaches, a posi-

tive and significant correlation was observed

between the number of registered nests and

time (rho = 0.850, P ≤ 0.01 for SPC, rho =

0.677, P ≤ 0.01 for PC, Table 2) and between

predated nests and time (rho = 0.454, P = 0.003

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TABLE 1

Annual data on nests and eggs collected as well as predation and poaching of olive ridley turtle (Lepidochelys olivacea)

nests in Santuario Playa Ceuta (1976-2016) and Playa Caimanero (1989-2016)

Santuario Playa Ceuta Playa Caimanero

Years

Registered

nest

Collected

nests

Protected

eggs

Predated

nests

Poached

nests

Registered

nest

Collected

nests

Protected

eggs

Predated

nests

Poached

nests

1976 84 40 4 013 14 30 - -

1977 129 112 11 414 12 5 - -

1978 104 75 7 646 8 21 - -

1979 65 48 4 993 5 12 - -

1980 39 35 3 696 4 0 - -

1981 52 47 4 774 5 0 - -

1982 46 35 3 476 4 7 - -

1983 72 47 4 993 4 21 - -

1984 82 65 4 858 0 17 - -

1985 67 51 6 448 5 11 - -

1986 125 104 10 631 14 7 - -

1987 208 179 15 720 23 6 - -

1988 222 197 18 336 25 0 - -

1989 61 61 6 076 0 0 124 117 11 710 1 6

1990 286 241 25 441 31 14 294 277 27 456 3 14

1991 300 253 24 441 32 15 205 193 18 351 2 10

1992 305 243 23 913 38 24 325 307 28 716 3 15

1993 294 240 30 047 21 33 187 176 15 853 2 9

1994 371 301 22 040 28 42 203 191 18 669 2 10

1995 251 187 14 930 9 55 165 155 14 046 2 8

1996 294 225 20 923 20 49 394 371 35 348 4 19

1997 348 343 30 785 2 3 318 300 29 111 3 15

1998 194 186 13 190 2 6 145 137 13 052 1 7

1999 237 219 24 069 7 11 129 122 11 168 1 6

2000 251 224 22 159 3 24 57 53 5 026 1 3

2001 196 169 18 474 8 19 30 28 2 873 1 1

2002 169 157 12 290 4 8 152 144 13 470 1 7

2003 208 188 19 166 18 2 12 10 903 1 1

2004 - - - - - 90 85 8 081 1 4

2005 246 239 26 872 3 4 781 737 67 262 7 37

2006 361 319 27 649 11 31 1 288 1 215 104 558 12 61

2007 398 388 35 176 3 7 1 815 1 712 151 899 17 86

2008 536 467 40 470 43 26 1 813 1 710 153 394 17 86

2009 462 392 23 673 39 31 1 415 1 335 101 560 13 67

2010 531 472 35 413 45 14 1 416 1 336 124 291 13 67

2011 403 353 24 994 44 6 2 108 1 449 127 723 232 427

2012 565 495 36 830 56 14 3 070 2 110 198 991 338 622

2013 473 398 37 854 70 5 3 332 2 290 218 051 366 676

2014 680 640 55 667 16 24 2 814 2 345 215 069 384 85

2015 932 821 61 695 93 18 4 859 4 305 399 453 323 231

2016 591 499 29 618 79 13 1 460 1 169 106 167 127 164

Total 11 238 9 755 844 853 848 635 29 001 24 379 2 222 251 1 878 2 744

Mean ±

Std Dev

281.0 ±

200.0

243.9 ±

179.8

21 121.3 ±

13 911.2

21.20 ±

22.7

15.9 ±

13.4

1 035.8 ±

1 249.2

870.7 ±

1 018.6

79 366.1 ±

93 792.3

67.1 ±

128.4

98.0 ±

180.0

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for SPC, rho = 0.789, P ≤ 0.01 for PC, Table 2).

The average number of poached nests at SPC

was 15.9 ± 13.4 nests/year (Table 1). A positive

and significant correlation between the number

of poached nests (98.0 ± 180.0 nests/year) and

time was observed (rho = 0.673, P = 0.01; Table

2) for only PC.

Hatching success: HS showed great vari-

ability over the years at both beaches. How-

ever, since 2009, these oscillations stabilized

for both beaches (Fig. 2). HS percentages of

65.09 ± 14.72 % for SPC and 60.72 ± 16.39 %

for PC were estimated, and these values were

not statistically significant between beaches

(Mann-Whitney U = 486, P = 0.360).

Prospective nesting in 2045: Accord-

ing to the annual data analyzed, a predictive

time-series model with Brown exponential

smoothing was constructed; in both cases, the

residual values were independent (DF= 17,

Ljung-Box Q (18) = 9.492, P= 0.924 for SPC;

DF= 17, Ljung-Box Q (18) = 6.498, P= 0.989

for PC). The observed values have annual

variations but suggest a positive trend, as

shown by the adjusted values for both beaches

(Fig. 3A, Fig. 3B). From a stationary R

0.649, the prediction for 2045 is 1 733 [-215,

3 681] nests at SPC (Fig. 3A) and 7 718 [-2

435, 17 871] nests at PC, with a stationary R

of 0.632 (Fig. 3B).

DISCUSSION

Due to the management and conservation

efforts of PROTORMAR-UAS for the olive

TABLE 2

Correlation of registered, predated and poached nests and the course of time (years) for Santuario Playa Ceuta (SPC)

during 1976-2016 and for Playa Caimanero (PC) during 1989–2016

Santuario Playa Ceuta Playa Caimanero

Registered

nest

Predated

nests

Poached

nests

Registered

nest

Predated

nests

Poached

nests

Years rho Spearman 0.850 0.454 0.145 0.677 0.789 0.673

P value ≤ 0.01 0.003 0.372 ≤ 0.01 ≤ 0.01 ≤ 0.01

rho = Spearman’s correlation coefficient, P < 0.05.

Fig. 2. Annual hatching success of the olive ridley turtle at Santuario Playa Ceuta and Playa Caimanero, Sinaloa, Mexico.

SPC: Santuario Playa Ceuta; PC: Playa Caimanero.

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ridley sea turtle in Northwestern Mexico, an

increase in the abundance of nests and eggs col-

lected at both biological stations was observed

from the start of operation until the last data

point. According to the correlation analysis,

there was an increase in the number of nests

throughout the study period at both beaches.

These increases may be due to different causes

or even a combination of several factors, which

together could influence the observed positive

trend of the increase in nests (rho= 0.850 and

rho= 0.677). These values coincide with that

reported in Playa La Flor in Nicaragua, where

a positive trend was observed over 8 years of

monitoring (Honarvar et al., 2016). Increases

in the numbers of nests were recorded at both

nesting beaches, which have similar lengths (≈

37 km), and the projection for 2045 was posi-

tive according to the time-series model with

Brown exponential smoothing. At both nesting

beaches, monitoring and tours were standard-

ized in 1992; in both cases, initial tours were

by foot and later by quad bike, depending

on the budget, available staff, and number of

volunteers, as well as weather conditions. The

current results are in accordance with those

reported by Anzanza-Ricardo et al. (2015), who

noted that in sea turtle conservation programs,

Fig. 3. Time-series predictive model for Lepidochelys olivacea nesting in A. Santuario Playa Ceuta and B. Playa Caimanero,

Sinaloa, Mexico, for the year 2045. LCS: superior confidence limit; LCI: inferior confidence limit.

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resource management is crucial to achieve

an adequate cost-benefit balance, and Hart et

al. (2018), who stated that an increase in and

consolidation of conservation and monitor-

ing activities will result in an increase in the

number of nests. However, monitoring and

conservation program evaluation continue to be

a challenge due to complications that can occur

during data collection and difficulty in obtain-

ing financial incentives to promote community

participation that promote positive attitudes

towards conservation and consistency in the

collection of information (Godley et al., 2020).

It is important to emphasize that although

there have been increases in the numbers of

nests on both beaches after effort standardiza-

tion, there has been a larger increase at PC,

with more than 1 000 nests, which is approxi-

mately 3-fold the number of nests than at SPC

after 2005. The conditions of both beaches are

quite different; SPC is a very spatiotemporally

dynamic beach in its granulometry and slope

(Sosa-Cornejo et al., 2019), while the condi-

tions at PC are more static. In addition, SPC

is in the Nearctic zone, and PC is in the Neo-

tropical zone. The El Verde Camacho nesting

beach, also in Sinaloa, has been considered the

Northern limit of nesting of the olive ridley

turtle in the Mexican Pacific (Ríos-Olmeda,

2005). However, SPC is located at a more

Northern latitude, and PC, which is South of El

Verde Camacho, has registered a larger number

of nests in the last 15 years than the El Verde

Camacho nesting site (Contreras-Aguilar, pers.

comm.). Genetic analysis of organisms inhabit-

ing SPC indicated that this rockery has moder-

ate genetic diversity that is very similar (h=

0.6) to that reported by Briseño-Dueñas (1998)

for El Verde Camacho (Campista-León et al.,

2019); therefore, the importance of monitor-

ing and conserving SPC and the need for more

studies at PC are highlighted due to the increas-

ing numbers of nests. In addition, climatic

variations, such as the El Niño Southern Oscil-

lation (ENSO), can influence the reproductive

success of sea turtles (Santidrián Tomillo et al.,

2020); these climatic variations could have no

effect or a moderate effect on olive ridley turtle

nesting (Ariano-Sánchez et al., 2020; Santid-

rián Tomillo et al., 2020). This was observed

during the extreme El Niño 2015-2016 event,

which resulted in decreases in the numbers of

nests on both beaches.

Additional factors that may have also

influenced the increases in the number of nests

are the age at sexual maturity (approximately

13 years [8-18 years]) of age (Márquez, 1996;

Zug et al., 2006), the total and permanent ban

of the capture of all species of sea turtles in

waters under Mexican jurisdiction (DOF, 1990)

and the use of sea turtle excluders since 1996

(DOF, 1996). Increases in nesting activity have

been reported for other species of sea turtles,

such as green and loggerhead turtles (Moncada

et al., 2014). Whether the main cause of the

increase in the number of nests is increased

monitoring effort, the total and permanent cap-

ture ban in 1990, spatial changes in the nesting

behavior of the olive ridley sea turtle as a result

of adaptation to environmental factors, or a

combination of these and other factors remains

unknown; therefore, it is necessary to carry out

additional studies and continue monitoring the

abundance of nests in this region. Nesting of

olive ridley sea turtles, although sporadic, has

been reported in the upper Gulf of California

in San Carlos, El Desemboque, and Puerto

Peñasco, Sonora (Seminoff & Nichols, 2007).

A record number of olive ridley sea turtle

hatchlings (2 241) was recently reported in

Desemboque, Sonora, which is located at a

very Northern latitude for olive ridley nesting,

where conservation has been performed for

more than 20 years (Arellano, 2020).

Although olive ridley turtles are the most

abundant sea turtles in the world, information

on olive ridley turtles is scarce compared to that

for other species (Abreu-Grobois & Plotkin,

2008). According to the IUCN red list, global

olive ridley populations are decreasing, with a

total decrease between 30 % and 50 %, and it is

not known whether this reduction has stopped

or if it is reversible (Abreu-Grobois & Plotkin,

2008). However, at the arribada beach, La Flor

de Nicaragua, a drastic increase in the num-

ber of nests was reported from 1998 to 2006

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(Honarvar et al., 2016), and at Playa Escobilla,

the most important arribada beach in Mexico,

sustained recovery was reported (1973-2010)

(CONANP, 2011). However, considering the

wide pantropical nesting habits of the olive

ridley turtle, evaluations on solitary beaches

are scarce. In the Mexican Pacific South of our

study area, in the states of Jalisco and Nayarit,

increases in the numbers of nests were reported

and attributed to conservation programs that

had been implemented for 29 years (Hart et al.,

2018). For a beach in Guatemala, a sustained

increase in the number of nests over the course

of 16 years was reported (Ariano-Sánchez et

al., 2020), while for the Pacific beaches of

Costa Rica, clear trends have not been reported

(James & Melero, 2015; Viejobueno Muñoz &

Arauz, 2015). For a beach in Brazil, an increase

in the number of olive ridley nests was reported

in 10 out of 11 years (da Silva et al., 2007).

Similar HS was recorded at both beaches

(65.09 and 60.72 % for SPC and PC, respec-

tively); these values were close to those report-

ed by Bárcenas-Ibarra et al. (2015) for El Verde

Camacho (58 %). Other studies have reported

a HS rate ranging between 75 and 85 % (Table

3). However, these studies were conducted in

more Southern latitudes of the Mexican Pacif-

ic, except for the study by da Silva et al. (2007).

A lower HS rate was reported for olive ridley

turtles than for other species, such as hawksbill

and green sea turtles (Bárcenas-Ibarra et al.,

2015); this discrepancy could be because for

other species, incubation regularly occurs in

situ, while for the olive ridley turtle, nests are

artificially incubated or relocated to hatcheries,

which affects mortality and HS (Mrosovsky,

1982). However, at an olive ridley nesting

beach in Costa Rica, Viejobueno Muñoz and

Arauz (2015) reported a HS rate of 61.38 %

for in situ nests, while the HS rate for nests

relocated to a hatchery was 77.9 % (Table 3). It

is necessary to compare the HS rates of in situ

and relocated nests to guide management deci-

sions, although predation and poaching may

limit these analyses for both nesting beaches.

Another factor influencing the incidence of

HS is temperature, as it has been shown that

in some cases, temperature exceeds the piv-

otal point of embryonic mortality (Rafferty &

Reina, 2014; Sandoval, 2012). In addition, it

is important to consider different management-

related factors, such as losses that occur during

monitoring phases on the beaches since these

also affect HS but are rarely evaluated.

Regarding the number of predated and

poached nests, both indicators were higher

at PC than at SPC. These results are not

TABLE 3

Hatching success at different nesting beaches of olive ridley turtle (Lepidochelys olivacea),

including Santuario Playa Ceuta and Playa Caimanero

Author (s) Year Country or region Hatching success (%)

Galván 1991 Jalisco, México 78.3

Cupul-Magaña & Aranda-Mena 2005 Jalisco, México 77.8

da Silva et al.

2007 Sergipe and Bahía, Brasil 78.7

Bárcenas-Ibarra & Maldonado Gasca 2009 Nayarit, México 79.4

Barrientos-Muñoz et al.

2014 Playa El Valle, Colombia 81.1

Bárcenas-Ibarra et al.

2015 Sinaloa, México. 58

James & Melero 2015 Península de Osa, Costa Rica 79.2

Viejobueno Muñoz & Arauz 2015 Punta Banco, Costa Rica 77.9

Carretero-Morales et al. 2018 Jalisco, México 79.7

Hart et al.

2018 Nayarit, Jalisco, México 85.4

This study SPC 2016 Sinaloa, México 65.08

This study PC 2016 Sinaloa, México 60.72

SPC: Santuario Playa Ceuta; PC: Playa Caimanero.

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surprising, as PC has a higher annual density

of nests than SPC, resulting in a greater avail-

ability of eggs for predators. Leighton et al.

(2010) suggested that the probability of nests

being predated or poached increases over time,

which was in accordance with the results of

the regression analysis for PC. The rate of

poaching of eggs at SPC did not increase over

time; this is likely because this beach is legally

protected and far from urban settlements. PC

is not legally protected, and coastal communi-

ties are present along the beach, which facili-

tates poaching even though it is prohibited.

Moreover, protection of the beach has not

been increased due to the lack of economic

resources, and protection status is an important

variable for monitoring (García et al. 2003).

On Venezuela’s nesting beaches, both preda-

tion and poaching rates were reduced over 10

years of conservation (2003-2012) (Ballad-

ares & Dubois, 2014). However, each nesting

beach and its surrounding environment have

very peculiar characteristics. Coyotes (Canis

latrans) are the most common opportunistic

predators of sea turtles in arid areas of Mexico,

and at both SPC and PC, the predation of eggs

by coyotes is common; in recent years, the

population of this predator has been increasing

(Álvarez-Castañeda, 2000; Méndez-Rodríguez

& Álvarez-Castañeda, 2016). At SPC, in addi-

tion to coyotes, the presence of new predators

such as raccoons and badgers has been reported

in recent years (2013-2016), and this may be an

explanation for the increase in predation. The

presence of these predators could be related to

the modification of habitats for shrimp farming

and agriculture.

Monitoring and conservation efforts for

the olive ridley turtle by the PROTORMAR-

UAS program have indicated that there has

been an increase in the number of nests at both

beaches since the establishment of the camps

to the present day. We suggest that PC, which

is located on the latitudinal limit of olive ridley

nesting, be designated as a legally protected

nesting area, given the need for resources for

the operation of the camp to ensure that nest

numbers continue to increase and address

predation and poaching. In addition, it is nec-

essary to carry out additional studies related

to the sex ratio of neonates, management and

conservation program success, and mortality

and congenital malformation incidence in this

species. With this information and data from

assessments of nesting trends, it will be pos-

sible to identify indicators and form a clearer

picture of the situation the olive ridley sea

turtle with regard to management and conser-

vation programs to guide appropriate decisions

regarding these programs.

Ethical statement: the authors declare

that they all agree with this publication and

made significant contributions; that there is no

conflict of interest of any kind; and that we fol-

lowed all pertinent ethical and legal procedures

and requirements. All financial sources are

fully and clearly stated in the acknowledge-

ments section. A signed document has been

filed in the journal archives.

ACKNOWLEDGMENTS

Thanks to the Autonomous University of

Sinaloa (UAS) for the continuous financial sup-

port for the operation of the Sea Turtle Program

(PROTORMAR-UAS); as well as students

and staff of the Faculty of Biology and Marine

Sciences of UAS. Thanks to the National Com-

mission of Protected Areas (CONANP), and

the people of the communities of Ceuta and La

Guasima, Sinaloa who participated during the

monitoring of this extensive study. Thanks also

to the companies Maricultura del Pacífico and

Agrícola Tarriba (Farmers Best) for the spon-

sorship of equipment and materials.

RESUMEN

Tendencias de anidación de la tortuga golfina

Lepidochelys olivacea (Testudinata: Cheloniidae)

en dos playas del noroeste de México después de

30 y 40 años de conservación

Introducción: A pesar de que las tortugas golfinas (Lepi-

dochelys olivacea) son las tortugas marinas más abundan-

tes del mundo, su información cuantitativa disponible es

1134

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escasa y se encuentra distribuida de manera desigual entre

regiones. Existen muchos programas de manejo y conser-

vación para esta especie, y sus evaluaciones son necesarias

para identificar tendencias de anidación y poder manejar de

manera efectiva los programas de conservación actuales.

PROTORMAR-UAS es un programa de Investigación y

Conservación de la tortuga golfina creado por la Univer-

sidad Autónoma de Sinaloa, México. El Programa cuenta

con dos estaciones biológicas: Santuario de Playa Ceuta

(SPC) y Playa Caimanero (PC).

Objetivo: Evaluar la tendencia de anidación de la tortuga

golfina en dos playas del noroeste de México y predecir

las tendencias prospectivas de anidación para los próximos

30 años.

Métodos: A partir de los datos de registros anuales de

anidación de 40 años para SPC (1976-2016) y 30 años para

PC (1986-2016), evaluamos las tendencias de anidación,

el éxito de la eclosión y los problemas de depredación y

saqueo de nidos de la tortuga golfina en las dos playas

del noroeste de México. Posteriormente, se calcularon las

estimaciones prospectivas de anidación para los próximos

30 años usando un modelo predictivo de series de tiempo.

Resultados: Se identificó una correlación positiva y

significativa entre el registro anual de nidos y el tiempo

de estudio para ambas playas (rho = 0.850, P ≤ 0.01 para

SPC; rho = 0.677 y P ≤ 0.01 para PC); así como el éxito de

eclosión promedio de 65.09 para SPC y de 60.72 % para

PC. El modelo predictivo de series de tiempo indicó que

las anidaciones continuarán aumentando para el 2045, tres

veces para SPC y seis para PC, con respecto al último año

de monitoreo.

Conclusiones: Hay una clara tendencia positiva de anida-

ción de la tortuga golfina en ambos sitios, lo cual es consis-

tente con la tendencia observada en otros estudios recientes

de la región. Por lo tanto, sugerimos incluir a PC como un

área de anidación legalmente protegida, la cual se ubica en

los límites latitudinales de anidación de la tortuga golfina,

dada la necesidad de contar con recursos disponibles para

la operación del campamento ante el aumento de anidacio-

nes y de problemas de depredación y saqueo. Porque en

México operar una playa de anidación sin ningún estatus

de protección implica no tener presupuesto para su manejo.

Palabras clave: nidos; conservación de tortugas marinas;

tortuga golfina; éxito de eclosión; saqueo; depredación.

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